Herschel Space Observatory
Herschel is the largest infrared space telescope ever launched. With its 3.5-m primary mirror, it is four times bigger than any previous infrared space telescope and almost one and a half times larger than the Hubble Space Telescope.
Herschel's primary mirror is the telescope's light collector. It captures the light from astronomical objects and directs it towards the smaller secondary mirror. The two mirrors work together focusing the light and directing it to the instruments, where the light is detected and analysed, and the results recorded by the onboard computer.
The size of the primary mirror is the key to a telescope's sensitivity: the bigger it is, the more light it collects, and the fainter the objects it sees. It also determines the telescope's ability to distinguish fine details. The surface of the mirror is very important, too. It has to be precisely shaped and perfectly smooth, since the slightest roughness distorts the final image.
The mirror must be light and sturdy to withstand the extreme conditions of launch (when it will be shaken with a force several times that of Earth’s gravity), and the low temperatures of outer space; and any bump on its surface must be less than a thousandth of a millimetre high. Herschel spacecraft
This technological marvel has been constructed almost entirely of silicon carbide. The primary mirror has been made out of 12 segments brazed together to form a monolithic mirror which was machined and polished to the required thickness (about 3 mm), shape, and surface accuracy.
Vital Stats:
The Herschel satellite is a tall cylinder, about 7.5 m high and 4.0 m wide, with a launch mass of around 3.4 tonnes.
The Herschel spacecraft Dimensions ~ 7.5 x 4.0 m (height x width) Mass 3.4 tonnes at launch Telescope mass 315 kg Spacecraft 3-axis stabilised Telescope size 3.5 m diameter primary mirror Science data rate 130 kbps Lifetime 3.5 years Operational orbit Lissajous orbit at an average distance of 800 000 km from L2 Attitude thrusters 12 thrusters, 20 N each Solar arrays Flat, fixed panels of triple-junction Ga As cells, Solar array area: about 12 m2 Batteries 39 Ah Lithium ion batteries Communication 2 low gain antennae 1 medium gain antenna
