Devices are proposed that would sublime solid propellants to generate small thrusts for maneuvering spacecraft with masses of no more than 15 kg. With solids rather than gases in propellant tanks, there would be no leakage and thus no waste of limited quantities of propellants. There would also be none of the bulk, weight, and cost of plumbing like that needed for handling liquid or gaseous propellants if the propellant tank would be integrated with the subliming solid thruster.

Figure 1. The Concept of the Subliming Solid Microthruster is illustrated in oblique view (a) and side view (b).

The propellant in a subliming thruster would be contained in an aluminum tank (see Figure 1) with an outlet connected to the subliming solid microthruster chip. This chip, micromachined from silicon, contains a nozzle and an integrated filter. Ultimately, a thruster valve will also be integrated into this chip. A wire electric heater could be wrapped around the tank, or else a film electric heater could be deposited on the tank. The propellant material (e.g., ammonium hydrosulfide) would be sublimed on command by activating the heater.

Figure 2. Microthruster Model shows the level of miniaturization that can replace bulkier units.

Opening a valve placed into a flowpath between the nozzle and tank (see Figure 2) will allow the vapor to flow to whichever nozzle faced in the direction opposite the required direction of thrust. The wall of the tank could be as thin as 0.020 in. (0.5 mm) because the vapor pressure that it would have to withstand would be very small; thus, the tank could be very light in weight.

This work was done by Juergen Mueller, Lilac Muller, and Thomas George of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Mechanics category. NPO-19926