A Novel Cold Gas Propulsion System for Nanosatellites and Picosatellites David Hinkley This work was supported under The Aerospace Corporation's Independent Research and Development Program 1
The Need for Miniature Propulsion Micro-Electromechanical-based PICOSAT Satellite Inspector (MEPSI) MEPSI Concept legacy Derivative of UFO (1995) Presented to SERB in 2000 Host-resident daughtership ~1 kg in mass ~Cubesat size Requirements Ejection system Sense host location Propulsion AFRL/IF MEPSI PICOSAT Concept The Aerospace Corporation 2
Mission Concept for MEPSI on STS-116 After ejection, PICOSATs separate and one PICOSAT inspects the other, downloading imagery directly to earth ground station Propulsion Target PICOSAT tether Inspector PICOSAT 15 feet max The Aerospace Corporation 3
MEPSI Hardware Delivery for STS-116 The Aerospace Corporation Inspector 4x4x5 1365 g 60 w-hr battery Target 4x4x5 1125 g 60 w-hr battery Space Shuttle Picosatellite Launcher (SSPL) 4410 4
Departing Shuttle Discovery (Dec 2006) photograph courtesy of NASA 5
Photographs of Discovery taken by MEPSIs T+20 seconds T+25 seconds T+10 seconds T+40 seconds 6
A Basic Cold-gas Propulsion System Basic propulsion system problems Each joint is a leak location Each Tube must be routed accurately Each element must be supported mechanically 7
The MEPSI Cold Gas Propulsion Manifold PROPELLANT STORAGE VOLUME x x V1 PLENUM 1 V2 x Normally closed valve x Thruster PLENUM 2 x x x x x V3 V4 V5 V6 V7 T1 T2 T3 T4 T5 8
Using Rapid Prototyping (RP) to Build a Leak-Free Manifold SLA = Stereo Lithography Apparatus Graphic courtesy of Spectrum 3D Built from a computer file no drawings req d Realize every impossible mfg feature your CAD has to offer Low cost Complexity does not increase cost Leak free No CTE issues (except at valves) Outgassing 2.85% TML 0.01% CVCM 9
Example RP Manifolds Design #1 The Aerospace Corporation Can a hollow enclosure be made? How strong will it be? Can a tube be made that is clear inside? Can a converging/diverging nozzle be made? Will the dimensions be stable? 10
Example RP Manifolds Design #2 The Aerospace Corporation Will a traditional geometry pressure vessel work? What percentage mfg success when all of the necessary plenums and valves are included? Other materials (both SLA and SLS)? 11
Testing Rapid Prototyping Manifolds The Aerospace Corporation Early design burst test (Be careful) The Aerospace Corporation Final design manifold burst test (900 psi) Note that room temperature propellant pressure was 115 psia 12
RP Detail and Allowable Complexity The Aerospace Corporation The Aerospace Corporation 13
The Final Design for MEPSI Propulsion Unit STL Propulsion system Detail DSM-SOMOS 11120 plastic Class C outgassing 6.8 Ksi strength Main tank Thruster nozzle (1 of 5) Reaction wheel (1 of 3) Main tank cover (1 of 2) Valves (7 total) camera 14
Final Assembled MEPSI Propulsion Unit The Aerospace Corporation 15
MEPSI on STS-116: Mission Hardware 16
MEPSI Inspector Thrust Axes A,B,C,D and E are thruster valves Y Z Y Z Y Z Y Z X X X X A + C + E or B + D + E A + D + E or B + C + E A + B or C + D E or A + B + C + D 17
MEPSI (STS-116) Satellite Rotation Rate Change 2.4 Z-rotation rate valve open to fill plenum #2 1.6 /s Rotation Rate (Volts) 2.35 2.3 2.25 Y-rotation rate valve open to fill plenum #1 valve open to expel gas from Nozzle A 3.2 /s 0.2 cc X-rotation rate 2.2 120 125 130 135 140 145 Seconds Spikes are electrical noise due to valve closure, ~ 1 sec after opening 18
Correlation with Prediction Calculation parameters Satellite Ixx = 3.0 x 10-3 kg-m 2 Iyy = 3.0 x 10-3 kg-m 2 Izz = 2.3 x 10-3 kg-m 2 Plenum #1 volume = 0.2 cc Main tank pressure = 115 psia Specific impulse of Xenon = 30s Estimated change in satellite rotation rate ω X = 2.6 x 10-3 N-s [sin (60) (0.057 m) + cos (60) (0.043 m)] / 3.0 x 10-3 kg-m 2 = 0.062 rad/s = 3.5 deg/s ω Z = 2.6 x 10-3 N-s sin (60) (0.033 m) / 2.3 x 10-3 kg-m 2 = 0.032 rad/s = 1.8 deg/s 19
Conclusion SLA RP is low cost and quick mfg time (typ. 1 week) SLA RP manifolds are leak-free (except at valve interface) SLA RP uses all the benefits of digital fabrication SLA RP material outgassing is reasonable (TML can probably be reduced further) SLA RP material is brittle and must be designed with significant margin (but that is easy) meniscus This unit has been stored for 1 year without any loss of propellant AeroCube-2 balloon inflation subsystem 20