Session
Technical Session III: Science & Exploration
Abstract
This paper describes a system concept for a NASA Small Explorer Mission to develop an all-skyviewing Advanced X-ray Monitor (AXM). The spacecraft is configured to be launched from a Pegasus XL vehicle. AXM is designed to provide unprecedented sensitivity to cosmic explosions seen in X-rays. These include the ejections of relativistic jets by black holes in the Galaxy, and the fireballs of gamma ray bursts that originate in distant Galaxies. Such events are captured with 31 cameras mounted on the AXM spacecraft to continuously view 97% of the celestial sphere, excluding occultations by the Earth. The camera detectors are Gas Electron Multiplier (GEM) devices, developed at CERN and used with coded masks for X-ray astronomy. The pointing orientations for the cameras presented a challenge to provide 4p steradian viewing, while accommodating spacecraft subsystems and deployable solar arrays for power. The mounting orientation resembles the 32 faces and vertices of a soccer ball, with one camera eliminated to avoid the saturating effect of solar X-rays. The objective of continuous, all-sky viewing is accomplished with a three-axis stabilized attitude control subsystem with the solar panels pointed close to the Sun. The AXM mission is designed for launch into a ~600-km altitude, circular, equatorial orbit. An approximately 1 degree spacecraft maneuver once per day will maintain the solar panels aligned with the Sun. The spacecraft is powered by solar arrays that deploy after launch and are then fixed for the mission duration. Within limitations, the AXM spacecraft has been designed to gracefully tolerate many kinds of anomalies.
Spacecraft System Design for an Advanced X-Ray Monitor (AXM) Mission
This paper describes a system concept for a NASA Small Explorer Mission to develop an all-skyviewing Advanced X-ray Monitor (AXM). The spacecraft is configured to be launched from a Pegasus XL vehicle. AXM is designed to provide unprecedented sensitivity to cosmic explosions seen in X-rays. These include the ejections of relativistic jets by black holes in the Galaxy, and the fireballs of gamma ray bursts that originate in distant Galaxies. Such events are captured with 31 cameras mounted on the AXM spacecraft to continuously view 97% of the celestial sphere, excluding occultations by the Earth. The camera detectors are Gas Electron Multiplier (GEM) devices, developed at CERN and used with coded masks for X-ray astronomy. The pointing orientations for the cameras presented a challenge to provide 4p steradian viewing, while accommodating spacecraft subsystems and deployable solar arrays for power. The mounting orientation resembles the 32 faces and vertices of a soccer ball, with one camera eliminated to avoid the saturating effect of solar X-rays. The objective of continuous, all-sky viewing is accomplished with a three-axis stabilized attitude control subsystem with the solar panels pointed close to the Sun. The AXM mission is designed for launch into a ~600-km altitude, circular, equatorial orbit. An approximately 1 degree spacecraft maneuver once per day will maintain the solar panels aligned with the Sun. The spacecraft is powered by solar arrays that deploy after launch and are then fixed for the mission duration. Within limitations, the AXM spacecraft has been designed to gracefully tolerate many kinds of anomalies.
