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#220
by
pm1823
on 17 Nov, 2011 16:56
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What is the basis for those error bars?
TLE fit error to the known owner's original ephemeris can be about 0.5-1km for the LEO sats.
look on the Fig. 7 in the
http://www.centerforspace.com/downloads/files/pubs/AIAA-2008-6770.pdfNotice that the original fit (the initial vector is epoched to the beginning of the interval) was about 500-600 m yet
after about 2 days, the error had only grown to about 4-5 km. This is fairly good for a LEO satellite.
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#221
by
FinalFrontier
on 17 Nov, 2011 16:59
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So its now the 17th, how much longer do they have before its a failure, and does it look like its hardware related at this point?
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#222
by
pm1823
on 17 Nov, 2011 17:13
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The higher inclination of PG on 8 December, plus being very near the end of the window may mean that PG may not have enough propellant to reach and then orbit Mars.
If the Russians can get in contact and control of PG before it re-enters and if its too late to send PG to Mars, a possible rescue plan could have PG fire its engine to put it into say a 350 by 600 km orbit. There PG will stay for two years until the next window arrives around November 2013. The period of the orbit being designed so that PG is in the right position for TMI in two years time. This will rely on the on-board batteries being able to sustain two years worth of charging and discharging, which they probably were not designed to do. Going for a higher apogee will mean less charging cycles, but PG will be passing through the Van Allen radiation belts. Using the Moon and the Lagrange points it might be possible to have PG hang around the Earth-Moon system and then dive to 300 km perigee for the kick to Mars in two years time.
So I think its possible that PG can be saved, but before this can happen contact needs to be made, which unfortunately has not happened yet.
100% agree with your words, Steven. Just add, FG has only fuel to correct calculated burns' errors. If they had more dV=~200-300m/s than they would fly at a faster trajectory.
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#223
by
kevin-rf
on 17 Nov, 2011 17:38
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So its now the 17th, how much longer do they have before its a failure, and does it look like its hardware related at this point?
I think they are hoping the press just goes away, someone mentioned upcoming elections. And without telemetry there is no way to ever know... Just very educated guesses.
...oooh shiny thing...
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#224
by
Sparky
on 17 Nov, 2011 17:40
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I apologize if this has already been brought up in this thread, but could the Luch 5-A satellite be (theoretically) able to communicate with PG when launched next month?
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#225
by
ChileVerde
on 17 Nov, 2011 17:58
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What is the basis for those error bars?
TLE fit error to the known owner's original ephemeris can be about 0.5-1km for the LEO sats.
look on the Fig. 7 in the
http://www.centerforspace.com/downloads/files/pubs/AIAA-2008-6770.pdf
Notice that the original fit (the initial vector is epoched to the beginning of the interval) was about 500-600 m yet
after about 2 days, the error had only grown to about 4-5 km. This is fairly good for a LEO satellite.
Isn't that the total error and not just the altitude? If so, then the altitude error will be considerably smaller, as satellite position uncertainties are typically mostly in the along-track position. I.e., the error ellipsoid is long and skinny, with its long axis aligned with the orbit.
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#226
by
pm1823
on 17 Nov, 2011 18:34
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Agree. It's total error, where cross track is much smaller than along track, but most part of it go to the range error, if you try to comm with FG. So, if they (RSA/ESA) tried to send RK command to FG it goes to targeting and doppler errors of antenna/transmitter, turned off receiver is locked on one freq... So...
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#227
by
Danderman
on 17 Nov, 2011 18:42
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All of this would have been avoid had Lavochkin implemented an uplink channel for the Fregat/MDU. The workarounds to avoid this turned out to kill the mission.
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#228
by
JWag
on 17 Nov, 2011 18:43
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I don't believe I've seen this information mentioned before:
http://www.russianspaceweb.com/phobos_grunt_launch.html#orbit1...Telemetry from the spacecraft showed that all its onboard systems had been in operational condition: solar panels had been deployed and the orientation and stabilization system, SOiS, correctly oriented the spacecraft toward the Sun...
