The WISE (Wide-field Infrared Survey Explorer) spacecraft houses an advanced infrared astronomical telescope and is currently in hibernation in low Earth orbit.
WISE’s primary mission upon launch in 2009 was to undertake an astronomical survey of visible space (about 99 per cent) with a huge series of images in the 3, 5, 12 and 22-micrometre wavelength range bands. This was successfully completed in 2011 and the finished ‘All-Sky’ survey data was released to the public on 14 March 2012.
As well as successfully providing this comprehensive infrared map of visible space – a map that contains the positions of over half a billion stars, galaxies and objects – WISE has also made a number of first-time discoveries.
The WISE spacecraft itself is approximately the height and weight of a fully grown polar bear, measuring in at 2.9 metres (9.4 feet) tall, two metres (6.6 feet) wide and 1.7 metres (5.7 feet) deep. It weighs 661 kilograms (1,457 pounds). The spacecraft is split into two main sections: the instrument array and system’s bus. The instrumentation side contains WISE’s telescope, detectors, mirror and cryostat, while the bus – which is essentially the chassis – supports the spacecraft’s computers, electronics, battery, reaction wheels, antenna and solar panel (see the ‘Anatomy of WISE’ diagram for more detail).
As mentioned, WISE is currently in hibernation within low Earth orbit and has been since February 2011. This is in part due to its successful mapping of the All-Sky survey, but also due to its cryo- coolant being exhausted (the frozen hydrogen used within the cryostat to keep two of its four detectors operational).
Importantly though – and the reason that the WISE craft has not been decommissioned entirely – is that the other two detectors do not require this coolant in order to function. As such, these remaining two detectors can be put to use when astronomers need to scan for near-Earth objects (NEOs), such as asteroids and comets.