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

control the belay line can be put under tension to arrest the hopper’s motion. Various tethers attach the
TALARIS hopper to weights on the ground; these lines are long enough to allow the hopper to move
freely within a restricted area, but if it gets too far out of range, the tethers catch and prevent the
hopper from moving further. These precautions both help to prevent crashes and to protect hopper
operators and test observers.
Initial plans are for the TALARIS vehicle to first demonstrate an ascent, hover, and controlled descent.
Once control is demonstrated for this primarily vertical maneuver, flights can expand to include
significant attitude changes and horizontal motion. Eventually, the goal is to perform a demonstration
hop at 2 m altitude with a 30 m horizontal traverse, as illustrated at left in Figure 3-1.
7.1.4 Summary of Validation Testing Efforts
Although the flight tests had not yet led to full validation of the CGSE at the time of writing this thesis,
they had revealed some important aspects of CGSE operation. The CGSE in general was found to be
quite reliable; in nearly all tests where the CGSE did not perform as expected, the problem was traced
back to another subsystem such as avionics or software, although in one case CGSE performance was
reduced because the cable carrying the signals from the RIO to the CGSE control circuit was not plugged
in tightly and the connection was intermittent. Furthermore, the majority of the CGSE components were
found to hold up well over the intensive testing schedule. The one hardware element found to be
subject to wear and tear was the seat of the valve in the main orifice of the Tescom flight regulator;
however, this seat is simply a small plastic gasket, and it is inexpensive and easily replaced when it
becomes too worn down to function properly.
The flight tests, in combination with the static characterization tests, also provided some points of
comparison to the flight times predicted by the MATLAB model. As mentioned in section 4.1.7, the
MATLAB model predicted maximum flight times of approximately 15 s. During the static characterization
tests, the CGSE was found to hold about 36 to 40 thruster-seconds of gas, as indicated by Figure 6-8. If
all four vertical thrusters had an average duty cycle of 50% (an approximate percentage based on the
total thrust available from all four vertical thrusters, the anticipated total vehicle mass, and the changing
thrust-to-weight ratios required during a hop), this would allow them to fire for 18 to 20 s. However, a
hop also includes horizontal maneuvers and attitude control; once these are taken into account,
estimated flight times decrease toward 15 s and below. The flight tests that were run generally
supported these estimates, although a full hop had not yet been flown at the time of writing this thesis,
113