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

2.3 Confirming the Decision to Use Cold Gas Propulsion
In summer 2009, detailed design work for the TALARIS spacecraft emulator propulsion system began.
One of the first tasks undertaken was a review of the decision to use a cold gas propulsion system for
this purpose. While a good deal of thought had been put into this decision in earlier stages of the
TALARIS project, it was deemed necessary to revisit the question in light of the progress that had been
made over time. This process not only confirmed that cold gas propulsion was the optimal choice for the
spacecraft emulator propulsion system, but it also highlighted strengths and weaknesses that shaped
the design of the cold gas propulsion system for TALARIS.
2.3.1 General Hopper Propulsion Design Considerations
One major design driver for the TALARIS spacecraft emulator propulsion system was hop trajectory. Two
types of trajectories were considered. The first is the ballistic hop, in which the hopper’s propulsion
system provides an initial acceleration to the vehicle at launch and, if necessary, a deceleration at the
end of flight for a softer landing. The majority of a ballistic hop is an unpowered coasting phase. For
example, as discussed in Chapter 1, the Surveyor 6 probe performed a ballistic hop on the Moon; the
accelerations involved were small enough that a braking phase was not required. The second type of
trajectory is called the hover hop. In a hover hop, the vehicle ascends to a given height above the
surface, translates horizontally while maintaining constant altitude and attitude, and descends vertically
to a soft touchdown. Both the ballistic and hover hop trajectories are illustrated in Figure 2-6.
Figure 2-6. Comparison of ballistic and hover hop trajectories [18].
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