-
#180 by hop on 16 Nov, 2011 18:48
-
JimO back -- that's the operative statement: "they still could not leave immediately". Waiting for orbital precession will see the Earth-Mars window CLOSE before the planar window re-opens.
I'm certainly not an expert, but it seems like there should be other options. For example, a long cruise + earth flybys like Nozomi. IIRC Nozomi also used a lunar flyby on departure. Now, the longevity of past Russian deep space probes suggests the odds are low, but it seems premature to assume the mission is lost even if the nominal trajectory is no longer available.
All of the official assurrances from Roskosmos, that they still have a chance to get off to a Mars mission after a little delay -- are totally BOGUS. -
#181 by Patchouli on 16 Nov, 2011 19:43
-
From Universe Today: Phobos-Grunt's Mysterious Thruster Activation
http://www.universetoday.com/91037/phobos-grunts-mysterious-thruster-activation-a-function-of-safe-mode-or-just-good-luck/
I wonder if it could be the Fregat doing what is known as a propellant setting maneuver. -
#182 by JimO on 16 Nov, 2011 19:51
-
I wonder if it could be the Fregat doing what is known as a propellant setting maneuver.
Excellent suggestion -- a low-thrust 'settling burn' ['setting' a typo?] is on the official Fobos-Grunt ascent profile, to precede each MDU (AKA 'son of Fregat'] burn.
It might be caught in a loop trying to get to MDU ignition but aborting prior to issuing that command. -
#183 by just-nick on 16 Nov, 2011 19:53
-
It might be caught in a loop trying to get to MDU ignition but aborting prior to issuing that command.
In which case propellant depletion is a real issue.
--N -
#184 by flagran on 16 Nov, 2011 19:58
-
I wander if Phobos - Grunt has an VHF antenna. Solar panels sides look like VHF antennas.
-
#185 by Patchouli on 16 Nov, 2011 19:59
-
It might be caught in a loop trying to get to MDU ignition but aborting prior to issuing that command.
In which case propellant depletion is a real issue.
--N
Esp if the RCS uses separate propellant tanks. -
#186 by theridane on 16 Nov, 2011 20:26
-
The original Fregat has 1350 seconds of RCS firing time (42 kg of hydrazine). That's not enough to explain the apparent boosts we've seen, I think.
Wouldn't hydrazine firings be visible on infrared? -
#187 by Danderman on 16 Nov, 2011 20:47
-
It might be caught in a loop trying to get to MDU ignition but aborting prior to issuing that command.
In which case propellant depletion is a real issue.
--N
Esp if the RCS uses separate propellant tanks.
Which it does. I believe the RCS tanks can contain 85 kg of prop.
-
#188 by Kaputnik on 16 Nov, 2011 20:59
-
Wouldn't hydrazine firings be visible on infrared?
Do you mean, if someone was constantly watching the spacecraft using the appropriate equipment?
To my uneducated mind it does seem plausible that the spacecraft could be stuck in a cycle where it prepares to fire the main engine, settles the propellant, and then hits a problem causing some kind of reset, and on it goes again.
Has it been established beyond doubt that the apparent increases in perigee are beyond the scope of observational innaccuracies? -
#189 by Comga on 16 Nov, 2011 21:27
-
JimO back -- that's the operative statement: "they still could not leave immediately". Waiting for orbital precession will see the Earth-Mars window CLOSE before the planar window re-opens.
I'm certainly not an expert, but it seems like there should be other options. For example, a long cruise + earth flybys like Nozomi. IIRC Nozomi also used a lunar flyby on departure. Now, the longevity of past Russian deep space probes suggests the odds are low, but it seems premature to assume the mission is lost even if the nominal trajectory is no longer available.
All of the official assurrances from Roskosmos, that they still have a chance to get off to a Mars mission after a little delay -- are totally BOGUS.
In this case I agree with hop's statements, but don't know if Roskosmos' statements reflect that or just a blind "I'm not dead yet!".
There may indeed be a trajectory that gets to Mars approximately one Martian year later, that still has the same hyperbolic excess velocity leaving Earth. A Martian year is (1.88 Earth years) is ~2.7 times the mean Hohmann tranfer time (0.71 years). JPL could probably find a solution within these constraints, and the Russians have plenty of people who are good at very high level math.
Whether a Russian spacecraft could last that long is questionable, as hop said.
edit: typo -
#190 by sdsds on 16 Nov, 2011 23:18
-
I want to totally thank those who patiently explained that even for an ecliptic plane departure the LEO doesn't need to be coplanar with the ecliptic! A big thanks also to JimO for his precession explanation, which actually does make intuitive sense.
Having displayed my orbital mechanics naivete I am now going to openly display a cultural prejudice: the Russian space program undoubtedly has (and always has had) people who are really good at this stuff. They may for example have someone who right now can visualize other departure opportunities in the coming days that are somehow trickier than the simple case we have mostly been discussing. (This would include the lunar flyby, the Earth-return flyby, and maybe others within the F-G delta-v budget which merely delay Mars arrival.) Maybe the Russian officials and spokespeople have access to that orbital mechanics wizard and trust him or her?
Oops: sort of cross-posted with and thus repeated Comga above. Sorry! -
#191 by kevin-rf on 16 Nov, 2011 23:32
-
Research: bi elliptical transfer orbits. If anything can save this mission, it would have to be some variation on it.
