Rosetta's comet mission discussion thread

In summary: The landing is expected to occur on Wednesday, November 12th at 12:35am PST.The Rosetta mission is a European Space Agency (ESA) mission with some US instruments on board. It carries a lander that will descend onto the comet surface, take pictures at the surface, and study the comet. The lander's feet will have to drill into the comet material in order to be anchored firmly, because the gravity is very slight.
  • #71
Jonathan Scott said:
http://www.esa.int/spaceinimages/Images/2014/11/Welcome_to_a_comet
Very nice! :)
I notice one possible problem: from the photo it looks as if the lander is laying on its side...
Happily the gravity there is so small, that even a landing on its side can hardly have damaged any instruments!
 
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  • #72
A rock has never looked this interesting.
 
  • #73
If the photo from the surface, linked above, has any resemblance to what a human eye would perceive it appears as might be expected at such great distance that the amount of sunlight is akin to something like Full Moon at night on Earth. As small as the lander is the surface area of photovoltaic cells is even smaller. ESA has stated they are already collecting electrical energy. Are these some sort of high performance cells? or is the unit designed with extreme! low power requirements... or both?
 
  • #74
enorbet said:
If the photo from the surface, linked above, has any resemblance to what a human eye would perceive it appears as might be expected at such great distance that the amount of sunlight is akin to something like Full Moon at night on Earth. As small as the lander is the surface area of photovoltaic cells is even smaller. ESA has stated they are already collecting electrical energy. Are these some sort of high performance cells? or is the unit designed with extreme! low power requirements... or both?
Here's a paper on the solar cells aboard Rosetta and Philae, which have a reported ~20% efficiency.
http://www.astrodynamics.eu/Astrodynamics.eu/Conference_Papers_files/Topputo-Paper-2009-2.pdf
 
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  • #75
http://www.bbc.com/news/science-environment-30034060#

Evidently Philae bounced a kilometer up off the surface and remained in flight for almost two hours as the comet rotated under it. So they are still trying to determine its exact location. The harpoons and ice screws still aren't deployed, so drilling experiments are canceled for the moment since it is untethered and too unstable. In the photo, you see a foot with an ice screw pointed "up", I suppose.

About the surface, I've seen a comment about what appeared to be a gooey or melted look, maybe toward the lower right in magnification. But mainly it looks like rocks to me.

http://www.esa.int/var/esa/storage/...omet/15048351-1-eng-GB/Welcome_to_a_comet.jpg
 
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  • #76
At 0.4 grams centimeter^-3 average density, rock stretches credulity. And a micro-G makes down on its side a good question.
 
  • #77
Yes, the presser just announced that Philae's location on 67P is still unknown, "Maybe tomorrow."

Solar arrays are "not illuminated" so power duration is limited.
 
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  • #80
Jonathan Scott said:
Given that it apparently bounced and that the momentum flywheel was being spun down, I hope that any "final" landing will be the right way up. I'd have thought a shape like that would only have a small chance of landing on its feet if it started tumbling.

Seems I was unfortunately right in my guess yesterday. Not only is it on its side, but it is also in shade a lot of the time, so the batteries are unlikely to last for long.

I don't know how much capability they have to move stuff, but they might be able to "twitch" it at least back to a more vertical position, as it would require very little force.
 
  • #83
I believe that the battery has 60 hours capacity. Where is the suggestion that Philae is "on its side", that is its normal force outside the area of its feet? The question of a "twitch" was asked at the presser, and I took the answer as not having that capability. The possibility of approaching escape velocity inadvertently is real and of concern.
 
  • #84
http://www.esa.int/spaceinimages/Images/2014/11/First_comet_panoramic

As mentioned in this afternoon's press conference, one of the panorama pictures is almost entirely sky and one to the side of it appears to be some sort of overhanging cliffs from the sun angle (you need to turn up brightness to see them) and a lander leg apparently pointing upwards. The pictures in the opposite direction are apparently of a surface close to the camera, presumably underneath the lander.

I don't think the lander has any official capability to do anything which would help it right itself, but I think there are bits which can be rotated or extended which might be used as a last resort.
 
  • #86
EU2AA said:
Yes, the comet is not going anywhere. But we are talking about Philae ...

