Phobos-Grunt |
Phobos-Grunt |
Nov 24 2011, 03:04 AM
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#601
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Member Group: Members Posts: 507 Joined: 10-September 08 Member No.: 4338 |
http://www.nasaspaceflight.com/2011/11/liv...forts-underway/
Another update. [EDIT: The flight computer reportedly may be switching in and out of safe mode as it travels between day and night] |
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Nov 24 2011, 04:09 AM
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#602
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Senior Member Group: Admin Posts: 4763 Joined: 15-March 05 From: Glendale, AZ Member No.: 197 |
From the Nasaspaceflight article:
QUOTE as far as the potential recovery efforts, it is unlikely the spacecraft can be sent on its primary mission to Phobos, given its window of opportunity has now elapsed – at least from a complete mission standpoint. Last week we were hearing "early December" as the close of the mission window. As has been the case since the launch we are getting a wide range of "authoritative" statements, many of them conflicting. Can someone pin down the drop-dead full-burn date definitively? -------------------- If Occam had heard my theory, things would be very different now.
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Nov 24 2011, 04:31 AM
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#603
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Member Group: Members Posts: 507 Joined: 10-September 08 Member No.: 4338 |
Can someone pin down the drop-dead full-burn date definitively? It might depend on how creative they can get. [Edit: Saw this link in a comment elsewhere: http://www.universetoday.com/91239/contact...-on/#more-91239 It discusses possible "saves" of the mission] |
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Nov 24 2011, 05:21 AM
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#604
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Member Group: Members Posts: 104 Joined: 1-June 08 Member No.: 4172 |
This paper (page 3, figure 3) has a "porkchop plot" of the 2011 Mars launch window (i.e. a contour plot of the energy and time it takes to reach Mars if you set out on a given day). In theory, at least, the answer is in there (there are complications, though - the spacecraft has to be in the correct orbital plane, a status which it won't return to until early December, I think).
That paper also has some more creative ideas on reducing energy costs. |
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Nov 24 2011, 01:00 PM
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#605
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Junior Member Group: Members Posts: 60 Joined: 1-August 06 From: Vienna, Austria Member No.: 1002 |
http://www.bbc.co.uk/news/science-environment-15872653
Contact update - BBC reporting that of the five attempts on Wednesday evening only the first returned data. EDIT: more info from ESA http://www.esa.int/SPECIALS/Operations/SEM5AJZW5VG_0.html " The signals received (on first attempt) from Phobos–Grunt were much stronger than those initially received on 22 November, in part due to having better knowledge of the spacecraft's orbital position." The second pass was short, and so was used only to uplink commands – no receipt of signal was expected. However, the following three passes in the early morning of 24 November proved to be more difficult: no signal was received from Phobos–Grunt. During the three later passes, the spacecraft's orbital position changed, and the second, opposing, antenna had to be used – but no signal was received. Another five communication slots are available during the night of 24–25 November, and the Perth tracking station will again be allocated on a priority basis to Phobos–Grunt. |
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Nov 24 2011, 03:03 PM
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#606
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Newbie Group: Members Posts: 16 Joined: 18-July 11 Member No.: 6068 |
Russian tracking station in Baikonur (Kazakhstan) established communication with "Phobos-Grunt" and was able to receive telemetry. Deciphering has began.
