vikingmars
Sep 23 2014, 12:16 PM
Click to view attachmentNow, it's time to open a new section devoted to the landing of the Philae lander itself on the nucleus of Comet 67P C-G.
Also to answer better the earlier post,
http://www.unmannedspaceflight.com/index.p...st&p=212943and for your information, here is the quick summary (as a "pdf" file) of the events that are expected to occur during landing on the nucleus and after : it's the timeschedule on which we are working to set up our EPO event in Paris.
Click to view attachmentThe landing itself should occur around November 11th.
We'll keep you informed
SpaceScout
Sep 23 2014, 02:14 PM
Great information, thank you!!
ROLIS will take nadir images all the way down from the separation to landing and I am sure the images will be of high scientific values, but as I am reading in the document, the images will be uplinked to Rosetta only after touchdown. Was there no way to transmit the images as quickly as possible, without waiting for the landing?
Phil Stooke
Sep 23 2014, 02:41 PM
The idea of transmitting images during the descent has been considered before, even as far back as the Surveyor landings on the Moon, and including Phoenix on Mars (actually, Phoenix MARDI images were not to be transmitted live, just transferred into the flight computer, and even that was too much of a risk).
Every time it has been abandoned because of the number and complexity of other operations at the same time.
Phil
vikingmars
Sep 23 2014, 03:40 PM
QUOTE (SpaceScout @ Sep 23 2014, 04:14 PM)
Great information, thank you!!
ROLIS will take nadir images all the way down from the separation to landing and I am sure the images will be of high scientific values, but as I am reading in the document, the images will be uplinked to Rosetta only after touchdown. Was there no way to transmit the images as quickly as possible, without waiting for the landing?
Dear SpaceScout, thank you for your kind comments.
Considering the great involvement of Germany in this mission, I should have put the timeschedule in German also, but my writing with Goethe's style is somewhat shaky : all my apologizes !
Yes, Phil is right : ESA does not want to interefere through the instructions with the transmitting of data during the landing phase. Sorry : so we will have to wait for the ROLIS images after a safe landing on the nucleus.
Phil Stooke
Sep 23 2014, 04:44 PM
I just realized that I forgot about Chang'E 3 in my comments above. We did have spectacular video of the descent and landing. But I realized - I don't know if that was transmitted during or after landing.
Phil
Explorer1
Sep 23 2014, 05:51 PM
I think it was halfway; I recall the streamed images were received at a much lower rate then the final landing movie; either only some were released on the live stream or only some were transmitted during the sequence.
Ok, found it:
Here is the live stream recording:
https://www.youtube.com/watch?v=jyg56VIKRNAAnd the 'complete' video:
https://www.youtube.com/watch?v=XNAGFTRvgDYTo not derail too far; what
will be sent from Philae during the descent if not images; there will be some telemetry?
SpaceScout
Sep 23 2014, 06:00 PM
QUOTE (Phil Stooke @ Sep 23 2014, 04:41 PM)
Every time it has been abandoned because of the number and complexity of other operations at the same time.
If I am getting this right, is the high number of processes that the computer needs to handle during descent (although is free fall) that prevent transmitting images ? Will Philae transmit live any telemetry at all to Rosetta before touchdown?
I am just thinking about the improvements that could be made for a next generation landing probe...
MarsInMyLifetime
Sep 23 2014, 06:15 PM
QUOTE (SpaceScout @ Sep 23 2014, 12:00 PM)
If I am getting this right, is the high number of processes that the computer needs to handle during descent (although is free fall) that prevent transmitting images ? Will Philae transmit live any telemetry at all to Rosetta before touchdown?
I am just thinking about the improvements that could be made for a next generation landing probe...
