[AR] Re: What happened to the Space Shuttle?
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Wed, 24 Jul 2019 06:19:05 -0400 (EDT)
On Tue, 23 Jul 2019, anthony@xxxxxxxxxxx wrote:
...mentions all [LM DPS] flight engines undergoing an acceptance firing --
length not specified -- before delivery. (The flight pressure sensors
had to be installed after that, else residual oxidizer caused some
etching of the sensor diaphragms, which messed up calibration.)
I recall the concern regarding propellant corrosion. The transducer
switch makes sense. Does the citation indicate to what extent purging
was carried out (a lot to consider in practice) and what the duration of
the test was?
No, the brief discussion of this is focused on the sensor calibration
issue, and just says that the fix was to install pressure sensors "after
acceptance firing and after cleaning the engine for delivery". There's no
discussion of acceptance procedures per se -- they just get mentioned in a
couple of places where one aspect or another caused trouble.
I don't think the LM propulsion systems made much of an attempt at
purging. Problem like this were specific to ground firings, since N2O4
won't stick around in hardware that's open to vacuum, and N2O4 vapor isn't
actually very corrosive if there's no atmospheric water vapor around to
combine with it.
(In the world of cost-constrained development, it is often well worth
adding a bit of mass to make hardware easier to test. But Apollo had lots
of money and no performance to give away.)
Henry
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