Rosetta lined up for lander delivery

Rosetta conducted an important manoeuvre this morning that shifted it onto the orbit it will maintain until 12 November, when Philae is set for dispatch to the surface of comet 67P/C-G.

The thruster burn took place starting at 02:09:55 UTC (03:09:55 CET), ran for 90 seconds and, based on an initial analysis of spacecraft radiometric data, delivered a delta-v – change in speed – of 9.3 cm/sec, as confirmed by the Rosetta Flight Dynamics team.

It was the second and final of two ‘deterministic’ (i.e. direction and thrust are prepared in advance) manoeuvres that moved Rosetta onto the planned lander delivery orbit, now at a height of about 30 km, which will be maintained right up until the pre-delivery manoeuvre at two hours before separation at 08:35 UTC (09:35 CET) on the morning of 12 November.

Note that mission control team at ESOC expect to conduct some additional, minor 'touch-up' burns between now and then just to maintain Rosetta on this orbit; these will not significantly change the orbit.

Rosetta & Philae at comet 67P. Credit: ESA–C. Carreau/ATG medialab

Rosetta & Philae at comet 67P. Credit: ESA–C. Carreau/ATG medialab

It’s also interesting to note, as mentioned by mission scientist Matt Taylor, that this moves Rosetta away from the closest bound orbits (10km) we will ever achieve during the mission.

“From now on, the closest distances we will achieve will be via flybys to provide the science instruments on the orbiter the closest look at the comet.”

As mentioned, the next planed orbit-changing manoeuvres will occur on the 12th at (a) 2 hours before separation and (b) about 40 minutes after (see animation below), in between which Philae will be released.

The pre-delivery manoeuvre will shift Rosetta's trajectory so that the orbiter would be on a path so as to pass over the comet at a distance of 5 km, while the separation will occur at 08:35 UTC on board the spacecraft about 22 km (the confirmation signal will arrive on Earth at 09:03 UTC).

The second manoeuvre will cause a deflection of the Rosetta trajectory away from the comet; it will occur 40 minutes after separation, and help guarantee visibility of Philae at touchdown.

Lined up for lander delivery

All in all, today’s burn means that the mission is lined up for lander delivery!

One of the questions frequently posted here in the blog (and via other channels) asks about the delivery height. Why is it set for 22.5km?

We passed the query to Rosetta Flight Director Andrea Accomazzo at ESOC, and he provided the answer below, with inputs from Vicente Companys from the Flight Dynamics team.

There were many constraints to take into account when designing a viable descent trajectory for Philae.

These constraints refer to minimum comet distance of Rosetta, performance of Rosetta, performance of Philae, requirements for touch-down conditions, attitude constraints of Rosetta, safety margins, etc.

The accuracy of the landing does not depend on the distance to the comet, but rather is a combination of the position and velocity errors of Rosetta at the last time its orbit is controlled (two hours before separation in the selected strategy) and their propagation up to touch-down time.

Flying closer to the comet is not necessarily more accurate than further away; thus initial navigation errors and time to touch-down have to be accurately balanced.

Further to this, the selected separation strategy foresees a fixed separation velocity of approximately 0.187 m/s. This imposes limitations on the capability of directing Philae towards the comet, i.e. it restricts the domain of possible positions and velocities for Rosetta at the time of separation.

If Rosetta were to release Philae from any closer distances, then it would have to fly with lower velocity to be able to direct Philae towards the comet (and still maintain the minimum safety distance). By reducing the velocity of Rosetta, however, we would have two negative effects:

•    Rosetta would not fly on an hyperbolic trajectory with respect to the comet; therefore the spacecraft would potentially fly towards the night side of the comet, which we want to prevent
•    The time from last orbit control manoeuvre to touch-down would increase, thus increasing the time over which navigation errors would propagate, affecting landing accuracy

In preparing the delivery operation, several options were analysed and the selected one is the one giving the best results in terms of landing accuracy and fulfilment of constraints.

