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Rosetta's comet mission discussion thread

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  1. Nov 13, 2014 #81

    Astronuc

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  2. Nov 13, 2014 #82

    Borg

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  3. Nov 13, 2014 #83

    Doug Huffman

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    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.
     
  4. Nov 13, 2014 #84

    Jonathan Scott

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    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.
     
  5. Nov 13, 2014 #85

    Doug Huffman

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  6. Nov 13, 2014 #86
    Yeah. I meant Philae. Was feeling sleepy.
     
  7. Nov 13, 2014 #87

    Imager

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  8. Nov 13, 2014 #88

    OmCheeto

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  9. Nov 13, 2014 #89

    marcus

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    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
     
  10. Nov 13, 2014 #90

    Jonathan Scott

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    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.
     
  11. Nov 13, 2014 #91

    dlgoff

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    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.
     
  12. Nov 13, 2014 #92

    Borg

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    For some reason, I keep picturing a piece of litter blowing along the street when I read about that.
     
  13. Nov 13, 2014 #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!
     
  14. Nov 13, 2014 #94

    marcus

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    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.
     
    Last edited: Nov 13, 2014
  15. Nov 13, 2014 #95

    dlgoff

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    You're a true science freak. I love you man.

    Edit: BTW No disrespect intended.
     
    Last edited: Nov 13, 2014
  16. Nov 13, 2014 #96

    dlgoff

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    Ever play Asteroids?

    Asteroi1.png
     
  17. Nov 13, 2014 #97

    Imager

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    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.
     
  18. Nov 13, 2014 #98

    marcus

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    "true science freak"
    That is a serious honor coming from you, DL. It takes one to know one. : ^)
     
  19. Nov 13, 2014 #99

    dlgoff

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    Note my edit on Post # 95. I feel better now.
     
  20. Nov 13, 2014 #100

    marcus

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    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.
     
    Last edited: Nov 13, 2014
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