Though this is from an unofficial source.
Also:
http://www.russianspaceweb.com/phobos_grunt_kik.html#esa...Roskosmos reportedly provided its European partners with orbital parameters of Phobos-Grunt for the purpose of guiding the antennas, as well as with software code...
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#229
by
Danderman
on 17 Nov, 2011 18:50
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I don't believe I've seen this information mentioned before:
http://www.russianspaceweb.com/phobos_grunt_launch.html#orbit1
...Telemetry from the spacecraft showed that all its onboard systems had been in operational condition: solar panels had been deployed and the orientation and stabilization system, SOiS, correctly oriented the spacecraft toward the Sun...
Though this is from an unofficial source.
I am sorry, but I don't have a lot of confidence in this type of report from Russia. There is always the possibility that someone simply relied data from the cyclogram, ie what was supposed to have happened by this date.
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#230
by
iamlucky13
on 17 Nov, 2011 18:53
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If the Russians can get in contact and control of PG before it re-enters and if its too late to send PG to Mars, a possible rescue plan could have PG fire its engine to put it into say a 350 by 600 km orbit. There PG will stay for two years until the next window arrives around November 2013. The period of the orbit being designed so that PG is in the right position for TMI in two years time. This will rely on the on-board batteries being able to sustain two years worth of charging and discharging, which they probably were not designed to do. Going for a higher apogee will mean less charging cycles, but PG will be passing through the Van Allen radiation belts. Using the Moon and the Lagrange points it might be possible to have PG hang around the Earth-Moon system and then dive to 300 km perigee for the kick to Mars in two years time.
So I think its possible that PG can be saved, but before this can happen contact needs to be made, which unfortunately has not happened yet.
This is one of the alternate scenarios I was considering in arguing against the fairly well-reasoned beliefs that orbital precession would doom the mission even if was recovered.
However, in addition to the challenges you mentioned that limit my confidence in it being a realistic option, I also have to also bring up thermal control. In particular, it seems likely the drop tank has no active thermal control for its fuel, since it was supposed to be empty and discarded a few hours after launch.
Perhaps passive thermal control would be sufficient to keep that fuel at an appropriate temperature (not frozen, not boiling and venting). Otherwise there is a limited time frame to utilize this fuel.
In such case, that may leave the only option as going immediately into a heliocentric orbit,
if one can be worked out that intercepts Mars at a later date.
Sufficient attitude control fuel for the extended mission is another concern.
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#231
by
kevin-rf
on 17 Nov, 2011 19:20
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I don't believe I've seen this information mentioned before:
http://www.russianspaceweb.com/phobos_grunt_launch.html#orbit1
...Telemetry from the spacecraft showed that all its onboard systems had been in operational condition: solar panels had been deployed and the orientation and stabilization system, SOiS, correctly oriented the spacecraft toward the Sun...
Though this is from an unofficial source.
Looks like an attempt to pull all available information into one place. There are many conflicting statements on the page. (I did notice that they mentioned NSF)
Nice summary, but a grain of salt...
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#232
by
hop
on 17 Nov, 2011 19:28
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In such case, that may leave the only option as going immediately into a heliocentric orbit, if one can be worked out that intercepts Mars at a later date.
If you can arrange earth swingby(s) in the interim, there is the possibility win back a substantial amount of dV. The Nozomi option, as it were. It seems this should be possible if you are willing to accept a long enough transit time.
Interesting posts on NK forum
http://www.novosti-kosmonavtiki.ru/phpBB2/viewtopic.php?p=839013&highlight=#839013http://www.novosti-kosmonavtiki.ru/phpBB2/viewtopic.php?p=839522&highlight=#839522The second one (if google translate hasn't completely lead me astray) purports to describe some details about what conditions could triggered safe mode and how it was supposed to work. I make no claims about the credibility or otherwise of the poster.