In summary:

•     Rosetta will start off on a slightly elliptical orbit at about 30 km distance from the comet centre
•     About two hours before separation, a manoeuvre will move Rosetta onto an hyperbolic orbit flying in front of the comet and with a miss-distance of about 5 km from the comet centre
•    Forty minutes after Philae separation, when Rosetta is at about 20 km distance from the comet, another manoeuvre will move Rosetta away from this orbit and move it to a region that guarantees visibility of Philae at touch-down

Rosetta lander delivery orbit Credit: ESA

Rosetta lander delivery orbit Credit: ESA



  • Alain says:

    Hello ! thanks for your news
    just to say that there is a little error at the beginning :
    no "08.35 UTC (10.35 CET)" but "08.35 UTC (09.35 CET)"


    bye bye

  • Dan Owen says:

    Wow, just wow. Glued to the tube.

  • morganism says:

    7 hours of terror, and a Hyabusa moment....

  • Bartosz Wnuk says:

    I think, there is small mistake in separation time description: it is: separation at 08:35 UTC (10:35 CET) on the morning of 12 November, while it should be (9:35 CET).
    Nevertheless - very interesting article and fascinating mission. I am so curious and excited of landing. Good luck Philae !
    Bartosz Wnuk, Poland

  • Turbo says:

    All this info is really fascinating! Thanks and congrats!

    I'd like to see a discusion about landing decisions translated by an expert 🙂 I mean maybe in the real discusion some people argue if the velocity has to be 2.2 m/s. Or 4.1 that no means nothing For someon like me but an "explainer" could take some minutes to tell us why is this important. I know in this moment something like that is imposible because of the priorities you have, but maybe in the future 🙂

  • sssalvi says:

    I am sure you must have answered it earlier:
    The time-tags in Rosetta timeline? .. Are they 'in situ' time or 'as received at Earth' time after delay?

  • Brendan Cooney says:

    Good luck at separation and landing!
    Hope there were no screws leftover at assembly.
    Pictures so much better than last time ESA was at a comet with Giotto.

  • Steve says:

    Dear Rosetta Team,

    I've heard that you want to transmit data from Philae during the whole 7 hours landing phase. This wasn't planned in the beginning. So how much of your initially planned 57 hours battery lifetime will be left after successful landing and how much time will it need to recharge the batteries agian?

    Thanks a lot and good luck!

  • One slight source of confusion (well, at least for me) in your article: it speaks about the "pre-delivery manoeuvre" for the movement that the video calls the "pre-separation manoeuvre", while the current orbit *before* that maneouvre is also named "pre-delivery" [orbit] in the video. I don't think that a manoeuvre should be given the same attribute as the orbit that it is effectively ending, so I'd say that the video has got it right and it would be helpful if you could change the text.

    I found it very interesting to learn about the details of Rosetta's movements before and after separation, so thank you for this. And of course I'll also be awaiting the results of all those movements with great anticipation 11 days from now (and I've just tweeted about that too), dare say that it will slightly distract me from work that Tuesday. 🙂 So the landing will occur at about 16:00 UTC, can you say when approximately we will know if it went well?

  • Cometstalker says:

    The only disadvantage at this mission is that once the lander is safe on the surface it is there for keeps. Would it be possible to use the foot to make a small jump once all the experiments are finished and shift its position by chance? A free fall from one meter takes over 80 seconds and if a small jump is made it would actually drift for several minutes until settling again. It is gyro stabilized so the toppling over is of minor concern its just a matter of the foot grip.

    • Armelle says:

      The Lander will securely anchor itself in the comet to make sure that it cannot move. The goal is all but moving it afterwards. If the ice-screws could be 'unscrewed', the harpoon cannot be detached from the ground. That's it's whole purpose!
      The gyro is not designed to be re-used after the (long) descent.

      Alsot, I doubt that the experiments will ever be finished. After the first science sequence, they will continue measuring the changes in the comet as it awakens, and it is likely that it will die before perihelion is reached.

  • sssalvi says:

    OK .. seen that the information given contains a line " Time as received on Earth"

    Thanks .. no reply needed from you.

  • Noel says:

    Let us hope nothing happens to Rosetta's propulsion once it is in its hyperbolic orbit!...
    Good luck For Philae!

