Some regions of space are so filled with hazardous radiation that most spacecraft zip through them as quickly as possible, switching off sensitive instruments. But Thursday morning, a rocket carrying twin spacecraft outfitted with a suite of instruments that were assembled by a team led by University of New Hampshire scientists is scheduled to ferry the two probes into the heart of the two doughnut-shaped radiation belts that girdle the earth.
The NASA mission to deploy two Radiation Belt Storm Probes into this harsh environment will explore basic scientific questions about belts of energetic particles that ring many planets. It will also help scientists better understand and predict space weather, which can harm telecommunications satellites, interfere with the global positioning system, and knock out power grids.
"The mission is exploring these extremes of space weather," said Harlan Spence, a University of New Hampshire physics professor and leader of a team in charge of detectors that will be used to measure particles in the radiation belt. "Variations in the space environment lead to dramatic effects and in the case of the radiation belts can have an impact on satellites and astronauts."
The two radiation belts — one inner, one outer — were discovered in 1958. They are made up of energetic particles trapped by the earth's magnetic field and, according to NASA, were first thought to be part of a Soviet nuclear test because the radiation levels detected by spacecraft were so high. Their distance above the earth can vary, but the inner belt starts above the earth's atmosphere about 60 miles above the earth, while the outer belt starts about 12,000 miles above the earth.
For decades, the radiation belts were thought to be predictable areas of space consisting of stable energetic particles. But in the 1990s, it became apparent they were constantly changing. The region responded to sun flares, and the belts could swell and shrink.
"They are extremely dynamic and are changing, both in energy and size, in response to what comes from the sun," said Nicky Fox, the deputy project scientist at Johns Hopkins University Applied Physics Laboratory. "When the sun sneezes, the earth catches a cold."
The probes are known simply as spacecraft A and spacecraft B, but Fox said she thinks of them as "Van" and "Allen," after the scientist James Van Allen, who discovered the radiation belts at the dawn of the space age. The spacecraft will travel through both rings, in orbits that come as close as several hundred miles above the earth and as far as 19,000 miles above the earth, Spence said.
The mission is expected to yield a fuller understanding of the dynamic nature of the radiation belts than past missions because it will gather more detailed data. It will place the satellites outfitted with identical instruments in close, but different orbits, and the information collected will be compared.
Fox compared it to an ant standing atop a cork floating in a bucket full of water. If the cork in the bucket rises, the ant won't be able to tell whether that is caused by a wave rippling through the bucket or someone adding water to the bucket. But if an ant sits on another cork nearby and they can compare observations, the first ant can tell what caused the rise.
Spence heads a team that worked on building detectors that will be able to track particles, measuring their energy and the flux — the number of particles at every location.
Other instruments will measure electric and magnetic fields and waves, giving scientists a detailed portrait of the region's weather, and the way it evolves and changes over time.
"You might have an analogy to a hurricane, features that look like tornadoes, drizzle like you might get in London every day," Spence said. "Society is now reliant on something in excess of 800 satellites. . . . These are operating near to or in the radiation belt. Understanding that region is just incredibly important for a society that has become increasingly reliant on space," for military and commercial reasons.
A clearer understanding of the region would not only probably result in more accurate space weather predictions but could ultimately help engineers design better spacecraft.
It also provides a laboratory near the earth for scientists to make measurements directly, knowing that many of the same processes occurring above the earth are also probably taking place in other corners of our solar system and beyond.
"It's kind of cool; it's like having laboratory in your own backyard," Fox said. "You can live and work and do really good studies in Earth's local laboratory, and we can apply that physics to our planets in our system."