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#360
by
robertross
on 23 Nov, 2011 15:07
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Congrats to the ESA engineers for getting their antenna to track and communicate with F-G.
Totally agree. They deserve a huge amount of credit for trying stuff out to see what works (especially the additional feedhorn as indicated in the ESA report)
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#361
by
alk3997
on 23 Nov, 2011 15:11
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As Jim said, the basic concept is that given enough propellant you can launch any time. As the launch window gets less optimal you use more propellant.
If you have a fixed amount of propellant like PG, the first thing that goes away is having enough propellant to land on Phobos. The next thing that goes away is having enough proellant to get to a low Mars orbit. Then the next thing that goes away is Martian orbit (you flyby instead). Eventually you cannot raise your solar orbit enough to get to Mars. And, so on, and so on.
Because of this you can have different answers to when does the Mars window close. The real question should be when does the window that allows for a full mission close? I believe that has already happened, based on previous reports.
So now we have no burn and a telemetry system that needed to be turned on at an optimal power time (see ESA article). It will be interesting to hear if the telemetry system is still transmitting the next time they try to contact the PG spacecraft or if there is a power issue.
Remember that the cause of the original problem (no burn) still has to be assessed and corrected (if possible) for any of this to matter for this spacecraft. Also remember that the Mars/Earth alignment in 2013 is different than the alignment in 2011 (I don't know which is more optimal).
Andy
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#362
by
Prober
on 23 Nov, 2011 15:16
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I've been around RF signals too long NOT to worry the simple tonal signal
might turn out to be spurious. Was the antenna tracking the source across the sky? Was any doppler observed? That would make me feel a lot less worried.
But the report that the tone appeared right after the on command, and the explanation for other failures to receive tone [shadowing after batteries have failed], does provide a warm fuzzy feeling.
doesn't this show that the batteries are not charging?
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#363
by
Chris Bergin
on 23 Nov, 2011 15:23
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Right then, so the general opinion is - providing this breakthrough leads to a command ability, and real soon - the mission is still possible?
Lots of ifs, but I want to establish the possibility still exists?
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#364
by
notsorandom
on 23 Nov, 2011 15:43
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What about Deimos? My assumption being that Deimos is not as far into the Martian gravity well and has less gravity to deal with when landing or taking off. I was doing some back of the envelope calculations about re-targeting to Deimos instead of Phobos and it looks like it would save a couple hundred m/s of delta V. However my knowledge of orbital mechanics is basic at best. Is this a possibility?
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#365
by
zeke01
on 23 Nov, 2011 15:45
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I've been around RF signals too long NOT to worry the simple tonal signal
might turn out to be spurious. Was the antenna tracking the source across the sky? Was any doppler observed? That would make me feel a lot less worried.
But the report that the tone appeared right after the on command, and the explanation for other failures to receive tone [shadowing after batteries have failed], does provide a warm fuzzy feeling.
doesn't this show that the batteries are not charging?
Yes. I was thinking that too. If the batteries can't be recharged, does this doom the mission since the same situation would arise at Mars?
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#366
by
plutogno
on 23 Nov, 2011 15:46
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Also remember that the Mars/Earth alignment in 2013 is different than the alignment in 2011 (I don't know which is more optimal).
Mars launch window have a 16-year cycle. The 2003 window was an optimal, minimum energy one, so I guess 2011 is a maximum energy one. 2013 should be slightly better.
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#367
by
imcub
on 23 Nov, 2011 15:57
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I've been around RF signals too long NOT to worry the simple tonal signal
might turn out to be spurious. Was the antenna tracking the source across the sky? Was any doppler observed? That would make me feel a lot less worried.
But the report that the tone appeared right after the on command, and the explanation for other failures to receive tone [shadowing after batteries have failed], does provide a warm fuzzy feeling.
doesn't this show that the batteries are not charging?
Maybe the batteries fine and they are not receiving enough charge to power the spacecraft while shaded. Maybe the solar panels have not deployed and are only providing a small portion of the planned charge when in full sunshine. Sunlight it wakes up, shade it powers down ...
Anyone know if how much of the solar panels are exposed when in the stowed position?
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#368
by
alk3997
on 23 Nov, 2011 15:59
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Right then, so the general opinion is - providing this breakthrough leads to a command ability, and real soon - the mission is still possible?
Lots of ifs, but I want to establish the possibility still exists?
Possibility of a "mission" - sure. Possibility of the original mission - I don't think so. My biggest concern is that if there is a power problem onboard and that is why the burn didn't occur (and the telemetry has been off), then you can't have a "mission" until that siutation is solved/bypassed.
I don't know enough to say whether that is possible or not.
Andy
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#369
by
Chris Bergin
on 23 Nov, 2011 17:19
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Right then, so the general opinion is - providing this breakthrough leads to a command ability, and real soon - the mission is still possible?
Lots of ifs, but I want to establish the possibility still exists?
