Development of a Cold Gas Propulsion System for the ... - SSL - MIT

Table 6-1. Maximum thrust levels for individual CGSE thrusters.
Vertical Thruster # Maximum Thrust [N] Horizontal Thruster # Maximum Thrust [N]
1 51.5 ± 2.5 2 57.9 ± 0.2
3 51.7 ± 3.2 4 56.7 ± 0.5
5 53.4 ± 2.0 6 57.4 ± 1.3
7 52.5 ± 2.2 8 57.0 ± 1.7
Each of the thrust values listed in Table 6-1 is an average of three tests, except for thruster 1, which had
a clearly anomalous measurement in one of the tests and is therefore the average of only two tests. The
uncertainty is the difference between the average and the actual thrust measurement furthest from it.
Table 6-1 shows that the CGSE thrusters in the full flight system significantly outperformed the single-
stream thruster. This was unexpected; it had been anticipated that the branches and bends in the feed
lines in the low side of the CGSE would result in greater pressure losses and thus lower thrust levels.
However, there was actually much less pressure loss during single thruster firings in the flight system;
with the flight regulator set at maximum output of approximately 620 psia, the low side pressure of the
CGSE was measured at about 590 psia while firing single thrusters, much higher than the chamber
pressure of 392 psia that had been attained with maximum regulator output in the single-stream tests.
The reason for the higher pressure loss in the single-stream setup is unknown, but one possible cause
was the flexible hose used between the regulator output and the thruster assembly. The hose had an
inner diameter of 0.25 in., which was the same size as the thruster valve orifice, but the hose was
relatively long with several bends which may have cumulatively created high pressure losses.
Alternatively, the four-way instrumentation crosses on the thruster may have adversely affected the gas
flow in the single-stream tests.
Table 6-1 also indicates that the horizontal thrusters outperformed the vertical thrusters by
approximately 4 to 6 N. All thrusters were built with the same components, but because of the three-
way tee fitting used to make the final split in the feed line to the two thrusters at a station pair, the gas
flowing to the vertical thrusters had to make one more 90° turn than the gas flowing to the horizontal
thrusters. It is believed that this caused enough additional loss to account for the lower performance of
the vertical thrusters.
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