  • Graham says:

    It seems to me that the pre delivery corrections are to get Rosetta on a path close to the equator plane of the comet. Release of the lander is timed for when the base of the "duck" is facing Rosetta and over the next 7 hours the comet will rotate so that the landing area has rotated under the lander as it falls under very weak gravity. The post release correction of Rosetta is so that the landing site will be visible from Rosetta for as many hours as possible the comet rotates.

    As I understand it the best approach path is one that allows the primary ejection mechanism (its adjustable) to be set to the same force as the backup mechanism (which isn't) so that both would permit the optimal landing position.

  • logan says:

    Hi Daniel. Best wishes to all Flight Dynamics Team. 🙂

  • Steve Wiggins says:

    Best wishes for a happy landing!

  • Kamal Lodaya says:

    Daniel: Not many amateurs have the equipment to see 67P, but if they do, would it be worthwhile pointing Earth-based telescopes there and hope to faintly detect the impact of the landing? Since the projected time is 15.35 UTC and the comet is in Sagittarius it would have to be the Australasian night sky.

    Best wishes!

    • Armelle says:

      Hi Kamal,

      You would not see anything. The ground based telescopes cannot see the nucleus because the coma is shading it from sight.
      Also, the landing is a soft landing, there will be no impact ! Just a "gentle touch-down".

  • Graham says:

    I posted yesterday about Rosetta having been put into a particular orbit to allow the landing and long observation afterwards - It hasn't appeared yet - did it break any rules?

  • Raphael says:

    Hey guys,
    wish you good luck for the whole manoeuvre! Proud to be a European!
    Good luck!

  • simon says:

    Hello , Is the choise of Site J 100% definitve now ? If so , with what vertical speed will the landing take place there at the moment of touchdown ?

    • AndreH says:

      And another question: What will be the horizontal speed (speed over ground so to say?)

  • sssalvi says:

    How Is Rosetta continuously revolving around 67P? Comet doesn't have sufficient gravity to support orbit of several kilometers around it. Moreover the orbit in last 1 month has complex maneuvers. .

    • AndreH says:

      @ssalvi: for any two masses (bodies), no matter how big or small you can have bound orbits.
      Practically it is not one mass(body) orbiting the other, but both masses orbiting their centre of mass.
      If one mass (body) is much bigger than the other, the centre of mass falls close to the centre of the bigger mass (body).
      It appears in that case at first glance that the body with the smaller mass is orbiting around the one with the bigger mass. Like the planets around the sun or the moon around the Earth.
      The key is orbital speed. If Rosetta would orbit the Earth it would have to have much higher speed at the same distance to the centre of the Earth than it has at the same distance to the centre of the comet. Ofcourse at distances lower than 6370 km it would hit Earth's surface whereas at the comet it can go much closer.
      Hoe this was not to complicated....

      • sssalvi says:

        Thanks AndreH for an enlightening reply,

        Working only with Earth model we just try to apply the same scale to every problem forgetting the basic physics.

        Will do some real maths to compute barrycenter etc.

        Thanks again.

  • Hansart says:

    "therefore the spacecraft would potentially fly towards the night side of the comet, which we want to prevent"

    If my memory is good, such a manoeuvre over the night side of the comet has already occurred, but no information was released. I would be very interested to get some feedback on this particular manoeuvre. Thank you!
    And all the best to mission controllers for the next coming activities, we all depend on your professional skills to make this mission a success!

  • Rustychain says:

    This is so exciting it's right off the scale. Good luck to everyone involved, and particularly to Philae of course!
    To potentially see images of her down there, on the surface of a comet, would have been beyond the imaginings of almost anybody on Earth 50 years ago.
    Just incredible.

  • tare2711 says:

    Fsinating time is coming. Great success , We are waiting.
    In 2005 11/20 & 11/26, JAXA website(Tokyo) is very crowded with
    30~40 thousand visitors, exited with first tochedown& go to asteroid Itokawa.
    Now, many Japanese fan is hoping first tochedown to comet C/P.

  • Niall says:

    How will everybody be viewing/tracking this event? Are there planned live streams, commentaries, twitter feeds I should know about?

  • opiochus says:

    Estamos pendientes para difundir momentos y detalles. Felicitaciónes a ESA! DESDE AMÉRICA.

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