[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

[Guest_BruceMoomaw_*]

The Langley technical report server seems to be on the fritz at the moment, so here's the relevant portion of that report:

"A number of failures have recently occurred in the use of single-shot, 'normally closed' pyrotechnically actuated valves (pyrovalves) in spacecraft hydrazine-powered attitude control systems. These pyrovalves, which were designed to prevent flow of hydrazine until actuation, are opened by electrically firing a pyrotechnic charge; this rapidly burning charge produces gases that drive an internal piston to shear off internal fittings to allow hydrazine flow.

"Two failure modes have occurred: (1) The burning of the valve's titanium housing threads allowed the initiator cartridge to be jettisoned by the valve's internal pressure at a velocity of over 600 feet/second, and (2) The 'blowby' or venting of hot gases and hot particles from the burning pyrotechnic charge around the actuating piston, prior to O-ring seating; these gases/particles entered the fluid path of the valve, and initiated a reaction in the hydrazine, which overpressurized and burst the system plumbing.

"The first failure mode occurred in a ground test in the European Space Agency Cluster Program. The second failure mode, as indicated by Lockheed Martin, was responsible for the loss of the Landsat 6 and Telstar 4. It was also considered by the Jet Propulsion Laboratory to be a possible cause for the loss of the Mars Observer spacecraft. All of these spacecraft employed essentially the same pyrovalve design."

The rest of the paper deals with a design change to prevent both failure modes.

[The Messenger]

The Langley technical report server seems to be on the fritz at the moment, so here's the relevant portion of that report:

"Two failure modes have occurred: (1) The burning of the valve's titanium housing threads allowed the initiator cartridge to be jettisoned by the valve's internal pressure at a velocity of over 600 feet/second, and (2) The 'blowby' or venting of hot gases and hot particles from the burning pyrotechnic charge around the actuating piston, prior to O-ring seating; these gases/particles entered the fluid path of the valve, and initiated a reaction in the hydrazine, which overpressurized and burst the system plumbing.

Thanks Bruce, these seem to me to be more likely failure modes than a minute amount of brazing corrosion in a dead-ended fitting. While these failure modes were just as fatal to the mission, these are somewhat less 'catastrophic', and may have been recoverable if the probe would have been more than three days from Mars at the time of the failure.

My only issue with navigation is that it was less precise in the 90's than we thought it was, and by inference, the MO may have also been on a tighter path and therefore more likely to have impacted with the planet.

[mcaplinger]

Thanks Bruce, these seem to me to be more likely failure modes than a minute amount of brazing corrosion in a dead-ended fitting. While these failure modes were just as fatal to the mission, these are somewhat less 'catastrophic', and may have been recoverable if the probe would have been more than three days from Mars at the time of the failure.

All I can say is that the failure review documents say otherwise. I worked on the project for 5 years, I was there when the spacecraft was lost, and I've read all the documents with a fine-toothed comb. What are your qualifications, exactly?

My only issue with navigation is that it was less precise in the 90's than we thought it was, and by inference, the MO may have also been on a tighter path and therefore more likely to have impacted with the planet.

I'm getting a little tired of these thinly-veiled references to "new physics" you keep tossing in here.

[djellison]

I'm getting a little tired of these thinly-veiled references to "new physics" you keep tossing in here.

So am I.

The Messenger, you've had warnings and indeed a suspension because you've refused to stop posting this garbage in the past. Consider this your final warning.

Doug