This article is mirrored from the ESA Web Portal.
Rosetta approaching comet 67P/C-G from afar.
Rosetta is set to complete its mission in a controlled descent to the surface of its comet on 30 September.
The mission is coming to an end as a result of the spacecraft’s ever-increasing distance from the Sun and Earth. It is heading out towards the orbit of Jupiter, resulting in significantly reduced solar power to operate the craft and its instruments, and a reduction in bandwidth available to downlink scientific data.
Combined with an ageing spacecraft and payload that have endured the harsh environment of space for over 12 years – not least two years close to a dusty comet – this means that Rosetta is reaching the end of its natural life.
Where is Rosetta on 30 September?
Unlike in 2011, when Rosetta was put into a 31-month hibernation for the most distant part of its journey, this time it is riding alongside the comet. Comet 67P/Churyumov-Gerasimenko’s maximum distance from the Sun (over 850 million km) is more than Rosetta has ever journeyed before. The result is that there is not enough power at its most distant point to guarantee that Rosetta’s heaters would be able to keep it warm enough to survive.
Instead of risking a much longer hibernation that is unlikely to be survivable, and after consultation with Rosetta’s science team in 2014, it was decided that Rosetta would follow its lander Philae down onto the comet.
The final hours of descent will enable Rosetta to make many once-in-a-lifetime measurements, including very-high-resolution imaging, boosting Rosetta’s science return with precious close-up data achievable only through such a unique conclusion.
Communications will cease, however, once the orbiter reaches the surface, and its operations will then end.
During Rosetta’s final descent, the spacecraft will image the comet’s surface in high resolution from just a few hundred metres. This OSIRIS narrow-angle camera image was taken on 28 May 2016, when the spacecraft was about 5 km from the surface of Comet 67P/Churyumov–Gerasimenko. The scale is 0.13 m/pixel.
ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
“We’re trying to squeeze as many observations in as possible before we run out of solar power,” says Matt Taylor, ESA Rosetta project scientist. “30 September will mark the end of spacecraft operations, but the beginning of the phase where the full focus of the teams will be on science. That is what the Rosetta mission was launched for and we have years of work ahead of us, thoroughly analysing its data.”
Rosetta’s operators will begin changing the trajectory in August ahead of the grand finale such that a series of elliptical orbits will take it progressively nearer to the comet at its closest point.
“Planning this phase is in fact far more complex than it was for Philae’s landing,” says Sylvain Lodiot, ESA Rosetta spacecraft operations manager. “The last six weeks will be particularly challenging as we fly eccentric orbits around the comet – in many ways this will be even riskier than the final descent itself.
“The closer we get to the comet, the more influence its non-uniform gravity will have, requiring us to have more control on the trajectory, and therefore more manoeuvres – our planning cycles will have to be executed on much shorter timescales.”
A number of dedicated manoeuvres in the closing days of the mission will conclude with one final trajectory change at a distance of around 20 km about 12 hours before impact, to put the spacecraft on its final descent.
The region to be targeted for Rosetta’s impact is still under discussion, as spacecraft operators and scientists examine the various trade-offs involved, with several different trajectories being examined.
Broadly speaking, however, it is expected that impact will take place at about 50 cm/s, roughly half the landing speed of Philae in November 2014.
Commands uploaded in the days before will automatically ensure that the transmitter as well as all attitude and orbit control units and instruments are switched off upon impact, to fulfill spacecraft disposal requirements.
Rosetta faces a dusty environment like this every day at Comet 67P/Churyumov–Gerasimenko. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
In any case, Rosetta’s high-gain antenna will very likely no longer be pointing towards Earth following impact, making any potential communications virtually impossible.
In the meantime, science will continue as normal, although there are still many risks ahead. Last month, the spacecraft experienced a ‘safe mode’ while only 5 km from the comet as a result of dust confusing the navigation system. Rosetta recovered, but the mission team cannot rule out this happening again before the planned end of the mission.
