Analytical Advances in Reciprocating Feed System Trade Study Code

The Reciprocating Feed System (RFS) is an alternative to conventional pressure fed and pump fed systems. It typically has three relatively small high-pressure “run tanks” located below or within each of the large low-pressure main tanks. Continuous flow to the engine is provided by sequential run tank expulsion, venting, refill, and pressurization, with cyclic refill flow from the main tanks. Past studies and tests outlined here have presented RFS benefits of low cost; high deliverable payload; high reliability; single-point fail-operational capability, deep throttling; rapidly variable pressure and flow rates; ease of restart in microgravity; enhanced propellant acquisition and control under adverse acceleration conditions; low propellant residuals; elimination of pump chill down cycles; long-term storage capability; long periods between scheduled maintenance; and much lower main tank pressures than required to achieve turbo-pump Net Positive Suction Pressure (NPSP) requirements. System sizing analyses have shown much higher deliverable payload than a conventional pressure fed system and competitive, and even higher, delivered payload, compared to an RP-LO2 or LH2/ LO2 gas generator powered turbo-pump fed system. Given these apparent advantages, it is critical that system comparisons be credible. Past RFS sizing code results have been shown to closely agree with hardware and expendable weights of legacy systems (e.g., Saturn V, Apollo lunar ascent/descent stage, Shuttle Orbiter OMS system). Recent improvements to this code now include (1) additional configuration options and (2) ability to accurately determine specific impulse as a function of chamber pressure, mixture ratio, and expansion ratio without the necessity of conducting laborious and time-consuming “off-line” thermochemical analyses using CequelTM (Chemical Equilibrium in Excel®). This improved code can now be used in an automated system optimization mode. We summarize (1) RFS concept of operation and validation tests; (2) comparisons of deliverable payload for the RFS vs. conventional pressure fed and pump fed systems; and (3) improvements to our system analysis code.