alb@alice.UUCP (12/14/83)
NASA said today that an apparent hydrazine leak in the APU compartment ignited and exploded during the reentry of STS-9, but that the fire (or its effects) was not noticed until the day after landing.
karn@allegra.UUCP (12/14/83)
One point: as I understand it, the explosion happened after the landing, not during, although the hydrazine fire was already in progress. Once again, the TV stations are screwing up the story. On tonight's news, at least two of the stations showed footage of a closeup of the yellow flame coming from the rear of the orbiter after landing. At least one of the commentators said "and you can see the flame there." It should be pointed out that NASA still believes that this flame (which is actually rather large) was the normal exhaust from the APU and the effects of the internal fire were not visible. This is a reasonable assertion since a quick check of the STS press information (which the TV reporters obviously didn't look at) shows that the APU exhaust vents are indeed in the location shown. They are clustered around the forward end of the base of the vertical stabilizer and exhaust upwards when the orbiter is sitting on the runway. The APUs are mono-propellant systems; straight hydrazine (N2H4) is catalytically decomposed and the resulting hot gases (I would suppose nitrogen and hydrogen) are used to drive the turbines. Since no oxidizer is used, I would certainly expect that the exhaust gases would spontaneously burn after coming out of the exhaust port and in contact with air. You can indeed see a gap between the port and the base of the flame, just as you would with a gas torch set on full rich mixture. Just wanted to set the record straight. Phil