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Re: Analysis of AO-40 Telemetry From BipropellantEngine Burn Attempts





Jon Ogden wrote:
> 
> on 12/21/00 12:23 PM, Phil Karn at karn@ka9q.net wrote:
> 
> >> rises from 0 to 15.6 Bar. Also the helium tank pressure may have
> >> cooled from 10.7 to 8.1 C.  (This may also be due to 'stirring' of
> >> tank contents caused by acceleration.) Later indications from
> >
> > No, just think of "adiabatic expansion".
> >
> > AO-10 was never able to do a second burn because the helium bottle
> > lost pressure after the first burn. The theory was that during the
> > first burn, which went long because of a wiring error in the LIU,
> > adiabatic expansion cooled the helium bottle enough for differential
> > contraction of the bottle cap to lose its seal, allowing the helium to
> > escape.
> 
> Phil,
> 
> I thought AO-10 had its problems because it collided with the launcher
> vehicle this damaging the engine.

Exactly, good that someone remembers..
AO-10 had a wrong attitude after the collison with the last stage.
The sun was almost on top of the spacecraft, thus the He tank got much
below the specified temperature range. This stress caused a seal to leak 
later on after the 1st firing.
BTW: the He bottle on AO-10 was 400bar, on AO-40 it is 200bar.

Peter


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