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National Aeronautics and Space Administration

Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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The Ura-Shuttle Flight

After nearly a decade of preparations and long delays due to the Challenger disaster, the Uniformly Redundent Array (URA) Shuttle experiment flew aboard Discovery from April 28 to May 5, 1991 on mission STS-39. URA-Shuttle is a 2 to 70 keV x-ray imaging experiment designed to investigate imaging issues such as moving targets, clusters of targets, thermal distortions, image compensation methods, and on-board background rejection methods. It uses an imaging technique called coded aperture imaging whereby an x-ray image is formed from a large number of pinholes, 13,267 in the case of URA-Shuttle. Although URAs were invented at Los Alamos and are now the standard method of imaging at high energy in space, this experiment was the first U.S. URA in orbit. This experiment also has potential for significant astrophysical research since the detector it employs has twice the normal energy resolution of a proportional counter. The 4 arc minute angular resolution and 4.5 degree field of view make it especially useful as a survey instrument.

URA-Shuttle is the first Department of Energy shuttle-bay experiment, that is, an experiment which stays in the bay and is operated by the astronauts. In the early 80's it was anticipated that the shuttle would be the only U.S. method of space experiments. As such, years of preparation had gone into planning for each moment of the 8 day mission, including 18 months of training for the astronauts. Much of the training was done at Los ALamos. The astronauts were responsible for sending all commands to the experiment: to turn it on, to clean and refill the proportional counter gases, to control the many adjustments on URA, and to point it at chosen targets. The Air Force removed the uplink and downlink from the pallet in order to test the astronauts ability to control complicated instruments wihtout help from the ground. All data was to be stored on two tape recorders for processing after the flight.

The URA experiment in the Shuttle bay of Discovery during flight STS-39, in the spring of 1991. The long box is the X-ray telescope and the cone is the sun shield of the optical star sensor

CAI home icon Go to general Coded Aperture Imaging page

Tod Strohmayer & Ed Fenimore, LANL, 1992. For more info, contact E. Fenimore at These pages have been compiled by Jean in 't Zand. They are intended to provide general information for those interested in coded aperture imaging. Any citations should reference original papers as noted in the bibliography, and requests for further information about any of the papers should be directed to the authors thereof.