Yeah. I meant Philae. Was feeling sleepy.
 
  • #89
Scroll down. One can see the lens flare OmCheeto mentioned. Probably just a guess as to the orientation.
this is the link Doug Huffman gave a few posts back.
.
Comet_panoramic_lander_orientation.jpg
 
  • #90
The top left corner needs brightening to see anything. They showed on the presentation today that if it's lightened up, one can see what appear to be overhanging cliffs.
 
  • #91
I haven't read all the post in this thread so maybe it's been mentioned before. Anyway, I just heard that the craft bounced twice before coming to rest. What a cool visualization this brings.
 
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  • #92
dlgoff said:
I haven't read all the post in this thread so maybe it's been mentioned before. Anyway, I just heard that the craft bounced twice before coming to rest. What a cool visualization this brings.
For some reason, I keep picturing a piece of litter blowing along the street when I read about that.
 
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  • #93
I just read the cells are only receiving sunlight some 1.5 hours/day and of course at that distance it is less energy per unit area, so quite insufficient. I don't know if this means that when it is closer things could improve (it was amazing enough that it "slept for 10 years and then awakened") but currently they are holding drilling off till near nominal charge when there's little to lose.

This turn of events is disappointing but really just a minor setback considering the number of bold firsts it has already achieved, and the orbiter is in perfect shape and will continue to do good Science for a long time. The most impressive thing to me is how "self-contained" the project is. They had so little information as to what to expect and instead of having a reconnaissance flight before final design and fabrication, they engineered an adaptable system that did both "by the seat of the pants" in one mission. That is some phenomenal engineering. That it even made orbit with such a wacky shaped object is laudable. That they had confidence in the orbiter to align itself to where the lander could drop like a brick with any modicum of accuracy demonstrates fantastic expertise and serious chutzpah (I almost said cajones) :) What a team!
 
  • #94
dlgoff said:
I haven't read all the post in this thread so maybe it's been mentioned before. Anyway, I just heard that the craft bounced twice before coming to rest. What a cool visualization this brings.
Yes! the touchdown times were quoted as 15:33, 17:26, and 17:33, and the takeoff speed from the first bounce was estimated at 0.38 m/s, as I recall from the press conference.
One can make a sloppy estimate of the surface gravity from that (assuming uniform field over the range of interest).
The first bounce lasted twice 56 minutes, or twice 3360 seconds. So if the acceleration were uniform it would be g = 0.38/3380 m/s2 = 0.113 mm/s2

This agrees with the order of magnitude estimate I've been hearing of 10-5 Earth gee,
a hundred thousandth of Earth surface gravity.
 
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  • #95
marcus said:
Yes! the touchdown times were quoted as 15:33, 17:26, and 17:33, and the takeoff speed from the first bounce was estimated at 0.38 m/s, as I recall from the press conference.
One can make a sloppy estimate of the surface gravity from that (assuming uniform field over the range of interest).
The first bounce lasted twice 56 minutes, or twice 3360 seconds. So if the acceleration were uniform it would be g = 0.38/3380 m/s2
You're a true science freak. I love you man.

Edit: BTW No disrespect intended.
 
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  • #96
Borg said:
For some reason, I keep picturing a piece of litter blowing along the street when I read about that.
Ever play Asteroids?

Asteroi1.png
 
  • #97
marcus said:
Yes! the touchdown times were quoted as 15:33, 17:26, and 17:33, and the takeoff speed from the first bounce was estimated at 0.38 m/s, as I recall from the press conference.
One can make a sloppy estimate of the surface gravity from that (assuming uniform field over the range of interest).
The first bounce lasted twice 56 minutes, or twice 3360 seconds. So if the acceleration were uniform it would be g = 0.38/3380 m/s2 = 0.113 mm/s2

This agrees with the order of magnitude estimate I've been hearing of 10-5 Earth gee,
a hundred thousandth of Earth surface gravity.

If it helps, the video mentioned they estimated 38cm/sec bounce went about about 1Km. The second bounce was 3cm/sec for 7min. I didn't hear the ESA mention the height for that bounce.
 
