Author Topic: LIVE: Zenit-2SB launch with Phobos-Grunt - November 8, 2011  (Read 427448 times)

Offline ChileVerde

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Re: LIVE: Zenit-2SB launch with Phobos-Grunt - November 8, 2011
« Reply #940 on: 11/13/2011 05:29 PM »

To add another graph to the mix, I've plotted Phobos-Grunt's "mean altitude", which is the semimajor axis minus a conventional value for the radius of the earth (6371 km). This has the advantage that it is an indicator of the total energy in the orbit and allows drag effects to be seen fairly directly. What it shows is that between about UTC days 314.75 and 316.50 of 2011 something was acting against the normal drag that affected the satellite before and after that interval.
"I can’t tell you which asteroid, but there will be one in 2025," Bolden asserted.

Offline simonbp

Ah, thanks Chile! I had thought of doing that myself, but you saved me the effort!

I don't know if I believe that there's really a turnaround at that kink. All you need to do is remove a single point, and the story changes to "high-drag, low-drag, high drag". This would make sense if the spacecraft has lost attitude control and is just very slowly tumbling (and thus oscillating between high and low drag states). Considering that one little increase is of the same size as the scatter of the clear deceasing points, I think that's statistically safe assumption.

So again, I'm not convinced the spacecraft has ever made a thruster burn. It's likely just stuck in the same software loop it was right after insertion, waiting for some sensor input that will never come...
« Last Edit: 11/13/2011 06:27 PM by simonbp »

Offline John Santos

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Re: LIVE: Zenit-2SB launch with Phobos-Grunt - November 8, 2011
« Reply #942 on: 11/13/2011 06:47 PM »
the inexorably planar shift [~6 degrees per day] of the Phobos-Grunt parking orbit
Indeed, it has already veered 24 degrees since early Nov 9...

From the original ground track, it appears the plan was to perform the two  Fregat burns while approaching the equator from the south, that is on an ascending node.  Is it possible that there would be a "descending node" opportunity when the orbital plane has shifted 180 degrees (i.e. on or about Dec 4?)  Of course, this assumes that control is recovered, PB is still alive, so much energy hasn't been lost to atmospheric drag by that time that it can no longer reach Mars, and that the planar shift continues at 6 degrees per day.

Offline Space Pete

Very interesting!

From ISS On-Orbit Status Report for 13/11/2011.

Phobos-Grunt Visibility:
The ISS crew was notified of viewing/photographing opportunities for the stranded Phobos-Grunt Mars probe from the DC-1 VL-1 and MRM-2 windows as it crossed the ISS trajectory this morning at 4:06:16 AM GMT and 4:52 AM GMT.
Electronic Engineer by day, NASASpaceflight's ISS Editor by night | Read my NASASpaceflight articles here

Offline Rocket Science

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Re: LIVE: Zenit-2SB launch with Phobos-Grunt - November 8, 2011
« Reply #944 on: 11/13/2011 07:43 PM »
Very interesting!

From ISS On-Orbit Status Report for 13/11/2011.

Phobos-Grunt Visibility:
The ISS crew was notified of viewing/photographing opportunities for the stranded Phobos-Grunt Mars probe from the DC-1 VL-1 and MRM-2 windows as it crossed the ISS trajectory this morning at 4:06:16 AM GMT and 4:52 AM GMT.
Thanks Pete,
It would be nice to see some pics…

Robert
"The laws of physics are unforgiving"
~Rob, Physics instructor, aviator, vintage auto racer


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