Did Philae drill the comet?

Philae’s Sampling, Drilling and Distribution (SD2) subsystem was activated towards the end of the surface operations that Philae performed on Comet 67P/Churyumov-Gerasimenko last week, despite fears that it might alter the lander’s precarious position following its third touchdown. Here we present the latest update from the SD2 team.

SD2’s goal was to drill into the comet surface in order to collect and deliver samples to the COSAC and Ptolemy instruments inside the lander (Click here for our introductory post on SD2). It was the last of the lander’s ten instruments to be operated.

Philae drill tweet

@Philae2014 tweeted that the drill was activated as planned

SD2 principal investigator Amalia Finzi has reported that the drill was deployed as planned, extending 46.9 cm below the balcony of the lander and 56.0 cm from its reference point.

“It was then retracted to the reference position, the carousel turned in a way that the sampling tube was in front of the right oven, the discharge operation from the sampling tube to the oven was completed, and the carousel rotated in a way that that oven was positioned at COSAC’s location,” she said.

Although the ovens worked correctly, the scientists do not yet know how much – if any – material was actually delivered to the ovens by SD2, or whether the instruments sampled dust or gas that entered the chamber during the touchdown.

Because Philae was not anchored to the comet surface, it is also possible that, if the drill touched a particularly hard surface material, it moved the lander instead of drilling into the surface. Furthermore, the SD2 instrument lacks dedicated sensors to determine whether or not the surface has been reached, whether a sample was then collected in the sample tube, or if it was then discharged into the oven.

But other instruments on board Philae can help understand what actually happened. For example, the downward-looking ROLIS camera obtained two images of the surface under the balcony, one before and one after the lander’s main body was lifted and rotated. Because of those movements, the SD2 ‘footprint’ may be included in those images and thus may be able to provide visual evidence that the drill interacted with the surface. We hope to be able to provide an update on this soon.

As for whether COSAC received a sample from the drill, the analysis is on-going.

“As far as we can see at the moment, SD2 and COSAC telemetry cannot reliably discern between lack of sample and insufficient gas generation from it,” says Amalia. “A CIVA-MV/MI image would have been needed for this purpose, which was not available for the first sample.”

Meanwhile, COSAC’s analyses on the data acquired from its surface measurements are on-going. But it is apparent that COSAC already ‘sniffed’ the comet’s atmosphere during the first touchdown, detecting organic molecules. The Ptolemy instrument is also reported to have successfully collected the ambient gases of the comet. Analysis of the spectra and identification of the molecules detected by both instruments are continuing.

Mario Salatti, Philae Program Manager for ASI adds: “We are all hoping that Philae wakes up and we can perform many more measurements on the surface of the comet, including the chance to drill again with SD2. The final site where Philae landed does not enjoy long exposure to sunlight, but on the other hand, it opens new perspectives. As the lander appears to be currently shielded by walls, the local temperature may be lower than it would have been at the chosen landing site. So if Philae wakes up, it might remain operative much longer than expected, possibly until perihelion, which is extremely exciting.”

Focus on SD2, COSAC and Ptolemy. Credits: ESA/ATG medialab

Focus on SD2, COSAC and Ptolemy. Credits: ESA/ATG medialab

The SD2 (Sample Drilling & Distribution) instrument was conceived by technologists at the Italian Space Agency, designed and developed by the SELEX ES in Milan, under the scientific responsibility of the Principal Investigator Prof. Amalia Ercoli Finzi from Politecnico di Milano: for more than 10 years, SD2 team has been planning SD2 operation sequences and validated them with the unit spare available at their institution’s laboratories.

COSAC Principal Investigator: Fred Goesmann, Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany

Ptolemy Principal Investigator: Ian Wright, Open University, Milton Keynes, UK.



  • Iban says:

    Hi there,

    This is my first post here, but I’ve been following this mission and twitter with interest.

    Anyway, I would like to make a comment about something I read on this post, and which reminds me another thing I though about a couple days ago, and lets see if someone can tell me if I’m right, or not.

    First, I’m no cientist or matematician, so these are just my crazy thoughs. Also, I didn’t do much research so forgive me if I post non-sense.

    First, this is related to the comment about the drill going inside the surface, or moving the lander. As I read some time ago, the Philae weights just 1 gr on this rock, instead of 100kg. I’m not sure of this, but wouldn’t even trying to drill on sand, or even cigar dust, make the lander go up? Not sure about the drill strenght or downwards movement speed, but it doesn’t take too much to move that weight up.

    Also, some days ago I read something about the landing being success in part thanks to the suspension (or legs) of the Philae. Maybe another stupid idea from me, but for this to work, the Philae shouldn’t be able to stand on its legs on earth, for it to succeed on the comet. I mean, instead of being prepared to hold 100kg, the legs should hold just 1 gr. On earth it should just bend and touch the floor.

    To explain it another way. A car’s suspension is prepared to hold 1 ton, and when it gets more weight, it goes down a little, or even bounces up and down. If we put 100 tons on it, the car will just go right to the floor. What I see here is that the suspension was designed to hold a 100000 ton car, and then used it on a 1 ton vehicle, which in my opinion makes the suspension useless as it would not show any elasticity at all. In Philae’s case I understand it as if legs were simply solid parts with no ability to bounce at all.

    I’m really curious about this thoughs of mine so I would appreciate if someone can explain this.


    • Gordan says:

      Hi Iban,

      For the second part of your remarks, you’re exactly pointing out the difference between mass and force:

      The attractive force between the comet and Philae is about one gram. But Philae’s mass is still 100 kg, so you still need a big force during a short amount of time to slow down its decent within a few tens of centimeters.

      The same effect can be observer if a big stone of 100 kg is hanging on a long rope: It is easy, with a force of a few grams to move it sideways; but if the same stone is moving towards you at a speed of 1 meter per second, you still need to apply a force of 100 Newton (about 10 kg) to stop it in one second !

    • Guili says:

      Hi Iban,

      I am pretty sure the legs have been desigend and tested for the conditions expected on 67P (with some conservatism).

      It’s the same issue for the solar arrays or reflectors deployment on any spacecraft : the mechanisms are not designed to be operated under 1G : they would not survive. But we still need to test them so during deployments, so they are attached to helium balloons/cables/rails to cancel the gravity effects.

    • B says:

      Philae’s mass is not the same as weight. It’s 100kg mass doesn’t change due to the lower force of gravity on the comet.

    • Daavs says:

      Interesting thoughts.

      For drill-induced movement, the drill speed is probably very important. Imagine the extreme case with no gravity at all: an astronaut floating in zero-g with a ball of flour in front of her. If she pushes on it slowly enough, it will stay solid and move apart from her, but she could easily smash it with a punch; the material strength limits how much reaction-force can be transmitted back at any given moment. The graph posted on this blog makes the drill movement look slow, but it’s hard to guess what constitutes a slow hit in the context of the comet’s weak gravity and material properties.

      Your analogy about Philae’s legs makes sense too. I think the key point is that their suspension strength is not tuned for simply sitting on the surface and absorbing small shakes like bumps on a road, but rather for the landing impact at high speed (well, “high” relative to the slow accelerations from weak gravity). So, if poor Philae were dropped onto Earth from several Earth-radii away, it would not make it…

    • Romain says:

      Dear Iban,

      As far as I know, Philae never had to stand on its legs on Earth. It as been caried by a crane all the time.

    • Mark Zambelli says:

      Philae does weigh just one gram on the comet but it still has 100 kg of mass so the legs, through ingeniuos engineering, have to absorb the inertia of 100kg of mass hitting at ~1 ms^-1.

    • Gianangelo says:

      You have to consider, in the landing/touchdown fase, the Philae momentum…

    • Arnav Wadekar says:

      about the suspension part, true philae doesnt weigh much on the comet but think about it! Philae still is in speed and going towards the comet. being in speed it should have some type of suspension to support its impact like the ones cars need to survive speed-breakers. imagine 67p as a speed breaker ;). everyone please correct me if im wrong!.

    • Jan says:

      Hello there,

      I can’t find the words that would properly describe my fascination by this project, congratulations and thanks to the team, and a bit of envy they are part of it.

      you have to distinguish between the “weght” based on gravitational force (static), and the “mass” related to inertia. (I’m sorry English is not my native language and the translation of terms may be wrong).

      Although the legs may seem overkill to (staticlly) carry 10 grams (if I’m not mistaken, the gravitational constant at 67P is about 1/10,000th of the Earth one, i.e. 100*1e3/1e4=10) they also have to absorb as much as possible of the energy of a 100kg lander approaching at 1m/s in several tens (hundreds?) of milliseconds after the touchdown.


    • Blaz says:

      I can’t provide you with the whole answer as I’m not an expert myself, but what you might have forgotten is that Philae landed with a speed of approximately 1m/s relative to the comet.

      Lets presume the landing gear moved 10cm when it cushioned the landing and that the deceleration was linear. That means the average speed during touchdown was 0,5m/s. The time of the deceleration would be calculated as the distance traveled in meters divided by the average speed in seconds. We get 0,1/0,5=0,2 seconds. Now that we have the time we can calculate the deceleration as the difference in speed(1m/s) divided by the time of the deceleration which gives us 1/0,2=5m/s^2. This means that during landing Philae would experience a force equal to approximately one half of Earths gravity which is not an inconsiderable amount.

      As I only speculated on the give that the landing gear has, these numbers are obviously only an educated guess but probably fall into the ballpark. Hope this helps.


    • Invisible says:

      Philae’s legs are of course not solid, as the were designed to dampen the landing (which they did perfectly: they absorbed about 2/3 of the lander’s momentum).

    • Nick says:

      Trouble with legs that are that flexible (to where they bend that far under Earth’s gravity), is that Philae may (and may have) bounced much further than desired as a result, once touching down.

      Interesting thoughts though. Hope someone else has input.

    • Bonny says:

      About the suspension, you are right in your thought that it would be useless to design it to support 100 kg whereas Philae on the comet itself would only weigh 1 gr (as you perfectly explained with the car suspension example). However I do not know wether this is the case, I’m sure the brilliant people @ ESA must’ve thought of this 🙂

      And yes, drilling will result in a force pushing in the opposite direction but Philae is secured to the comet via some kind of harpoon system to prevent this sort of thing from happening.

      Hope I helped!

