Rosetta's comet mission discussion thread

AI Thread Summary
The Rosetta mission, led by the European Space Agency, aims to study comet 67P/Churyumov-Gerasimenko, featuring a lander named Philae that will descend to the comet's surface. The mission will last approximately 16 months, observing the comet as it approaches the sun and develops a tail. The chosen landing site, now called Agilkia, is on the comet's smaller lobe, and the landing is scheduled for November 12. Challenges include the weak gravity of the comet, requiring Philae to use harpoons and drills to secure itself upon landing. The mission represents a significant milestone in space exploration, being the first attempt to land on a comet.
  • #51
marcus said:
links to some side information:
http://en.wikipedia.org/wiki/Philae_( spacecraft )
http://nssdc.gsfc.nasa.gov/nmc/ spacecraft Display.do?id=PHILAE
My rough guess is that the gravity where she is is about 1 mm per second per second. or about 1/10000 of a gee.
the mass of the lander is about 220 pounds, so the weight force would be about 0.02 pounds.
I could be off by quite a bit, can someone help with more accurate estimate of the comet's mass and surface gravity at the landing site?
Marcus, alas, gravity at the surface is equal to 0 (zero).
Chance only: enable the jet to fillet, fillet to flatten the surface, drill, drill two or three holes and drive there are two or three garpupa. All. The engine can be turned off.
 
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  • #52
There was some engineer on Slooh who said that even though of the harpoons have failed, the comet will remain on the surface.
 
  • #54
EU2AA said:
Marcus, alas, gravity at the surface is equal to 0 (zero).
no, the comet has mass, its gravity is non-zero, its just very small
 
  • #55
Yashbhatt said:
There was some engineer on Slooh who said that even though of the harpoons have failed, the comet will remain on the surface.
Yes, the comet is not going anywhere. But we are talking about Philae ...
 
  • #57
  • #58
Yeshe has a chance

It is possible that the engine is still running Philae?
It is possible that at least one harpoon can be recharged.

Then you need to download a new program at Philae:

- Landing soveshat harpoon forward as whaling boat;

- Aim your harpoon AML large stone such BLD;

- Shoot harpoon before touching the surface.
 
  • #59
davenn said:
no, the comet has mass, its gravity is non-zero, its just very small
MIB!

Frank also points out that humans must learn to understand the notion of scope in the universe; i.e. a very important and grand thing can be very small.

Ok. This might be a bit of a stretch in my "movies can inspire people to think" mindset.

But, um, I'm going to take a nap now.
 
  • #60
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.
 
  • #61
Dotini said:
A friend on another forum informs me it's on the surface, but moving around some.

It's a Rover! :)
 
  • #62
This so cool. :)
- Oops OK, looking at the news again!
 
  • #64
The latest that I am seeing from the ESA site is the notice of touchdown by the Philae probe. Is there anything more recent information available?
 
  • #65
It's hard to find anything other than some unofficial speculation about Philae having bounced when it landed.But that aside, I think that it may be possible to get some good estimates of how the comet's gravitational field varies. The Rosetta team has released a 3D model of the comet, Measuring comet 67P/C-G | Rosetta - ESA's comet chaser, and one can use a voxelizer like "binvox" on it to find a voxel representation of it. A voxel is a 3D pixel. One can then calculate the comet's gravity by assuming something like constant density then integrating over the voxels found for it.

http://www.cs.princeton.edu/~min/binvox/ is open source, but I've had trouble getting it to work in OSX Yosemite, the latest version. Even compiling it has trouble.

From Rosetta's motions, the Rosetta team has likely calculated some of the multipole coefficients of the comet's gravitational field. But I haven't seen them published anywhere.
 
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  • #66
SciFi channel said they picked site J. Not sure but I think it's on top of the large lobe.
 
  • #67
Emily Lakdawalla, Senior Editor & Planetary Evangelist, The Planetary Society. Planetary scientist, writer, public speaker,
is in Darmstadt Germany making reports via Twitter also.
I don't think she sleeps.

IMG_0359_pp_square_normal.jpg
Emily Lakdawalla @elakdawalla · 7h
! ... ! ... ! RT @Philae_ROMAP: @Philae_ROMAP magnetic field analysis revealed 3 landings at 15:33, 17:26 and 17:33 UTC

IMG_0359_pp_square_normal.jpg
Emily Lakdawalla @elakdawalla · 11h
I seem to have picked up >5000 new followers today :O Welcome, all of you, and I hope you like planetary exploration and space photos.​

One of them was me.

I was just listening to a BBC broadcast recorded yesterday following the landing. One of the commentators said that the landing itself was an experiment. ~9:45 - 10:15.
At 44 minutes, it's a bit long, but they discussed a lot of interesting things, with a lot of excited scientists.
 
  • #68
Greg Bernhardt said:
Google changed their logo doodle to a Rosetta animation
they rushed
 
  • #69
I've not yet seen a photograph taken from the landing site...
 
  • #71
  • #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.
 
  • #82
  • #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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