A Refined Model for the Behavior of Nitrous Oxide to Assess the Limits of N2O Cooling

The proposed project is crucial to enabling safe flight research on a rocket nozzle that is based on our recent innovation, which is to use the refrigerant capabilities of nitrous oxide (N2O) to provide cooling for an aerospike nozzle on hybrid rocket motor using N2O as the oxidizer. The phase change cooling as liquid N2O is flashed from a liquid into a vapor, limits to acceptable levels the erosion of both the nozzle throat and spike, thereby enabling reusable operation and/or long burn times. The N2O used for cooling will be reintroduced into the rocket motor and used to boost performance. Because of potentially the violent exothermic decomposition of N2O, a thorough understanding of N2O behavior is crucial to developing an aerospike nozzle and hybrid rocket motor that are sufficiently safe for flight testing, where cooling the aerospike is necessary to get the burn duration required for good flight tests to yield the illusive flight test data for aerospike nozzles. Our prior work seeking to develop a fundamental understanding of the behavior of N2O when it is used in applications has answered some important questions about the behavior of N2O, yielded significant advances in designing instrumented nozzles for N2O cooling experiments, and generated important advances in making accurate temperature measurements on the coolant flowing in these nozzles. However, our work in developing and validating analytical models for predicting heat transfer coefficients in N2O-cooling applications was only partially successful due to unanticipated levels of uncertainty from a variety of sources. By addressing the sources of the above-mentioned uncertainty using a combination of nozzle design, novel construction, analytical, FEA, and CFD modeling, along with experimental validation of all models, this work will yield the refined models of N2O behavior that are necessary for the future design of safe N2O-cooled aerospike nozzles.

The proposed work will enable the design of safe N2O-cooled hybrid rocket motors having truncated aerospike nozzles, which will allow cost effective, reusable, and less expensive rocket designs. The potential non-NASA users of this technology are the U.S. military and companies providing inexpensive access to low Earth orbit. In addition to the business of launching satellites, there is a burgeoning interest in space tourism. Scaled Composites and Virgin Galactic have teamed up to develop SpaceShipTwo specifically to pursue the space tourism market. Likewise, Benson Space Company is developing the Dream Chaser, which is a 4-passenger suborbital or 6-passenger orbital vehicle. Each of these vehicles will use a hybrid rocket motor. Under study in the U.S. is a sewage treatment process that intentionally increases the production of nitrous oxide and methane, and uses the gases to power the treatment plant. In a low-oxygen environment in the treatment plant, where N2O-producing bacteria are favored, while aerobic species die off, the N2O-producing microbes consume relatively small amounts of organic matter, which allows for an increased production of methane. The methane will be used as a fuel, and the N2O will be burned in a hybrid rocket motor, where it will decompose into pure nitrogen and gaseous oxygen, both of which are completely green from a sustainability viewpoint. N2O-cooling could produce rocket nozzles with very long burn times for the use in this process.

The proposed work will enable the design of safe N2O-cooled hybrid rocket motors having truncated aerospike nozzles, which will allow cost effective, reusable, and less expensive rocket designs. NASA could use this technology in any single-stage-to-orbit program.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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