      • Bonny says:

        Oh my god, I am terribly sorry for my profile picture! Did not mean to insult anyone, but apparently this blog utilizes the profile picture from gravatar.com and a friend of mine once changed it, we had to create a gravatar for a game that I don’t play anymore but the picture continued existing.

        So sorry for this, it was in no way my intention for my comment to show up with such a disrespectful picture!

        • Bonny says:

          Great, I managed to change it to a picture I had laying around! no worries 😀

    • BIC says:

      I think it isn’t unlikely that Philae lifted it self up as you said. I guess there are instruments on-board which could have detected a small acceleration or rotation during the drilling. Hopefully the scientists at esa can find out about it.

      Concerning your second thought. Espacially during launch very strong forces act on the spacecraft inside the rocket which could have led to a broken leg or other damages on the lander or even the satellite. Furthermore I guess that the gravity of the comet was not known before they arrived there. So the forces on the legs during the landing of Philae could have been much bigger than they were in the end. I think no one wanted to risk a smashed lander in case of a higher gravity.

    • Nikki says:

      Iban, although the Philae probe weighs only 1 gram on the comet, its mass is about 100kg. The suspension is needed to soften the blow of the landing of the probe. A 100kg mass is still a 100kg mass, whether it’s in space, a comet or on Earth.

      Imagine a 100kg mass on a sled on an ice skating rink sliding at 1m/s and ramming into a wall. If this was a person, it would hurt or do damage!

    • Hi Iban–
      The inertial mass is Philae is still 100kg, so when it bounced, the legs had to be strong enough to decelerate that much mass. However, the gravitational pull of the nucleus on Philae (it’s “weight”) is equivalent to that on a 1 gram mass on Earth. You must get away from thinking like an Earth-dweller when it comes to mass and weight.

    • Spyros KANOURAS says:

      Physics and engineers say that concerning the response of the shock absorbers we must take under consideration the momentum of the moving vehicle during the touch down. It is equal to the product of mass and the velocity (m*v) which means that you are dealing v times with the mass and not only one…

    • Gerald says:

      Adding one more ingredient to your thoughts may improve your understanding. That’s intertia. You may have experienced inertia when accelerating a car on a plane surface, or accelerating/decelerating a boat or a yacht, or maybe a large and heavy shere balancing on a film of water.
      So besides weight the landing gear needed to handle the inertia of Philae, slowing it down from 1 m/s (3.6 km/h). to zero within a few decimeters, at most.

    • dave says:

      While the lander has a far reduced weight, it still has momentum (p=mv). A force is required to stop the lander and slow it down, hence the thrusters and landing gear.

      • dave says:

        Sorry I just realised I answered your question In a very roundabout way.

        As I realise it Philaes legs aren’t designed to cope with earths gravity as they aren’t used on earth, but would still be quite stiff as they’d have to overcome the force of the lander hitting the surface which would still be reasonably high.

    • Ayrton says:

      > I read something about the landing being success in part
      > thanks to the suspension (or legs) of the Philae.
      > […]
      > the Philae shouldn’t be able to stand on its legs on earth,
      > for it to succeed on the comet. I mean, instead of being prepared
      > to hold 100kg, the legs should hold just 1 gr.

      Well, the suspension’s job was not holding equivalent of 0.001 kg on the surface but absorbing the force of the impact. Philae mass is still 100 kg and it hit the comet faster than 1 m / s. Absorbing energy from such a collision has nothing to do with lander’s weight (which depends on gravity) but the mass.
      Now, when the lander doesn’t move, suspension should be “relaxed”, I think.

    • Paul Nel says:

      Hi Iban

      With regards to your question about how Philae is able to drill without going up- the lander has a very specialized slow-turning drill bit which drills into the surface of the comet very slowly with extremely slight downward force. In its current mode, the downward force that SD2 applies to the drill never exceeds the weight of the craft. (because of uncertainty about how well the lander is anchored to the comet.)

      As for the legs on Philae; they have an adjustable stiffness and a lot of the force of impact (which is tiny) is absorbed by the anchoring drills on each leg.

      I hope this answers some of your questions!

    • Kasuha says:

      Philae might have weight one gram on the comet, but it still has mass and inertia of 100 kg.
      Imagine you suspend a 100 kg weight on a long rope. You don’t need any strength to keep it lifted (as it is on a rope) but you need to push pretty hard to get it swinging because of its inertia. You’re not fighting gravity when pushing horizontally. You’re fighting only its inertia.
      So even if the drill was lifting Philae off the surface, it was still pushing against the surface somewhat – certainly more than if there was just one gram of weight on it – and that could have allowed if not a deep drill then at least chipping some material off the hard surface.

      The same with landing. The legs did not brake 1 gram of weight, they were braking 100 kg of mass moving at 1 m/s. Imagine that weight swinging on that rope at 1 m/s and that you were told to stop it at its lowest point.

    • Greg says:

      1. Regarding the drill. The lander was supposed to be anchored to the comet using the harpoons and the screws in its legs. If that had been the case, then the drill would not have lifted up the lander. There is still a possibility that one or more leg screws have worked keeping the lander somewhat on the ground during the drilling.

      I think that another problem may have caused the drilling not work properly. From some pictures it looked like the lander may have not rested in fully upright position, possibly on an angle close to a cliff or a wall. In this case the drill may not even have reached the ground by being extended on an angle.

      2. The suspension. The lander was traveling with some speed towards the comet. So, the impact would have caused more push on the suspension. In addition, there was a jet on top of the lander, which was supposed to have fired and pushed the lander even harder towards the surface. So the original calculation of rigidity of the suspension was probably correct.

    • Terran says:

      It’s not the weight the landing gear needs to dampen, but the acceleration towards the ground, right? Also I don’t think they “forgot” the weight / gravity condition on the comet while designing it.

    • Amateur says:

      I’m also a mere amateur, but like everyone else have been following this mission with interest. I met one of the team socially about 10 years ago and have been looking out for it ever since.

      I would guess that the suspension would need to be more or less the same stiffness as would be required on earth, because during landing it is acting against the momentum of the craft and not merely its weight. Momentum depends on mass (and velocity), and therefore the weak gravity makes little or no difference to the forces involved.

      The drill, however, _is_ potentially acting against a static weight, so you could well be right that it would just lift the lander.

      It seems the surface hardness caught everyone by surprise so it might be expected that the design turns out not to be ideal.

      It would be a big slice of luck if the lander wakes again. If it survives to perihelion the abundant gases given off might mean there is no need to drill for interesting samples.

    • notSoSmartME says:

      hi iban,
      im not a scientist too (though im a chemical engr) and ive been following tis mission since the plan of landing appeared on google news,
      (forgiv my spelling, english is not my mother tongue)
      anyways, about the first question, you cud also consider tat in a place of having microgravity, any body movements (of tat of philae’s per se) would cause turbulence/agitation in the atmosphere (seen astronauts “swimming” in empty space?). though i presume the drilling process hav been done in a scrupulously (or maybe intermitently?) slow manner, if it hits a solid surface (without it anchored on the comet’s surface), it myt move itself instead of drilling.
      the second is tat ter s a good mass ratio (not considering other factor like orientation and dimensions) between the philae’s legs and body to meet equilibrium. if it is on earth then the legs (say with mass A) will support Lander Instruments (with mass B).. if it s on the comet’s surface then mass A will still support mass B. (if u noe wat i mean) as change in gravity will not change tis ratio for balancing.. Plus, the design of the lander (if u can see it) has certain sampling apparatus at bottom (tat wud not be smart to hav it touch d floor for tat matter).
      im not also sure bout tis idea though. tahaha

    • Gary says:

      With a weight of one gram, and the knowledge another instrument (the “hammer”) actually broke due to the surface of the comet being harder then expected, I don’t think there’s any realistic expectation the drill penetrated the surface the way you’d expect a drill to work.

      I’d be glad if it even scuffed the surface & got the slighted hint.

      Regarding the legs, the lander may weigh less on the comet but the mass – and critically the impact forces – are not different then earth.

      Meaning, when the lander smacks into the comet at X mph (presumably on it’s legs) those forces are identical to the corresponding forces on earth if it were to smack down beside you at X mph (or kmph is you’re not in the US).

      I will wait with baited breath to see if the lander wakes up again. How cool would surface pics of the comet exhaling gases be, oh man.

      What’s not clear to me is how long the orbiter itself will last as it approaches the sun. Pretty sure the lander requires the orbiter to communicate with earth.

    • Pags says:

      I am not an esa scientist, but I will try to answer your question anyways.
      The gravitation on the comet is quite small. For simulations they used the value 0.001m/s². This would translate into a weight of 10 grams for the lander.
      But the lander still has its entire mass of 100kg(it has the same inertia as on earth). This means you need quite some force to accelerate it.
      Sd2 is hammering the drill bit in with a vertical force of up to 100 N (if I remember correctly). While this is a lot and would accelerate the lander at a speed of 1m/s² into space, it only lasts for a fraction of a second (usually those types of drilling machines exert this force for 0.01s max, but this is a wild guess since I do not have correct data)
      This means the resulting speed would be only 0.01m/s.
      And because the gravitational pull of the comet is 0.001m/s², the lander would start to fall back to the surface after only 10 seconds. The lander would only lift for around 5 cm (assuming that all the force of the drilling is going into the lander) before it drops back to the surface and the drill could be used again.
      In reality a lof of the force would be consumed by the drillbit being forced into the ground and the scientists would not use the maximum force from the beginning.
      So the lander would certainly hop a bit during the drilling. And if too much force is used and the frequency of the “hammerblows” is too high, it could cause quite some problems.

      As for the landers legs:
      As far as I know the legs are rigid. But between the legs and the main body is a friction-dampener, which is designed to take the impact during the landing (which is comparable with someone jumping down a sidewalk or 5 to 10cm).
      Elasticity is actually the last thing you want on such a mission, since it would catapult the lander back into space at nearly the same speed as it landed, hence the damping element and the relatively rigid legs.

    • Jitech says:

      I’m not a physicist but the reason the supension bent is that the kinetic energy of Philae wasn’t null because it doesn’t consider the g-force (1/2*m*v*v).

      Concerning the drill I asked myself the same question and I think it’s the inertial force of the drill which can prevent Philae from lifting.

