Two space probes launched toward the Van Allen radiation belts today. They’ll help scientists observe and predict the behavior of ultrafast, and potentially harmful, charged particles.After minor delays scrubbed three earlier launch attempts of the Radiation Belt Space Probes (RBSP), the fourth try was the charm. At 4:05 am (EDT), an Atlas V rocket shot two identical probes toward a region of space most satellites dread to enter. The Van Allen radiation belts are filled with trillions of charged particles, some of them whipping around the Earth at nearly the speed of light. Even something as small as an electron can harm satellites at those kinds of speeds. Yet the RBSP won’t just survive their journey through the land of the “killer electrons” — they will thrive.
“Our ‘armor-plated’ spacecraft will do a far better job [than previous probes] of modeling the environment where satellites live and work,” says Nicky Fox (Johns Hopkins Applied Physics Laboratory), the mission’s deputy project scientist.
That’s because the RBSP has advantages that were missing from previous missions to the Van Allen belts. First, the two identical spacecraft will whizz around the Earth in highly elliptical orbits so they can sample the full extent of the radiation belts. That way they’ll be able to track changes in the belts through space and time.
Both probes are carrying an array of instruments to study the structure and dynamics of the radiation belts. “We’ve developed instruments that are nominally more capable than anything that’s ever flown before,” says Harlan Spence (University of New Hampshire), one of RBSP’s principal investigators.
A NASA animation gives a good look at the octagonal probes as they orbit the Earth. Each spacecraft weighs in at almost 1,500 pounds (680 kg) and carries five instrument suites:
The instruments will tease apart the various mechanisms that engage in a perpetual tug-of-war for the attention of energetic particles. Different types of electromagnetic waves can speed particles up, or eject them from the belts altogether. Sometimes the same wave does both in different circumstances.
Scientists can measure the electromagnetic waves to learn about and predict particle behavior. Some of these waves are even in the range of human hearing, such as the so-called “whistler mode waves,” radio waves that sound much like their name. Listen to a recording of whistler waves. (And find more recordings here.)
Solar activity complicates the electric and magnetic fields around the Earth, and that makes it harder to predict what the particles will do.
“The Earth responds to what’s coming from the Sun,” Fox explains. “So we say that if the Sun sneezes, Earth catches a cold.”
A solar sneeze spews plasma and radiation toward us, where Earth’s magnetic field stands ready to trap high-energy particles. During a geomagnetic storm, the belts often swell in size. The inner belt can come so close to Earth that its charged particles could affect astronauts aboard the International Space Station. And the outer belt can swell outward to cross orbits with geosynchronous satellites.
An animation of the twin probes (red and green dots) orbiting through the van Allen radiation belts shows the influence of two solar storms, which disturb the Earth's magnetic field (white lines) and swell the size of the belts:
Understanding the behavior of the radiation belts won’t be easy. Until now, scientists have had a hard time predicting their response to solar storms. “It’s like baking a cake,” explains Fox. “You know the ingredients, but you don’t know their proportion in each given storm.”
But Spence anticipates that, with the help of RBSP measurements, the predictive models will get much better — something for which astronauts, satellite operators, and GPS-dependent navigators can all be grateful.