“Although we’ll do the best job possible to keep Rosetta safe until then, we know from our experience of nearly two years at the comet that things may not go quite as we plan and, as always, we have to be prepared for the unexpected,” cautions Patrick Martin, ESA Rosetta’s mission manager.
“This is the ultimate challenge for our teams and for our spacecraft, and it will be a very fitting way to end the incredible and successful Rosetta mission.”
Details regarding the end of mission scenario are subject to change. Further information will be announced once available.
Background information on ending Rosetta’s mission on the comet was published on the blog last year.
Discussion: 46 comments
Why lethal and not death-defying?
https://marcoparigi.blogspot.com.au/2016/06/rosetta-lament.html
Did we give up on Akatsuki?
Do we ignore Voyagers because they are too far away?
Do we have an opportunity to receive the last hi res picture taken before crashing? No – We could have time to receive it if Rosetta moves away!
Spacecraft were born to fly.
Sleep is the best ending, not euthanasia!
Is anybody else going to find changes in this nucleus?
I’m sure there are some – go to the following link to see some:
https://blogs.esa.int/rosetta/2016/06/03/the-changing-comet-call-for-contributions/
How to end a mission with an inoperable spacecraft.
Step 1: Make sure that your spacecraft is dead.
Eg. For Hitomi – Do all you can to save it and check every possibility before realising that it is inoperable (do to spin and break-up)
For Rosetta – Make sure that the final act guarantees that it is indeed dead (deliberately crash it into the object of observation)
I had heard from someone that a similar popular campaign to the “Wake up Rosetta” was being planned for the ending, but kind of reverse as in “Goodnight Rosetta”
The campaign would culminate in a final close fly by at about 20cm per second and only 200m from the surface. Rosetta would take many images, sniff for many more substances as they are easier to detect close up, collect mor dust samples and so forth. There would be a slight thruster burn of around 50cm/sec to escape the gravity of 67P, and then all that data would be sent back through the “Goodnight Rosetta” final farewell. The final act of the campaign and the mission would be to put Rosetta into renewed hibernation and abandon the mission. It would be a very fruitful end to a fruitful mission and would generate a last fantastic boost of support, perhaps comparable to the Philae landing. Such close data would be as powerful as data right on the surface, because of its close proximity and many instruments, and would give the public a proper chance to farewell the probe on a high note!
Hi Emily,
I can sleep better now that I know what happened to Philae.
https://marcoparigi.blogspot.com.au/2016/07/i-know-what-happened-to-philae.html
Hi Emily
Marco Parigi has suggested on several occasions that Rosetta should perform a close flyby and escape, rather than a crash on 30th September 2016. His ‘Rosetta Lament’ linked in his comment above, lays out his view. If Rosetta performed such a flyby and escape, she could then possibly return in 2020 to reacquire the comet.
I, on the other hand, have suggested several times that Apis should be targeted for a close flyby because, according to stretch theory, Apis must be the least processed and therefore most primordial region on 67P.
I’ve therefore put together an Apis flyby scenario for September 30th 2016. It’s in a blog post linked here, Part 59 of 67P/Churyumov-Gerasimenko- a Single Body That’s Been Stretched:
https://scute1133site.wordpress.com/2016/09/01/part-59-the-dare-devil-apis-flyby-escape-and-2020-reacqusiton/
The flyby scenario outlined includes escape burn to a heliocentric orbit that’s also a quasi orbit of 67P. This ensures automatic return to 67P in January 2021, when 67P will be at the August 2014 acquistion point in its orbit. The scenario details all necessary orbital elements, delta v transfer burns, a plane change and parabolic escape prior to full escape so as to ensure an orthogonal Rosetta departure radiant from 67P’s orbital plane. It also includes the initial configuration of the flyby ellipse in the heliocentric ecliptic reference frame so as to make the parabolic escape and quasi orbit work.
There’s also a twin post addressing any possible objections to the flyby, escape, reacquisition option, Part 58:
https://scute1133site.wordpress.com/2016/08/31/part-58-the-case-for-a-dare-devil-flyby-of-apis/
This post addresses the difficulties that deeper hibernation causes for solar power generation, the delta v budget, DSN time, the gravitational anomalies on close approach to Apis, and much more. It also presents a ‘crash avoidance trick’ that exploits the unique position of Apis on the long-axis tip, thus allowing Rosetta to run the gauntlet of such a low-altitude flyby.