    • MRW says:

      Iban, your line of thinking is not stupid, however you are mixing units of mass (kg) with the concept of weight. 1 kg only weighs 1 kg here on Earth, but it always has a mass of 1 kg, no matter what the gravitational pull.
      For example, your 1000 kg (mass) vehicle moving at 10 km/hr possesses a certain amount of kinetic energy which must be absorbed on impact (converted to heat, flying bits, etc). It doesn’t matter how it got to 10 km/hr – if it was pushed by a race engine (or Earth’s gravity), or a skinny 10 year old (or P67’s gravity).
      Your suspension argument makes sense for the force exerted on the suspension by gravity for a lander that is already resting on the surface, with zero kinetic energy. But it doesn’t work for an object already in motion and already possessing kinetic energy (which is only a function of mass and velocity).
      Sorry the explanation is not very rigorous. I’m trying to avoid going into textbook explanations. I hope it helps somewhat.

    • Konrad says:

      I will day: inertion! 100kg in microgravity conditions is still… 100kg of mass. If the lander have to reach speed of zero from 0.5 m/s in a fraction of a second it’s rather obvious that legs have to be a prepared for forces of thousands of newtons.

    • Leo Vuyk says:

      You foreget about the difference between the weigth ( 1 gr) and mass of 100 kg.
      The recoil effect is based on the recoil of 100 kg mass!!

    • Νίκος says:

      I think that the main problem engineers had to face was inertia from the landing, even if at walking pace. So weight is out of the equation for Philae’s suspension.
      You are probably right about lifting the lander up when drilling. The only material that could go in is only dust I guess, and then only if the surface underneath was close enough.

    • praealtus says:


      You are correct in the weight of Philae being just 1 gram on the comet. However, its mass is 97.9 kilograms.

      The lander first touched down at a speed of 1 meter per second.

      This means that when the lander touches down on the comet, it has a momentum (mass time velocity) of 97.9 kilograms-meter per second.

      Since the harpoon anchors on the landing “pads” didn’t fire, the suspension bounced the lander back up quite a bit (due to the low gravity).

      They probably designed the suspension so that the lander would be nearly at rest when the harpoons should have fired. Since they didn’t, the stored energy on the suspension (from landing on the comet) push the lander away from the comet.

      As far as drilling into the comet (when the lander finally came to rest after bouncing again), the drill would have been pushing against the comet with a mass of 97.9 kilograms behind it. This could have lifted the lander a bit, but it would depend on how fast the drill was deployed downward.

      To provide a comparison, one can push a car on a level surface, even though the car has a mass of 1000 kilograms or so. Or think of a heavy boat at a dock. One can push the boat away from the dock, but the mass of the boat means that it takes a quite bit of force to get the boat moving.

      Hope this helps!

    • Rookie3 says:

      The Philae Lander has a highly sophisticated landing system.
      The “Shock Absorber” if you want to call it that way absorbs the impact of touchdown and converts it into energy. Also it can tilt and does set the lander after impact in a upright position. The legs itself do not help dampening AFAIK.

    • Mario says:

      Iban, very interesting thoughts. I think you touched a real engineering problems that Philae operating guys have for sure faced. This however does not mean that the issues were unresolvable 🙂 personally I think that the danger of moving unanchored lander lowers with the speed and hardness of the drill and the force it pushes the surface. Regarding the suspension thing – I would say it could be tested by just simple holding the model on some lines, which for sure makes things work on Earth in terms of recreating low gravity of a comet. Maybe simple example, but shows the “gravity simulation” possibilities 🙂 I also follow this mission with goose flesh. It is the most exciting mission since I remember in my opinion 🙂 regards, Mariusz

    • Kelduck says:

      It has to do with the difference between weight and mass.

      While the weight of an object will vary with gravity the mass of an object stays exactly the same. ie (lower the gravity, lower the weight)(lower the gravity, exactly the same mass)

      If I propelled Philea at you while you were standing on the comet it would hit you with its full 100kg mass even though it would only weigh approx. 1 gram if placed on scales. F=ma. (Force =mass x acceleration)

      If you put Philea on a body that had double the gravity of Earth it would weigh 200Kg on scales but its mass would still be 100Kg.

      The suspension had to contend with the momentum of Philae which is p=mv (mass x velocity)

    • Jeroen says:

      Hey Iban,
      I’m not an expert on physics by any measure, but I do think I can clear something up for you.
      First of all, the three legs of Philae each have small ‘screws’ that are drilled into the surface. So even though the harpoons failed, the lander is still firmly attached to the surface.
      Secondly I think you’re confusing weight and mass. Philae has a weight of only 1gr because of the low gravity at the comet, but the mass remains the same. The suspension wasn’t designed to support a stationary lander weighing just one gram(or 100kg for that matter) , but to absorb the impact of a lander with a mass of 100kg impacting a surface at about 1 m/s.

    • João Prates says:

      I believe the estimated ratio to earth gravity is 1/100, so if Philea weights about 100 kg, it should behave as if only 1 kg, not 1 g.

      Even so, your thoughts seem to point in the right general idea, specially as we know the drills and harpoons are not holding Philae tight to the ground.

      Your logic makes sense to me. If it finds hard enough surface while trying to drill, it will simply raise itself up while extending the drill down against the ground IMHO.

      • Joao Prates says:

        I would like to make a correction and apology in my own previous post. After reading the reditt session I stand corrected that indeed Philae is only 1g in P67, not 1 Kg.

        My source for the gravity pull was wrong.

        My apologies.

    • DEDT says:

      I do not follow Rosetta regularly… But as far as I read about it, the legs were primarily designed to carry the harpoons, which in turn should drill into the comet like screws and hold onto it. Since there is almost no gravity on the comet, there was no reason to design a suspension whatsoever and the lander was deployed by Rosetta to the comet at an extremely low speed. It bounced back because the harpoons and other system to push the lander to the comet failed to function

    • LC says:

      To answer your question I believe the legs shock absorbers were used cushion the landing so that the module didn’t bounce of into space. Also each leg is equipped with a drill that on contact with the surface will drill into the comet and secure it. hopefully when the comet starts to have a coma the gasses doesn’t push the module off the surface. and as a back up they also fired a grappling hook into the comment to reinforce the hold..

      So in order to drill into the comment although the drill is producing downward force while the comment it pushing upwards the hold of the legs and grappling hook should be enough to keep the module in place for a successful drill and sample collection. They just need the power from the sun to do it now. 😀

      Disclaimers: I am not a scientist or Mathematician either just a hobbyist who has been following this launch for a while.

    • Dan says:

      Iban wrote,

      >> …wouldn’t even trying to drill on sand, or even cigar dust, make the lander go up

      Yes. Philae was designed with a thruster to press it into the comet, while two different types of anchors (screws and explosively propelled harpoons) attempted to firmly attach it to the surface. It appears that the neither the thruster nor the explosive harpoons functioned properly. For more details, use Google to search for details on Philae.

      >>I mean, instead of being prepared to hold 100kg, the legs should hold just 1 gr.

      You (and many news reports) are confusing mass with weight. The lander mass is 100kg regardless of the gravitational force exerted by the comet. The suspension was designed to cushion the impact of this 100kg mass when it impacted the comet at a certain velocity. Imagine a 100kg boat drifting free through the water: if it hits you, it will feel like a 100kg object despite the lack of gravitation or other forces pulling it toward you. The suspension was required to cushion the landing of the 100kg lander against the hard surface of the comet. For more information, search for “mass vs weight”.

      • Iban says:

        Thanks. Honestly I had that mass vs weight thing forgotten. I guess we had that lesson at school many years ago 🙂

        I was just wandering my mind, and I just imagined that 1gr object as a weightless object, as if it was a feather on earth, meaning I could even push it with my finger without effort.

      • armando says:

        Thanks Dan. Very clear explanation

    • Catherine says:

      Everything that has happened so far was predicted by physicist Wal Thornhill at thunderbolts.info. If you see the comet as a hard electrically charged rock, then all of this is understandable. The dirty snowball theory is soon to end up in the same trash can as flat earth theory.
      Where is all the snow and the ice?

    • James says:

      Hi Iban,

      There is a difference between the wieght of an object and the mass of an object. Weight is a measure of the gravitational force exerted between 2 objects (i.e. you and the earth). the weight of an object will change if the gravitional field strength acting on it changes. The mass of an object is a measure of how much stuff the oject is made from and this stays the same unless you add or take stuff from the object. On earth, gravity is pretty much constant over the entire surface so we generalise by saying that weight and mass are the same, so the lander with a mass of 100kg ‘weighs’ 100kg on earth. On a small comet it weighs much less but it still has a mass of 100kg. This means that the force holding it to the surface is much less but it is still made of the same amount of stuff. Imagine it was on a cart on a set of horizontal rails and you were trying to push it. Its mass is 100kg anywhere regardless of gravity it will still take the same force to start moving it along the rails whether it is on the earth or on the comet. In other words weight is only the gravitational attraction but mass detemines how much force is required to move (accelerate or decelerate) the object. Therefore when Philiae landed its legs still had to decelerate a 100kg mass (not a 1g mass) to a standstill in a short space of time and that’s why they are built the way they are.

      Hope that explains,

      • Iban says:

        Hi James,

        Yes it’s clears things up, thanks! As I posted replying to another post here, I had the mass/weight thing completely forgotten… So now I have the answer to both my questions.

        Thanks for the detailed explanation.

    • Daniel says:

      I believe you’re confusing mass and weight in your post. Pushing a car on the moon is (almost) as hard as pushing it on earth since it’s really not gravity that keeps it in its place. Despite the reduced weight on the moon the mass of the car hasn’t changed at all and you still have to overcome inertia to get it rolling

  • Simon says:

    I’ve heard the lander isn’t expected to survive close to the sun yet Rosetta is also supposed to be following the comet around the sun and expected to give us a picture of the comet’s cycle. Is Rosetta more robust or are you sending Rosetta on a path further away from the sun?

  • THOMAS says:

    I’m delighted to see this MUPUS update “DID PHILAE DRILL THE COMET?” which, in much more scientific wording, attempts to correct the disastrous impression left (even for the common layman, apparently…) by the previous ESA press release ” PHILAE SETTLES IN DUST-COVERED ICE”.

    I assume there is no longer any question of “dust-covered ice”.

  • Cathulhu says:

    While its weight may be only 1gr on the comet, it didn’t lose any mass, which is important regarding inertia. The legs also still have to support the mass, even if it weighs less.

    Don’t you think that engineers that worked for decades on this project know what’s possible and what not in space?

