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

Figure 3-1. Scaling of TALARIS terrestrial hop compared to GLXP lunar hop [38].
As shown in Figure 3-1, the proposed altitude of the GLXP lunar hop was 2 m. This altitude, as indicated
in Figure 3-1, was subject to revision, but it was expected that this altitude would allow the GLXP hopper
to easily clear most rocks or other obstacles in its path. It was decided to use a 2 m altitude for the
TALARIS terrestrial hop as well, since it would be difficult to duplicate the accelerations expected for the
GLXP hopper over smaller ascent and descent distances. Furthermore, 2 m was considered to be a good
altitude for demonstration purposes, as the TALARIS hopper would then be clearly above the ground
and visible at some distance.
Since the vertical dimensions were kept the same for the TALARIS and GLXP hops, the horizontal
distance had to be reduced to scale the TALARIS hop down from the planned GLXP lunar hop. The
horizontal distance of the lunar hop, 500 m, was set by the GLXP rules as described in Chapter 1, but it
was anticipated that the majority of this distance would be a constant-velocity cruise. The 16.898 design
class in fall 2008 recommended a horizontal distance of 30 m for the TALARIS hop, and this
recommendation was carried forward through the spring 2009 16.83/89 class as well. It was expected
that this would be a sufficient distance to allow for acceleration, cruise, and braking phases while still
remaining within the impulse capacity of the TALARIS hopper. Later MATLAB modeling, as described in
section 4.1, indicated that this target distance was likely achievable, though ambitious.
3.1.3 Requirements Flowdown
With the dimensions of the TALARIS hop defined, each of the three main functional requirements was
taken in turn to determine quantitative performance requirements for the TALARIS cold gas propulsion
system.
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