NASA ISS-RapidScat Built On The Fly
October 30, 2013

NASA Builds RapidScat Mission With Spare Parts And Short Time

Brett Smith for - Your Universe Online

The best chefs in the world can create a gourmet dish from leftover ingredients and NASA scientists have set out to show they can accomplish a similar feat though the ISS-RapidScat science mission.

An abbreviated form of Rapid Scatterometer, ISS-RapidScat was fashioned from spare parts and put together on a relatively short time scale. The mission will monitor ocean winds from the International Space Station.

Scientists study ocean winds for a variety of meteorological reasons, and also because winds affect ocean currents - shifting nutrient-rich waters and potentially providing a major source of food for coastal fisheries.

Scatterometers can track ocean winds by safely bouncing low-energy microwaves – similar to the high-energy waves used to warm up food – off the sea surface. By measuring the strength and direction of the microwave reflection, a scatterometer can calculate the direction and speed ocean that winds are blowing.

"Microwave energy emitted by a radar instrument is reflected back to the radar more strongly when the surface it illuminates is rougher," explains Ernesto Rodríguez, principal investigator for ISS-RapidScat at NASA's Jet Propulsion Laboratory in Pasadena, California. "When wind blows over water, it causes waves to develop along the direction of wind. The stronger the wind, the larger the waves."

Scatterometers are typically aboard Earth-orbiting satellites that fly in a sun-synchronous orbit – or an orbit that crosses the Earth's equator at the same local time every orbit. However, because the RapidScat will be aboard the space station, it will travel in an orbit non-synchronous with the sun, meaning it will observe different parts of the planet at different times of day. These out-of-sync measurements will allow ISS-RapidScat to sense the effects of the sun on ocean winds as the day progresses. In addition, the space station's orbit over the tropics means the scatterometer will offer extra tracking of storms that could turn into hurricanes or tropical cyclones.

ISS-RapidScat is particularly unusual because of the way in which it was developed. The scatterometer will be the first to be attached to the ISS and the first to be delivered to its destination via a commercial space company.

"Space Station Program Manager Michael Suffredini offered us a mounting location on the space station and a free ride on a SpaceX Dragon cargo resupply mission launching in early 2014," explained Howard Eisen, the ISS-RapidScat project manager at JPL. "So we had about 18 months to put together an entire mission."

Instead of using newly-developed instruments, which can be expensive and time-consuming to create, Eisen’s team had to get creative with the mission's hardware. ISS-RapidScat employs leftover hardware originally built to test parts of QuikScat, a satellite-based NASA scatterometer that shut down in 2009. Fortunately, the old hardware was still in working order. "Even though they were spares, they've done an excellent job so far," said Simon Collins, ISS-RapidScat's instrument manager at JPL.

In addition to old spare parts, Eisen’s team turned to off-the-shelf, commercially-available computer hardware instead of the pricey, radiation-resistant computer chips that are usually used in space missions.

"If there's an error or something because of radiation, all we have to do is reset the computer. It's what we call a managed risk," said Eisen.

Rodríguez said he is confident that overcoming these design difficulties will be rewarded with a bounty of important new data.

"Because it uses much of the same hardware QuikScat did, ISS-RapidScat will allow us to continue the observations of ocean winds already started," said Rodriguez. "Extending this data record will help us observe and understand weather patterns and improve our preparedness for tropical cyclones."