Lisa Grossman, reporter
(Image: JHU/APL, NASA)
Armoured tanks are about to enter dangerous territory: rings of charged particles that surround the Earth. On 23 August NASA will launch the Radiation Belt Storm Probes, a pair of satellites specially designed to collect information about the Van Allen radiation belts, concentric bands of plasma where highly energetic charged particles get trapped by Earth's magnetic field.
Studying the belts in detail could lead to better predictions of space weather, including the effects of storms on the sun that can send blobs of plasma hurtling towards Earth. These storms can spark auroras and - in extreme cases - wreak havoc on telecommunications and power grids.
Shifts in the Van Allen belts seem to be tied to solar activity. The inner belt, which stretches from about 1600 kilometres to 12,900 kilometres above the surface, is fairly stable. But the outer one, normally spanning 19,000 to 40,000 kilometres away, can swell to 100 times its usual size, engulfing communications and research satellites and bathing them in harmful radiation.
In a puzzling twist, the outer belt doesn't always respond the same way to each sun eruption, sometimes growing, shrinking or staying the same.
"The Van Allen belts are perhaps the oldest discovery of the space age," NASA's Madhulika Guhathakurta said today during a press briefing. "But it remains a mystery because this is a very harsh environment and there's not a lot of data."
(Image: NASA/T. Benesch, J. Carns)
Inside the Radiation Belt Storm Probes, delicate electronics will be well-shielded in 9-millimetre-thick aluminum cages called "dog houses", with small apertures to allow some particles to strike only the robust detectors.
"We essentially go there in a suit of armor," says project leader Rick Fitzgerald. The detectors will record the numbers of particles, their energy levels, their composition and their direction in relation to Earth's magnetic field, shedding light on what types of particles become trapped during a solar event.
The spacecraft will also carry magnetic and electric field detectors to measure the local environment. To keep them from picking up the spacecraft's own electric and magnetic fields, the detectors will be held on long, tentacle-like booms, which will unspool once the probes are in orbit.
Both spacecraft will follow elliptical orbits at slightly different speeds, to make sure they sample as much of the radiation belts at as many different times as possible. Getting data in both space and time will be key to understanding the belts' shiftiness, says program scientist Mona Kessel.
"One satellite could not unravel this complex behavior," she says.