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Thread: Rosetta and 67P/Churyumov-Gerasimenko

  1. #1
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    Rosetta and 67P/Churyumov-Gerasimenko

    To celebrate Rosetta closing in to less than 10,000 km from its target comet as of today, i'm gonna start a new thread for that.

    Because it's started to become interesting. On the weekend the following picture of the comet was leaked (yes, leaked), showing a "contact binary" consisting of two distinct nuclei for the comet:

    Attachment 37415

    Someone also took the time to create an animated gif of the comet's rotation:

    Attachment 37416

    These images were taken on July 11th, one week after ESA released the first grainy pictures of 67P/C-G's shape.

    The leak came through CNES, the French Space Agency, and has apparently since been deleted from there. ESA swiftly reacted to the leaking by doing a lengthy post in the Rosetta blog on why there's limited imagery released officially. Along with that comes the promise for an image package - images newer than July 11th - and a movie being officially released tomorrow, so let's wait for that.

    Based on Hubble Space Telescope imagery, the shape of the comet was originally, at Rosetta's launch, estimated to look roughly like this:

    Attachment 37417

    ... which mostly tells us that Hubble of course can't really discern details of rocks at most a few km wide at multi-AU distances.

    Posts by Rosetta's managers yesterday already hinted at an entirely "new" shape being revealed in tomorrow's image package.

    The shape will not impact Rosetta's planned orbiting of the comet much, since the orbits are finetuned to high detail to consider outside gravitational influences - in particular of the sun when approaching, passing and leaving perihelion - anyway and do no resemble "standard" orbits around a equilibrated spherical object like Earth or other planets.
    The navigator for the lander Philae though apparently thinks the shape might complicate finding landing sites.


    Rosetta will come within 100 km of the comet on 6th August, which is treated as the official "arrival date". She completed the 7th of 10 planned burns to slow her relative velocity to 67P/C-G this noon. There will be one more FAT (Far Approach Trajectory) burn next wednesday, then after that two CAT (Close Approach Trajectory) burns. The first CAT will occur on August 3rd (at a distance of probably somewhere around 400-500 km), slightly altering her trajectory - currently a 200-km safety flyby - to a 70-km target flyby distance and lowering her speed to 1 m/s relative. The second CAT burn will be on the "arrival date", and will insert Rosetta into the orbit.

    Both Rosetta and Philae are now fully operational and have started running their sensors. Philae is currently in a cool-down phase after running its instruments over a 30-hour phase from Monday to Tuesday.
    Last edited by kato; 17 Jul 14, at 05:59. Reason: link fixed

  2. #2
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    Last FAT burn successfully completed today. Rosetta is now 3500 km from the comet, with planned arrival in two weeks.

    Next OSIRIS image package announced for tomorrow.

    German Aerospace Agency DLR today launched a "virtual control room" for the Philae lander on its DLR_next youth outreach site today. The control room's main feature is telemetry data - temperature sensors for the instruments and electric currents at various points - from the Philae lander updated live as they come in after 22 minutes at lightspeed. Site only available in German.

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    ESA is responding to criticism about slow image updates.

    Latest OSIRIS pic published today is only four days old (distance is 5500 km, resolution is 100m/px, zoomed 4x in this version):

    Attachment 37498

    In addition ESA from now on will publish NAVCAM pictures daily. Unlike OSIRIS, ESA owns the full right to the NAVCAM pictures (OSIRIS is run by a German Max Planck Institute). NAVCAM is a lower-res camera. The image published today was taken yesterday (zoomed 10x):

    Attachment 37499

    A model of the likely shape of the comet has been created by the OSIRIS team from the image data collected on July 14th:

    http://www.esa.int/var/esa/storage/i...l_of_comet.gif
    (animated GIF, 9 MB!)

    Next OSIRIS image release announced for July 31st (next Thursday, as usual).

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    Latest released picture of the comet taken yesterday (14/08/01) by the narrow-angle camera of the OSIRIS instrument, from a distance of 1000 km:

    Attachment 37565

    The black spot is a CCD artefact.

    Tomorrow a CAT burn, dubbed CATP (pre-insertion), planned for 11 am CEST will reduce relative velocity to 1 m/s and bend trajectory considerably towards the comet. The second CAT burn planned for wednesday, dubbed CATI (insertion), will bring relative velocity to 0 m/s.

    Following CATI, Rosetta will perform a series of triangular movements around the comet in 100-km legs, adjusting angle towards the comet with each reorientation. The first "circumnavigation" will be at 100 km distance, the second at 50 km, the third at 30 km. During the third run, the comet's rather low gravity should manage to pull Rosetta into a proper orbit. Depending on the activity of the comet - halo dust clouds, jets etc - this orbit may then be lowered to down to 10 km.

    Edit: The triangular movements will run on microthrusters and will be extremely slow. Each leg in these triangular movements takes about 3.5 days to complete. Full orbital insertion is planned for late September. A video of the complicated orbit approach concept can be seen here:

    Last edited by kato; 03 Aug 14, at 00:59.

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    CATP completed successfully.

