A Case Study in NASA-DoD - The Black Vault

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version of the STPSS uses the same cold gas system, except that the
twelve 0.1 lb B thrusters are replaced with eight 4 lb F thrusters of
the same basic configuration. The unit weights and costs of these
thrusters are estimated to be the same as the three-axis units. All
components in both cold gas systems are flight-proven.
While the component development status of both the AEM hydrazine
system and the STPSS cold gas systems appears to be about the same, different
costing bases will be required to reflect the relative degrees
of component complexities between them, particularly for tanks and
thrusters.
Hydrazine tanks typically use diaphragms or bladders for
propellant expulsion and gaseous nitrogen (GN 2 ) for pressurization and
require two drain and fill valves per tank. Cold gas tanks simply contain
GN 2 under high pressure (in this case, 4000 psia) thus eliminating
the diaphragm/bladder and one drain and fill valve. Hydrazine thruster
assemblies typically consist of propellant flow control valves, injector
thermal standoff and capillary feed tubes, catalytic decomposition
chamber, injector, thrust nozzle, heaters (for thrust, chamber, valves,
and catalyst bed), temperature sensors, and in some-cases, filters and
cavitating venturis; whereas cold gas thruster assemblies consist
essentially of solenoid valves and a thrust nozzle. Hence, a sizable
component cost differential is justifiable between these two types of
RCSs, as well as some anticipated difference in system integration and
test costs.
DESCRIFI'ION OF THE STPSS ALTERNATIVE HYDRAZINE REACTION CONTROL SYSTEM
AND COMPR!.RTION TO AEM
An alternative to the STPSS three-axis version spacecraft is to
use a transfer/orientation module in place of the cold gas equipped
orientation module and solid rocket propulsion for orbit transfer.
This transfer/orientation module contains (in addition to attitude
control system equipment) a hydrazine RCS to perform all of the spacecraft
functions, such as three-axis stabilization, reaction wheel unloading,
and orbit transfer and adjustment. Table E-1 shows the component
breakdown for this system.
The 36-in. diameter spherical tank will be fabricated using the
end forgings from the Viking Orbiter tank and incorporating an existing