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#233
by
Lee Jay
on 17 Nov, 2011 19:30
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None of what we've been talking about makes one bit of difference if they can't get command and control over the spacecraft. Unless I've missed something, there has been no sign of that happening. Have I missed something? Without it, we're looking at an uncontrolled entry, and nothing more.
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#234
by
hop
on 17 Nov, 2011 19:41
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None of what we've been talking about makes one bit of difference if they can't get command and control over the spacecraft.
Obviously.
Unless I've missed something, there has been no sign of that happening.
Correct. The probability they will regain control appears extremely low, but it's not completely ruled out yet.
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#235
by
alk3997
on 17 Nov, 2011 19:48
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Still no ground-enabled command or control.
I find it strange that Fobos-Grunt is supposedly in a safe mode, which has locked it into solar inertial. Yet, there is no telemetry. Usually a "safe mode" means you cut power to all science, keep power going to the spacecraft and then radio home that you have a problem at the lowest possible bitrate and listen for help. I understand that listen for help may be blocked but telemetry-out should not be blocked (or at least not blocked completely). Also solar inertial means that at some part of the orbit, the "side" of the spacecraft is facing Earth and at least one antenna should not be blocked.
As far as I know, except for possibly shortly after spacecraft separation, there has been no telemetry. If we believe the spacecraft is getting power, then that implies that the radio-transmission system (including possibly the telemetry formatting computer system) has a problem, doesn't it? Add the lack of a burn and that the spacecraft is apparently successfully orienting itself to the Sun as other clues. With those three items, perhaps the only single failure that could account for both and leave the spacecraft apparently intact would be a partial loss of power.
A massive computer hardware failure where only the safe mode capability was left (a separate safe-mode processor?) doesn't explain the lack of telemetry. A failure of the propulsion system doesn't explain the lack of telemetry or having attitude control. A partial failure of power where there isn't enough power (or a fuse has tripped on one power bus) for the telemetry system but is enough for solar inertial might. Just not sure how realistic a partial failure is.
Really before worrying about how to command the spacecraft, maybe the first step those who would like to play armchair-spacecraft operator should consider is why isn't there any telemetry? That should be first on this list. If you can't solve that problem, then commanding a burn is out of reach.
Just thought I'd add to the speculation...
Andy
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#236
by
Prober
on 17 Nov, 2011 19:56
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Anyone know the expected life of the drop tank?
The drop tank was only designed for short term no?
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#237
by
Svetoslav
on 17 Nov, 2011 20:17
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I don't know if this has been copied here already, but:
http://www.russianspaceweb.com/phobos_grunt_launch.htmlOn the night from November 15 to November 16, a ground station in Ussuriisk in the Russian Far East made a desperate and, apparently, completely hopeless attempt to communicate with the spacecraft, as if it had been in the Earth escape trajectory following a nominal burn of the MDU propulsion unit. Unnamed officials reportedly insisted on this "communication session," after reading on the Internet that some observers in Brazil had seen what looked like a firing of the probe's main engine. Obviously, nothing came out of this effort, except for more comments on the web about gross incompetence of the mission management.
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#238
by
HIPAR
on 17 Nov, 2011 20:25
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Still no ground-enabled command or control.
...
I find it strange that Fobos-Grunt is supposedly in a safe mode, which has locked it into solar inertial. Yet, there is no telemetry.
Really before worrying about how to command the spacecraft, maybe the first step those who would like to play armchair-spacecraft operator should consider is why isn't there any telemetry? That should be first on this list. If you can't solve that problem, then commanding a burn is out of reach.
Just thought I'd add to the speculation...
Andy
One really needs to understand the subsystem interfaces to interpret those observations and intelligently speculate about the spacecraft failure mode.
--- CHAS
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#239
by
Danderman
on 17 Nov, 2011 20:35
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I don't know of a "safe mode" that precludes communications. This seems more like "dead mode".