This is an interesting paper on the original conceptual design of Philae--from 1997! (just to remind ourselves of the era for which available stable technologies were being considered, and what incredible now-stable things might be in a next-gen lander)
http://www.open.ac.uk/personalpages/a.j.ba...ine/capcom.htmlNo descent imaging was even described in that paper, so the present capability and operational plan is a privilege, considering. Whole careers go by in the course of one such mission!
djellison
Sep 23 2014, 06:47 PM
I don't believe they'll be taking a lot of descent images....indeed, there's not much point. OSIRIS resolution will out-perform that of the descent imaging until we're pretty close to the surface. One before bettering OSIRIS res , one at some intermediate point, one just before touch-down.....that would be enough for a very good localization.
vikingmars
Sep 23 2014, 08:29 PM
QUOTE (djellison @ Sep 23 2014, 08:47 PM)
I don't believe they'll be taking a lot of descent images....indeed, there's not much point. OSIRIS resolution will out-perform that of the descent imaging until we're pretty close to the surface .../...
Yes, Doug : indeed ! OSIRIS has a far better resolution than ROLIS from orbit.
This is why ROLIS will take just a few images during the descent. BUT at a low altitude (i.e. tens of meters from the surface) and until touchdown, it will start taking one image every 5 seconds...
machi
Sep 23 2014, 10:04 PM
Original plan was (and it looks still is) to take few images after release from Rosetta and then few images before landing.
"Few" means up to 8 images.
Tom Tamlyn
Sep 24 2014, 03:21 AM
QUOTE (Phil Stooke @ Sep 23 2014, 10:41 AM)
The idea of transmitting images during the descent has been considered before, even as far back as the Surveyor landings on the Moon, and including Phoenix on Mars (actually, Phoenix MARDI images were not to be transmitted live, just transferred into the flight computer, and even that was too much of a risk).
Every time it has been abandoned because of the number and complexity of other operations at the same time.
Phil
The Ranger moon spacecraft perforce transmitted images during descent, because there wasn't any afterwards, but I can't think of any others. Well, maybe NEAR, if you call the whole approach a descent because the spacecraft eventually touched down, but that would be whimsical.
Can't think of any others, but of course I don't have the encyclopaedic recall of the two Dougs.
Hungry4info
Sep 24 2014, 03:42 AM
MSL did a whole descent movie. MER did a couple descent images if I recall right.
Edit: Nevermind. The discussion was about transmitting them during descent rather than storing and transmission later.
Explorer1
Sep 24 2014, 03:47 AM
And don't forget Huygens!
It's true that discussing why Huygens transmitted pictures on the way down and Philae won't is comparing apples and oranges (one had atmospheric observations as the primary objective with landing as a bonus, while the other is exclusively a lander), but there is a precedent of descent imaging from ESA.
Hungry4info
Sep 24 2014, 03:51 AM
QUOTE (Explorer1 @ Sep 23 2014, 10:47 PM)
...there is a precedent of descent imaging from ESA.
Was there anything similar planned for Beagle 2?
MarsInMyLifetime
Sep 24 2014, 04:11 AM
QUOTE (Hungry4info @ Sep 23 2014, 10:51 PM)
Was there anything similar planned for Beagle 2?
Beagle's airbag-wrapped landing process precluded the need for descent imaging. But this discussion is drifting from the subject of Philae itself. Philae will be a free-falling object without the ability to use the descent images for terrain avoidance; figuring out where it landed after the fact is much more important, so deferred imaging is fine. The issue is less about precedents than about requirements for the mission, with science and engineering both as stakeholders in the outcome.
Explorer1
Sep 24 2014, 04:20 AM
A big difference from Beagle 2 is that OSIRIS will be able to resolve Philae on the surface right away, so even loss of contact would be a learning experience. This will not be a shot in the dark.
SpaceScout
Sep 24 2014, 03:37 PM
QUOTE (Explorer1 @ Sep 24 2014, 06:20 AM)
[...] so even loss of contact would be a learning experience. This will not be a shot in the dark.
and I think this is the most important point. Whatever happen to the lander, it will be possible to reconstruct its approach and touchdown.
