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RCS Propulsion

RCS Propulsion. Critical Design Review Casey Kirchner 2/27/01. Overview. Hab Concept Thruster placement Thruster sizing Descent motor sizing ERV Concept Thruster placement Reliability. Thruster Placement - Hab. Ten thrusters each on Hab and NTR

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RCS Propulsion

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  1. RCS Propulsion Critical Design Review Casey Kirchner 2/27/01

  2. Overview • Hab Concept • Thruster placement • Thruster sizing • Descent motor sizing • ERV Concept • Thruster placement • Reliability

  3. Thruster Placement - Hab • Ten thrusters each on Hab and NTR • Oriented so that two engines provide thrust in each roll, pitch, yaw • Hab thrusters provide 666 N each, NTR thrusters are 250 N each

  4. RCS Thruster Applications • Tether spin-up contributes one of largest DV budgets at 100 m/s • Thruster sizing determined primarily from historical acceleration rate of vehicle (a = 0.005 m/s^2 on Galileo) • Due to small accelerations and large masses, will take ~73 minutes to spin up • Enroute DV set at 100 m/s • Parking orbit DV ~ 20 m/s • 20 s of hovering DV ~ 20 m/s

  5. Engine Sizing - Thrusters • Performance code reworked to improve Ispv to 330 seconds (up from 300 s) at an expansion ratio of 40… can go higher with larger ratios but space constraints prohibit going too large • Engine thrust = 666 N (on Hab) and 250 N (on NTR) • Engine length = ~ 0.3 m • Engine diameter = ~ 0.16 m • Engine mass = 305 kg (Hab) and 90 kg (ERV) total (all 10 engines)

  6. Engine Sizing - Descent • Treat this engine as an ascent engine for puposes of calculation • T/W for launch vehicles historically 1.0 to 2.5 – chose 1.2 for this vehicle because of cost and short burn time to surface(10 s) • Engine thrust = 322,000 N (72,400 lb) • Engine length = 3.4 m • Engine diameter = 1.6 m • Historically close to size of J-2, Saturn second-stage rocket

  7. Representative Descent Engine Astronautix.com

  8. All propellant was figured with 10% margin All propellant volumes figured with 5% ullage space Propellant tanks are cylindrical with spherical endcaps Tanks are 4.6 m long including endcaps Tank diameters are 1.1 m Tanks are made of graphite and weigh 45 kg Tank Sizing - Propellant

  9. Safety factor of 1.25 on pressurant tanks Pressurant tanks are spherical and incorporate pressure drops due to: Feedline losses Injector losses Dynamic pressure Tank diameters were 1.8 m on the Hab and 1.4 m on the ERV Pressurant tanks weigh 90 and 55 kg, respectively Tank Sizing - Pressurant

  10. Subsystem Mass • Propellant: 9.5 tonnes • Pressurant: 0.120 tonnes • Tanks: 0.180 tonnes • Plumbing: 0.300 tonnes • Engines: 1 tonne • Total: 11.1 tonnes

  11. Thruster Placement - ERV • RCS thrusters must be present on • Crew Transfer Vehicle • Upper stage engine from Mars surface launch • ERV module left in orbit • Possibly NTR stage for Earth-Mars RCS about CG • Exact numbers will be dictated by redundancy among constituent parts, and will contribute only slightly to mass budget for ERV vehicle

  12. Reliability • RCS thrusters of this type (blowdown, hypergolic propellants) are replaced for: • Valve leakage (usually due to NTO corrosion) • Contamination • Failure to fire • Historical Failures • Shuttle RCS fire in the OPF • Mars Observer attributed failure to migration past isolation valves through pressurant system • NTO corrosion causes “frequent” valve and line replacement and caused extensive orbiter damage on STS-2 • Risk Reduction • Heat propellant lines to prevent from freezing/rupturing (NTO freezes at 11°F) • Use high-quality high pressure valves • Use materials compatible with NTO

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