The relative speed to Apis at close approach is 0.251 m/sec as opposed to the crash trajectory relative speed of 0.5 m/sec. The low-altitude ground track is at least twice as long by definition of it being a flyby and not a crash (with periapsis under the surface). This makes for a close approach duration that’s four times the crash approach duration with the added advantage that data transmission doesn’t have to be performed in real time. This means more data per unit time can be taken, throughout the four-fold duration period, and sent back later in dribs and drabs.
Marco and I think this scenario is a very much better option for scientific data return than crashing on the comet and returning a fraction of the data that flyby and return could furnish. Moreover, whilst the chance of Rosetta never waking from hibernation is real, it isn’t zero and may be less than we might try to quantify. Why not run the scenario in real life, rather than run the numbers and declare it a small chance? It costs nothing to suck it and see, except for an hour of DSN time in 2020. The dare-devil flyby, escape and return attempt is a bold test for Rosetta, and the ingenuity of the ESA scientists. It’s a fitting finale which may yet turn into a 1-year comeback act. The controlled crash means simply going out with a whimper. So I can’t help but see this Rosetta blog post as being rather like a suicide note.
(This is a belated comment, dated 1st September 2016- it took some time to write the two posts among other posts and other things!).
Some very important questions:
WHERE have you decided to land ?
If the landing location is not yet decided, have you made
some choise of possible landing locations ?
In any case, what are the prefered properties of the
optimal landing target.
Thanks a lot for a reply
There are several trajectories under discussion, as mentioned in the text. We’ll let you know as soon as we can what has been decided!
Hi Cesarean,
Let us for argument’s sake, this landing site that is a once in a lifetime opportunity to take all sorts of measurements up close. Let us call it “Pluto”. Now – do we fly by really close and fill our little hard drive with data as much as possible, and then send it all back over low bandwidth for the next few hours/days, for a mountain of once in a lifetime data, or do we use this opportunity to pollute a once pristine comet?
Let’s go for the crash ending – Yay for objective scientific logic!
Hi Cesare Guaita,
Sorry about the autocorrect fail on your name. I don’t think the plan is the best one on several grounds.
Why do the transmitter and instruments have to be switched off before impact? If Rosetta bounces back into orbit, would we know?
Dear Superlumiinal,
Once Rosetta hits the surface, its main transmitter will be turned off to meet regulations aimed at avoiding interference on deep space network channels. No automated re-activation will be possible.
Hi Claudia,
Thank you very much for your answers. I would have thought the interference is very unlikely except for future missions to 67P. In which case, having a spacecraft possibly bounce and have solar panels detach would be a surface and surrounds contamination issue. In my mind that is a comparable scale of problem as the radio interference issue localised to the same comet under question. I am always suspicious of regulations for regulation’s sake. Do fly by missions have that regulation? Eg Giotto. When did the regulation start?
That is to say, I think scientific or mathematical calculations should trump regulation. Ie, what risks are there on this particular probe in this particular orbit for deep space network channel interference (If the probe did not land on the comet and is in a similar heliocentric orbit with a hibernate/wake long term cycle) Of course if the probe is abandoned in an unrecoverable state anyway, there is no extra risk in shutting these down. I guess if we change our mind later and wish we had done things differently we do not have that option.
May I ask for a more throughout explanation as to why it’s decided to shut it down at landing? If I’m not misremembering they did communicate with NEAR Shoemaker did communicate after landing (presumably with the low-gain antenna?). Obviously Rosetta doesn’t have the same design as NEAR Shoemaker and presumably the Rosetta team has looked into such a scenario and deemed it unsuitable, but it would be interesting to know a more in-depth reason as to why it isn’t done either way.
