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

1 Introduction
The TALARIS (Terrestrial Artificial Lunar And Reduced gravIty Simulator) hopper is a small prototype
flying vehicle designed to serve as an Earth-based testbed for guidance, navigation, and control (GNC)
algorithms that will be used to explore lunar and other planetary surfaces. To date, nearly all robotic
exploration on the surface of the Moon and other planets has been done by stationary landers or
wheeled rovers. Hoppers would open up new modes of exploration with their alternate form of
mobility. However, because they are a new technology without the long heritage of landers and rovers,
there is a greater need for testing to reduce the risk associated with hoppers. The TALARIS testbed
provides the opportunity to develop and mature hopper-based GNC algorithms on Earth, which allows
for a more controlled environment and easier human access for modifications, upgrades, and repairs if
necessary.
A hop consists of three main phases: propulsive ascent, traverse flight, and soft landing. A commanded
maneuver of this type has been performed off the Earth once, by the Surveyor 6 spacecraft on the
Moon. On November 17, 1967, after Surveyor 6 had been sitting on the lunar surface for a week, the
spacecraft’s three liquid-fueled vernier rocket engines were reignited and fired for 2.5 s [1]. The control
system was set such that the spacecraft would tilt 7° to the west upon liftoff, and the thrust generated
was sufficient to cause the spacecraft to rise to an altitude of about 3.5 m and to land 2.4 m away from
its starting point. This allowed Surveyor 6 to send back images of the surface disturbances at its initial
landing site, providing information on mechanical properties of the lunar surface as well as the effects of
firing rocket engines near the surface. Furthermore, the displacement of the spacecraft provided a
baseline for stereoscopic viewing and photogrammetric mapping of the surrounding lunar terrain [1].
However, the Surveyor 6 hop is merely the tip of the iceberg in terms of the potential value that could
be gained from exploring with hoppers.
Hoppers could improve planetary exploration from both the science and engineering perspectives.
Hoppers can travel more quickly than rovers, and they can also cover a greater diversity of terrain.
Hoppers could fly over large obstacles and traverse steep inclines, possibly even hopping into or out of
craters. They might also provide unique opportunities for science during a hop, such as low-altitude
aerial observations or examinations of cliff faces or canyon walls at various heights. For more in-depth
analysis of the ways in which hoppers might contribute to planetary exploration objectives, see [2] and
[3]. Hoppers have certain advantages from an engineering perspective as well. For a rover, initial landing
and travel over the surface involve two dissimilar types of propulsion; by contrast, a hopper can be
19