Iso Orbit

Infrared Space Observatory--

Figure 7.23. Orbit of the Infrared Space Observatory (ISO) about the Earth. Courtesy of ESA. 7.7.2 ISO

Infrared Space Observatory--

Figure 7.23. Orbit of the Infrared Space Observatory (ISO) about the Earth. Courtesy of ESA. 7.7.2 ISO

The ESA ISO was launched on November 17, 1995 by an Ariane 44P launcher from Kourou, French Guiana into a highly elliptical orbit with a perigee altitude of 1,000 km, an apogee altitude of 70,500 km, and a period of approximately 24 hours (Figure 7.23). The design of the orbit allowed for very long integration times to record extremely faint objects and also ensured that ISO minimized its time within the Earth's radiation belts, which interfere with the operation of its detectors. The orbit chosen allowed 17 hours of continuous telescope operation per orbit.

Although the physical size of ISO is large (5.3 x 3.6 x 2.8 m), the telescope itself is relatively small with a primary mirror diameter of only 0.6 m (Figure 7.24). Most of the volume was filled up with liquid helium, which cooled the entire optical system to a temperature of 4K, reducing the noise of the detectors to their minimum theoretical values and allowing the measurement of images and spectra of extremely cold objects over the spectral range of 2.3 ^m to 240 ^m (41-4,300 cm-1). ISO was originally planned to be operational for 20 months, but eventually the working life was stretched to more than 28 months; ISO operated until May 1998. ISO had four main instruments which will now be reviewed.

Infrared camera: ISOCAM

The ISO camera, ISOCAM, provided imaging in the spectral range 2.5 ^m to 17 ^m. The instrument was split into a short wavelength (SW) channel covering 2.5 ^m to

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