Dear Daniel,
As we approach 30 September, the solar power available will be declining, and Rosetta won’t be able to operate all of its instruments anymore. Soon after, the satellite will be on the other side of the Sun as viewed from Earth, and very hard to communicate with. That’s why the mission will end on that date, with the decision to descend slowly to the comet’s surface made to obtain final excellent science.
Once Rosetta hits the surface, its main transmitter will be turned off to meet regulations aimed at avoiding interference on deep space network channels. No automated re-activation will be possible. The impact is very likely to damage the spacecraft in any case and the main communications link with Earth via the high-gain antenna would be broken with even a slight change in spacecraft orientation.
Hi Claudia,
The “final excellent science” would be just as excellent with a hyperbolic non-impacting orbit as it would with an impacting. Subsequent extra transmission time would allow for way more data from that “final excellent science”
There is no guarantee that future missions would find Rosetta anyway – After all we lost Philae, and we know where it impacted (with far more appropriate landing legs)
@Marco,
Sorry, I don’t get what you’re saying here. A hyperbolic orbit means a very quick, close pass, and then off into space, never to be seen again: https://en.wikipedia.org/wiki/Hyperbolic_trajectory
What scientific benefit would that bring? It’s already had numerous close approaches to the comet; a quick fly-by will provide nothing to the sum of the knowledge we already have.
The same applies to a captured orbit. Been there, done that. And that will likely end with the craft crashing into the comet at some stage anyway.
Given that the fuel and solar power are going to run out shortly, and the probe will be uncontactable from Earth, I can’t see that there is a better option than the one that has been planned.
Hi Ianw16,
Due to the low gravity of 67P, any speed above the escape speed of 1 m/s is in a hyperbolic trajectory. 1 m/s is hardly a quick close pass. For the moment, no passes closer than about 5 km from the surface have been made.
The advantage of a speed just above escape velocity is that a safe mode would not result in the risk of impact, and allow time away from danger to transmit information, recover and extract maximum data before eternal hibernation. Close bound orbits and impacting trajectories are much riskier in the sense of unrecoverable modes such as shadowing of solar panels before the planned ending. An embarrassing loss of contact well before impact would be quite an embarrassing end to a fine mission.
A close pass in the order of between 100m and. 2 Km would get incredible NEW data from many instruments and many images. An elliptic or borderline hyperbolic trajectory would allow the time to transmit that back in the last gasp (transmitting does not require fuel, but requires time at such a low bandwidth)
A hibernation end would allow future amateurs a shot in the dark for a Phoenix reawakening in another 4 years. That could allow, with even 1 % fuel remaining, for a new fly by to see changes next perihelion.
@Marco,
(I’m not sure where this reply will end up, as there was no reply option on your latest post).
However, as mentioned in the main article, hibernation, particularly for 4 years, simply isn’t an option:
“The result is that there is not enough power at its most distant point to guarantee that Rosetta’s heaters would be able to keep it warm enough to survive.
Instead of risking a much longer hibernation that is unlikely to be survivable, …….”
And I’d be far more interested in what may be gained from a “downward” descent to a particular spot on the surface at 0.5 m/s, than the relatively quick fly-by from say 1 km at 1 m/s.
Hi Ianw,
Yes. Best bet for replies is to reply again to the first reply spot in the last thread.
The key word with keeping components warm over hibernation is “guarantee” We are not looking for guarantees. The Apollo 13 crew had no “guarantees” that their command module could survive several days of freezing conditions and still be able to fire up for re-entry. Rosetta could survive, while it couldn’t if we impact 67P. If Apollo 13 thought it “impossible” to survive the return trip to Earth – yes. They may as well have landed on the moon. Why die pointlessly in the middle of space if they could have a few days exploring on the moon first?
Additionally to that argument, landing Rosetta at 50 cm per second does not get any better science than going almost all the way to landing, and then powering away to give more transmission time for the data.
Can you please briefly highlight the reason for the spacecraft disposal requirements. What could happen if they are not met?
Dear Jochen,
Please see the reply to Daniel’s comment above, where the reasons for the spacecraft disposal requirements are outlined.
Best wishes
Do I understand this correctly, that the low gain antenna may still be able to transmit telemetry, and maybe a small amount of instrument data after td?
