Hybrid Propulsion for Solar System Exploration

Abstract

Hybrid rockets are promising candidates for in-space motors because of their throttling capability, ability to stop and restart and their tolerance to low temperatures. The advantages of a hybrid system compared to other chemical propulsion systems are quantified through a specific example: an orbit insertion (OI) stage. While the orbit insertion is left somewhat general, it is representative of a Mars orbit insertion (MOI) and will be compared to past MOI engines. For this example, system studies were conducted to design and optimize the hybrid propulsion system. The design is optimized for chamber pressure, O/F ratio, minimal gravity loss, oxidizer and fuel selection. The hybrid OI motor uses a paraffin-based fuel with MON3 (97% N 2 O 4 and 3% NO) as the oxidizer. Areas where further research is required are identified. Nomenclature ACS = attitude control system Isp = specific impulse IRFNA = inhibited red fuming nitric acid MMH = monomethyl hydrazine MOI = Mars orbit insertion MON3 = mixed oxide of nitrogen (97% N 2 O 4 and 3% NO) NTO = nitrogen tetroxide OI = orbit insertion O/F = oxidizer to fuel ratio T m = melting temperature TVC = thrust vector control δ thermal = characteristic thermal thickness ΔV = delta velocity

Hybrid rocket propulsion systems for outer planet exploration missions

“…This is not a free variable in the design with the current formulation, as the burn rate of the fuel is a function of the fuel grain geometry and oxidizer mass flux, which is already fixed if one is to achieve the ideal O/F. At a given axial position x along the port, the fuel mass transfer rate is proportional to the mass flux averaged across the port, this relationship is known as the regression rate law for a hybrid rocket, see equation 4.…”

“…According to the analysis presented in Reference [3] a hybrid MAV could have a mass saving of up to 79 kg, representing a 22% total system wet mass saving, compared to the baseline solid propulsion system. Reference [4] investigated using a hybrid propulsion system for a main in-space propulsion motor and found that the hybrid propulsion system could have a significant propellant mass saving over the baseline liquid system. Reference [6] investigated a small-scale hybrid propulsion system for a Mars aerocapture demonstration mission, and also found the hybrid propulsion system to be a viable alternative to the baseline monopropellant hydrazine system.…”

“…Reference [6] investigated a small-scale hybrid propulsion system for a Mars aerocapture demonstration mission, and also found the hybrid propulsion system to be a viable alternative to the baseline monopropellant hydrazine system. This paper extends the analysis of Reference [4] by applying the more rigorous design approach adopted in Reference [6] to exploration missions requiring significant in-space propulsive capabilities.…”

“…DESIGN METHODOLOGY A simplified overview of the design process adopted to calculate all primary propulsion system masses presented in this paper is shown schematically in Figure 1. Current literature on hybrid rocket system design, References [3][4][5][6], does not describe the methodology used to generate the final hybrid rocket motor design. This detail is provided here in order to both provide guidance for researchers wishing to evaluate hybrid rocket motor designs for other missions and applications, and to elucidate some of the challenges involved with designing these systems given the current Technology Readiness Level (TRL) of hybrid rocket motor technology and the limited availability of test data for these systems.…”

“…Preliminary design studies have shown hybrid motors to be viable alternatives to conventional propulsion systems for some exploration missions [3][4][5][6]. Reference [3] and Reference [5] investigated utilizing hybrid motor technology for a Mars Ascent Vehicle (MAV).…”