March 4, 1999
ARGOS Mission Seeks New Information about Black Holes and Neutron Stars
|.||An experiment to study black holes, neutron stars and other exotic
celestial objects was launched Feb. 23 from Vandenberg Air Force Base in
California, with the goal of learning more about matter in its most extreme
A collaboration of astrophysicists the Department of Defense's Naval Research Laboratory (NRL) and particle physicists from SLAC and have built an x-ray detector that will be used in one of nine primary experiments on board the Air Force Space Test Program's Advanced Research and Global Observation Satellite (ARGOS). The detector is called the Unconventional Stellar Aspect (USA) experiment. The Department of Defense and the Department of Energy have provided funds for USA.
ARGOS was launched by a Delta II rocket that placed the satellite into a polar orbit where it is expected to operate for at least three years.
The USA experiment was designed to observe bright x-ray sources, mostly binary star systems, including a black hole, a neutron star, or a white dwarf, orbiting with a more typical star. In neutron stars, gravity has compressed matter down to densities larger than those found in the nucleus of an atom. In all of these types of binary systems, extraordinarily strong, relativistic gravitational forces and enormous magnetic fields act in concert to produce dramatic phenomena not observable from Earth-based laboratories.
In addition to providing valuable new information for astrophysicists and particle physicists, USA has been designed to make significant contributions to applied science, environmental science, and engineering research. It will use x-ray sources to test new approaches to satellite navigation and to conduct the first tomographic survey of Earth's atmosphere. It will also test new concepts for making spacecraft computers more reliable, an approach called fault-tolerant computing.
To search for interesting new physics, USA can observe variations in x-ray intensity with a time resolution of less than 100 microseconds. The experiment consists of two large area x-ray sensors on a gimbaled mounting. The sensors are collimated proportional counters, sensitive to X-rays between 1 and 10 angstroms, and with a field-of-view of 1.5 degrees. SLAC's main role in the experiment was to build and test the collimators, and construct the mounting. SLAC scientists and graduate students also helped to debug and test the readout electronics. They are currently busy trying to understand the calibration of the instrument, and preparing to analyze the large quantities of scientific data that are expected shortly. USA has an average telemetry rate of about 40 Kbytes per second - small by particle physics standards - but equal to that of the largest space-based experiments currently in orbit.
As part of its engineering research goals the USA experimental team
will test new concepts for fault-tolerant computing in space. To achieve
this goal, USA carries a two-computer testbed that consists of a military
radiation-hardened processor side by side with a commercial off-the-shelf
processor. The testbed will allow scientists to determine the effectiveness
of advanced fault-tolerant software algorithms designed to allow the processor
to continue operating even when damaged.
More ResourcesFor website information on ARGOS and its payloads, please refer to http://bcoe.nrl.navy.mil/SSD/Argos/html/index.html and http://xweb.nrl.navy.mil.