ISS-RapidScat

ISS-RapidScat was an instrument mounted to the International Space Station's Columbus module that measured wind speeds. It was launched aboard SpaceX CRS-4 in September 2014 and operated until August 2016. ISS-RapidScat was a scatterometer designed to support weather forecasting by bouncing microwaves off the ocean's surface to measure wind speed. It featured a 75 cm (30 in) rotating radar dish that operated at 13.4 GHz (K_u band). It could collect data between 51.6 degrees north and south latitude, with a swath 900 km wide (560 mi).

The ISS-RapidScat program was initiated in response to the failure of the QuikSCAT satellite's antenna rotation mechanism in November 2009. While the spacecraft continued to function, it could only gather data in one direction, significantly limiting its data collection ability. ISS-RapidScat was built by the Jet Propulsion Laboratory from elements of QuikSCAT's SeaWinds instrument engineering model, originally used to validate that instrument's flight hardware prior to its launch in 1999. It was constructed in 18 months; re-using the QuikScat hardware had the double benefit of reducing cost and using already flight-proven hardware that functioned well in orbit.

ISS-RapidScat was very similar to QuikSCAT in functionality. However, the instrument suffered due to peculiarities of the International Space Station, such as the station's varying altitude due to increased drag, its variable orientation due to the demands of visiting spacecraft, and its lack of a Sun-synchronous orbit. By the time of ISS-RapidScat's launch, the European Space Agency's MetOp series were the only two satellites with fully functioning scatterometers in orbit. Some of these peculiarities were also advantages. Its mid-latitude orbit meant it was able to collect data about the same spot on Earth at different times of day, whereas the Sun-synchronous orbits used by other scatterometer-equipped spacecraft would re-visit the same location on Earth at the same time daily. This allowed scientists to study how the wind changes at one location over the course of a day. This orbit also gives better coverage of the tropics, and by crossing the orbit of other satellites, it was able to observe the same area at the same time as them, allowing for cross-calibration between the different data sets.

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