  • Vincenzo says:

    A) – Iban understanding looks acceptable, with proper corrections of figures to compare to other experiences of landing on different grounds for gravity and nature of the surface. It’s a funny case the impulse given by the drilling force without any leg anchorage. The powdery coating of the base could be sufficient to adsorb the stress input…

    B) Imagine that the nature of the coating powder be just water ice. At local ground condition (ca -150 °C) would it stand the transfer to the testing tube? Simulation on Earth could be tried in lab at Poli with N2 ice… or even with CO2 ice… Interesting experience was made in the ’80s at PERA (Meltom Mowbray, UK) using CO2 jet to clean a surface for
    remouval of all dirty contamination by local explosion of solid to vapour…

    C) I feel confident that in weeks or months we could enjoy new conditions and local effects of the landing experiment… and the detailed knowledge of the model in lab and on place!

    Forza Amelia, con calma e intuizione a copertura dei dubbi è incredibile il successo che ci consente di scambiare anche un po’ di creativa positività! Berto cosa dice?

  • Guili says:

    The change of wording from “First comet drilling is a fact” to “Did Philae drill the comet ?” is really welcomed.

    We all hope Philae will wake up in some months and allow the scientists to perform a real drilling and analyze real samples !

  • Steven says:

    The answer to your question is that the relative weight of the lander on earth and on the comet are not the issue. The legs were designed to prevent the lander from crashing on the surface of the comet, and so must be able to counter the lander’s momentum. As you know, momentum=mass*velocity. The mass of the lander, 100 kg, is invariant of whether the lander is on earth, the comet, or in space, where weight is zero. As for the drilling question, that is different. The lander is at rest, and the only force applied to it is the comet’s gravity, which pulls it downward. If the force needed to drill downward is greater than that pulling down on the lander, the lander will move, not the drill bit. My guess is that the smart people at ESA already thought about this. While the screws that were supposed to hold the lander down are not working, the drill bit doesn’t actually push straight down on the ground. No drill bit ever does – that’s how they work so well. The drill turns and the force is applied somewhat laterally and perpendicular to the lander’s gravity vector. That’s why you need far less effort to turn a screw than to hammer a nail. If the drill didn’t work, it’s because the surface is too hard, and the lander has no anchoring on the surface, so, again the lander would rotate and not the drill.

  • Ben says:

    Hello Iban,
    I can try to give you how I see the things, even though it may be not completely accurate !
    Concerning your first point, I agree with you, the small weight on the comet could allow a reaction movement of Philae. We can hope that the feet are engaged in some place where they cannot easily be removed, giving a kint a stability to Philae…
    On your second point, difference between mass and weight must be considered. The weight is low on the comet, but the mass remains the same. Inertial effects are still present with the same intensity : stop the movement of a car moving horizontally (no weight to be taken in account) is hard ! It is the same on the comet, the legs have to stop the whole mass of Philae, which is moving.

    Hope it was useful for you !

  • elronxenu says:

    @Iban, the lander would weigh very little on 67P but still have the same mass, so it has considerable momentum. A drill pushing against the comet’s surface isn’t necessarily going to make the lander fly away like a feather; its momentum (stationary on the surface) will allow the drill to push into the surface for a while, at least.

    Also I think the lander leg springs need to be designed for the mass rather than the weight. If you’ve got a lander approaching the comet surface at 1m/s, the legs might have a 30cm travel between first touch and fully loaded. The lander velocity needs to be reduced by 1m/s over that 30cm distance, which requires just as much “spring” as on Earth.

    Finally, spinning drill bits tend to bite into the surface being drilled, so once deployed the SD2 drill will probably help the lander stay in position, or at least not push it away.

  • marco salvatici says:

    Hello universe
    Every time scientiest seemed to fail a scientific research it always ended with a great discovery. Let’s think positive and wait a positive Phylae destiny

  • Tycho says:

    You have to consider the mass which is still 100 kg. Imagine an easy going shopping cart filled with mineral water. Accelerate it to walking pace and bump it against some wall. That’s where you need the suspension for.

  • Inertia has to be accounted for all those cases: Philae may not be gravitationally attracted to the comment as was to Earth, but it still takes the energy to push 100 Kg mass and get it moving. Similar for braking on contact without breaking.

  • Martin Brenner says:

    Iban, I’m trying to answer the suspension question: The “weight” doesn’t have to be compensated, but the impulse of Philae needs to be compensated. Driving a (frictionless) car into a wall is probably the better analogy of what happened to Philae where the bumper needs to absorb the kinetic energy of the car.

  • Roberto Perez says:

    To Iban, Philae may weight only one gram but that is the weight, no the mass. The mass is still the same than at Earth. Same Inertia. So while it is easy to move with little force, the acceleration is minuscule, giving it some time to drill.

  • Philippe says:

    Hi Iban,

    About your second interrogation, I think that the weight (force-equivalent of 1gram) of the spacecraft is of no particular concern on initial contact, however, the mass (100kg) is. The energy of the collision is driven by the mass and the speed of both objects, that energy must be absorbed by the legs.


  • Dilip Shran says:

    I wonder how many photographs were taken by the Philae Lander after it’s final touch down and what that would tell us about the orientation of the drill with respect to the surface. Secondly, if Philae was tilted would we be able to determine if it actually touched the ground?

  • Giampietro says:

    Hi Iban,

    that’s a good thoght what you just wrote, and for what I know you are right about the dimension of the landing gear. There is a basic rule in the aerospace sector. You want to have any component as light and as strong as possible. Following this strategy, components of the Spacecraft are designed in order to perform well in space and withstand the G-Forces during launch. The legs of Philae wouldn’t withstand a jump from 2 meters height I guess, but I’m not sure about that. I am confident that there was a safety factor of 3, that would mean the lander would withstand the landing from 1 meter height on earth.
    About elasticity, that is not something you really want to have, and it would be also difficult to have in a material that is at -200°C !
    The legs of Philae were solid, but the main body can move up and down. That is, so to say, the suspension of the spacecraft.

    I hope I could help in some way

  • Fun1k says:

    Hi Iban,

    the lander may weigh only so little in the comet’s weak gravitational field, but the mass of it is the same (weight is not the same as mass).

    If done slowly and carefully, the lander may not be pushed away. Picture floating in space with a car – if you hit the car with your fist it doesn’t fly away, because you would have to use a lot more energy to give the car’s mass any noticeable push.

    I don’t know much about Philae’s legs, but I’d guess they didn’t test it on the ground on its own weight.

    Also, yes, the legs’ suspension system helped, if it wasn’t for that, the bouncing would be more serious.

  • tomduf says:


    Thank you for this post.

    Could you explain one point please ?

    In the description of SD2 sub-systems, I read that a volume checker mechanism allowed measurement of the amount of material discharged into the oven.


    Did the checker check or not ?…



  • Redgy Devos says:

    Interesting question , maybe a factor in designing the landing gear was the force required to rewind the harpooncables to pull the footpads against the cometsurface.Should certainly be much more than the weight of the lander on the comet if you want to anchor the lander and conduct safe drilling and hammering operations.Hope someone else can answer this one…

  • Sputnik01 says:

    After the momentous Cassini arrival and release of Huygens to Titan, I enquired about how long Huygens could stay active on Titan. I received an authoritative answer from Professor Emily Lakdawalla of The Planetary Society that the extremely low temperature made it impossible to operate after the short input of the native batteries. Therefore I now rather wonder how:

    “As the lander appears to be currently shielded by walls, the local temperature may be lower than it would have been at the chosen landing site. So if Philae wakes up, it might remain operative much longer than expected”

    How on earth (sorry, on 67P) can a lower than expected temperature be anything other than an extra problem?

    Philae can only wake up if her batteries are recharged, just like our mobiles. But to do that, her batteries must not become so discharged as to be unusable. Once again, we have all been there with our mobiles.

    Hence my renewed questions to the Darmstadt team, which I have posted earlier on these blogs but which has not yet been answered:

    My questions:
    – about battery life: How long have we got?
    – what is the current surface temperature on the comet?

    Is anyone listening? Thank you for your reply!

  • Augusto Einsfeldt says:

    Wondering if the Safe plugs were replaced by Arm plugs in the harpoon system.

    After all, there were two harpoons and none did work as expected. Without anchoring none of the material collecting experiments would be possible.
    A redundant descent thruster should have been used.
    It is amazing that 3 separate systems (2 harpoons and 1 descent thruster) did not work. Due to the quality of the designs and components used the most probably cause of this failure was human.

    The most important instruments inside the lander are useless if the lander does not land as expected. So, in the economic way of view would be better to have less science (and more landing systems) than nearly none.
    Okay, everyone knows the lander was just a topping in the cake but, after all, it’s landing success would mean a lot in the human history. Clearly, as seen now, more than the amazing engineering and mathematics necessary to place Rosetta at the comet.

    In this case the Rosetta team should have asked a marketing guy to join the mission planning…

  • Cientist says:

    You’re not considering the forces involved in landing. If you just gently set the lander down the force it exerts on the comet is small. But you have to think of gravity as simply an acceleration coefficient. When the lander decelerates from transit velocity to standing still, there is negative acceleration. In that case, you still have to decelerate the 100Kg mass in a short amount of time. Think of throwing a glass jar at the floor in zero G. The glass would exert minimal force on the floor when at rest but gravity is not what is accelerating it in this case, it is your arm. Similarly, the lander has been accelerated previously to a speed that will allow it to transit to the comet. So in the end you still have to decelerate a 100Kg object over some time/distance.

  • Jarkko Hakkarainen says:

    The landing gear is not totally rigid. It does have elasticity.

    “The Lander will rest on a landing gear forming a tripod. This tripod is connected to the structure by a mechanism that allows rotation of the complete Lander above its legs and adjustment to surface slope by a cardanic joint. It will dissipate most of the kinetic impact energy upon landing by a dumping mechanism based of a motor that acts as a generator and converts the impact energy into electric energy.”


  • Sven says:

    Hey there!

    I’m not sure, if the numbers are correct, but I think, I can contribute at least to the second question:
    First of all, you should think in terms of Force (Unit: Newton or N, often written as F) rather than mass (tons or kilogram).
    On earth, Force and mass (m) are connected by the g, equaling roughly 10 [m/s²]. As an equation:
    F = m*g

    Generally, acceleration is written as a.

    However, if you want to decelerate (-a) anything, you want to know how fast it is (velocity of the lander v_l) how fast it should be (v_0, standing = 0) which distance (s) is available for deceleration.
    Velocities in space tend to be very high.