Gerald.
Yes, I’d mentioned that possibility. But only for a short time on residual battery power. Also not clear what instruments might operate (no imaging certainly) and whether the system is configured to transmit instrument data over the low gain; it may not be. At best a very, very thin chance of not much.
Whilst I can certainly see why the disposal regulations exist for planetary orbiters etc, using them as the primary justification for switching off seems a bit thin. The probability of interference is clearly low, and Rosetta will fail pretty soon anyway.
So a high risk very close flyby with the chance to transmit data back afterwards on the last gasps of fuel and solar power seems attractive.
But personally I do have considerable confidence in the ESA team that has delivered so much from Rosetta and would accept their decision, though I don’t think it has been very well explained really.
Harvey,
thanks! I guess, that monitoring the td, and possible bounces would allow for some rudimentary “contact science”. Knowing where Rosetta will have been coming to an eventual hold would be more satisfying than an unnecessary interruption of transmission. Otherwise we would get an indefinite cliffhanger.
Other planetary probes also use to transmit until natural loss of contact.
I personally would have tried some hops, no matter how damaged the solar panels may get, in order to obtain an option to learn more about the surface composition. 50 cm/s isn’t that fast on soft ground with an optimzed spacecraft attitude.
On the other hand, I think we cannot complain about the huge amount of data collected by Rosetta. The mission scientists and the community will have work for years or even decades to dig through all the data.
Not sure how much you would learn from the bounces, if the low gain survived. You will not know much, if anything, about orientation (certainly after the first bounce) & the mechanical properties of crumpling bits of spacecraft. Also you dont have Rosetta watcing to give you track, just Doppler, & whether the low gain is stable enough (after impact…) to be any use for that, at very low velocities…………..so at best youd have very limited information on the first impact only I suspect.
May get ruled out of order, but the lyrics of an old Dave Brubeck song sung by Carmen McRae come to mind.
They seem very aposite 🙂
https://www.youtube.com/watch?v=mWH_siLE56Q
Ah the prinyed lyrics are here, but better listen to Carmen!
https://www.getalyric.com/mp3/lyrics/songs/dave_brubeck_amp_carmen_mcrae-15558/take_five_live_with_carmen_mcrae-38385/there_39_ll_be_no_tomorrow-188952/
Ps Logan, Marco, somehow I think you might like those links 🙂
Nice suggestion for an EOM cartoon soundtrack. The whole world can participate in feeling sad. 🙂
Rosetta has an inertial unit. This could be read-out to infere surface properties — and used as technical test-to-fail data of solar panels and booms in the context of the comet surface.
Ideally some instrument like dust counters would be able to return grain data, or the magnetometer could verify or return small-scale EM data.
NASA is working on an asteroid sample return mission (OSIRIS-Rex: https://www.nasa.gov/mission_pages/osiris-rex/index.html), well it’s almost assembled.
I could imagine, that any bit of information about the surface of small (celestial) bodies would be welcome.
“…whisper farewell.”
Ah, didn’t know it had accelerometers. That would increase the chances of something useful – if there is a data channel to the low gain. The magnetometers are out on booms almost certainly so likely to be wrecked.
Though you might like the Brubeck 🙂
I think the. ‘Ugly Duckling Song’ is quite fun too!
About Rosetta’s navigation system, at least as it has been considered:
https://www.maia.ub.es/~gerard/AstroNet-II/IFC/Vicenc_Companys.pdf
“Three inertial measurement units (IMU), each with three gyroscopes and three accelerometers. The gyros measure accurately the direction and magnitude of the S/C angular rate. The acceleros are used to measure and control velocity increments.”
More technical: https://emits.sso.esa.int/emits-doc/ESTEC/AO6080-RD3-AANT-article.pdf
@Gerald.
Thanks.
That must have been jet lag talking when I said ‘I didn’t know…..’, of course it has.
Go the first link (interesting summary of many other issues there) but the second won’t load over the hotel WiFi.
