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

simplicity of control, it was decided to use four thrusters, evenly spaced so that they could be fired in
pairs to control pitch and yaw of the vehicle (rotation about the Y and Z axes, as defined in Figure 3-2
below). Upward-pointing vertical thrusters were not necessary, since the hopper was designed to
operate in a gravity field that would constantly pull it down.
As for horizontal thrusters, at least two were required: one pointing forward to accelerate the hopper in
the desired direction of travel, and one pointing backward to decelerate the hopper at the end of the
horizontal transit phase of the hop. Again, though, it was decided to use four horizontal thrusters for the
purposes of attitude control, with two pointed forward and two pointed backward. They were to be
spaced at equal distances from the center of mass such that they could be fired in pairs to roll the
vehicle (rotation about the X axis, as shown in Figure 3-2). With this capability, it was decided not to
place any horizontal thrusters in the orthogonal direction. This limited the TALARIS hopper to primarily
two-dimensional flight profiles, though it did retain some ability to adjust its course similar to the way
that a car can change direction by steering. However, a 2D flight profile was deemed sufficient to
demonstrate hopping, and it was believed that the reduced mass and simpler plumbing would increase
the likelihood of completing a functional cold gas propulsion system within the tight schedule. The idea
of mounting the horizontal thrusters at an angle, such that firing an individual horizontal thruster would
produce components of thrust both parallel and perpendicular to the intended direction of travel, was
briefly considered. However, there were concerns that this would simply reduce the thrust available for
the primary direction of travel without providing significant control authority in the orthogonal
direction, and also that it would be more difficult to mount and align the thrusters. Thus, the idea of
mounting horizontal thrusters at an angle was discarded.
Finally, it was decided to place the horizontal and vertical thrusters near to each other, again to simplify
the plumbing as much as possible. This resulted in the thruster geometry shown in Figure 3-2.
Figure 3-2. TALARIS cold gas thruster geometry.
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