    As an equation:
    a = ( v_l² – v_0² ) / ( 2 * s )

    This means basically: The longer your way of “braking” is, the less acceleration occurs.
    This acceleration now inflicts a Force on the lander, which is like the first equation:
    F_l = m*a

    I don’t want to speak bad about media, but what they tend to do for simplification is translating this Force (F_l, which only occurs for short times) into “earthly” units, which are basically everywhere (like gravity). The lander of course is built to withstand a force F_l. Combined with earth gravitational acceleration g (roughly 10, as stated), you can change the formula to:
    m = F_l/g
    Note, that I put g, not a_l – but a_l is supposedly much larger than g, and with the Divisor shrinking, m increases.

    For the drill: No clue. If it is supposed to rely on the Lander standing firmly on the ground, it should be hard to get a sample.

    Hope I could help – shout, if not 😉

  • Mariusz says:

    Iban, very interesting thoughts. I think you touched a real engineering problems that Philae operating guys have for sure faced. This however does not mean that the issues were unresolvable 🙂 personally I think that the danger of moving unanchored lander lowers with the speed and hardness of the drill. And the force it pushes the surface. The suspension thing – I would say it could be tested by just simple holding the model on some lines, which for sure makes things work on earth in terms of recreating low gravity of a comet. Maybe simple example, but shows the “gravity emulation” possibilities 🙂 I also follow this mission with goose flesh, it is the most exciting mission since I remember in my opinion 🙂 regards, Mariusz

  • Stefano says:

    About leg strength IMHO they should be dimentioned to support both static (ie gravity) and dynamic (ie inertia) load when hitting the comet. Thin legs may break easily at impact.
    About the drill penetration I believe it may depend on blade inclination and drill speed. However scientist are not sure themselves as the surface is not flat under the lander.

  • Inertia says:

    The suspension needs to handle the inertia of the impact, not just the weight. Gravity may be low on the comet but the inertia is a property of the lander’s mass that doesn’t change.

  • JohnM says:


    I suspect that you are getting confused between mass and weight. The mass of the lander is still 100 kg so the energy that has to be absorbed in the landing is 1/2 m v^2. Assuming the landing was at 1m/s the energy to be absorbed is 1/2 *100 kg * 1^2 = 50 Joules. This exactly the same energy if you dropped it from a small distance on earth so it landed at 1 m/s.

    Using the laws of motion V^2 – u^2 +2as

    we get 1/(2*9.81) = 51mm

    So if we dropped Phillae from 51 mm on earth this would produce the same energy and is probably the case the landing gear needs to be designed for. In practice I am not sure they knew the mass of the Comet and thus the landing velocity so the energy absorbtion and strength may have been ‘over designed’. Don’t forget Phillae was intended to go to another comet 76P was the second choice after the launch delay so the original may have been even bigger ?

  • Spyros KANOURAS says:

    Is this the case with APXS, too? Telemetry of this instrument showed that it completed one operational cycle (level lowering to approach comet’s surface, spectrometer operation, data transfer). However, did you have substantial results concerning the composition of the comet’s “soil” from this instrument, as well?

  • Jack Sand says:

    Iban, you are right about the design of the legs. They are designed for the come, not earth. Actually they could not be deployed on earth.
    This is also the case for any moving part of a spacecraft like high gain antenna or solar cells. The mechanical parts are designed for 0 gravity and to test then on earth you need special testing facilities, like the ones in ESTEC in the case of ESA.

  • Graham says:

    The landing gear has to cushion the weight of the lander during touchdown where the lander is moving and therefore has momentum. 100kg moving at a couple of metres per second takes a lot of stopping even in zero g. The important thing is the damping capability of the gear and whether it can absorb the momentum without reaching the limit of its travel and causing a bounce yet not be too stiff either.

    Regarding the drill, the lander was supposed to be anchored which would overcome this issue, but who knows…!

  • drugeon says:

    thank you for this update !

    please keep on letting us inform about all those on-going analysis, thx again !

    all the best

  • Guig2000 says:

    The weight is 1g but the mass is still 100Kg.
    It means that your 100Kg mass is attracted by 67P like 1g on earth. But the inertia is still the inertia of a 100Kg object.
    If you have on earth 100Kg of products witch you move with a manual pallet truck, you have to push hard to make it move fast and then pull hard to stop it.
    I think that 100Kg mass give enough inertia to drill a hole into ice.
    Maybe the drill bit into the ice is enough to stop the starting jump.

  • Mario says:

    You’re probably right about the drill. Because the probe is now stationary, any downward force it exerts on the surface will create an equal and opposite reaction. So, if the drill presses hard to penetrate the surface, the probe will lift upwards in response with only the very weak [1 g] gravity to oppose it. This problem might be countered, though, by having a very narrow drill operated at high speed – this requires less downwards force. But if the surface is very hard, that’s unlikely to help very much, unless the probe is somehow anchored in place or wedged tight, i.e. stuck.

    So far, so good. Now the problem! Your thoughts of the craft onlyweighing 1g misunderstand [sorry!] how the legs would have to work. The 1g is the probe’s WEIGHT on the comet, but when the craft is moving [i.e. when it landed] it would have a lot of momentum behind it: you see, the force required to bring it to a standstill has nothing to do with its weight in this particular situation: the force in the suspension has to counteract the downward momentum. The 1g weight would then be on top of that. In other words, most of the force needed to stop the craft when it lands comes from the equation: “Force = mass x deceleration”. So, the ‘spring’ in the suspension has to provide that [big] force to counter its movement, not just the [tiny] force of gravity.

    Think of a car on earth travelling horizontally on a road. The faster it’s going, and the more mass it has, the more force you need to bring it to a stop, yes? {Force = mass x acceleration again.} That’s got nothing to do with how much springiness you need in the suspension to keep the car steady against it’s DOWNWARD weight when it’s just sitting there. What’s confusing you here, I suspect, is that Philae was moving in the same direction as its weight, so it’s very easy to mix up the TWO forces [Force 1 = force needed to counteract its weight = 1g PLUS Force 2 = force needed to bring it a stop = a much bigger force].

    I hope that helps! Mario

  • Guillermo says:

    Iban, I think there is a confusion between weight and mass. The mass of the lander is still 100kg, and moving to a speed of 1m/sg, the legs has to stop those 100 kg moving at 3.6km/hr. It is like the astronauts outside the space lab. They weight almost nothing, no gravity for them, but to move they have to push their weight or mass.

  • Johnny says:

    A higher temperature would be to prefer, not a lower? Right?

  • Phil Jones says:

    A quick note to say that I really appreciate you sharing your analysis with the public in such a timely way. I also like the way you’re turning a problem with Philae’s final landing position into a long-term opportunity!

  • Jelle says:

    The device has a mass of 100 kg but a weigth of 1 gram because of the extremely low gravity. Springs and suspension systems as used in the legs of Philae are mainly dealing with the mass of 100 kg. The mass is relevant in a dynamic situation, not in a static siutation.
    So, yes the dril may lift the device but with a certain vertical velocity of the device the mass is still 100 kg and the springs and suspension is required to smooth the ‘landing’ of Philae.

  • William says:

    In answer to your questions from myself an amature onlooker. The lander legs were stronger because as the lander was about to touch down a thruster rocket was supposed to fire and push it into the surface so that the harpoons could be fired and lock the lander down. The thruster was found to be faulty before it left the mother ship and hence the delay with go/nogo`s. But it was decided to go ahead as there was no other choice apart from abandoning that part of the mission altogether.
    The lander is now freestanding I imagine but it could have been trapped against the cliff face they suspect it is at. If so they have really got nothing to lose in trying the drilling to see what might happen as the last step before batteries ran out of power. Hopefully Philea might get a bit more sunlight asit nears the sun and recharge the batteries enought o carry out more research with the best systems available to the team.

    Hope this is a correct interpretation of what i`ve seen as a very keen onlooker.

  • steve cheung says:

    I am no mathematician or scientist. You make a lot of common sense, however, I would like to offer my opinion on a couple of minor points.
    First, the rotation of the drill wouldn’t make any difference since the torque depends only on the mass. The torque required to rotate the Pilae would be the same as on Earth. Additionally the torque arm of the drill is much smaller than that of Pilae. Not a concern, I say. The downward movement speed is not the factor, acceleration is. It is not likely that the drill is designed to accelerate downward. So not a concern. The suspension makes total sense ! Thank you.

  • logan says:

    Thanks Emily and Amalia 🙂 That answers several questions. See you have a lot too. Best wishes for the data packets.

  • What you need is the distinction between weight (which depends on the amount of gravity) and mass.

    Philae only weighs a gram, but it’s got the same mass as it has on Earth, about 100 kg.


    You can’t experiment with low gravity directly here on Earth – but rather similar – if you have something really heavy and then put it on a sheet of ice – or an air cushion – or magnetically levitated – is really easy to push it around. But if you get in its way it can still crush you – and if really heavy – takes quite a while to get it moving at any speed if you just push.

    So it is like that. So for the impact – well it’s the same as any impact at a few meters per second, and something that weighs 100 kg. It takes a fair bit to cushion it.

    And with the drill, the drill is small, it’s got to accelerate a 100 kg lander – change its momentum. Was a risk that it would send it into space again. But not as much of a risk as if the lander itself had only a mass of 1 gram.

    E.g. – not sure what mass the drill is – but for 1 gram in mass, and velocity of 1 meter per second just to show how the calculation works, it would impart a velocity of 0.00001 meter per second to the lander in the opposite direction. So wouldn’t take that much resistance to stop that. Multiply that number by the actual number of grams and the actual velocity in meters per second to find what initial velocity it would impart to the lander assuming no friction at all. If there was nothing to stop it, then the lander might do little “jumps in place”. But with a bit of friction, not much, it might not leave the ground at all.

    So that’s the principle, as for actual figures I don’t know.

  • paul says:

    Hi there,
    whilst it is true the lander weighs less on the comet than it does on Earth, the inertial loadings the spacecraft is subjected to during landing are dependent on the mass of the lander and it’s velocity on landing. Whilst the weight changes due to the reduced gravitational acceleration on the comet, its mass remains the same, so the forces on landing or during drilling even, are dependent on any momentum changes that occur and are not related to the weight of the craft. This is why the landing gear needs to be fairly sturdy. It is not a 100000 ton suspension holding a 1 ton car because the one ton car will still need the same force to accelerate (or decelerate it) it to a given speed in a given time regardless of where it is. (assuming no external forces acting) This is an application of Newton’s second law of motion which further describes the impulse on the lander on touchdown in terms of its change in momentum.
    On the comet the weight of the lander is less due to the lower g value of the comet. According to Newton 3 a force greater than the weight will cause it to move upwards. This may well be provided by the drill if the rate of descent of the drill is fast enough and resistance to drilling is encountered.