Phil Stooke
Sep 24 2014, 05:37 PM
One aspect of landing which I don't think has been mentioned is that it takes 7 hours for the lander to descend from release to the surface. That's over half a rotation. So it's not like hovering over the landing site and letting go - the landing site is far away, and as the lander falls the landing site moves until, at the appointed time, it's just under the lander. Like one of those action movies where somebody jumps off a bridge to land on the top of the train car as it passes underneath ... only a bit slower. It's easy to see that any uncertainty in the descent rate translates into a change in location on the surface.
Phil
vikingmars
Sep 24 2014, 06:12 PM
QUOTE (Phil Stooke @ Sep 24 2014, 07:37 PM)
One aspect of landing which I don't think has been mentioned is that it takes 7 hours for the lander to descend from release to the surface. That's over half a rotation. So it's not like hovering over the landing site and letting go - the landing site is far away, and as the lander falls the landing site moves until, at the appointed time, it's just under the lander. Like one of those action movies where somebody jumps off a bridge to land on the top of the train car as it passes underneath ... only a bit slower. It's easy to see that any uncertainty in the descent rate translates into a change in location on the surface. Phil
Well seen Phil ! This is not a descent, but a low-speed free-fall, hoping that the lander will not gain too much horizontal velocity at touchdown...
PS : the 7 hrs descent, from "T0" to "T0 + 7h", was duly mentioned inside the "PDF" timetable attached to the 1st post 
centsworth_II
Sep 24 2014, 06:51 PM
I'm wondering what percent of Phillae's descent rate is due to the mechanical push toward the comet it receives and how much is due to gravity and how that changes over the course of the descent. Has this been described?
Edit: After some more reading and thought, I've concluded that the mechanical shove is almost entirely devoted to counteracting orbital velocity (and not to push the lander toward the comet) and that the descent is pretty much 100% due to gravity.
charborob
Sep 24 2014, 07:49 PM
Is there an animation somewhere that shows the complete Philae landing sequence, including the comet rotating in the background? From the descriptions I read, I can't figure out how exactly it's going to work out.
Gerald
Sep 24 2014, 08:42 PM
QUOTE (vikingmars @ Sep 23 2014, 05:40 PM)
... I should have put the timeschedule in German also, but my writing with Goethe's style is somewhat shaky : all my apologizes ! ...
Far from competing with Goethe (I'm sure he would be excited by the mission), here my amateur translation of your appreciated survey into German:
Click to view attachment
MahFL
Sep 25 2014, 12:08 AM
QUOTE (charborob @ Sep 24 2014, 07:49 PM)
Is there an animation somewhere that shows the complete Philae landing sequence, including the comet rotating in the background? ..
Yes, it's at 12:40 on this presentation, the comet actually hits the lander, albeit softly. If they did not have the hold down thruster, the harpoons and screws on the legs the lander would bounce away from the comet.
Landing Site Announcement.
charborob
Sep 25 2014, 03:11 AM
That's exactly what I wanted to see. Thanks. Unfortunately, I didn't have the time to watch the presentation.
vikingmars
Sep 25 2014, 07:12 AM
QUOTE (Gerald @ Sep 24 2014, 10:42 PM)
Far from competing with Goethe (I'm sure he would be excited by the mission), here my amateur translation of your appreciated survey into German:
Click to view attachmentThanks a lot Gerald for this nice work !
I keep the German translation in my records.
We may have also some German visitors in Cite des Sciences in Paris and they may like some documentation in German too (I'll put your name as translator then)...
Click to view attachment"Goethe mit uns"
TheAnt
Sep 26 2014, 01:09 AM
Landing site J with C as backup if they spot anything untoward on the first selection.'
(Edit: Since I heard it verbally I got it wrong still think they really said 'G'.)
vikingmars
Sep 26 2014, 03:14 PM
A new set of 2 Rosetta NavCam images was released this afternoon by the Rosetta team... (sorry, again, no OSIRIS images).
