Soft X-Rays and a Data Relay

Twenty years ago today — April 25, 1993 — the first satellite completely sponsored by the Department of Energy launched on a Pegasus booster, dropped from the wing of NASA’s B-52.


(ALEXIS satellite artist’s conception. NASA image from Wikimedia Commons.)

The Array of Low Energy X-Ray Imaging Sensors (ALEXIS) satellite’s primary instrument was an X-ray telescope array tuned to “ultrasoft” X-rays for making a sky map in that part of the electromagnetic spectrum, as well as the “Blackbeard” VHF receiver “for studying the effect of lightning and electromagnetic impulse from exploding [nuclear] devices on the ionospheric transmission.”

During its flight, one of the satellite’s solar array paddles was damaged, and controllers could not establish contact with the spacecraft for 3 months. Once they established contact, they had to develop specific attitude control procedures to bring the satellite under control, after which the spacecraft performed well although “the astronomy data needed a full pointing and aspect solution in order to be interpreted.”

And, to complete the promise implied by the title of this post: 5 years ago today — April 25, 2008 — China launched its first data-relay satellite, Tianlian 1, on a Long March 3C rocket from Xichang Launch Center.

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