Computer Science – Sound
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.871s&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Sound
Scientific paper
The SPHERES (Synchronized Position Hold Engage and Reorient Experimental Satellites) payload is an innovative formation-flying spacecraft testbed currently being developed for use internally aboard the International Space Station (ISS). The purpose of the testbed is to provide a cost-effective, long duration, replenishable, and easily reconfigurable platform with representative dynamics for the development and validation of metrology, formation flying, and autonomy algorithms. The testbed components consist of three 8-inch diameter free-flying "satellites," five ultrasound beacons, and an ISS laptop workstation. Each satellite is self-contained with on-board battery power, cold-gas propulsion (CO2), and processing systems. Satellites use two packs of eight standard AA batteries for approximately 90 minutes of lifetime while beacons last the duration of the mission powered by a single AA battery. The propulsion system uses pressurized carbon dioxide gas, stored in replaceable tanks, distributed through an adjustable regulator and associated tubing to twelve thrusters located on the faces of the satellites. A Texas Instruments C6701 DSP handles control algorithm data while an FPGA manages all sensor data, timing, and communication processes on the satellite. All three satellites communicate with each other and with the controlling laptop via a wireless RF link. Five ultrasound beacons, located around a predetermined work area, transmit ultrasound signals that are received by each satellite. The system effectively acts as a pseudo-GPS system, allowing the satellites to determine position and attitude and to navigate within the test arena. The payload hardware are predominantly Commercial Off The Shelf (COTS) products with the exception of custom electronics boards, selected propulsion system adaptors, and beacon and satellite structural elements. Operationally, SPHERES will run in short duration test sessions with approximately two weeks between each session. During operations, satellites will autonomously perform various maneuvers with one to three satellites operating simultaneously, involving a crew member only to upload protocols and replace satellite consumables (gas and power) during the test session. Once completed, data will be downlinked to the ground for analysis by the SPHERES team, facilitating the iterative process of new and/or modified protocols being uplinked for use in the next test session. SPHERES has prior flight experience on the NASA KC-135 Reduced Gravity aircraft and has also been in constant use in laboratory air table testing for almost two years. Slated for launch to the International Space Station on ISS12A.1, SPHERES will use its six-month flight to conduct risk-reduction investigations involving the coordinated motion of multiple satellites in a micro-gravity environment.
Chen S. E.
Sell S. W.
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