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MRO MOI Events Timeline, Time Zone Friendly
Bob Shaw
post Mar 16 2006, 04:21 PM
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QUOTE (Bubbinski @ Mar 16 2006, 05:47 AM) *
More and more spacecraft will hopefully make it to Mars in the near future....it might be prudent now to start on a more extensive COLA/tracking/space debris reduction program before it becomes an issue. Same with the Moon.


Lunar orbits tend to be quite unstable, especially low ones, so there's almost certainly nothing other than SMART-1 in Lunar orbit at present - we're a long way from needing traffic cops there!

Bob Shaw


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Guest_BruceMoomaw_*
post Apr 26 2006, 09:56 AM
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An odd note from the March 6 Aviation Week: The pre-MOI repressurization of the hydrazine tank "caused a little anxiety because Mars Observer was lost at the same point in 1993, believed due to overpressurized tanks from a faulty orifice in the pressure regulator sensing line."

This is a totally different theory for Mars Observer's loss from the one I've always seen listed as most probable: nitrogen tetroxide oxidizer leaking past a check valve into the hydrazine lines and setting off an explosion in the latter when the hydrazine first came down them. Is AW mistaken and the pressure-regulator theory is just one of the less likely alternate possible causes listed in the MO failure report, or has there been some recent rethinking on the most probable cause of the accident?
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edstrick
post Apr 26 2006, 10:25 AM
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I was looking at that report and wondering the exact same thing....

I suspect a lot of the engineers and reporters have never read or essentially forgotten the full range of plausible failure modes ... I sure have forgotten all but the "somewhat most plausible" one.... and the reporter may be quoting one engineer or manager's take on the MO failure who's also working from memory.
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Jim from NSF.com
post Apr 26 2006, 10:43 AM
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Maybe this was the only plausible failure mode applicable to MRO
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edstrick
post Apr 26 2006, 11:19 AM
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Engineers and mission controllers on these missions have incredible regenerative abilities .... they routinely chew their fingernails back to their armpits during the runup to these mission critical events.
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mcaplinger
post Apr 26 2006, 01:01 PM
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QUOTE (BruceMoomaw @ Apr 26 2006, 02:56 AM) *
Is AW mistaken and the pressure-regulator theory is just one of the less likely alternate possible causes listed in the MO failure report, or has there been some recent rethinking on the most probable cause of the accident?

The latter. From "Propulsion Lessons Learned from the Loss of Mars Observer", Carl S.Guernsey, JPL, 2001:
"This paper presents an overview of the potential failure modes identified by the JPL review board and presents evidence, discovered after the failure reviews were complete, that the loss was very likely due to the use of an incompatible braze material in the flow restriction orifice of the pressure regulator."

Complete paper is online at
http://www.klabs.org/richcontent/Reports/F...y_a01-34322.pdf


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Disclaimer: This post is based on public information only. Any opinions are my own.
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Guest_BruceMoomaw_*
post Apr 27 2006, 12:09 AM
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Ah! This is a big item that's totally new to me. Thanks.
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tuvas
post Oct 13 2006, 11:25 PM
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QUOTE (BruceMoomaw @ Apr 26 2006, 02:56 AM) *
An odd note from the March 6 Aviation Week: The pre-MOI repressurization of the hydrazine tank "caused a little anxiety because Mars Observer was lost at the same point in 1993, believed due to overpressurized tanks from a faulty orifice in the pressure regulator sensing line."

This is a totally different theory for Mars Observer's loss from the one I've always seen listed as most probable: nitrogen tetroxide oxidizer leaking past a check valve into the hydrazine lines and setting off an explosion in the latter when the hydrazine first came down them. Is AW mistaken and the pressure-regulator theory is just one of the less likely alternate possible causes listed in the MO failure report, or has there been some recent rethinking on the most probable cause of the accident?


If I remember right, the pressurization was such a big deal because there was a fairly last-minute change in the code, as I recall, it was set up so there wasn't a redundancy previous to a reprogramming only a few weeks before MOI. I attended a MOI party at the University of Arizona with the HiRISE team (This was right before I joined, my hiring was contitional upon the safe MOI of MRO, imagine that!), and I think that was the story that I heard at the UA MOI party... But, it's been quite a while... Also, please note that I wasn't a HiRISE team member at this point in time, so I don't know if that's really the reason. If that was the reason, then it just goes to show that NASA isn't taking any more chances with it's spacecraft, they are constantly checking things to make them better. MRO has performed almost flawlessly, even with it's more complex than normal instruments.
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