This NavCam image is a very interesting one : it shows the backup "C" landing ellipse (see the superimposed yellow ellipse I draw on the left-hand side of the image)...
Wow ! Look carefully at it : its the only "safe" place around, among truly chaotic terrain ! What a GREAT mission indeed
Click to view attachment
Gerald
Sep 26 2014, 10:28 PM
The timing of the landing options has been pinned down for November 12 (GMT) :
QUOTE
Two robust landing scenarios have been identified, one for the primary site and one for the backup. Both anticipate separation and landing on 12 November.
For the primary landing scenario, targeting Site J, Rosetta will release Philae at 08:35 GMT/09:35 CET at a distance of 22.5 km from the centre of the comet, landing about seven hours later. The one-way signal travel time between Rosetta and Earth on 12 November is 28 minutes 20 seconds, meaning that confirmation of the landing will arrive at Earth ground stations at around 16:00 GMT/17:00 CET.
If a decision is made to use the backup Site C, separation will occur at 13:04 GMT/14:04 CET, 12.5 km from the centre of the comet. Landing will occur about four hours later, with confirmation on Earth at around 17:30 GMT/18:30 CET. The timings are subject to uncertainties of several minutes.
The 22.5 km look rather distant. I'm not quite sure about the reason. Might be it turned out, that Philae is more predictable than Rosetta regarding drag due to outgassing? Or it has something to do with the observability of Philae during the descent and communication early after landing.
MahFL
Sep 26 2014, 11:10 PM
QUOTE (Gerald @ Sep 26 2014, 11:28 PM)
The 22.5 km look rather distant.
Remember you do not want the orbiter to accidentally hit the comet too, so someone decided 22.5 km was the distance to use.
MarsInMyLifetime
Sep 27 2014, 01:54 AM
The latest NavCam composite shows that the left (main lobe) side of the valley seems to have cliffs with deep shadows, possibly vents. Now, seeing the line of boulders in the valley, I have a more distinct impression of gases from both sides of the valley impinging in the middle, creating on one hand a zone of stagnated velocities in which levitated boulders could lose escape velocity and drop down along that preferential zone, and on the other hand forming a plane of converged gas and dust. That plane would appear like a jet along the zone of impingement, and appear diffuse when viewed away from that plane. Just a thought, but it could explain why single sources for the "jets" have not been clearly identified yet, and why they appear variable based on direction.
Phil Stooke
Sep 27 2014, 03:12 AM
That idea of jets forming where two or more broad cones of emission meet, channeling dust into sheets (two cones) or collimated jets (three cones) was referred to earlier in our discussions and originated with Jean Crifo 20 years ago (Icarus, 1995, v. 116, pp. 77-112).
Phil
MarsInMyLifetime
Sep 27 2014, 04:28 AM
Thanks for the reminder, Phil. All very easy to visualize now.
Paolo
Oct 15 2014, 01:19 PM
MahFL
Oct 15 2014, 01:44 PM
It's not exactly flat is it ?
Those cliffs have to be at least 20 feet high ?
centsworth_II
Oct 15 2014, 03:56 PM
On the left, the original ESA landing oval in white and my red ovals on the other two images. On the right, ESA's red circle marking landing site J on the latest image (rotated) with my green oval marking where I think the original ESA white oval would be located.
Click to view attachment
fredk
Oct 15 2014, 06:15 PM
It's not clear these are landing error ellipses, since I couldn't see any such description in the captions of either image. The caption of the latest image just says
QUOTE
The circle is centred on the landing site and is approximately 500 m in diameter.
The cross marking the central landing position in the old image is pretty close (but not exactly) at the centre of the new red circle. There's no way to know if that's just plotting error or a slight adjustment in the central position.
SpaceScout
Oct 16 2014, 07:42 AM
I have not seen this very high close up of the landing site J posted here, so here
is the image in full resolution. Many wonderful details! thank you ESA
Phil Stooke
Oct 16 2014, 11:32 AM
http://blogs.esa.int/rosetta/2014/10/16/la...tes-from-30-km/The individual images for the Osiris mosaic of the landing area are here, plus - very nice - two images for site C as well.