  • steve cheung says:

    A second thought about your suspension concern. I think the design was focused on the first impact. If I remembered right, they expected the descending speed to be 1 meter per second. Lets say the impact time is about 0.05 second, that will be a deceleration of (1/0.05) = 20 m/s^2 resulting in a force of (100kg)x(20)= 2000 N of force,
    about the weight of 2000 small organic apples.

  • ZongYe says:

    @ Iban: maybe its just like how a mosquito would drill a hole on your skin to get to your blood…

  • steve cheung says:

    In space, you should think about mass, not weight. Common sense on earth may not apply but the principle of Physics will.

  • Scott cosmi says:

    Any chance the solar panels of the delivery vehicle can be used to reflect light onto the lander to help charge the batteries…long shot but hey..it was already an amazing feat.

  • cornet françois says:

    Same feeling about the drill , it sems to me very difficult to make a hole whithout weight . i asked the same question
    yesterday ,no answer yet .
    many scientists post on this blog , maybe one of then could answer our beotian question .

  • Uli says:

    Hallo Iban

    with the drill you my right but I know to less about it to answer your first question.
    But I try to answer your secound one.
    There is ab big difference if the mass is accelerating or not. If it is positioned on 67p’s surface you are right. Then the force of weight is about 1gramm. But if you decelerate the mass of 100kg from 1m/s to zero (landing of philea) the foce of deceleration will be the same as on earth. The formular F=m*a (with f=force, m=mass a= acceleration) counts also on 67P.
    Lets say, if you crash a car into a wall on 67P it will be damaged like on eath. The only differenc is that on earth it will stay on the ground and on 67P it my fly away after the crash.

    I hope i could help you.

  • Rodrigo Cunha says:

    Iban, you can read more about the landing gear here:


    and here:


    And yes, they were designed considering the very low weight of the lander under the comet’s gravity.

  • Gabriel says:

    @Iban It needs to be prepared to withstand the impact, not just a static stress. 1 gram at whatever maximum speed it was designed for may translate into well over 100kg.
    Think of it like this: if you lightly stepped on an empty soda can it could probably support you. If you stepped off a stepstool onto the can it would collapse; step onto it with the velocity of several seconds of acceleration and that can would be crushed.

  • notSoSmartME says:

    hi iban,

    im not a scientist too (though im a chemical engr) and ive been following tis mission since the plan of landing appeared on google news,
    (forgiv my spelling, english is not my mother tongue)
    anyways, about the first question, you cud also consider tat in a place of having microgravity, any body movements (of tat of philae’s per se) would cause turbulence/agitation in the atmosphere (seen astronauts “swimming” in empty space?). though i presume the drilling process hav been done in a scrupulously (or maybe intermitently?) slow manner, if it hits a solid surface (without it anchored on the comet’s surface), it myt move itself instead of drilling.

    the second is tat ter s a good mass ratio (not considering other factor like orientation and dimensions) between the philae’s legs and body to meet equilibrium. if it is on earth then the legs (say with mass A) will support Lander Instruments (with mass B).. if it s on the comet’s surface then mass A will still support mass B. (if u noe wat i mean) as change in gravity will not change tis ratio for balancing.. Plus, the design of the lander (if u can see it) has certain sampling apparatus at bottom (tat wud not be smart to hav it touch d floor for tat matter).
    im not also sure bout tis idea though. tahaha

  • kj henriksen says:

    your forgetting that the lander had ‘harpoons’ to hold it to the ground. also a downward thruster to push and hold it down. both systems failed. hence, the bounce.

  • Ricardo says:

    Hi Iban.

    I don’t know about the suspension.
    What I do know is that Philae when toucjphed the ground for the first time its harpoons didn’t work, so the lander just jumped back into space for two times. Now is under a shadow and only recieves 1h of sunlight per day, not enough to charge the batteries. We need to wait until the comet gets closer to the Sun.
    About drilling, if the harpoons didn’t work, the drilling and collecting task wasn’t a complete success for sure, because as soon as the screw touches the surface the lander lifts, because it just weights 1gr.

    Kind regards,

  • Riccardo Vacchi says:

    Take a big plastic box, fill it with ice packs gel. Take a cordless drill set at lower speed of rotation, turn it on, fix the trigger. Now throws the drill in the box. What’s up? Nothing! Simply the drill from spinning freely. When you are able to calm your wife, can repeat the experiment by adjusting the maximum speed of rotation…

  • Gavin says:

    Mass is still the same even though weight is low. So inertia can be used. Thus hammering in.

  • Ken L says:

    Although it could have done so, I find it hard to believe the lander drilled into the comet. Here’s why. This thing, with the available gravity, and nothing holding it down would only weigh a few grams. You have to push on a drill a little to drill a hole. It could have disturbed the surface and picked up some debris though.

  • Jamie Grover says:

    I am also very curious about the ability of the drill to move the lander in the microgravity. I wonder if there is an accelerometer on Philae or some other means of registering motion that could tell us how much Philae moved when the drill was deployed. Would an accelerometer even be useful in such a microgravity environment? It shouldn’t depend on that right? Also, I wonder if drill deployment speed, and rotation speed was programmed with the lack of anchoring in mind, after that was known or if it just used the original programming.

    Also regarding Iban’s question above, I too am not a scientist (at least not in a field remotely related to this), but I have a hard time imagining that the engineers did not engineer the suspension appropriately so that it would in fact absorb some of the landing with the actual estimated effective weight of the craft on the surface at an impact speed somewhere near the 3.5 kph that it reportedly first touched down with.

    What is the approximate weight of Philae on the comet? I have seen estimates of the gravity on the surface of the comet ranging from 1/10,000th of that on Earth, to considerably less. At 1/10,000th it would of course weigh 10g. The comet is of course rather irregular in shape, and perhaps does not have a particularly homogeneous density either, so I expect the gravity may vary quite a bit.

    Finally, does anyone know what prevented the anchors from deploying?

  • Chris A says:

    I would like to address your last comment about the legs for a 100000 ton car being used on a 1 ton vehicle. You need to realize that weight and mass are NOT the same thing.

    Using the same logic, the comet itself should weigh effectively nothing because it’s floating through space, and therefore you should be able to just give it a light push and it will go flying off in a different direction. Clearly this isn’t the case, the MASS of the comet is 10 billion tonnes and theres no amount of pushing that will make its course vary.

    The same concept applies to Philae. The comet’s gravity might only exert forces on Philae equivalent to one gram, but Philae’s mass is 100kg odd. It’s not going to just bounce off like a ping pong ball when it hits the comet at 0.5m per second. It has inertia and like any 100kg object hitting an immovable object, there is significant energy that has to be absorbed to prevent damage to Philae.

    The legs are designed to absorb this energy. The problem is, without the downforce from the thruster, or the tethering from the harpoons, this same energy was released back into Philae from the legs and it rebounded, same as you would expect from a suspension spring. The design of the legs had to take into account the kinetic energy imparted by the lander, which is a function of its speed and mass, not its ‘weight’. Remember weight is a relative term; it is a function of proximity to some other object; eg. 100kg relative to earth = 1gram relative to the comet = a billion tonnes relative to a neutron star.

    Regarding the drill, I understand the ice screws may have deployed but its not clear how securely they are fixing Philae. This may have been sufficient to hold it down. Not sure. New reports indicate it may not have collected a sample at all, possibly because of the angle of Philae, no confirmation yet on that though.

  • Geoff Skelton says:

    Hi Iban,
    The issue is one of mass and not weight. Force is equal to mass time acceleration or in this case negative acceleration when it hits the comet. Remember it was still moving at walking pace. A bit like if you walked at a fast pace straight into a wall, I’m sure in that instance you would appreciate some shock absorbers. This is the reason that the Starship Enterprise has inertial dampers, going from faster than light to zero velocity in an instant would leave a nasty mess on the inside of the windscreen.
    This is indeed an extremely interesting mission and I also hope that a bit like my solar garden lamps Philae manages to trickle charge enough to at least say hello again.

  • Darren Thorneycroft says:

    A long post with a simple reply: Philae was supposed to be anchored to the comet’s surface, which would have made weight irrelevant. Unfortunately it is not so your concerns are valid.

  • RomainB says:

    Please publish more pictures of everything !!! 🙂

  • Dr. V. Laxmanan says:

    With all the questions here about the drilling operation and the sampling, I am amazed that earlier blogs claimed SUCCESS. I had already posted (on my Facebook page) about ESA claiming success prematurely. ESA’s credibility will be lost if unfounded success stories are put out for PR purposes. Looking forward to more definitive info.

  • Astroholic says:

    Hi Iban,
    First, mass is not the same as weight. Mass does not change whether something is here on earth, or out in space, or on a comet.

    Weight is a measure of the force exerted between two masses (the lander and the comet in this instance) due to gravity.
    The force the lander experienced during “landing” which was more like an impact, was much greater than 1g.

    If you want to learn all about this, Google “Newtonian Mechanics”

  • Steph says:

    Hi there,
    I read that some organic compound have been detected after early analysis conducted by Philae. Could you please let us know how we can be sure that this material has not been hitch-hiked (through the galaxy 🙂 ) from Earth and make sure that data are not polluted . Thanks and Congrats again for this beautiful achievement !

  • Mark Lee says:

    Even though the weight is only 1/50,000th what it would be on earth – the mass is till the same, so it would have collided with 67P pretty much the same as a 100kg mass on earth colliding with a wall at about 3.6km/h. The legs would need to absorb that with very little rebound. If the legs had 18cm (0.18m) of travel and the comet was incompressible, the force per each of the 3 legs would be about 93N (force about the same as the weight of 9.5kg mass) to bring it to a stop.
    I read it rebounded at about 1km/h or 0.38m/s and the legs compressed much less so the forces would have been greater. But the impact was still too little to set off the harpoons so there must also have been “give” in the cometary surface.