    Picture from 500 km distance using NAVCAM, enlarged by factor 5 (instead of 10 in previous NAVCAM pics):

    Attachment 37572

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    New community outreach website launched for the arrival:

    Rosetta | rendevous with a comet

    There'll be a live webcast for the arrival tomorrow morning (tonight for most on here), at 0800 GMT.

    Comet from 234 km yesterday:

    Attachment 37592

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    Trust gets you killed, love gets you hurt, and being REAL gets you hated.

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    Rosetta completed its first triangular flight around the comet on August 17th. For the first triangular flight, all pass-by heights were at 100 km distance to the comet.

    Since August 17th, Rosetta has begun socalled transfer arcs which will continuously bring her closer to the comet; currently she's on the first such arc, and three further CATC (close approach trajectory change) burns are planned.

    August 20th : CATC4 burn (arcing down to pass-by distance of 80 km)
    August 24th : CATC5 burn (arcing down to pass-by distance of 50 km)
    August 27th : CATC6 burn
    August 31st : TGM burn phase ("transfer to global mapping"), moving to 29 km distance to be captured by the comet
    September 10th : Circular orbits at 19-29 km distance*; mapping of comet; to be completed by October 7th
    November 11th : Philae landing

    * which is probably going to be the "home zone" for the orbiter.

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    Getting closer and closer: NAVCAM from 64 km, yesterday.

    Attachment 37745

    The five candidate landing sites for Philae will be chosen this weekend and presented on monday. The OSIRIS team will provide digital terrain models of these sites. Subsequent downselection will narrow this to one primary and one or more backup landing sites to be decided upon on September 14th (i.e. after three weeks). Rosetta will then gather high-resolution data for the landing sites including boulder distribution from between 30 km and 20 km distance, with a Go/No Go decision to be taken on October 12th (i.e. four weeks later). Philae crew will then have three weeks to adapt the lander's science program for the site chosen, and one week after that Philae will land.

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    The five candidate landing sites have been published. Since i'm too lazy to copy the article, read it here:

    Rosetta: Landing site search narrows / Rosetta / Space Science / Our Activities / ESA

    (also contains some mid-res pictures of each site taken from 100 km)

  11. #11
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    ESA has released a first proper OSIRIS NAC picture:

    Attachment 37895
    Jagged cliffs and prominent boulders are visible in this image taken by OSIRIS, Rosetta’s scientific imaging system, on 5 September 2014 from a distance of 62 kilometres from comet 67P/Churyumov-Gerasimenko. The left part of the image shows a side view of the comet’s 'body', while the right is the back of its 'head'. One pixel corresponds to 1.1 metres.
    Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA


    Note that - like with the other pictures - lighting is enhanced so you can actually see more than just pitch black with "light" spots of at most dark anthrazite grey. The surface of the comet roughly has the color of charcoal. The picture as far as I know was part of a limited public release for the EPSC 2014 conference* along with a thermographic map of the comet taken by the VIRTIS instrument, a map published by OSIRIS that differentiates the surface by its geomorphology, and a picture of cosmic dust grains caught during August by the COSIMA instrument.

    The full-sized version of the picture (2048x2048) can be found here:
    Space in Images - 2014 - 09 - Comet on 5 September 2014

    Primary and backup landing site selection next weekend. Public Announcement Event will be livestreamed on monday at 1100-1230 Paris time.

    * NASA went ahead and already published data from their single instrument aboard Rosetta (ALICE) ahead of it, basically detection of water in the coma and - contrary to what people think about comets - not a single ice patch on the surface.
    Last edited by kato; 09 Sep 14, at 12:41.

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    Photo by CIVA-P camera aboard Philae, showing a part of Rosetta, one of its 14-meter long solar panel wings and the comet in the background:

    Attachment 37904

    The same camera was also used to do the selfie during the Mars Flyby posted here: http://www.worldaffairsboard.com/sci...tml#post964907
    Note the different rotational angle of the solar panel, which is moved in accordance with power and cooling requirements. Distance to the comet is about 50 km.

    Edit: The picture is probably from the CIVA-P Imaging Test taken during the test phase Sep 4th-8th. There will be another CIVA-P Imaging Test Sep 24th-25th, and another Oct 6th-8th (so possibly more pictures after those?). The magnetometer ROMAP, isotope analyzer PTOLEMY and COSAC spectrometer also receive in-flight operational tests. SESAME and CONSERT (acoustic and radar instruments) will be tested Oct 16th-17th. Haven't found test plans for the other instruments - SD2 (drill), MUPUS (surface analysis), ROLIS (descent camera) and APXS (x-ray spectrometer).