Phil
fredk
Oct 16 2014, 02:49 PM
Primary landing site in anaglyph stereo. There are severe distortions here and I've only done a quick a dirty job aligning the frames, so this may be headache-inducing:
Click to view attachment
fredk
Oct 16 2014, 02:50 PM
fredk
Oct 16 2014, 03:06 PM
And a better-aligned crop of a scarp, showing precariously perched boulders/protrusions that couldn't exist in Earth-like gravity. Anaglyph:
Click to view attachmentCross-eyed:
Click to view attachment
climber
Oct 16 2014, 03:25 PM
I'm wondering how far we'll see once on the ground. If we were to land on a perfectly flat surface, horizon would be very very close I believe, but on THIS, it's hard to predict anything.
jhagen
Oct 17 2014, 07:15 AM
QUOTE (Phil Stooke @ Oct 16 2014, 04:32 AM)
http://blogs.esa.int/rosetta/2014/10/16/la...tes-from-30-km/The individual images for the Osiris mosaic of the landing area are here, plus - very nice - two images for site C as well.
Phil
Here's my version of a site J anaglyph...
Click to view attachment
MahFL
Oct 17 2014, 11:15 AM
QUOTE (climber @ Oct 16 2014, 04:25 PM)
I'm wondering how far we'll see once on the ground...
If we see something, it's going to be awesome. I would guess the horizon would be 300 meters away or so. The jets though should be something else.
katodomo
Oct 17 2014, 05:28 PM
QUOTE (climber @ Oct 16 2014, 05:25 PM)
horizon would be very very close I believe
More so because the CIVA-P cameras are mounted tilted 15 degrees downwards.
vikingmars
Oct 25 2014, 10:17 AM
Click to view attachmentFor those interested to attend this historic landing and take this opportunity to fly to Paris (and pay us a visit : TPS / UMSF Members, please, tell us in advance), here below is the link to the only other official ESA/CNES event set-up for the landing of Philae (with the one held in ESOC in Darmstadt).
As you may know, the engineering of the Philae lander is under the responsibility of CNES (the French Space Agency), as well as its CIVA cameras and instruments suite.
This event will take place at the National Science Museum (Cite des Sciences) in Paris :
http://www.cite-sciences.fr/fr/au-programm...-sur-la-comete/ ...and thanks again for your kind support over all those nice comments and posts !
Enjoy !
PS : Societe Astronomique de France is the partner of TPS in France since 1982
polaris
Oct 25 2014, 12:48 PM
Bonjour Olivier !
Faut-il s'inscrire ?
Même s'il faut attendre pour y participer, j'y serai !
Cdt
vikingmars
Oct 25 2014, 11:10 PM
QUOTE (polaris @ Oct 25 2014, 02:48 PM)
Bonjour Olivier ! Faut-il s'inscrire ?
Même s'il faut attendre pour y participer, j'y serai ! Cdt
Thanks a lot, Polaris
Please, try to arrive at 14:00 at the latest... And name you : I'll try to arrange so that you are well seated ! Friendly yours, VM
mcgyver
Oct 28 2014, 02:24 PM
QUOTE (Phil Stooke @ Sep 23 2014, 03:41 PM)
The idea of transmitting images during the descent has been considered before, even as far back as the Surveyor landings on the Moon, and including Phoenix on Mars (actually, Phoenix MARDI images were not to be transmitted live, just transferred into the flight computer, and even that was too much of a risk).
Every time it has been abandoned because of the number and complexity of other operations at the same time.
Why can't they just use a separated and standalone camera to take snapshots during landing? If it works, that's fine, else, who cares?
Is there a detailed 3d model of the landing site available for 3d printing? I already printed the comet model, but the landing site detailed 3d model would fit well close to it on my desktop. :-)
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