  • Mauro says:

    Hello Iban,

    The question about the drill is not easy to answer. How far could the drill go? As we know, Philae was not securely anchored to the surface. Since any force applied to a surface induced an opposite force at the surface, drilling might have lifted the lander from the ground. At the same time, the legs of Philae might have been buried deep enough to keep the lander on the surface. Depending on how loose the material being drilled was, how thin the drill tip was and how “gently” it was operated (its power was just 10 watts), the operation might have succeeded.

    As for your other question, the first impact occurred at a velocity of about 1 m/s (meter per second). This means that Philae impacted the surface with a kinetic energy of about 50 joules (the same energy that Philae would have generated on the Earth surface if it had been dropped from a height of 5 cm). Bear in mind that although, the lander weighed about 1 g on the comet, its mass was still 100 kg. Weight is the force that pulls down an object in a gravitational field.
    When Philae bounced back the first time, its velocity had gone down to 0.38 m/s (38 cm/s). The kinetic energy of a moving object is equal to half the value of its mass times the velocity squared. This means that the energy when down to a seventh of its original value, or about 15%, if you prefer. In a gravitational field that was 100,000 times weaker than the Earth’s; that was enough energy to allow the lander to go “up” to about 700 meters (on the Earth it would have been just 7 mm).

    I hope that answers your questions.

    Best wishes,

  • tkop says:

    Although it “weighs” only 1 gram over there, to delecerate (accelerate) is not affected by it. In other words, if you had to hold the probe, you’d do that easily, but if you had to push (accelerate/decelerate) you had to use the same force as on Earth (assume you’re pushin on level surface with no friction let you can omit G force). So as the legs have to delecerate the probe, they have to be way stronger than to support 1 gr.

  • Axel Enuset says:

    I guess Philae’s legs weren’t meant to support his weight on Earth, but only on 67P, with gravity conditions different from here. I don’t know if ESA’s folks exactly knew the strength of the gravity on the comet, but they may have got some good ideas of it.

    (just a comment from an other no scientist guy)

    Anyway, thanks ESA for this mindblowing experience.

  • luigi says:

    @ iban: about the suspension part, I suppose they were calibrated for the comet’s gravity and never used on earth. the lander didn’t have to be resting on its legs as they worked on it. using it on earth gravity may even have broken them.
    furthermore, they were not exactly suspensions, because their role was to prevent bouncing, so they were made to deform unelastically. and then they could still be controlled robotically. i don’t know what that entails from a projectation point of view.

    About sampling, I also have no idea how they could drill if the lander was not anchored.

  • Dan says:

    Amazing stuff! Question: as I understood it, Philae’s batteries (and electronics?) need keeping at or above zero celsius to be able to charge. This is why they can’t currently be trickle-charged with the small available sunlight – a certain constant wattage is required to keep the heating system working.

    Given that, how can Philae wake up again at some point in the future through battery charging? Is there a small reserve kept that could heat the battery when Philae detects enough power coming into the solar panels?

  • Jack says:

    Great question from Iban!! I would like to know as well, please. Thanks!

  • Jonas says:

    I am curious about the small dust that seems to be covering the comet. How can the almost nonexistent gravity of the body suffice to attract the dust particles and overcome the centrifugal force produced by the rotation of the comet? Could the dust be electro-statically attracted to the comet?

  • Vince says:

    Iban, no need to apologize for not being a scientist. I notice your comments and think they are very thoughtful. I am a retired scientist, so have slightly more information to fill out your question.

    Regards the hazards of drilling. ESA qualified the risks of tipping the lander over in a previous blog and decided to take it, but only as the last experiment (I think in case there was some difficulty, and also since the batteries were starting to get weak). First off, as you mentioned, there is some upwards pressure (mostly delta Z and since there is some tilt smaller components of delta X and delta Y) imparted by the drill. However during the drilling phase one can expect a great deal of the forces to be rotational about the Z axis as the drill encounters resistance. The rotational component would not be as likely to impart lift, so there is less risk to the lander. ESA also indicated in a further post that the drill encountered a hard impenetrable surface soon after starting the drilling process. So it could go no further. In any case ESA sensors showed that the drill finally retracted after this attempt at drilling. Results are inconclusive at this time.

    As to the second question, regards the land gear, again no need to apologize, it is actually a good question.
    There is a two part answer. First, according to Newtons first law of motion. “An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.” Simply, the full weight of 100kg had to be arrested and absorbed absorbed by the landing gear as it did a controlled crash into the much larger mass of the comet. ESA selected the best concept they had available for this purpose and I believe it did it’s job of arresting the full 100kg as perfectly as it could. So the result, the lander was not destroyed on impact. So according to Newtons law most of the energy of impact was absorbed into the surface of the comet by the comet. However, the second part of the answer, a much smaller component of that force was still stored in the compressed springs of the landing gear, then since the harpoons were not deployed as planned, then there was the unfortunate lift off when that much smaller component of energy was released by the springs into the landing gear. There is some estimate as to how far up this bounce took the lander. In any case it was suspended above the comet for nearly 2 hours until it was captured a second time by the comet. That capture was I believe due to the rotation of the comet under the lander and I believe to a lesser extent by the micro gravity of the comet. Basic best guess by most of us is that the lander collided with the larger lobe of the comet, and luckily settled down still upright on its landing gear. The best way to visualize this is imagine Sandra Bullock in the thriller Gravity making her way to the Chinese space capsule. I can imagine if Philae was not just an inanimate object, that the terror of that second landing would have been as great as depicted in Sandras flight.

  • Frank Bryant says:

    Did you consider the calculated weight of a moving object?

  • Andi says:

    About the legs and bouncing:

    Even with almost zero deformation things bounce. Think about a steel ball hitting a steel plate.

    They say that Philea approched with about 1 m/s.
    Let’s say the dampers are optimal and have 10cm to decelerate the lander to zero in a linear way.
    The time for that procedure is
    0,1m / (1m/s / 2) = 0,2s
    The resulting negative acceleration is
    1m/s / 0,2s = 5m/s²
    So the equivalent “force” effective during the deceleration would be about 50kg.

    I think that force would bend the long legs enough to rebounce the lander.
    I personally think because of the failing thruster that poor thing was doomed.

  • DEDT says:

    Your answer to the question about the drill lies in the post itself. The scientists are yet to decide if at all the comet was drilled successfully and matter taken out to the analyser. They say they will have to confirm the pics before/after from the panaroma camera and decide.

  • Horia says:

    hi, Iban! I think you are right. I also was wondering how should that work: to drill on a piece of rock and ice that has such a low gravity. The idea seems to me simple: To drill, you need always the same force (a force that is higher than the resistance of the material you are drilling) irrespective where you are in the universe. So if the drilling force has to be much higher than the gravity, pressing the drill to the surface would simply push the Philae lander away from the surface.
    An important thing: the lander was equipped with a gas thrust. It was intended to pus the lander onto the surface. I presume that the force of the thrust was as big as necessary to counter the forces of reaction caused by the harpoons (two of them) and by those little spikes that are present in the three feet of the lander. But the gas thrust did not work at all, and this is the main problem, as you have now a lander that is almost levitating on the surface of the comet (1g weight!), and which is not anchored at all, to assure, through friction between the harpoon or other anchoring systems and the rock/ice beyond, a force big enough to counter the force of the driller.
    I think that the velocity of the driller, etc, makes no difference – even if the driller moves very slowly to the surface, it won’t get in, because the surface is too hard for that.
    Another possible hope of the scientists: they said that they calculated a layer of about 1-2 cm (or was it 10-12 cm?) of dust on the surface of the comet. This would explain a lot – they probably hoped to take a spoonfull of that dust with the SD2, as the dust has virtually no resistance, needs not to be “drilled”.
    I would expect, if the ESA started so open and with so much details in the news, to get more infos from them, so that they make sense for the average person who reads these news. In this moment, this is not the case, any you just ask yourself a lot of questions when you read these news…

  • Spike Snell says:

    This comet has some pretty amazing EM emissions: https://www.youtube.com/watch?v=HA_J_3xyt8g

  • Yuriy Kartuzov says:

    I think Newton would have the same question. If nothing is holding Philae (which weighs presumably 1gr as per Iban ) to the comment, how it is expected to drill into rock? Or was the drilling instrument designed to collect mostly dust from the comments surface?

    I am interested to know, thanks Yuriy K

  • Greg says:

    First, it is a drill not a nail gun. Drills spin to cut the rock, THEN start to go deeper. So it is apparent that you are neither a “cientist” nor a “matematition.” Second. The legs are built to hold the 100kg so if it only weighs 1gr on the rock, it would definitely be able to hold it up. I mean… get it together Iban

  • Dave says:

    The legs were also designed to stop the 100kg lander. The Philae’s inertial mass doesn’t change just because the gravity is nil.

  • Steve says:

    regardless of the weight of the lander, I would expect that the flutes of the drill would pull it into the surfate and therefore the drill arm would simply assist in the drill keeping contact with the surface, Additionally, the comet does have gravity albeit weak, so the lander would still have at least some nominal weight to it, so as long as the downward pressure exerted by the drill is less than the weight of the lander, the drill should still be able to perform.

  • Lindsay Ward says:

    Philae was the best calculated guess as to something that would work in quite unknown conditions and it did a remarkable job. If the down thruster had worked and the harpoons deployed it would have done an even better job. There was obviously some redundancy built in and also some teamwork from the two craft which was all part of its design and credit to the team. Doing it again would be so much easier with the data that the team now have. I have seen people talking about the rock in pretty much the same way as talking about the types of formations that you might find on earth, remember this stuff has never been subject to earth type processes. I would imagine it to be more like clinker from a coking oven with all the elements kind of mixed up and not sorted out all. On earth gravity will cause a constant dance between wind and water erosion and sedimentation, compaction, volcanism and dissolving and crystallisation. On this comet this comet its raw ungraded unsorted primordial material mixtures of elements and compounds formed in space concreted together by gas and liquid ice, interesting stuff. weighing as little as philae does on the comet. I see why a hammer corer was used because if you tried to drill the it would stick and Philae would spin! Congratulations to the team a truly inspired first try and we will be learning for years from the data already gathered.

  • RG says:

    When I look at the pictures from the Philae, it looks off. To me, the panoramic pictures show a little of the comet on one half and nothing on the other half, as though when Philae finally stopped bouncing, it rested on its side. I would say that Philae was unable to drill into the comet because the drill was pointing in an incorrect direction- because Philae is oriented on its side. The drill essentially drilled space and only collected some of the dust and gas that was surrounding Philae. I would venture to guess that this is one of the causes of low batteries, possibly because the solar panels are covered on the side that is facing the comet.