Btw. It is a Russian variation on the method that is used for most (all?) Russian GTO/GSO missions. -
#192 by Eric Hedman on 17 Nov, 2011 00:56
-
I found some interesting pages on the Phobos Grunt spacecraft on the RIA NOVOSTI web site. It's worth looking at
http://en.rian.ru/infographics/20111115/168723275.html -
#193 by Rocket Science on 17 Nov, 2011 01:06
-
I found some interesting pages on the Phobos Grunt spacecraft on the RIA NOVOSTI web site. It's worth looking at
Nice page Eric, thanks for posting it.
http://en.rian.ru/infographics/20111115/168723275.html
Robert -
#194 by Eric Hedman on 17 Nov, 2011 01:18
-
You are welcome. After looking at those pages it is even sadder that this spacecraft probably won't be able to carry out its mission.I found some interesting pages on the Phobos Grunt spacecraft on the RIA NOVOSTI web site. It's worth looking at
Nice page Eric, thanks for posting it.
http://en.rian.ru/infographics/20111115/168723275.html
Robert -
#195 by jcm on 17 Nov, 2011 01:36
-
The four separation motor covers from FG's Zenit second stage have now been cataloged, with out of sequence catalog numbers 37862 to 37865 (previously reserved from the Shenzhou 8 sep motor covers, which apparently were not tracked).
These debris objects are as expected and have higher (500 km) apogees as usual; they
originate from the Zenit second stage.. so don't make the mistake of thinking they are evidence of some kind of failed FG burn or breakup. -
#196 by flagran on 17 Nov, 2011 02:50
-
1) The status of Fobos-Ground is known as long as they have downlink.
2) Sending an intervention mission to repair Fobos is out of question as long as it will be cheaper to send a Fobos 2 mission in 2013 and abandon the current one.
3) The Orbital plan needs a full 360 rotation in order the satellite comes in the initial position with the same speed as a vector.
http://www.atmos.albany.edu/deas/atmclasses/atm422/polanim.gif
Even the orbit is circular and it looks like an 180 degree rotation is enough to have the same situation as in the beginning, in reality it is not, simply because the satellite will have the wrong speed, it will rotate in reverse. It is not self evident but the satellite will rotate the opposite direction after a 180 degree rotation of the orbital plane. -
#197 by Jim on 17 Nov, 2011 03:20
-
1) The status of Fobos-Ground is known as long as they have downlink.
If they had downlink, then there might not be a problem. -
#198 by alk3997 on 17 Nov, 2011 04:19
-
Could the shuttle have rendezvoused with F-G? Would there be any chance that an EVA could find a fixable problem?
Here's my answer to your question from the launch (and first few days thread). On second thought I don't think I made it sound difficult enough at the end. We haven't even discussed the difficulties with rendezvousing with a small non-cooperative object in space. By non-cooperative I mean there is no way to turn off the attitude hold (assuming the observer reports are true). Imagine if the attitude control system decides to perform attitude control after the RMS grapples FG (don't know how the grapple would be done since it doesn't have any grapple fixtures) or when an astronaut touches it. Not a pretty picture!
However, there are plenty of other reasons that a rescue mission wouldn't work.
And we wouldn't risk a Shuttle orbiter and a Shuttle crew for the off-chance that you might find something to fix even if you had two years.
Andy
----------------------
Let me see if I can help with your question. Under normal circumstances it took about 2 years to design a Shuttle mission. This was if everything went well. We didn't just drop some SRBs on the mobile crawler, slap a tank between then and then run the orbiter up the side. It took lots of planning, analysis and checking to make sure everything would work right (or at least had a reasonable chance of everything working right).
Don't forget there is crew training. Not just the learning to fly but the parts about what to do once you got to the objective.
In the case of this supposed "rescue" mission. What was the objective? To bring up a new upper stage or to magically fix the spacecraft? If it is the former, someone would have to make the new upper stage and a cradle for the cargo bay as well as the design safe and arm circuitry - among a whole slew of things. If it is the latter objective, then how do you fix the spacecraft? Kind of hard to train for a spacecraft rescue when no one knows what went wrong. If you're just up there to take a look, that doesn't buy you anything since you would probably not have the right equipment to fix the problem.
I believe if we were repeating a mission with the same orbiter (each orbiter had unique parameters), we could have done it in 2-3 months (see STS-94) but something new and untried - I'd guess about 2 years.
I might argue the supposed cost of a Shuttle flight from a few pages back (the real number depends upon who gets charged and how much of the cargo bay was used), but it isn't relevent because this rescue mission during the same launch window couldn't be done, no matter how much money was available.
So you would have as much chance as the President of the United States and the four Beatles performing the rescue mission themselves as you would being able to launch this so-called rescue mission during the current launch window.
-
#199 by Comga on 17 Nov, 2011 05:27
-
(snip)
3) The Orbital plan needs a full 360 rotation in order the satellite comes in the initial position with the same speed as a vector.
http://www.atmos.albany.edu/deas/atmclasses/atm422/polanim.gif
Even the orbit is circular and it looks like an 180 degree rotation is enough to have the same situation as in the beginning, in reality it is not, simply because the satellite will have the wrong speed, it will rotate in reverse. It is not self evident but the satellite will rotate the opposite direction after a 180 degree rotation of the orbital plane.
I believe that this statement is incorrect. If the orbit passes through the point opposite the departure direction, the same burn is required when the S/C hits the tangent circle to escape with the requisite excess velocity . Whether the S/C is heading north or south shouldn't make a difference.
Do others concur?
Are there subtle differences in the required burn?
It will still take about 30 days for the orbit to precess 180 degrees at 6 degrees per day, and the primary window may have close by then, even if they manage to gain control in that time.