Not clear how capable they would be of instrumenting an impact/bounce scenario, very different from their intended use, in terms of sensitivity, bandwidth etc.
A bigger problem would probably be extracting much from the messy crumpling spacecraft etc data.
I propose Memphis as the name for the final landing site of the Rosetta craft.
The Rosetta Stone contains a text known as the “Decree of Memphis,” the capital of ancient Egypt in which it was published, issued by the Pharaoh Ptolemy V.
Like Memphis.
Time comes at every visit to say goodbye. Fine for Coraline, also for Us.
These are the Voyages of our times.
A sheep over a trunk. Cotton was drawn this way when first talked about. How are We drawing 67P? Is 67P still a little, dark Ducky?
Oh dear; after my usual rather serious and mainstream interventions, Logan has triggered a second musical reference in two posts.
It’s maybe not quite so good as the Brubeck, but you will find the lyrics of the ‘Ugly Duckling Song’ below. Lots of tube performances if you want to hear it 🙂
https://www.angelfire.com/film/dannykaye/UglyDuckling.htm
(Moderator; apologies, I promise to return to scientific rigorous forthwith :-). )
@Harvey,
Oh dear. Might I suggest the title of another Brubeck track as advice to yourself and Logan?
‘Take Five’ 🙂
@ianw16
Yes, I know it well.
In fact There’ll Be No Tomorrow is in the McRae album Take Five Live.
Thoughts of that and Ugly Ducklings probably engendered by a violent dose of jet lag in Japan. The cumulative lack of sleep over several days does weird things to my head!
Anyway, I consider myself rebuked, I shall return to the vector calculus……. 🙂
“One day, a space colleague said: ‘I don’t understand why, if you’re so into space, you didn’t just study astronomy or astrophysics to begin with?’
‘I did want to be an astrophysicist’, I replied, ‘but I was told that I didn’t get a high enough mark in physics’.
When I confessed the mark – 62%, it was burned in my brain – he revealed it was the same he got for his HSC physics.
The world turned slowly upside down and then the right way up again. We got the same mark; he went on to get a PhD in astrophysics; I was encouraged to stay with words.”
Dr. Alice Gorman. Senior Lecturer in archaeology and space studies, Flinders University.
resource https://theconversation.com/we-should-encourage-boys-and-girls-to-reach-for-the-stars-59905
via https://phys.org/news/2016-07-opinion-boys-girls-stars.html
Time will come when needing Lecturers on Paleontology and Space Studies 😉
Is there an orientation for Rosetta where the patch of sky it uses for navigation (ie strong bright maybe symetrical star patterns), is more distinctive and less subject to false reading?
If so maybe it could use that criteria to make a very close approach to 67P/Churyumov and hang around for a bit before biting the dust (ice?)
An excellent idea Rod 🙂
Limiting factor is that IF you fix ROSETTA attitude toward a ‘clear, contrasting face’ of the sky, THEN you are also displacing the main antenna, quite probably out of Earth focus.
The star tracker can only give you the angular orientation of the spacecraft. It’s unlikely star tracker confusion is much of a problem now, there is little activity.
It probably is true some areas of sky are better than others for the star tracker – but then you are stuck with pointing the spacecraft that way! And it’s not solving any actual problem.
0.5 metres per second. Gravity on 67P is about 0.001 m/s/s. So Rosetta’s dropping from a height of about 125 metres, taking about 500 seconds to do so.
If she was dropped from 20 km, she would hit at 6.3 m/s after a fall of 6300 seconds (105 minutes).
So clearly controllers are scheduling controlled flight to within 125 m of the surface.
It would be really very nice to get a glimpse of dear Philae before we say goodbye for ever. Since Rosetta will be in thruster-controlled flight down to 125 metres above the surface, it would be really great if she could do a slow low pass over Agilkia and have time to send the pictures home before Rosetta hits the dust. Please!
“Philae Reclining on Comet 67P/Churyumov ”
What a great photograph.
It would also be an accurate scale reference to surrounding material both disturbed and undisturbed.
Better scoop than Veneras’ landscapes or Curiositys’ selfies!!