Possibility of a "mission" - sure. Possibility of the original mission - I don't think so. My biggest concern is that if there is a power problem onboard and that is why the burn didn't occur (and the telemetry has been off), then you can't have a "mission" until that siutation is solved/bypassed.
I don't know enough to say whether that is possible or not.
Andy
Thanks. That's what I think we all want to hear about.
No point rewritting the ESA release - prefer the news articles here to add something new (especially when we've got this update thread) - so we'll wait for that update.
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#370
by
lbiderman
on 23 Nov, 2011 18:22
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The ESA press release does not stablish that ESA will be modifying their systems to transmit commands to the spacecraft, right? Anatoly Zak mentions that, and I was wondering if there is any "news" that confirm that, or that is just a rumour (or inside sources).
Besides this, kudos for the ESA team!
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#371
by
Sesquipedalian
on 23 Nov, 2011 18:50
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I suppose the different trajectories are also relevant.
Fobos-Grunt is flying an 11 month trajectory culminating in entering orbit.
MSL is flying something like an 8 or 9 month trajectory, culminating in a direct entry.
I don't know enough to explain the reasons for the those differences, so that would be an appreciated point for anyone who may be more knowledgeable to expand upon.
Type 1 vs Type 2 trajectories.
Can someone elaborate on this answer? Jim's post is no more meaningful to me than if he had said "Number 1 vs Number 2 trajectories."
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#372
by
JWag
on 23 Nov, 2011 18:52
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Can someone elaborate on this answer? Jim's post is no more meaningful to me than if he had said "Number 1 vs Number 2 trajectories."
First hit on Google with "mars type 1 2 trajectories":
http://www2.jpl.nasa.gov/basics/bsf4-1.php
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#373
by
HIPAR
on 23 Nov, 2011 19:02
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So they have finally heard some babble from the probe. Now they need to collect useful data and determine the nature of the problem.
If the rocket motor is broken then 'Go directly to jail, do not pass go, do not collect $200'
If the software is broken, they need to reprogram something .. at least new ephemeris so the probe knows where it is and receives its new marching orders.
So that means, new code or commands must be generated and uplinked. Then some kind of verification of receipt must be received. All of this has to happen a piece at a time when the probe overflies Perth.
Perhaps they can accomplish this over the course of a few passes and get on with an abridged mission. But until there's a report of intelligent two way communication, I'm not optimistic about salvaging anything.
--- CHAS
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#374
by
alk3997
on 23 Nov, 2011 19:14
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Keep in mind that they are getting 6 minutes of downlink (at most) when the pass over Perth Austrailia. So, let's see on a good day that would be three orbits ascending and three orbits descending. So 6 orbits with 6 minutes (at most) each means they will get at most 36 minutes of data a day.
Now, if the spacecraft is shutting itself down when it goes into shadow (as the AP reported), that means some of that up to 36 minutes is spent waiting for the spacecraft to restart and then sending it the please start telemetry command. It also may be Groundhog Day on the spacecraft everytime it wakes up.
I'm guessing it's maintaining attitude only when enough sunlight reaches the spacecraft. That would means during each orbit, there would be long periods of drift, followed by sudden corrections when it wakes up, then attitude hold, followed by long periods of drift as the Sun sets.
Now somewhere in the available time, you want them to reprogram the spacecraft? (and remember I gave them more time than they would likely get on an average orbit). I think their first priority (at least it would be mine) would be to determine the cause of the power loss and correct for that so the spacecraft wouldn't be shutting down once an orbit.
Of course, this might explain one thing - the first burn was supposed to be over the night time part of the orbit, wasn't it? I'll go out on a limb and predict that a spacecraft with no power can't initiate a burn.
Andy
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#375
by
Svetoslav
on 23 Nov, 2011 19:20
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Just a little reminder... six minutes remain until first attempt to contact the probe for tonight - 20:25 GMT
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#376
by
Svetoslav
on 23 Nov, 2011 19:57
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People on NOVOSTI-Kosmonavtiki forum got embarrased by a message : "There's downlink, there's a TMI". It's most probably a joke, however.
EDIT : The author of this rumor says it's not a joke : The source of information comes from Europe. There's a set of data that implies TMI, he says...
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#377
by
Michael J
on 23 Nov, 2011 20:14
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People on NOVOSTI-Kosmonavtiki forum got embarrased by a message : "There's downlink, there's a TMI". It's most probably a joke, however.
EDIT : The author of this rumor says it's not a joke : The source of information comes from Europe. There's a set of data that implies TMI, he says...
Ria Science just Tweeted that telemetry was received, but there is no link to the story.
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#378
by
Svetoslav
on 23 Nov, 2011 20:17
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#379
by
Moskit
on 23 Nov, 2011 20:19
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http://ria.ru/science/20111124/496387514.htmlRIA News. European tracking station in Australia received telemetry from Russian Fobos-Grunt station, which was not communicated for last two weeks, told RIA a person from European Space Agency in Moscow, Rene Pishel.