A Group of Suitcase-Sized Satellites Will Transform Hurricane Tracking
Earlier this month, NASA launched a constellation of small satellites that will transform hurricane forecasting and enable new insights into storm formation and activity. Called the Cyclone Global Navigation Satellite System (CYGNSS), eight spacecraft, each the size of a carry-on suitcase, are flying over the tropics to measure and map ocean winds. Because of their altitude, heavy rain and storm surges are no obstacles to the satellites, and when hurricanes form, the spacecraft will be able to peer through walls of water into the storm’s core and continue to collect data—something no space-based system has ever done before.
“CYGNSS is a tool that will provide us 24/7 coverage of the tropical cyclone zone. It will improve our knowledge of how hurricanes grow so that we can better prepare and protect people in the path of each hurricane as it comes,” Christine Bonniksen, CYGNSS program executive with the Science Mission Directorate's Earth Science Division at NASA Headquarters, tells mental_floss.
THE RAIN BARRIER HAS BLOCKED OUR VIEW
Over the past several decades, there has been a steady improvement in storm track forecasting—or where storms will hit—and the National Hurricane Center’s error rate is half of what it was 20 years ago. The same cannot be said for storm intensity forecasting—how strong these storms will be. “If you look at the record for their intensity forecast, there has been very, very little improvement in the last 20 years,” said Chris Ruf, the principal investigator on the CYGNSS mission and a scientist at the University of Michigan, Ann Arbor. One of the primary reasons for this is that today’s satellites are unable to measure what’s going on in the inner core of hurricanes. “This has been identified for many years as a primary lacking ingredient in the numerical forecasts that are used by the National Hurricane Center. They wish they had information on the inner core of the storms and they don’t.”
Storm cores have so far been impenetrable because current wind-observing spacecraft cannot see through rain. This is because their on-board instruments emit signals at an 8-millimeter wavelength—about the same size as a large raindrop. When the signals encounter rain, they are simply scattered and absorbed. (Hurricane paths depend on environmental factors outside of the storm, which is why this rain shroud has not been an impediment to predicting where storms will hit.)
Additionally, it takes about three days for current systems to collect data to build a map of global wind speeds and precipitation. This is a big problem if you’re trying to track the rapid intensification of tropical storms and hurricanes, which can happen in a matter of hours. So until now, scientists have had to rely on so-called “Hurricane Hunter” aircraft to fly into the storm to perform wind speed reconnaissance.
THE CYGNSS SOLUTION
CYGNSS changes all of this by using GPS satellite signals, which were designed to penetrate heavy rains. GPS operates at a 19-centimeter wavelength—more than long enough to avoid rain interaction. When GPS satellite signals hit the ocean, they reflect back into space and are received by CYGNSS observatories. Think about the way the Moon reflects on a placid lake: When the lake is calm, the Moon's image is sharp. When the wind blows, the water roughens and the image diffuses. CYGNSS relies on a similar principle, reading the clarity of the GPS signals to reveal the characteristics of the wind. It measures the strength of the GPS signal as it scatters off the ocean surface to determine wind speed.
The eight CYGNSS observatory spacecraft operate evenly in a single orbital plane around the Earth. Each satellite has a payload called a Delay Doppler Mapping Instrument, a GPS receiver capable of tracking four different GPS signals simultaneously. Two antennas look down at reflected GPS signal and take measurements of the diffuse scattering, and from those derive the wind speed and activity. Meanwhile, one antenna looks up and receives a direct GPS satellite signal for geolocation. In essence, each 65-pound satellite is doing the work of four Hurricane Hunter airplanes. Collectively, CYGNSS is like a squadron of 32 such planes flying continuously over the tropics taking simultaneous measurements.
The system gives a total refresh of the entire tropical wind distribution map every seven hours, even under heavy precipitation. In a hurricane or tropical storm—including in areas with the highest wind speeds and the most powerful surges—CYGNSS can immediately answer questions about the storm size, intensity, and the reach of its strong winds. Moreover, because the satellite constellation has such expansive coverage of the Earth, it can collect massive amounts of data on the entire storm environment. There are three different data downlink points around the world, and the data can be downloaded from the satellites within the hour—an unprecedented timeframe.
HOW THE LAUNCH WENT DOWN
CYGNSS launched on the morning of December 15, 2016 from Cape Canaveral with the help of a Pegasus rocket, an air launch system. The rocket was mounted to the bottom of an L-1011 airplane called Stargazer that took off from a runway, just like any other plane you’ve ever seen. At 39,000 feet above the Atlantic Ocean, the plane released the Pegasus rocket, which ignited five seconds later and powered its way into space. The fairings hatched away and the deployment vehicle separated, and the eight small satellites released themselves in pairs over 30-second intervals. Ten minutes after separation, their solar arrays deployed. They then moved into position in orbit and began operation.
By 4:12 pm ET that same day, the CYGNSS team had successfully made contact with all eight satellites. "It is an amazingly rewarding feeling to spend such an intense and focused time working on CYGNSS and then, in a matter of just a few hours, have the entire constellation suddenly come to life," Ruf said in a brief mission update. "I am excited (and a little exhausted) and really looking forward to diving into the engineering data in the coming days, and then into the science data in the weeks to follow."
This is NASA’s flagship Earth Venture–class mission, which is a new NASA program designed for low-cost, high-technology suborbital (think aircraft and balloons) and orbital (CYGNSS) projects. Two previous missions of this class were aircraft designed for atmospheric research and communications. This is the first spaceborne Earth Venture endeavor. Southwest Research Institute in Boulder, Colorado runs CYGNSS mission operations, and science operations are run from the University of Michigan. The primary $160 million mission will run for two years—enough time to fill in blank spots in the hurricane dataset, get a grip on how storm cores intensify, and hopefully refine the forecast models that lives depend on.