Robert T. MacMillan,* Jason J. Westphal,* Christopher W. T. Roscoe
CubeSat Proximity Operations Demonstration (CPOD): Enabling Technologies for Future Space Robotic Servicing Missions Robert T. MacMillan,* Jason J. Westphal,* Christopher W. T. Roscoe,* Marco Villa,† *Applied Defense Solutions, Columbia, Maryland Mission Overview Abstract Rendezvous Demonstrator Cygnus COTS Dragon COTS DART Orbital Express Mass >2000 kg Power 3.5 kW Fuel Hydrazine Mass >4200 kg Power 5 kW Fuel NTO/MMH Mass 360 kg Power Batteries Fuel Hydrazine Mass 952 kg Power 1.2 kW Fuel Hydrazine CPOD is Evolving Proximity Operations and Docking to a Low Mass/Low Power CubeSat Platform Navigation Sensors NFOV Camera Docking Camera IR Cameras ISL Ranging GPS Mass 5-6 kg Power <50 W Fuel R134a 2 x 3U CubeSats CPOD Spacecraft Challenges Processor Limitations Distributed Architecture Sensor and Range Agnostic The CubeSat Proximity Operations Demonstration (CPOD) mission, currently scheduled for launch in late 2015 or early 2016, will demonstrate rendezvous, proximity operations, and docking with a pair of identical 3U CubeSats. This program uses innovative hardware and software solutions to address several of the unique challenges associated with using small, low-cost, low-power components to accomplish complex mission objectives, previously demonstrated only by much larger and more sophisticated spacecraft. This poster presents an overview of the CPOD mission and spacecraft, key aspects of the software design and architecture, and novel hardware and software design features, including an electromagnetic threefinger universal docking mechanism, a miniature cold-gas propulsion system, and onboard autonomous GNC algorithms utilizing passive optical sensors, range capable inter-satellite link radios, and limited computing resources. We postulate how small autonomous spacecraft like CPOD will enable future space robotic servicing missions at low cost with acceptable risk. How can small autonomous spacecraft contribute as components of future space robotic servicing architectures? Solar Panel Arrays with MPPTs Thermal Radiators GPS Patch Inspection Docking Mechanism Maneuverability for diverse viewing angles, distances, and fields of view using a wide variety of sensor modalities … S-Band Patch Thermal Radiator Separation Devices Star Trackers UHF Antennas GPS Receiver Cold Gas Thrusters (8) Battery Module Redundant capabilities available through on-orbit spares or via replenishment ondemand enhance system availability … Multiple diverse sensor modalities for additional characterization of space weather, vehicle status, or … Logistics and Upgrade How can small autonomous spacecraft contribute to your mission? Inertial Reference Module (IRM) Battery Module Guidance Solution RPOD Module • Valid for circular, eccentric orbits, including J2 • Impulse times determined by primer vector history • Optimization uses iterative solution, low computational burden • Solves n-impulse optimization but avoids implementing nonlinear numerical solver • Fuel cost is much lower than traditional 2- or 3-impulse analytical methods Endeavour Bus Docking Mechanism – Chaser Docking Mechanism – RSO Chaser moves to 0.5m of RSO +V-Bar + - Relative Altitude (m) RSO Initial Misalignment Chaser Electro-magnets activate to bring vehicles together +R-Bar -0.1 -0.2 -0.3 -0.4 -0.5 Downrange Distance (m) Locked Together Self Aligning 200m Rbar Inject into Walking Safety Ellipse 200x400x200m 400m 200m 100m 5.2 6 Reduce Size Safety Ellipses & NFOV checkout 100x200x100m 50x100x50m B Vbar A 5.3 Stabilize into Safety Ellipse about CubeSatB 200x400x200m -200m 4 NFOV Bearings & Ranging Drift ~2km during checkout ( assumes mirrored Attitude ) ISL Ranging Docking Bearings Docking Ranging IR1 B & R IR2 B & R Rbar 6.3 Reduce Size Transfer to V-bar @ 20m Approach to 5m 7.5 & IR2 checkout 10m 7.3 15m 20m 7.2 Reduced Size NMC & IR1 checkout 10x20m 7.4 7.6 Approach & Dock Approach to 10m & IR1 checkout Nominal trajectory – 4-burn sequence Radial offset provides safety in case of abort fuel cost: 0.14 m/s 50m A Vbar fuel cost: 0.225 m/s Safety Ellipse & Docking Sensor checkout 25x50x25m 25m B Example: Formation Reconfiguration • Initial configuration: 400 x 200m Natural Motion Circumnavigation • Final configuration: 800 x 400m Natural Motion Circumnavigation • Analytical solution uses two radial burns at v-bar crossings (top figure) • Optimal solution results in three predominantly alongtrack burns at various locations (bottom figure) Initiate Safety 5.1 Ellipse 200x400x200m 5m Fuel-Optimal n-Impulse Maneuver Targeting Propulsion Module NFOV Ranging 2 km Replenishment of degraded functionality or upgrade to new capabilities; potential to raise TRL of experimental capabilities … S-Band Transmitter UHF Radio ∆GPS via ISL ISL Ranging NFOV Bearings Anomaly Assessment Segmented and distributed spacecraft architectures offer additional opportunities … Resiliency Concept of Operations RENDEZVOUS Large Mass – Mission Application DOCKING CPOD †Tyvak Nano-Satellite Systems, Irvine, California 7.1 Transfer to In-Plane NMC 25x50m
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