Preliminary Development of an Experimental Lightweight Pulsed Plasma Thruster for Solar Sail Attitude Control

Transcription

1 Preliminary Development of an Experimental Lightweight Pulsed Plasma Thruster for Solar Sail Attitude Control Kevin Pryor, Bong Wie, and Pavlos Mikellides Arizona State University 18 th Annual AIAA/USU Conference on Small Satellites SSC04-XI-4

2 Outline Attitude Control needs of a solar sail Baseline attitude control systems Pulsed plasma thrusters basics, benefits, and design Prototype details

3 Attitude Control Requirements Small solar disturbance torque must be counteracted Many possible methods Sun Line Yaw Control Thrust l α M Roll α = Sun Angle ψ = Yaw Angle = π/2 + α Solar Thrust F Control Mass m ε c.p. Pitch y(t)

4 Attitude Control System Brief ACS overview Inertial Stellar Compass (ISC) Attitude Determination System 2.5 kg, 3.5 W, 0.1 deg (1σ), 5 Ηz Active-Pixel Star Camera MicroGyros Attitude Determination Algorithm (Quaternions) Sail Attitude Control System (SACS) 3-axis Attitude Stabilization & Thrust Vector Control Logic yaw Control Ballast pitch Primary ACS for Normal Flight Mode Propellantless 3-axis Trim and Control Mechanisms (total 5 kg, 10 W) Roll Stabilizer Bar Pulsed Plasma Thrusters (total 8 kg, 32 W) Secondary ACS for Backup Mode Sail Carrier Spacecraft ADCS: reaction wheels, thrusters, magnetic torquers, sensors, (total 20 kg, 50 W) Sailcraft attitude stabilization prior to sail deployment, during post-deployment checkout, and for pre-flight standby mode

5 Main Control System Propellantless Primary ACS Pitch Ballast mass for cm/cp trim balance j y Roll x i Orbital Flight Path Yaw k z r θ Micro-PPT module (conceptual drawing) Earth Perigee

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7 Backup System: Pulsed Plasma Thrusters Flight proven technology Decades of flight experience More Robust and Maneuverable Not dependent on sun angle Moment arm proportional to sail size

8 PPT Basics Electromagnetic Thruster Power Processing Unit converts voltage Capacitor charges over ~1 sec Releases in µs Solid Teflon Plasma Lorentz (jxb) force accelerates plasma

9 PPT Benefits High Specific Impulse (Isp) Typically from s Solid Fuel = Low Volume Simplicity of device leads to more reliability and lower cost PPT vs Cold Gas: Comparison Cold Gas Thruster Pulsed Plasma Thruster I sp = 700 s I sp = 100 s V (m/s)

10 Design Requirements Control requirements based off of predicted cm- cp offset Sail Size m Mast length m cm-cp offset* m Solar disturbance torque* N-m Control torque N-m Total impulse (required) N-s Total pulses (required) million * the normally worst case for untrimmed sailcraft using one thruster this torque can be doubled using a pair of thrusters

11 Previous PPTs AFRL s micro-ppt University of Washington Dawgstar s PPT GRC s EO-1 PPT

12 Design Approach Comparison of previous PPTs to choose baseline design EO-1, LES 8/9, TIP-II II NOVA, and Dawgstar LES 8/9 was fully flight qualified, but was never flown, though its predecessor LES-6 6 operated successfully for 10 years. EO-1 s PPT acquired 33 hours of in flight use in 2002 Selection Design reuse of EO-1 1 PPT Lowest dry mass of many recent PPTs Due mostly to advances in electronics Decreased mass through electronics changes Lower power levels allow smaller electronics

13 Specific Components Power Processing Unit 94 x 38.1 x 19.6 mm Off the shelf from UltraVolt Available up to 30W and 6,000 V at same dimensions and weight Capacitor Sample from Dearborn Electronics 50 µf, 1000 V only 2 2 diam, 4.5 long and 250 grams Spark Plug Other 1000 V rated from Unison Assembly made from Ultem 2300

14 Prototype: PPT150 Picture of PPT150 prototype and weight breakdown Discharge Circuit *, kg, 25% PPU, kg, 10% Capacitor, kg, 17% Thruster Assembly, kg, 48% Optimized Prototype ITEM Mass (kg) Mass (kg) Three Thruster Assembly Capacitor PPU Dis charge Circuit * Misc Total

15 Initial Vacuum Testing Preliminary Vacuum Testing shown success Picture shows plasma discharge in vacuum Utilized acrylic housing for visualization

16 Conclusion Lightweight and reliable pulsed plasma thrusters can perform attitude control of solar sails The simplicity of the devices operation creates an excellent backup system The higher efficiency of propellant and higher reliability leads to a better overall system