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Garvey Aerospike

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Status: Development ended 2005. Date: 2001-. Thrust: 44 N (9 lbf).

During 2005, GSC and California State University, Long Beach (CSULB) conducted several notable small launch vehicle R&D activities through their partnership in the California Launch Vehicle Education Initiative. Using a single-chamber, liquid-propellant, annular aerospike engine concept developed by CSULB, the GSC/CSULB team validated the basic design and ignition sequence with a successful static fire test at the Reaction Research Society's Mojave Test Area (MTA) in June 2003. The team then mounted one of these 4,444-newton thrust LOX/ ethanol ablative engines onto their Prospector 2 vehicle and proceeded to conduct the first-ever powered liquid-propellant aerospike flight test at the MTA in September 2003. In response to several issues observed during that flight, modifications were made to the engine fabrication process. Another flight test with the Prospector 4 vehicle followed in December 2003. Performance was entirely nominal, resulting in complete recovery of the vehicle and key trajectory data.

These CALVEIN flight tests represent the first steps toward obtaining the critical empirical data needed to validate whether the predicted benefits of such aerospike engines versus those equipped with standard bell-shaped nozzles can be achieved. This goal had been one of the primary objectives of the X-33 program, which featured the XRS-2200 linear aerospike engine.

The CSULB students were now investigating a next-generation aerospike engine design, featuring a more traditional multi-chamber design. This design would enable the large expansion ratios required to fully evaluate engine performance throughout the entire flight regime of an orbital launch vehicle. As part of an evaluation of fuels for the NLV that could provide greater performance than the ethanol used in the current CALVEIN research vehicles, the team has identified propylene as a promising candidate meriting further attention. Liquid oxygen and propylene have the potential to provide higher specific impulse than the traditional LOX/RP-1 propellant combination. Unlike another alternative hydrocarbon that has received extensive discussion (methane), propylene can achieve comparable densities to that of RP-1 when chilled to cryogenic temperatures. A widely available commodity because of its role as a feedstock in the plastics industry, propylene also has favorable characteristics with respect to toxicity and environmental hazards. Some of the potential concerns about propylene, most notably its potential for polymerization, were only relevant for turbopump-fed regenerative engines. Therefore, those concerns were not issues for the pressure-fed NLV stages that feature ablative and radiative engine chambers.

The GSC/CSULB conducted a series of static fire tests at the MTA to identify logistics and handling issues associated with propylene and to evaluate a preliminary engine design for the NLV second stage. Preliminary results confirm that the ignition sequence was more susceptible to a hard start than liquid oxygen and ethanol. For this initial phase of testing, the propylene has been at ambient temperatures. A round of follow-on testing would evaluate several different ignition sequences and engine performance with propylene at cryogenic conditions. Upon successful completion of that phase of research, the team planned to conduct a LOX and propylene flight test using a modified version of the Prospector-class vehicles.

The next important milestone was achieved by the joint industry-academic team in December 2004 when they conducted their initial launch and recovery of a full-scale flight development unit for NLV. The Prospector 5 vehicle, and early version of the NLV first stage, was launched and then recovered by parachute.

Thrust (sl): 44 N (9 lbf). Thrust (sl): 4.44 kgf.