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

One of the characterization tests was run with the static test stand elevated so that the thrusters were
at the operational altitude of the hopper, about 2 m above the ground. This was done to check for
ground effect, which had been observed in EDF testing. However, the elevated CGSE test was
inconclusive. Thrusters 5 and 7 produced about 2 or 3 N less thrust at the 2 m altitude than they had in
the weaker of their two ground tests, but that was also the approximate spread between the weaker
and stronger ground tests. Thruster 3 produced a thrust level at the 2 m altitude that fell between its
two ground test results. And thruster 1 produced its anomalous thrust reading during the elevated test.
The measured thrust from thruster 1 in the elevated test was 10 N less than any other single thruster
output measurement in the averages presented in Table 6-1, which was a decrease of about 20%;
nothing of that magnitude was seen in any other thruster firings during this set of tests. Therefore, that
measurement was considered invalid and not used in the analysis of thruster performance. All of the
horizontal thrusters produced very similar amounts of thrust at both altitudes. Time and other resources
did not permit a repeat of the elevated test, so all non-anomalous test results were averaged together
regardless of altitude, resulting in the larger uncertainty for the vertical thrusters shown in Table 6-1.
The maximum thrust levels presented in Table 6-1 were substantially higher than the original design
goal of 35 to 40 N. These thrust levels could have been decreased by setting the flight regulator output
to a lower pressure. However, the expected total mass of the TALARIS hopper had risen to 51 kg by the
time characterization of the CGSE flight system was underway, and it was anticipated that the mass
might increase even further. 7
Furthermore, as shown in Figure 6-8,
a very large decrease from the initial
thrust levels was expected by the end of a hop. Therefore, additional thrust margin was considered
desirable, and the flight regulator was left at its maximum output set pressure of 620 psia.
Thruster directions
Single-thruster firings were also used to make a better determination of the direction in which each of
the CGSE thrusters were pointing. Although each thruster was supposed to be parallel to one of the
vehicle axes, the construction of the CGSE was imprecise, and each thruster had some degree of
misalignment, as shown in Table 6-2.
7 The mass of the TALARIS hopper did continue to rise, largely due to changes in the EDF system which required
heavier wires and the addition of more lithium polymer batteries for power. At the time of writing this thesis, the
estimated mass of the entire vehicle was approximately 60 kg.
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