http://www.interfax.ru/politics/news.asp?id=218367 |
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Nov 24 2011, 05:34 PM
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#607
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Senior Member Group: Members Posts: 2492 Joined: 15-January 05 From: center Italy Member No.: 150 |
Look at the recent orbit data:
http://www.satflare.com/track.php?q=phobos#MAP Starting from Nov,22 perigee height is decreasing! Could this abrupt trend change be related with restored communication? (based what I know, this isn't possible because first commands were sent only last night from Perth antenna...) Added- this is what I meant: -------------------- I always think before posting! - Marco -
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Nov 25 2011, 03:48 PM
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#608
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Junior Member Group: Members Posts: 60 Joined: 1-August 06 From: Vienna, Austria Member No.: 1002 |
http://www.esa.int/SPECIALS/Operations/SEMQTNZW5VG_0.html
No contact last night - 'Despite listening intently during four scheduled communication passes during the night of 24–25 November, ESA's 15 m-diameter dish antenna at Perth, Australia, did not receive any signals.' 'One piece of positive news: observations from the ground indicate that the orbit of Phobos–Grunt has become more stable. "This could mean that the spacecraft's attitude, or orientation, is also now stable, which could help in regaining contact because we’d be able to predict where its two antennas are pointing," The next scheduled communication slot for ESA's Perth station is set for tonight, 25 Nov. A good log of all communication attempts since 22 Nov is given in http://www.zarya.info/Diaries/Misc/PhobosGrunt1.php |
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Nov 25 2011, 04:28 PM
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#609
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Senior Member Group: Members Posts: 1018 Joined: 29-November 05 From: Seattle, WA, USA Member No.: 590 |
@dilo I'd be more inclined to blame it on atmospheric drag. Drag at perigee leads to apogee lowering and vice versa, so it makes sense that the apogee would be dropping a lot faster than the perigee, even though there's far more drag at perigee.
The bit I can't make sense of is why there was ever any perigee raising. --Greg |
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Nov 27 2011, 01:30 AM
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#610
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Senior Member Group: Members Posts: 1621 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
I've read bits and pieces online that speculate that maybe the spacecraft is doing some of its own orbit adjusting to account for the raise in perigee.
Also read that data so far received isn't easy to decipher. -------------------- Steve [ my home page and planetary maps page ]
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Nov 27 2011, 01:48 AM
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#611
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Junior Member Group: Members Posts: 83 Joined: 19-April 05 Member No.: 251 |
Could a fuel leak raise perigee?
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Nov 27 2011, 02:05 AM
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#612
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Merciless Robot Group: Admin Posts: 8783 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
That would have had to be a very well-timed fuel leak that apparently also ceased at the precise time(s), in my opinion.
I don't think that we have enough information to speculate about causes of this purported perigee adjustment (not really convinced that it even occurred, actually; may have been an artifact of the early orbital parameter uncertainties). If anything, it seems that the sources themselves are speculating due to the extreme paucity of information from the spacecraft. -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Nov 27 2011, 02:28 AM
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#613
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Interplanetary Dumpster Diver Group: Admin Posts: 4404 Joined: 17-February 04 From: Powell, TN Member No.: 33 |
If anything, it seems that the sources themselves are speculating due to the extreme paucity of information from the spacecraft. Nick, the fact that the upper stage that was in roughly the same orbit at the time of launch and has since decayed out of orbit is good evidence that the spacecraft is doing something. -------------------- |
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Nov 27 2011, 02:33 AM
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#614
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Merciless Robot Group: Admin Posts: 8783 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
Oh, sure, and didn't mean to imply that it might not be executing orbital corrections. I think that we just don't know what's really going on with F-G as yet...hopefully we will in the very near future.
-------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Nov 27 2011, 04:54 AM
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#615
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Senior Member Group: Members Posts: 1578 Joined: 14-October 05 From: Vermont Member No.: 530 |
The spacecraft is likely using thruster firings to maintain sun pointing in safe mode. They have said several times that optical imaging indicates that the spacecraft isn't tumbling.
And if you read the recent Mars Express reports, they note that safe mode uses a lot of thruster firings... something like 6 months of station keeping fuel to run one safing event. Find the sun, turn towards it, stay pointed at it. Perhaps the net force of the thruster firings when the spacecraft is able to locate the sun happens to be to do whatever it's doing to its orbit. And if it's running a sun finding routine every time that it leaves eclipse, it could be a lot of thrusting that's occurring. Especially if the s/c has more mass than it is nominally supposed to. |
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