[X] My Assistant

[PhilHorzempa]

My purpose in starting this new thread is to review what we know
about the demise of the Mars Observer. As most know, the Coffey
review board concluded that vapor migration in the propellant
lines led to explosive mixing whenthe system was pressurized.
However, several other possible scenarios for the mishap were
possible, and in my opinion, perhaps, more likely than vapor migration.

My 'favorite' alternate model for MO's end concerns the pyro valves on
the Mars Observer. As I recall, they were similar to ones on Landsat 6.
I have not been able to find a final report for the demise of Landsat 6 on
the Internet. However, if my memory is correct, it was concluded that
the pyros in the Landsat 6 attitude control system ruptured the propellant
lines during the launch process. The Landsat 6 was launched on a Titan 2
and depended on an SRM for the final kick to orbit.

Landsat 6's ACS was to control attitude during the solid rocket burn.
However, the rupture in the prop lines caused all prop to bleed away.
Therefore, the satellite tumbled during the SRM burn, causing it to fall
short of orbital velocity.

I think that something similar may have happened to the Mars Observer.


Another Phil

[djellison]

Contact with Mars Observer was lost on August 21, 1993, three days before scheduled orbit insertion. Navigation has no part to play.


Doug

[The Messenger]

I agree, but consider this: MCO did not undergo any coarse corrections in the final days - the path was running a little tighter than expected, but within acceptable limits. If for any reason, MCO would have gone into safe-mode days before orbital insertion, and we had not been able to wake it before it reached the orbital insertion point, it would have still fallen into Mars, but we would have no knowledge of the navigational disparity and what happened after the safing event.

The same is true of Mars Observer: Navigation had nothing to do with the initial failure, but we do not know whether or not the initial failure might have been recoverable if there had been more time to work the problem. Unfortunately, this opens the possiblity to other, less catastrophic initial failure modes that may have placed the probe in hibernation - we will never know.

The point I am trying to make is that we should put more sensors on our probes, and generate as much real time telemetry as possible during critical operations. This way, when failures do occur, we might end up with a better idea about what went wrong.

[djellison]

Navigation had nothing to do with the initial failure, but we do not know whether or not the initial failure might have been recoverable if there had been more time to work the problem.

There was no 'working' of the problem to be done. The spacecraft essentially vanished.

What you are speculating is IF the failure had not been fatal ( which it was ) AND the navigation had been wrong ( of which we have no indication ) THEN they would only have had 3 days to correct any problems before arriving at Mars.

But they were going to be arriving at Mars in 3 days anyway - the three navigation options are impact or flypast. Either of them were coming up 72 hours later, navigation right or wrong.

I'm not sure what point you're actually trying to make apart from being intentionally hyper-speculative and obtuse.

Doug