  • Vay says:

    Good quuestion #1. I woonder too.

    For #2, remember Philae did have a speed of one m/s or similar when it touched down. That kinetic energy must be damped exactly as on earth or against a wall if you will. When standing still, however, gravity is very week holding it down. So, #1 is still a good question.

  • Alan says:

    Can we not bounce the suns rays off of Rosetta onto Philae’s solar cells? It may take a while to charge, but a bit is better than none.

  • Looping says:

    Hi everyone and especially the ESA’s bloggers.

    First of all, congratulation to all the teams involved in this Rosetta/Philae mission, you’ve done something incredible and unique.

    Now I’m very interested in this question.

    “As far as we can see at the moment, SD2 and COSAC telemetry cannot reliably discern between lack of sample and insufficient gas generation from it” […] “We need to see Rolis images”.

    Come on ! These 2 images have been send by Philae almost one week ago !
    How long does it take to watch (or even “process” = adjust brightness & contrast curve) 2 images ?!?

    Why Philae’s team didn’t answer this question until now (and seems to avoid to do it) ?

    The only reason I see (and this disappoints me a lot, after having followed the epic saga of Philae journey) is that the drill bit didn’t reach the surface (due to Philae position… nasty bounce!), which explains the lack of sample…

    And I suppose that you try to not weaken the image of success of this mission (which is UNDOUBTEDLY A SUCCESS, but with some “normal unforeseen”) until the media attention goes down.

    Because (correct me if I’m wrong) I cannot imagine that a sample, heated to 600° C, doesn’t outgas enough to have a spectrum different to the one obtained with the ambient gas.

    Hope to have an answer that will surprise me…

    Thank you for sharing details to public throughout your great scientific exploration missions (space science is a pleasure for me and many other people I guess).


    A science lover (long before this mission) from Europe, particularly proud of the European science (long before this mission too ;)).

  • adam says:

    I think the highly intelligent engineers at the ESA took into consideration all the aspects of a micro gravity environment when designing the suspension and drill systems.

    Your example suggests they used an earth appropriate suspension system and I highly doubt that aspect overlooked them.

  • Stephen Kramer says:

    Gravitation of the comet causes a force on the 100kg lander which is equivalent to the force of earth’s gravity on one gram of mass. The lander still has a mass of 100kg – this is important because it determines the Inertia and kinetic energy of the lander when it lands. So as it is contacting the comet when landing, the suspension must still counteract the lander’s inertia and absorb the lander’s kinetic energy. Like walking into a wall at a few mph, a significant force can be developed on the lander depending on how stiff the suspension is and how quickly you try to stop the lander. If the lander was moving at 1 m/s, the suspension would need absorb 50 Joules of energy to stop it. If the suspension absorbed the lander’s energy evenly in 1 second, it could have done so at a rate of 50 Watts of power, with an average force of 50 N (11.4 pounds).

  • Iban says:

    Hi there,

    Thanks to all who replied clearing things up. I completely forgot about the mass/weight thing, so I was just thinking on a weightless (mass-less?) object. My mistake.

    Now understanding the idea of having 100kg mass to slowdown on landing, or even having to be pushed up by a drill with enough force, I get the answer to both my questions.


  • Drewll says:

    The electric universe theory of comets fits exactly what they’ve been troubled with. I’m guessing the harpoons didn’t hold because they expected to hit soft ice and dust rather than rock. I’m guessing that the drill didn’t pentrate because they hit rock, also the other experiment they were talking about hammerd into a hard surface like they weren’t expecting such as rock….but I’m sure they will play it off as the lander landed on a small rocky surface just by bad luck. I very much hope it wakes up soon enough to keep analyzing the comet so we all see that the whole comet theory needs to be reevaluated and major steps in science need to be rethought.

  • balki says:

    Please let me share my idea about better chances to “hook” harpoons deeper in surface during landing without making “bouncing” force:
    Harpoons driven by explosive can be fired down and in the same time the same explosive can fired uposite site some “counter weight”. By calculating mass and speed of both sides can be setup needed “hook up” force that oposite mass no need to be too heavy.
    On this way we can have needed force for deep penetration of harpoons without bouncing effect for “lander”.

    Good luck!

  • Jacques Gilman says:

    Comment from another non-scientist. The very first picture from Philae post-landing shows a series of rock which seems to demonstrate that the comet is, or at least was at one stage, made of ice (next to other materials). One can clearly see several small stones of a few cms encrusted in another ingredient made of dust and ?? That reminds me of the aspect of the moraines left by retracted glaciers which are visible in the Alps, Himalayas, etc. The small stones in these moraines appear to be set (encrusted) in the sand resulting from the grinding of the glacier on rocks progressively reduced to sand and dust.

  • Robin Sherman says:

    Hi Iban, no I’m not going to tell you about mass and weight again. For a long period of time your post was the only one visible, hence numerous people tried to answer your question. I hope you don’t feel like you are being picked upon.

    The evidence from the lander team is that when the drill was used and all the other instruments deployed Philae did not move. The MUPUS “hammer” is deployed away from the lander and is not attached to the lander when operating so would have no affect on the lander whether it was firmly attached to the ground or not. Because the MUPUS hammer was able to deploy and work, the attitude of Philae’s main body must have been reasonably close to vertical. There are systems in the suspension to enable Philae to be upright even if the landing gear is on a slope, up to 30 degrees of compensation I believe.

    One must presume that before these science tasks and instruments were initiated the team would instruct Philae to adjust her position to be as vertical as possible, indeed it may be inbuilt into her software. Though as we have seen on 67P defining “vertical” is problematic at best. Stephan said, the signal strength of the telemetry indicates that the top of Philae was pointing pretty close to vertical as do the team studying the light falling on the solar panels. The angle between the side of the lander where the SD2 drill is located and the ground could therefore be sufficient to mean the drill did not actually reach the ground, or at best the top of the proposed layer of dust.

    It is my guess and I think quite few of the team think that Philae is actually wedged between the cryorock we see in the CIVAS image and the cliff. One view Stephan has expressed is that below Philae is a crevasse or hole which could also explain no drill sample. It may be that Philae is stuck half way up a cliff on a ledge wedged between some outcrops or boulders.

    We also know the harpoons did not fire at the first landing. If they had I am sure we would have heard the explosive charges in the sound recording released. The mystery is, it was reported that the signal to rewind the harpoon cables was confirmed as having been sent. This implies an internal force was being applied to rewind cables that were not unwound. This force must, instead of acting on the cable and harpoons, acted on Philae. Maybe this is what changed the direction of Philae’s first bounce.

    It is now over week since the epic saga of Philae’s landing unfolded in such dramatic fashion, yet still we have no coherent timeline of events that did or did not happen. We are not talking velocities, angles of bounce, causes and results, just a list of events. What pictures did ROLIS take and when, was the first science program initiated and if so which instruments gathered data, was Philae’s internal software aware that she was still moving and therefore stop the science package at some point, and what, if any, sensor and instrument data was obtained from the second and third touchdown? I realise that data has to be examined and interpreted, but a world wide audience is still asking, what actually did happen on that day? Most of us are scrabbling around to find quotes from various people in multiple outlets to try and piece together the scenario, and the evidence is, singularly failing to do so. At the moment its like trying to chose which bloke down the pub is telling the real story, if any of them. An attempt to clarify what ESA does know about what happened would be very welcome. Perhaps a 5 minute video using the backup Philae lander to show what should have happened and what actually happened. I am sure Emily, you and your outreach colleagues would jump at the chance to do something like that.

  • Dave says:

    I agree with your article Rob, we don’t often agree, we have very little to work with.
    I would also question if any of the feet of philae are actually on the ground or even on the wall facing it?
    If they are not on the ground then not only is there a doubt that the drill or the hammer contacted anything. Also, most of the rest of the Mupus measurements must be compromised in some way, if the lander is on its side where on 67p did the probe go and what is it measuring? It’s no wonder the instruments are not recording much activity, they are probably in space. So where does consistant with water ice come from?

  • dnussb says:

    Would like to have a plausible terrain profile of the place the lander ended rocking on.

  • Edgar José Guimarāes says:

    Considerando que Philae está em contato com a superfície do cometa e portanto adquiriu a mesma velocidade deste, nāo havendo nenhuma outra força capaz de deslocá-lo da superfície,qual seria a possibilidade de perder a aderência?

  • Aidan Karley says:

    [quote=”Iban”]Philae shouldn’t be able to stand on its legs on earth, for it to succeed on the comet. I mean, instead of being prepared to hold 100kg, the legs should hold just 1 gr. On earth it should just bend and touch the floor.[/quote]
    You’re missing the point that Philae travelled from Earth to Rosetta with the legs folded up into it’s +/-cubic form, before detaching and deploying the radio antennae and legs. During assembly, launch, and travel to Rosetta Philae was supported on parts of the main frame. Only after launch from Rosetta were the legs spread out. The legs never once had to support Philae except on landing on Rosetta.
    Look at a ship being built in a dry dock : it’s supported on piles of wood. Does the same ship rest on the same piles of wood after 10 years travelling the seas? No ; the wood is still in the dry dock (Rosetta).

  • Claudio says:

    Iban, you are right!
    I think that Philae can not drill the Comet, because the anchoring force can NOT BE obtained. If I launch a gun-maked anchor I have to react the gun with a spray. The question is: Can a spray generate a gun force able to anchor Philae? I think this is not possible. In fact the ancoring force has not been reached!

  • Drewll says:

    Have any of you guys on the team considered that the Electric Universe theory of comets is correct? They state that comets are in fact solid rock and not dust and ice, hence why the harpoons didn’t grip, the drill didn’t work and you think you hit dense ice when it was rock. I also wonder how dust-ice could be darker than coal? I really hope you guys take a look at rewriting the standard theory after his mission finishes its last phase so we can advance science to the next phase not controlled by religious dogma to the old theories.

  • zefr says:

    Greetings ESA-Philae. When can we expect an update on results from each of the instruments to put the landing and discoveries into perspective of what we have learned thus far? Thanks and many congratulations from British Columbia, Canada.

  • Ambroise says:

    Hi guys, I was reading today on the web that the drilling was not sucessfull. only one peace of dust came inside. can we have an update please?

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