Radiation detectors being launched will map zones that imperil spacecraft, disrupt communications.
A device designed at the University of Minnesota will soar to a hostile and largely unexplored region of space in September, seeking ways to make travel safer there for satellites and astronauts.
Physics Prof. John Wygant's electric field and waves instrument, 15 years in the making, is one of five devices that will study magnetic and electrical forces and high-energy particles in radiation belts surrounding Earth. Those phenomena generate the diaphanous northern lights but also have a more forbidding quality.
"Spacecraft tend to die in the radiation belts," said Wygant, citing "killer" electrons moving near the speed of light. "This region of space has never been explored with the kind of instrumentation and capabilities we have on this mission."
Wygant is one of several principal investigators on NASA's $700 million Radiation Belt Storm Probes (RBSP) project, joining scientists from five other universities and several space research institutes. His $26 million portion of the project is designed to develop a sort of map of the radiation belts and learn how and why the belts can change shape and intensity when struck by waves of solar radiation. The belts, which trap some of that radiation, are like doughnuts around the Earth; an inner ring is about 4,000 miles out and an outer ring extends from 8,000 to 36,000 miles out.
The mission recently got a lucky break in the solar weather. Although launch dates are planned far in advance, "we're overjoyed to be launching during a solar maximum," Wygant said, referring to the recent surge in solar activity after a long quiet period. "That's the greatest intensity [of radiation disturbances]. That's what we're interested in."
There are two major reasons to study the radiation belts, said Wygant, who describes the project with such enthusiasm that he often runs out of breath at the end of his sentences.
"The first is because it does impact spacecraft, how we live our lives and how we're going to live our lives in the future," he said. "We're going to put up more spacecraft, and these spacecraft are going to have to be more and more capable. They're going to have to be designed for the intense environment they exist in."
And the other?
"I'm a physics professor," he said. "I'm interested in the entire [magnetic and electrical] system. What are the different mechanisms that cause particles to pick up energies or lead to them being lost? I see in the universe a lot of different astrophysical objects -- neutron stars, supernova, the surface of the sun, the magnetosphere of Jupiter -- and all these different objects have some things in common with the Earth. ... They're likely to be different from one place to another. But there are bits and pieces and lessons to be learned that can tell us things about the Earth's magnetosphere."
The data collectors
The heart of the RBSP is a pair of 1,200-pound octagonal boxes, each about a meter high and 1.7 meters across and carrying more radiation shielding than most spacecraft to protect electronic gear. In addition to the hardware designed by Wygant and partners from the University of California, Berkeley and the University of Colorado, they'll carry equipment for studies developed by the University of Iowa, the University of New Hampshire, the New Jersey Institute of Technology and the National Reconnaissance Office. The spacecraft have been built and are being tested at the Johns Hopkins University Applied Physics Laboratory in Maryland.
The two orbiters will ride into space aboard a single Atlas rocket. They will then separate and make nine-hour, elliptical orbits that extend about 24,000 miles from Earth on one side and 360 miles on the other. The boxes will be opposite one another roughly every 90 days, and their shifting orbits over time will describe a sort of flower-petal pattern, providing overlapping measurements of the radiation belts.
The key features of Wygant's project are four baseball-sized spheres at the ends of cables as thin as coat-hanger wire that will extend from four sides of each spacecraft. Separated by nearly a football field's distance, they will measure electrical fields, and Wygant and several graduate assistants will be looking for differences between the spheres as well as differences over the sometimes-vast distance between the two spacecraft. Wygant likened the strategy to having two weather stations in an area instead of one, to detect changes in forces from one place to another.
The orbiters are expected to send useful data for two years -- or four "if it's good, and still interesting. After four years, we run out of rocket fuel," Wygant said.
The RBSP is one of many U of M projects sent into space over the decades. One ongoing operation, called Stereo, has had two spacecraft circling the sun at the same distance as Earth since 2006, providing images of the sun as well as tracking how intense blasts of electrified gas called "coronal mass ejections" travel through the solar system, blowing past Earth and warping its magnetic field. The recent rise in solar activity is also beneficial for Stereo, said Keith Goetz, a U of M physicist who designed the hardware on Stereo and is the project manager for the U of M device on the RBSP.
"Now that things are heating up on the sun," he said, intending the pun, "we're seeing a lot more action and starting to build up a good case of statistics."
Goetz is also involved in a project that in 2018 will send a craft within about 4 million miles of the sun -- extremely close by solar system standards -- to find out why the sun's corona is more than 150 times hotter than its surface. Solar Probe, as it's called, will also try to help researchers determine what causes the solar wind, the constant flow of protons and electrons that flows outward from the sun through space.
Kris Kersten, a Ph.D. student, is working with Wygant and writing a thesis on acceleration waves in the radiation belts. Kersten said he and his wife plan to be at the launch at Cape Canaveral.
"Hopefully, it all goes as planned," he said. "Some of the scientists here have been through failed launches. It's a huge commitment and you definitely want to see it work the way it was planned. Especially with a thesis riding on it."
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