The Satellite
The basic design of ISO was strongly influenced by that of its immediate predecessor. Like IRAS, ISO was composed of two major components:
- Payload module, composed of a large cryostat holding the telescope and the four scientific instruments.
- Service module, supports the activities of the payload module by providing electrical power, thermal control, attitude and orbit control and telecommunications.
The payload module also held a conical sun shade, to prevent stray light from reaching the telescope, and two large star trackers. The latter were part of the Attitude and Orbit Control Subsystem (AOCS) which provided three-axis stabilisation of ISO with a pointing accuracy of one arc second. It consisted of Sun and Earth sensors, the before-mentioned star trackers, a quadrant star sensor on the telescope axis, gyroscopes and reaction wheels. An complementary reaction control system (RCS), using hydrazine propellant, was responsible for orbital direction and finetuning shortly after launch. The complete satellite weighed just under 2500 kg, was 5.3 m high, 3.6 m wide and measured 2.3 m in depth.
The service module held all the warm electronics, the hydrazine propellant tank and provided up to 600 watts of electrical power by means of solar cells mounted on the sunpointing side of the service module-mounted sunshield. The underside of the service module sported a load-bearing, ring shaped, physical interface for the launch vehicle.
The cryostat of the payload module surrounded the telescope and science instrument with a large dewar containing a toroidal tank loaded with 2268 litres of superfluid helium. Cooling by slow evaporation of the helium kept the temperature of the telescope below 3.4 K and the science instruments below 1.9 K. These very low temperatures were required for the scientific instruments to be sensitive enough to detect even the smallest amount of infrared radiation from cosmic sources. Without this extreme cooling the telescope and instruments would literally be 'blinded' by their own infrared emissions.
Read more about this topic: Infrared Space Observatory
Famous quotes containing the word satellite:
“Books are the best things, well used; abused, among the worst. What is the right use? What is the one end, which all means go to effect? They are for nothing but to inspire. I had better never see a book, than to be warped by its attraction clean out of my own orbit, and made a satellite instead of a system.”
—Ralph Waldo Emerson (1803–1882)