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

and adjustments made to account for decreasing thrust levels throughout a hop as discussed in section
6.4 might shorten the actual flight time slightly. But a 15 s flight time would be a 50% increase over the
10 s limit on flight time reported by the NASA Marshall CGTA [14], showing that the TALARIS propulsion
architecture could indeed achieve the goal of longer flight times with a cold gas system without loss of
simulation fidelity that was described in chapter 2.
As mentioned previously, the TALARIS vehicle had not yet performed a full demonstration hop at the
time of writing this thesis. Although the CGSE horizontal thrusters appeared to provide sufficient control
of horizontal motion and roll about the hopper X axis as reported in section 7.1.1, vertical motion of the
hopper had not yet been fully controlled, and the ascent phase of a hop was proving particularly difficult
to perform. There were two main possible reasons for this: either the GNC algorithms had simply not
been tuned correctly yet, or the vehicle hardware was deficient in some way that precluded the
development of a successful GNC algorithm. For the CGSE hardware, the issue of thrust decrease with
gas usage and the borderline acceptability of the 5 Hz control cycle have already been discussed.
However, in integrated flight tests, the EDFs might also be a source of problems. Like the CGSE, the EDFs
were only partially characterized, but there were indications from RPM sensors that they might not be
producing enough thrust for full 5/6 weight relief, and also that individual fans might be producing
different thrust levels, which could contribute to vehicle instability.
If further flight tests are unsuccessful, and it is too difficult to isolate the GNC algorithms, CGSE
hardware, and/or EDF hardware as the cause, it may become necessary to perform additional static
characterization tests of both the CGSE and the EDFs. In addition to running more tests of each
propulsion subsystem individually (such as the CGSE thrust loss characterization plans discussed in the
following section 7.2), it would also be worthwhile to test them together, to attempt to determine the
degree and consequences of interaction between the two. In this way, it might be possible to identify
hardware deficiencies, hopefully correctible by small changes rather than a major redesign causing one
or both of the propulsion systems to be rebuilt. Alternatively, the tests might simply provide a clearer
picture of the propulsion systems’ performance, leading to the development of better GNC algorithms.
7.2 Improved Characterization of Thrust Levels Throughout a Hop
As mentioned in section 6.3.3, characterization of thrust levels for the CGSE flight system was limited
due to the aggressive schedule of the TALARIS project. However, work is ongoing to provide both a more
detailed theoretical understanding of the factors affecting thrust level and improved methods of
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