Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Development of Formation Flight and Docking Algorithms Using the SPHERES Testbed Prof. David W. Miller MIT Space Systems Laboratory Allen Chen, Alvar Saenz-Otero, Mark Hilstad, David W. Miller

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Introduction SPHERES: Synchronized Position Hold Engage Reorient Experimental Satellites SPHERES is a cost-effective, risk-tolerant, interactive testbed operated inside the ISS for the development and maturation of formation flight and autonomous rendezvous and docking technologies (autonomy, control, and metrology). Multi-vehicle Testbed - long duration micro-gravity environment allows 6DOF per vehicle and close proximity maneuvers representative of envisioned missions: TPF, Starlight, TechSat 21, Orbital Express, and Mars Sample Return. Cost-effective - replenishable consumables, IFM and observations by crew reduce operation costs; data (up)downlink and video coverage expedites algorithm design; reconfigurable and upgradeable hardware accommodates new technologies. Risk-tolerant - ill-behaved algorithms can be stopped and corrected without affecting future operations. Allows software to mature from conception to flight quality without danger of mission failure.

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Design Philosophy Experimental Research in a micro- Gravity Environment Allows: –Demonstration and validation. –Repeatability and reliability. –Determination of simulation accuracy. –Realization of performance limitations. –Discovery of new physical phenomena. –Understanding of operational drivers. Laboratory Attributes: –Delineates between generic and test- specific equipment. –Allows reconfiguration of hardware for mission-specific equipment. –Supports extended investigations with multiple experiment iterations. –Accommodates unforeseen failures in a risk tolerant environment. –Provides software reconfiguration for rapid changes of algorithms. –Enhances the iterative research process via interaction and observation by humans. –Supports multiple investigators. If one cannot simulate the space environment in the laboratory, simulate the laboratory environment in space.

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES SPHERES Testbed SPHERES free-flier units –Up to 3 units can be used simultaneously (with possible upgrade to more units). –Each independent unit contains propulsion, power, wireless communications, metrology, and processing sub-systems. –Sensors and actuators provide full state vector (6DOF, 12 states) of each unit. Laptop unit –ISS standard PC laptop serves as a base station for software reconfiguration and telemetry downloads. STG Metrology STS –Provides access to the Ku-band for ISS to ground communications. Communications –Satellite-to-satellite (STS) for formation/docking control. –Satellite-to-ground (STG) for telemetry download and software upload. Metrology –Four external metrology transmitters, mounted to the body of the ISS, create frame of reference.

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES SPHERES Testbed Structures –Aluminum internal frame, covered with Lexan panels. Propulsion –Cold-gas thruster system using CO2 at 70psig. –Micro-machined custom nozzles attached to electric solenoid valves. Metrology –IR/Ultrasound ranging system resembles GPS within ISS environment (1Hz). –6DOF IMU system for high frequency data (50Hz). Avionics –C40 DSP Main Processor (will be upgraded to a C6701) Power –16 AA batteries

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Testbed Validation KC-135 Reduced Gravity Airplane –Full 6DOF dynamics –Short duration Tests Performed (2/01 and 3/01) –System checkouts –Single SPHERE attitude control –Master/Slave formation flight 2D Laboratory Experiments –Long duration 2D tests (3DOF) –Can use fixed supplies instead of consumables –Preliminary low-cost testing prior to KC or ISS deployment Tests Performed (ongoing) –Master/Slave formation flight –Docking algorithms

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Formation Flight KC-135 Frame Follower –Master unit attached to KC-135 frame. –Slave commanded to follow the rotation of the Master: should remain oriented with frame. –10Hz STS communications of full attitude state (3 angles and 3 angular rotations). –Slave must recover from initial deployment.

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Docking Research 2D Docking Demonstrations –Cooperative docking: Master unit awaits the arrival of the slave with full actuation to align docking port. –Slave unit starts with initial attitude offset, aligns itself with the master, and then translates to perform the docking. –10Hz STS communications of full 2D state (4 position, 2 attitude).

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Team Capability MIT Space Systems Laboratory –David W. Miller Formation flight, rendezvous and docking research in support of Techsat21, ST-3, Terrestrial Planet Finder Design and PI of 0-g dynamics and controls laboratories –MODE STS-40, 48, 62 –DLS on MIR –MACE STS-67, 106, ISS –Jonathan P. How Formation flight, differential GPS, robust control –Brian Williams Spacecraft autonomy, remote agent, Livingstone autonomous model-based diagnosis on DS-1 Payload Systems Incorporated –Developer and integrator of experiments in human-rated space platforms (Shuttle, MIR, ISS) The fact that our facilities have more reflights & first flights is testimony to the versatility of, and demand for, our dynamics and controls laboratories

Space Systems LaboratoryMassachusetts Institute of Technology SPHERES Conclusions SPHERES has demonstrated operation as a Formation Flight and Docking Algorithm testbed in 2D and KC-135 environments. –KC-135 experiments validated the operation of SPHERES in a 6DOF environment. –2D Laboratory testing provided initial insight into communications requirements for Formation Flight systems –2D Demonstrations of both Formation Flight and Docking Algorithms are ongoing. ISS Deployment in early 2003 –Manifested in Flight 12A.1 of the ISS for April 2003 (with possible 11A launch) –Minimum mission span of 6 months. Programmatic Status –DARPA (AF) Orbital Express Program In-space assembly, upgrade, and servicing –NASA Goddard Space Flight Center Formation Flight Algorithms. –NASA Starlight, ST6, and Terrestrial Planet Finder missions. –Capture of Mars sample return vehicles.