This page no longer updated from 31 October 2001. Latest version can be found at ALEXIS

Alexis -

Credit: LANL. 16,604 bytes. 276 x 201 pixels.

Other Designations: Array of Low-Energy X-ray Imaging Sensors. Class: Astronomy. Type: X-ray. Nation: United States. Agency: LANL. Manufacturer: AeroAstro.

ALEXIS is a small spacecraft built for the Los Alamos National Laboratory (LANL). Its mission is to provide high resolution maps of low-energy astronomical x-ray sources. The mission is also intended to demonstrate the feasibility of quickly building low cost sensors for arms treaty verification. The spacecraft's cost is reported to be approximately $17 million. An anomaly caused one of the satellite's four solar panels to break away from the vehicle during launch, causing a temporary loss of the spacecraft. Ground controllers were eventually able to control the spacecraft and begin on-orbit operations.

Spacecraft: Four deployed solar panels provide 50 watts average power. Four NiCd batteries. Redundant 80C86 processors. S-Band communications with downlink rate 750 kbps and uplink rate of 9.6 kbps. Mass memory of 100 Mbytes EDAC solid state storage. The bus points the payload in the anti-sun direction and rotates at 2 rpm about that sun-line. Sun sensors and limb sensor provide attitude knowledge of 0.1 deg. Attitude is controlled using magnetic torque coils. Single ground station installed at LANL has 2 m antenna. Payload: An ultrasoft X-ray monitor which consists of 6 compact normal-incidence telescopes tuned to narrow bands centred on 66, 71, and 93 eV. Status as of 1/21/97: ALEXIS continues to operate nominally, sending the results of EUV telescope observations on every pass. ALEXIS has identified a number of transient outbursts in near real time and sometimes is able to supply such target opportunities to operators of the EUVE satellite which contains instruments that are sensitive on similar wavelengths. During occasional "hot times" when ALEXIS is illuminated by the sun during 100% of it's orbit, the telescopes cease operations to avoid overheating the spacecraft (Normally the spacecraft passes through the earth's shadow. ) This anomaly was probably caused by a tear in the thermal insulation, associated with the solar panel damage that occurred during launch.


Design Life: 1 year, goal of 3 years. Total Length: 1.0 m. Maximum Diameter: 0.6 m. Total Mass: 115 kg.

ALEXIS Chronology

25 April 1993 Alexis Launch Site: Edwards . Launch Vehicle: Pegasus. Mass: 115 kg. Perigee: 741 km. Apogee: 746 km. Inclination: 69.8 deg.

Test of X-ray imaging sensors; solar array deployment malfunction. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).


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Last update 12 March 2001.
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© Mark Wade, 2001 .