Plasma propulsion for three terrestrial planet finder architectures - Free-flying, monolithic and tethered

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A systems-level trade-off study is presented comparing the propulsion requirements and associated final masses for different architectural implementations of the Terrestrial Planet Finder (TPF) mission. The study focuses on the mN-level propulsion chores associated with rotation and repointing. Three interferometer configurations; free-flying, monolithic and tethered; lead to estimates of power requirements and spacecraft masses associated with different plasma propulsion systems required to maneuver the interferometer throughout its lifetime. The parametric study includes the following plasma propulsion options: Hall thruster, Field Emission Electric Propulsion (FEEP), Ablative Pulsed Plasma Thruster (APPT), Ablative Z-pinch Pulsed Plasma Thruster (AZPPT) and Gas-Fed Pulsed Plasma Thruster (GFPPT). For the different thruster and architecture combinations, it is found that the initial mass for a system falls between 3200 and 4200 kg. Also, in general, for a given architecture, the tether has the lowest initial mass followed by the free flyer and the monolith. Finally, the initial mass was found not to be particularly sensitive to the type of plasma propulsion system so the choice should be made based on technological readiness, systems integration considerations and spacecraft contamination issues associated with the chosen system. Nomenclature M moment applied to spacecraft [N-m] Ms/c per spacecraft M [N-m] a square side length [m] ras/c per spacecraft m^ [N-m] go gravitational acceleration [m/s] rricomb combiner mass [kg] / moment of inertia [kg-m] rrif final (propellantless) mass [kg] hit max max. deliverable impulse bit [mN-s] m fixed fixed mass excluding propulsion [kg] IS/G ' P spacecraft / [kg-m] m^ initial (total) mass [kg] Isp specific impulse [s] mp (fixea) fixed power supply mass [kg] 'Graduate Student, Electric Propulsion & Plasma Dynamics Lab (EPPDyL). Applied Physics Group. Member AIAA. * Chief Scientist at EPPDyL. Assistant Professor, Applied Physics Group. Senior Member AIAA. * Post-Doctoral Researcher, Dynamics and Controls Group. Member AIAA. § Assistant Professor, Dynamics and Controls Group. Senior Member AIAA. f Presented at the 31 AIAA Joint Propulsion Conference, Salt Lake City, Utah, July 8-11, 2001. Copyright © by authors. Published by the AIAA with permission. c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s) Sponsoring Organization. POLZIN, et al: PLASMA PROPULSION FOR THREE TPF ARCHITECTURES payload mass [kg] power processing unit (PPU) mass [kg] propellant mass [kg] mps total power supply mass [kg] mps (fa,.) thruster power supply mass [kg] mtank tankage mass [kg] TM>thr (fixed) fixed thruster mass [kg] Pfixed constant (fixed) power required [W] maximum required power [W] in minimum required power [W] required power for thruster [W] Ptotai total required power [W] R circular radius [m] RS/C ~ P spacecraft R [m] T/P thrust-to-power ratio [mN/W] Tmax maximum deliverable thrust [mN] tmis mission length [s] T^q required thrust [mN] trot rotational period [s] TS/C ' P spacecraft Treq [mN] x,y lateral spacecraft dimensions [m] a specific mass [kg/kW] aa average angular acceleration [rad/s] At time for a maneuver [s] AT^ characteristic mission velocity [m/s] A0 repointing angle [rad] r? thruster efficiency w rotational velocity [rad/s]