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

documenting progress takes time which could be spent doing other kinds of work, but it is an
investment which can pay off well in future.
Safety is essential.
Safety was a central consideration in all phases of CGSE development. Sometimes actions taken for
safety reasons came at the cost of performance, such as the overall decision to develop a cold gas
system rather than a monopropellant hydrogen peroxide system. Often, extra time had to be taken to
ensure safety, as with the effort put in to developing, following, and updating checklists for CGSE
operation. However, safety is another area in which effort put in up front pays off later. For example, at
one point during CGSE flight system testing, the low side became overpressurized enough to vent the
two rupture disks in the system. The root cause of the overpressurization was eventually traced to a leak
in the main orifice of the flight regulator due to wear and tear on the seat in the valve, as mentioned in
section 7.1.4. This specific problem had not been anticipated, but the possibility of overpressurizing the
low side had been considered, and measures had been put in place to handle that situation as safely as
possible. The rupture disks functioned as expected and released the pressure in a relatively controlled
and predictable way; they were simply replaced after the incident, and it was possible to return to
testing very quickly. Had the rupture disks not been in the system, the overpressurization might have
been severe enough to cause a component to fail in an unpredictable way and to cause damage that
might have been more difficult to repair. More importantly, no one was injured when the rupture disks
vented, partly because everyone present at the test was following established safety procedures and
staying in shielded zones. Because time and effort had been invested in safety beforehand, the rupture
disk incident was a small hiccup rather than a major roadblock, and progress in the development of the
CGSE was able to continue on smoothly.
There is a balance to be struck between modeling/simulation and hardware testing.
Modeling and testing were both important elements of the CGSE development process. However,
limited resources meant that neither activity could be pursued in as much depth as might be desired,
and compromises had to be made. For instance, the MATLAB model had many inherent simplifications
and sources of error, as listed in section 4.1.5. For some of these, such as the lack of a heat transfer
model, a method of addressing them was known but would take time to implement. Instead, it was
decided to use the model as it was, make component purchasing decisions with the help of its results,
and spend the time on testing instead. This turned out to be the right decision; the components selected
proved to be acceptable in the single-stream tests, and CGSE development proceeded. However, testing
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