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ISS-RapidScat was an instrument mounted to theInternational Space Station'sColumbus module that measuredwind speeds.[1] It was launched aboardSpaceX CRS-4 in September 2014 and operated until August 2016.[1] ISS-RapidScat was ascatterometer designed to support weather forecasting by bouncing microwaves off the ocean's surface to measure wind speed viawind waves.[1] It featured a 75 cm (30 in) rotatingradar dish that operated at 13.4 GHz (Ku band).[2] It could collect data between 51.6 degrees north and south latitude, with a swath 900 km wide (560 mi).[3]
The ISS-RapidScat program was initiated in response to the failure of theQuikSCAT 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 theJet 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.[4] 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.[5]
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.[2] By the time of ISS-RapidScat's launch, theEuropean Space Agency'sMetOp series were the only two satellites with fully functioning scatterometers in orbit.[6] 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 theSun-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.[5] This orbit also gives better coverage of thetropics, 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 differentdata sets.[3]
Objectives of the ISS-RapidScat program were to mitigate the loss of and provide continuity of wind data products from the QuikSCAT SeaWinds instrument, to serve as acalibration standard for the international constellation of scatterometer-equipped satellites, and to sample thediurnal and semi-diurnal wind variations that occur between ISS flightlatitudes at least every two months.[4][2]
The scatterometer was launched as external cargo aboard theSpaceX CRS-4 mission on 21 September 2014, attached to the unpressurized section of theDragon capsule.[1] Dragon was berthed to the station on 23 September.[7] The instrument was removed from Dragon, robotically assembled and attached toColumbus between 29 and 30 September. It was powered up on 1 October and immediately began gathering data, which was first processed into an uncalibrated product on 3 October.[8] ISS-RapidScat was declared fully operational and its data products properlycalibrated on 10 November.[9]
One of ISS-RapidScat's first observations was ofTropical Storm Simon off the coast of theBaja California Peninsula on 3 October 2014.[8] It also played a role in observing the Category 5Hurricane Patricia in October 2015, which was noted as one of the most powerful hurricanes on record, with maximum sustained winds of 185 kn (343 km/h; 213 mph).[10][11] Data from ISS-RapidScat was disseminated worldwide for use in weather forecasting, and was used by theUnited States Navy,NOAA, andEUMETSAT, among others.[10]
On 19 August 2016, theColumbus module, which ISS-RapidScat was attached to and reliant on for resources, suffered apower distribution unit failure, which resulted in ISS-RapidScat shutting down. This was followed by an electrical overload in the power distribution unit during recovery efforts. Attempts to restore the instrument were without success, and NASA formally terminated operations on 28 November 2016.[12][13] No replacement or successor device was planned.[14]
ISS-RapidScat was removed from theColumbus module on 1 January 2018 and stowed inside theSpaceX CRS-13 Dragon trunk.[15] On 13 January 2018, the trunk section and ISS-RapidScat re-entered Earth's atmosphere and were destroyed as planned, while the Dragon capsule and its cargo landed in thePacific Ocean and were recovered.[16]