    Rosetta is performing the insertion burn for a 29-km circular orbit today. The circular orbits around the comets (relative to the distance travelled in each) are travelled rather slow, each week below is half an orbit travelled. Orbit planning:
    • today: move to 29.4 km distance circular orbit
    • in one week (opposite side of comet): change inclination of orbit from ca -60 to +60 degrees (i.e. a burn moving the craft 60 degrees off from its previous bearing)
    • one day later (after last burn): GO/NOGO decision on lower orbit, if yes (otherwise keep orbit until lander delivery):
    • in two weeks (at same position as now): go to elliptic orbit with 29 km apogee, 18.6 km perigee [note: this is the only half-orbit that does not take exactly one week, but five days instead]
    • in three weeks (opposite side): go to circular orbit with 18.6 km distance; change inclination to +-90 degrees (i.e. move the craft exactly into a polar orbit running along the terminator)
    • five days later (before next burn): GO/NOGO decision on lower orbit, if yes (otherwise keep orbit until lander delivery):
    • in four weeks (same side as now): go to elliptic orbit with 18.6 km apogee, 9.8 km perigee
    • in five weeks (opposite side): go to circular orbit with 9.8 km distance
    Last edited by kato; 10 Sep 14, at 20:46.

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    NASA has released a re-colorized version of the image in Post #11 above: APOD: 2014 September 15 - 62 Kilometers above Comet Churyumov Gerasimenko

    Primary and backup landing sites have been chosen. Primary is on the "head" of the duck, secondary on the "back".

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    The landing date for Philae has been set.

    Rosetta will release Philae at 8:35 GMT on November 12th from 22.5 km distance towards Landing Site J. This is timed so that confirmation of landing will arrive on Earth at pretty much exactly 4 pm GMT. Philae will spend about 7 hours in free flight.
    If a decision is taken that the primary landing site J is unfeasible for some reason, Rosetta will release Philae at 13:04 GMT the same day from 12.5 km distance towards Landing Site C. Confirmation of landing would arrive at 5:30 pm GMT, with Philae only spending 4 hours in free flight.

    The release point is T0 below.

    The release of Philae will simply counteract Philae's motion with regard to the comet. Philae will then be drawn in by the comet's miniscule gravity. While the lander hits the ground, an "active descent system", i.e. a small air pressure valve, will push the lander down so it doesn't "bounce off". At the same time the lander deploys its two harpoons to anchor itself and ice screws on the three legs will screw themselves into the ground.

    Timetable for the landing:

    • Release
      • T0 + 0 h - Philae separation; Philae takes a number of farewell pictures of Rosetta
    • Descent Phase
      • T0 + 1 h - CONSERT antennas, ROMAP boom and landing gear unfolded; active telemetry between Rosetta and Philae; ROLIS begins taking downward-looking descent images
      • T0 + 2 h - ESOC in Germany receives the "farewell pictures"
      • Throughout descent:
        • measuring coma environment through spectroscopic analysis (COSAC and Ptolemy)
        • measuring interaction between coma and solar wind (ROMAP)
        • measuring dust and plasma environment in the coma (SESAME/PP and SESAME/DIM)
        • measuring descent rate and surface below by radar (CONSERT)
    • Landing
      • T0 + 7 h - Touchdown
      • T0 + 7 h 45 m - ESOC receives first 360 panoramic picture of landing site taken by CIVA-P
      • Throughout landing:
        • Uplink of descent measurements (see above) incl. descent image series
        • CIVA-P takes panoramic and stereo images of landing site
        • Telemetry subsystem checkup (solar panels, instruments)
        • Evaluation of landing ground by measuring the deceleration of harpoons after entry (by MUPUS) and measuring the elastic properties (by SESAME/CASSE)
    • Initial Science Phase
      • T0 + 8 h - Initial Science Phase begins
      • T0 + 9 h 45 m - ESOC receives more 360 panoramic pictures taken by CIVA-P
      • Throughout:
        • microscopic/high-resolution images of ground under Philae (ROLIS)
        • measuring magnetic and plasma properties of surface (ROMAP)
        • measuring surface and subsurface temperatures (MUPUS)
        • radar sounding of comet interior (CONSERT)
    • Long-Term Science Phase
      • T0 + 54 h - Transition to Long-term Science Phase
      • T0 + 72 h - Initial battery charge would run out if not recharged by solar panels by then
      • T0 + 90 +-30 days - Planned Long-Term Science Phase ends as Philae is rendered inoperational by rising temperature while comet comes closer to the sun
      • Throughout:
        • Scientific experiments with lesser power needs in accordance with battery recharge cycle
        • Drilling and sampling the ground


    Philae will be the farthest from Earth that anyone will have brought a lander meant to operate on the ground for a longer time, and only the second landed anywhere further away than Mars. Rosetta, Philae and 67P/C-G are currently about halfway between the orbits of Jupiter and Mars, at a distance of about 3.1 AU from Earth. The time delay for communications at touchdown is about 28 minutes. Mars, when furthest away from Earth in their orbits, has a time delay of about 21 minutes and a distance of 2.4 AU.

    The only lander further away, the ESA probe Huygens on Titan, the only one farther away, operated for about 133 minutes on the surface - 130 minutes longer than initially planned. Huygens was at the time somewhere around 10 AU from Earth.
    Last edited by kato; 27 Sep 14, at 17:07.

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    Newest montage of NAVCAM pictures, taken from 26.3 km distance on September 26th showing distinct jets:

    Attachment 38125

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