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#280
by
HIPAR
on 19 Nov, 2011 20:01
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So why is venting occurring? Is some kind of pressure relief mechanism commonly designed into the tanks or pressure vessels? Or did something occur to cause a leak?
--- CHAS
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#281
by
ChileVerde
on 19 Nov, 2011 20:15
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So why is venting occurring? Is some kind of pressure relief mechanism commonly designed into the tanks or pressure vessels? Or did something occur to cause a leak?
--- CHAS
Nobody seems to know. It might also be that the apparent force causing the orbital behavior is not due to a leak but to slightly uncompensated firing of attitude thrusters. Or something else. (Somehow this reminds me of the "Pioneer Anomaly.")
I attach a plot of the mean altitude generated from the latest Space Track orbital elements.
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#282
by
kevin-rf
on 19 Nov, 2011 20:49
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So why is venting occurring? Is some kind of pressure relief mechanism commonly designed into the tanks or pressure vessels? Or did something occur to cause a leak?
--- CHAS
Can I remind everyone that Jim Oberg had a good explanation several posts back that centered around cross-coupling. No mysterious venting or leak needed...
100 Fire thruster to keep sun lock
200 goto to higher Perigee
300 wait until the sun moves again
Let me add my 2 kopecks to the mystery of the orbit rise and its hypothetical connection with attitude control firings.
The effect that is being postulated was called 'cross-coupling' in the MCC when I worked there, and reflects the fact that small thrusters which are dedicated to specific translational or rotational modes are rarely 'pure' in their force. Along with major intended contribution to specific roll/pitch/yaw and X/Y/Z translation, they induce forces in other modes as well, sometimes minor, but not always so.
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#283
by
iamlucky13
on 19 Nov, 2011 23:54
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Attached is diagram showing what is happening.
According to your diagram, on or about November 21st Phobos-Grunt will be in a polar orbit. We know that’s not true, so the diagram does not capture the actual situation.
I don't think you're envisioning following the evolution of the orbit correctly. You seem to be envisioning the next step in the precession to be like the first image I'm attaching. That's not a precession, but a plane change.
It's closer to the second attached image. As viewed from the original perspective, the next orbit appears slightly oblate, progressively more so until it has fully cycled past appearing circular towards oblate in the direction of the 180 degree plane.
Kind of like, although for different reasons, the way the orbits of Saturn's ring particles appear at different angles and obliqueness as it moves around the sun:
http://apod.nasa.gov/apod/image/0909/6yearsofsaturn_friedman.jpgUnfortunately, it's not quite obvious diagramming it from above either (actually along the earth's axis, rather than over the sun), although I think that is a slightly easier way to view it.
I apologize - I realized after I created the images I reversed the dates. The principle holds, but in the opposite direction.
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#284
by
sdsds
on 20 Nov, 2011 00:25
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As viewed from the original perspective, the next orbit appears slightly oblate, progressively more so until it has fully cycled past appearing circular towards oblate in the direction of the 180 degree plane.
Yes, I think this is almost correct, and certainly better than thinking the orbital plane of the satellite always appears "edge on" from this perspective! Your additional images are really helpful in clarifying this.
My only minor nit to pick: from the point of view of these diagrams, the orbit never appears fully circular. When it is maximally oblate, the vector normal to the plane of the orbit still isn't pointing in the direction of the Earth's motion around the Sun. (It is, if you will, pointing someplace directly "over our head" or "under our feet.") Only if that normal vector were pointing directly at us or directly away from us would a circular orbit actually appear circular.
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#285
by
Chris Bergin
on 20 Nov, 2011 00:34
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A reminder to everyone to stay on topic. This is about the spacecraft and the efforts to save it. Nothing else, such as personal preference of programming lanuages.
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#286
by
iamlucky13
on 20 Nov, 2011 02:08
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As viewed from the original perspective, the next orbit appears slightly oblate, progressively more so until it has fully cycled past appearing circular towards oblate in the direction of the 180 degree plane.
Yes, I think this is almost correct, and certainly better than thinking the orbital plane of the satellite always appears "edge on" from this perspective! Your additional images are really helpful in clarifying this.
My only minor nit to pick: from the point of view of these diagrams, the orbit never appears fully circular. When it is maximally oblate, the vector normal to the plane of the orbit still isn't pointing in the direction of the Earth's motion around the Sun. (It is, if you will, pointing someplace directly "over our head" or "under our feet.") Only if that normal vector were pointing directly at us or directly away from us would a circular orbit actually appear circular.
I agree. Good correction.
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#287
by
Michael J
on 20 Nov, 2011 21:22
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#288
by
Michael J
on 20 Nov, 2011 22:35
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#289
by
Steven Pietrobon
on 21 Nov, 2011 06:43
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Thanks Michael J. According to Ria Novosti, the launch window closes today on 21 November and if the orbital precession of the orbit for alignment is after this date (I calculated 4 December, but Molzan has said that the rate of precession is increasing which would move the date up), then there's nothing that can be done to get to Mars now. The only chance is to get in contact, fix the problem and then move PG into another orbit so that it can have another chance in two years time.
What I don't understand is that the Mars Science Laboratory (MSL) launch window is from 25 November to 18 December which is after the end of the window according to Ria Novosti.
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#290
by
input~2
on 21 Nov, 2011 07:12
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#291
by
joncz
on 21 Nov, 2011 11:24
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What I don't understand is that the Mars Science Laboratory (MSL) launch window is from 25 November to 18 December which is after the end of the window according to Ria Novosti.
Launch site inclination.
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#292
by
Michael J
on 21 Nov, 2011 12:11
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It looks like the Roscosmos is resigned to Phobos Grunt reentering, and Vladimir Popovkin said that while the engines may survive, the hydrazine will not:
http://bit.ly/vzJuoV.
And the story continues to evolve.
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#293
by
Ben the Space Brit
on 21 Nov, 2011 12:37
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It looks like the Roscosmos is resigned to Phobos Grunt reentering, and Vladimir Popovkin said that while the engines may survive, the hydrazine will not: http://bit.ly/vzJuoV.
And the story continues to evolve.
I think that the hope is that the heat of re-entry will cause the propellant to explode. However, if the tanks retain integrity (and the Russians do like building stuff tough), you get several 'bombs' full of pressurised, boiling hydrazine dropping on a random part of the globe.
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#294
by
kevin-rf
on 21 Nov, 2011 13:37
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Question, these tanks, are they Stainless, Al, of Ti? Certain materials survive reentry better than others.
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#295
by
JRThro
on 21 Nov, 2011 14:21
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The velocity vectors at perigee and apogee are at right angles to each other, so the force would have to act in different directions.
No, since perigee and apogee are on opposite sides of the Earth from each other, the velocity vectors at those two points are at 180 degrees from each other.
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#296
by
ChileVerde
on 21 Nov, 2011 16:05
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#297
by
arkaska
on 21 Nov, 2011 16:43
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What's the possibility that they will shoot down it before re-entry as the US did?
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#298
by
Ben the Space Brit
on 21 Nov, 2011 16:49
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What's the possibility that they will shoot down it before re-entry as the US did?
It depends on several things: 1) That the Russian Fedeation has an operable ABM/ABL/ASAT system and 2) the risks to a friendly civilian population is high enough to risk the exposure of a likely-classified weapon whose existance would also be politically awkward to admit.
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#299
by
rdale
on 21 Nov, 2011 17:02
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Shorter answer - close enough to zero that it's not worth it...
