I'm having a bit of a conundrum regarding the OMS and RCS propellant for my ROCS spacecraft. These are my options;
- Gaseous pressurised oxygen/Sintin - Propellant combination used on the Buran shuttles. Sintin hydrocarbon fuel has an appreciable density, but gaseous oxygen has relatively low density and increasing density requires an increase in pressure, which requires a heavier pressure vessel. Astronautix gives a exhaust velocity figure of 3550 m/s for Buran's OMS, and 2796-2892 m/s for the RCS. Fuel needs external pressurant to force it to the engines.
- Liquid oxygen (LOX)/Sintin - similar to the first option, but oxygen is kept in cryogenic, liquid form. Achieves an increase in density for the oxidiser but is cryogenic and requires temperature/boiloff regulation. Both propellants require external pressurant to force them to the engines.
- Hydrogen peroxide/Sintin - Similar to the first two options but with high-test peroxide instead of oxygen. British Gamma engines had a specific impulse of ~2400 seconds. Both propellants need external pressurisation, but are self-igniting if the peroxide is partially decomposed by a catalyst first. Hydrogen peroxide is non-toxic but is a powerful oxidiser that can cause irritation/burns, and which also requires safety measures to prevent inadvertant decomposition.
- 'Self pressurising' Hydrogen peroxide/Propane - Requires no external pressurants. Described in this patent and also here. Propellant tank is filled with a volatile hydrocarbon (such as propane), within which a flexible or accordion-like membrane is placed, which is filled with a liquid oxidiser such as hydrogen peroxide. Example specific impulse given of 2990 m/s. Some advantages; shares some disadvantages with other H2O2 based concepts. Gas can be drawn off for use in cold-gas thrusters, which yield a lower impulse but may be useful for fine manuvering close to delicate equipment.
- Gaseous oxygen/Propane -Similar problems to GOX/Sintin, except that density issues also arise regarding the use of propane.
- Hydrogen peroxide/Propane in seperate pressure vessels - increases complexity somewhat and warrants the requirement for seperate pressurant gas for the oxidiser, but eliminates any possibility of oxidiser and fuel intermixing.
- Hypergolic propellants, UDMH/N204(MON) or MMH/N204(MON) - Known and predominant in spaceflight, hypergolic, but expensive and highly toxic.
- Gaseous pressurised oxygen/Sintin - Propellant combination used on the Buran shuttles. Sintin hydrocarbon fuel has an appreciable density, but gaseous oxygen has relatively low density and increasing density requires an increase in pressure, which requires a heavier pressure vessel. Astronautix gives a exhaust velocity figure of 3550 m/s for Buran's OMS, and 2796-2892 m/s for the RCS. Fuel needs external pressurant to force it to the engines.
- Liquid oxygen (LOX)/Sintin - similar to the first option, but oxygen is kept in cryogenic, liquid form. Achieves an increase in density for the oxidiser but is cryogenic and requires temperature/boiloff regulation. Both propellants require external pressurant to force them to the engines.
- Hydrogen peroxide/Sintin - Similar to the first two options but with high-test peroxide instead of oxygen. British Gamma engines had a specific impulse of ~2400 seconds. Both propellants need external pressurisation, but are self-igniting if the peroxide is partially decomposed by a catalyst first. Hydrogen peroxide is non-toxic but is a powerful oxidiser that can cause irritation/burns, and which also requires safety measures to prevent inadvertant decomposition.
- 'Self pressurising' Hydrogen peroxide/Propane - Requires no external pressurants. Described in this patent and also here. Propellant tank is filled with a volatile hydrocarbon (such as propane), within which a flexible or accordion-like membrane is placed, which is filled with a liquid oxidiser such as hydrogen peroxide. Example specific impulse given of 2990 m/s. Some advantages; shares some disadvantages with other H2O2 based concepts. Gas can be drawn off for use in cold-gas thrusters, which yield a lower impulse but may be useful for fine manuvering close to delicate equipment.
- Gaseous oxygen/Propane -Similar problems to GOX/Sintin, except that density issues also arise regarding the use of propane.
- Hydrogen peroxide/Propane in seperate pressure vessels - increases complexity somewhat and warrants the requirement for seperate pressurant gas for the oxidiser, but eliminates any possibility of oxidiser and fuel intermixing.
- Hypergolic propellants, UDMH/N204(MON) or MMH/N204(MON) - Known and predominant in spaceflight, hypergolic, but expensive and highly toxic.
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