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Phobos-Grunt
marsophile
post Nov 24 2011, 03:04 AM
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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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ElkGroveDan
post Nov 24 2011, 04:09 AM
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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?


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marsophile
post Nov 24 2011, 04:31 AM
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QUOTE (ElkGroveDan @ Nov 23 2011, 08:09 PM) *
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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jekbradbury
post Nov 24 2011, 05:21 AM
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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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Leither
post Nov 24 2011, 01:00 PM
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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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GEmin1
post Nov 24 2011, 03:03 PM
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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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dilo
post Nov 24 2011, 05:34 PM
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Look at the recent orbit data:
http://www.satflare.com/track.php?q=phobos#MAP
Starting from Nov,22 perigee height is decreasing! blink.gif
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:
Attached Image


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Leither
post Nov 25 2011, 03:48 PM
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http://www.esa.int/SPECIALS/Operations/SEMQTNZW5VG_0.html

sad.gif 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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Greg Hullender
post Nov 25 2011, 04:28 PM
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@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.

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scalbers
post Nov 27 2011, 01:30 AM
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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.


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ddeerrff
post Nov 27 2011, 01:48 AM
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Could a fuel leak raise perigee?
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nprev
post Nov 27 2011, 02:05 AM
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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.


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tedstryk
post Nov 27 2011, 02:28 AM
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QUOTE (nprev @ Nov 27 2011, 03:05 AM) *
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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nprev
post Nov 27 2011, 02:33 AM
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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.


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stevesliva
post Nov 27 2011, 04:54 AM
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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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