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ALEXIS
The Array of Low Energy X-Ray Imaging Sensors
(ALEXIS) was a U.S. Department of Energy mission, built by the Los Alamos
National Laboratory in collaboration with Sandia National Laboratories and the
University of California-Space Sciences Laboratory.
It was launched by a Pegasus “winged rocket” booster,
dropped from an B-52 bomber, on April 25, 1993.
During the launch, the hinge failed on one of the solar paddles, which hung
loose and was left connected to the spacecraft only by a bundle of wires.
The paddle would flap around from thermal effects, causing spin rate and
direction changes. After developing new procedures for operations to account
for the loose paddle and recovering some of the spacecraft attitude control,
operations commenced in late July, 1993. Operations continued until
April 29, 2005, well beyond the original one year planned mission duration.
However, not all instruments
were usable through the entire mission: a RAM failure in late 1999 resulted in
data being unavailable from one of the EUV telescope pairs.
The ALEXIS satellite carried two instruments: three pairs of EUV telescopes
collectively forming the ALEXIS instrument, and BLACKBEARD, a radio frequency
monitoring instrument for studying ionspheric effects on VHF radio signals.
The latter had no high-energy astrophysics science goals.
The ALEXIS instrument consisted of three pairs of EUV telescopes with
overlapping 33° FOV, scanning the entire anti-solar hemisphere during
each 45 second spin of the spacecraft. Each telescope contained a multi-coated
spherical mirror, a curved profile microchannel plate detector at the prime
focus, a background rejection filter, electron rejecting magnets at the
telescope aperture, and associated electronics. The telescope mirror
coatings and filter settings gave each telescope narrow band observations
at 66, 71, or 93 eV.
The ALEXIS insrument mapped the EUV diffuse background in three distinct
wavelengths (130, 172, & 186 angstroms; 93, 71, and 66 eV respectively),
produced a narrow-band survey of point sources, searched for transient
phenomena, and monitored ultrasoft X-ray sources such as cataclysmic variables
and flare stars.
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Page authors: Lorella Angelini Jesse Allen
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Last modified: Thursday, 24-Sep-2020 17:21:49 EDT
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