There are difficulties related to storing enough gas to propel a CubeSat within an onboard tank. Currently, a CubeSat requiring a large volume of gas for extended propulsion (outside Earth orbit) would need to store liquefied gases that require heavy-bodied tanks that add significant weight to the spacecraft. Safe storage of gases is difficult and not suited well to the CubeSat platform.
Modern automotive airbags use simple chemical gas generators (sodium azide or MNP352) to provide massive volumes of nitrogen gas in an instant, for the purpose of inflating large airbags for cushioning or mass deceleration. The device charges are small and can be placed into small tanks. When triggered, large volumes of nitrogen will immediately be released. Treatment of the chemicals to create safe byproducts is easily accomplished with the addition of a simple salt. If massive volumes of gas can be generated from a diminutive compact solid at will, then it would follow that by combining several of these into a larger tank assembly and initiating them when needed, multiple sources of gas could be provided when desired. A large, heavy tank of compressed liquid gas designed to withstand thousands of psi can be effectively replaced with a smaller tank with multiple generator sources in which each actuation would yield a rise of only a few hundred psi. Because many of these can be combined in one collection, “refills” of this tank could be provided within the considered trajectory.
Solid generator pellets would be placed into miniature cylinders (charges) capable of safely containing the reaction. These miniature cylinders would be installed into a multiple-port manifold tank through threaded ports in the collection tank. To avoid overheating and initiation of neighboring ports, a series of baffles and focus orifices would be employed to reduce the temperature of the discharge. Each time an electronically controlled charge is initiated, the resulting gas will fill the cylinder. An electronic solenoid valve will allow the gas to fill a secondary accumulator cylinder that would hold gas, cool it, and serve as a main gaseous nitrogen tank reserve. Gas would be removed from that tank for use through a solenoid valve-controlled outport, and any resultant particulate would be removed through a series of filters. Clean gas would flow out for use in the spacecraft’s cold gas propulsion system. When the accumulator tank runs low, the next charge will be initiated, and a new source of gas will be supplied ready to be moved to the accumulator tank. This repeats until all charges are used. Potentially, the number of charges available is only limited by the spacecraft’s size and calculated safety margin in the unlikely event all charges execute at once.
This work was done by Thomas Reynoso of Caltech for NASA’s Jet Propulsion Laboratory. For more information, contact