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  • #98
"true science freak"
That is a serious honor coming from you, DL. It takes one to know one. : ^)
 
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  • #99
marcus said:
"true science freak"
That is a serious honor coming from you, DL. It takes one to know one. : ^)
Note my edit on Post # 95. I feel better now.
 
  • #100
Imager said:
If it helps, the video mentioned they estimated 38cm/sec bounce went about about 1Km. The second bounce was 3cm/sec for 7min. I didn't hear the ESA mention the height for that bounce.
Thanks for the confirmation, Imager! 7 minutes is 420 seconds which is twice 210 seconds so let's see if we get the same takeoff speed they do.
Multiply 210 s by 0.113 mm/s2. Well we don't get their 3 cm/s, more like 2.4 cm/s, but it is close enough.
 
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  • #101
Thank you, Vagn, for that enlightening paper you linked. It supports what I suspected, that not only has the mission as a whole raised the bar but it extends all the way back to component level. This mission is very likely something of a "game changer", at least one could hope.
 
  • #102
dlgoff said:
Ever play Asteroids?

Asteroi1.png
Of course. :)

Now that I've seen the calculations by Marcus, It sounds like it bounced like a piece of litter in extreme slow motion.
 
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  • #103
I underestimated the surface gravity at the landing site by assuming acceleration g was uniform during the first jump, whereas it starts greater at the surface and falls off with altitude. So 0.113 mm/s2, a kind of average, underestimates the real surface gravity, which I guess would be more like 0.13 mm/s2 or 0.14.
That would agree with the 3 m/s takeoff speed on the second hop. Let's say 0.13.
That fits with the estimate they gave for the escape velocity from the surface, at the landing site. As I recall they said it was about 0.5 m/s.

DL, I treasure the compliment without reservation! Regardless of whether deserved : ^)

BTW anyone who can correct or improve the estimates here, or supply better data, is cordially invited to do so.
 
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  • #104
OUR LANDER’S ASLEEP

With its batteries depleted and not enough sunlight available to recharge, Philae has fallen into 'idle mode' for a potentially long silence. In this mode, all instruments and most systems on board are shut down.

"Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence," says DLR's Stephan Ulamec, Lander Manager, who was in the Main Control Room at ESOC tonight.

That sure was an exciting 3 days. :)

But I wonder though, will the comet becomes more active, and would the glow of the coma act as a 24 hour light source? Do we have any comet experts on staff?

wiki on cometary coma
The coma is generally made of ice and dust. Water dominates up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun.

And where is 67P anyways?

Ah ha!
[/quote]
Comet 67P (Churyumov-Gerasimenko)
2.97 AU from the sun

Not a New Comet
Discovered in 1969, Comet 67P (Churyumov-Gerasimenko) is a Jupiter family comet measuring 4.5km across. It has an orbital period of 6.5 years and its closest point to the Sun at perihelion is 1.2458 AU (186m kilometres). Although Comet 67P won’t be visible with the naked eye from Earth, the Rosetta Spacecraft will make sure it is seen around the world in unprecedented detail.
[/quote]

Sweet! That site has little buttons you can push to change the date. The comet will pass through the orbit of Mars around May 30, 2015.
Kind of reminds me of a program I typed into my computer from a book one day, only it doesn't take 10 minutes to render the image.
Anyone else remember this book?

Celestial.BASIC.by.Eric.Burgess.1982.jpg

Published in 1982
 
  • #105
OmCheeto said:
[...] "Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence," says DLR's Stephan Ulamec, "[..]

That sure was an exciting 3 days. :)

But I wonder though, will the comet becomes more active, and would the glow of the coma act as a 24 hour light source? Do we have any comet experts on staff?[..]
Apparently they did dare to do some drilling:
http://www.theguardian.com/science/2014/nov/14/philae-comet-lander-drills-hammers-rosetta

Combining those different news reports, it looks like they actually pulled it off - to get data from all their instruments including from drilled samples just before the lander went in stand-by. :)

If so, [update, I just heard that this is indeed the case] then it's a huge success despite the problems.

I don't know about the glow, but surely when the lander gets closer to the sun, much more energy will be collected in 1.5 hours (if that is still valid after the drilling and hammering) than currently. It would be great if the lander manages to send back more data when things are getting hot - that would be the cream on the cake. :D
 
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