NASA SBIR 2003 Solicitation


PROPOSAL NUMBER: 03- II E2.02-7276
SUBTOPIC TITLE: Guidance, Navigation and Control
PROPOSAL TITLE: Development of a Tethered Formation Flight Testbed for ISS

PRINCIPAL INVESTIGATOR/PROJECT MANAGER (Name, E-mail, Mail Address, City/State/Zip, Phone)
Steven Sell
247 Third Street
Cambridge, MA 02142-0000
U.S. Citizen or Legal Resident: Yes

We propose an innovative, cost-effective flight experiment that will not only reduce the technology risk for future NASA missions but also take full advantage of the unique capabilities available on the International Space Station (ISS). For our Phase II effort, we plan to modify the Synchronized Position, Hold, Engage, and Reorient Experimental Satellites (SPHERES) system to serve as an on-orbit testbed for Tethered Spacecraft Interferometer (TSI) autonomous software technologies. The SPHERES system, developed by Payload Systems Inc. and the MIT Space Systems Laboratory, is currently scheduled for its first mission aboard the ISS in 2005 to demonstrate metrology, formation flight, and autonomy algorithms. The modifications proposed here would include the addition of a tether reel, momentum wheels, and software modules to the existing SPHERES satellite system. These modifications would enable several new functions, including coarse spacecraft formation initialization, deployment and retraction, and multi-stage precision pointing control, as would be needed for tethered satellite constellations such as the NASA's Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) mission. Our proposed effort would result in a flight-identical qualification hardware and software at a small fraction of the typical development cost.

Forming reconfigurable sparse aperture arrays in low Earth orbit using tethers is of interest to the DoD for observations which require the fine ground resolution achieved by separating the sub-apertures further apart (5 km). The DoD could also benefit from the momentum exchange technique for the transfer of satellites from LEO to higher orbits. It may also be possible to provide a plane change capability using tethers. Additionally, university research programs studying tether dynamics could participate and gain valuable data. These applications may be tested on SPHERES-Tether, either on the ground or on ISS.

NASA is considering several missions that will involve the use of tethered spacecraft. Missions such as the Sub-millimeter Probe of the Evolution of Cosmic Structure (SPECS) will use tethers to precisely control the relative positions of multiple satellites for interferometry. NASA has been considering the use of electro-dynamic tethers (Momentum-exchange / electro-dynamic re-boost (MXER)) as a means for boosting payloads in low Earth orbit (LEO) to higher orbits as well as Earth-escape without the use of propellant. SPHERES-Tether would directly benefit such missions by providing a low cost 6-DOF 0g testbed for proving out these high-risk technologies.