National Aeronautics and Space Administration

Van Allen Probes Exploring the Extremes of Space Weather

NASA’s Van Allen Probes, launched in 2012, will explore how space weather creates and affects the hazardous radiation belts above our planet, and how the intense energy from solar storms interacts with Earth’s magnetic field. This critical science mission will be carried out by a pair of identical spacecraft that will orbit our planet, gathering data to help scientists understand the physics processes in the radiation belts and their role in space weather. The radiation belts respond to solar storms in unexpected ways, and the changes in the belts can endanger human spaceflight missions and disable satellites. What Is Space Weather? Why Study the Radiation Belts? Just like on Earth, a type of “weather” exists in space. Earth’s radiation belts represent a natural laboratory for The sun emits constantly varying streams of ionized studying how regions of particle radiation are created, gases called the solar wind, and periodically, the sun and how they vary over time. The belts also represent releases much larger bursts of billions of tons of matter an important yet hazardous environment that we must called coronal mass ejections (CMEs). These variations understand better, to ensure safer human spaceflight cause large magnetic storms in the space environment and to safeguard increasingly sophisticated satellites around Earth, which can be hazardous to humans in and technology systems. space, disable satellites, cause power grid failures and disrupt global positioning system (GPS) operations. The Van Allen Probes will reveal how the radiation belts are created, what causes them to change, and how What Are the Radiation Belts? particle acceleration and other processes occur there In 1958, the team led by University of Iowa professor and likely throughout the universe. Observations will James A. Van Allen, using observations from Explorer also enable scientists to develop behavioral computer 1 (the first American satellite), made the surprising models for the belts, which will be used to design better discovery that intense radiation – highly-energized radiation-resistant spacecraft, as well as by forecasters charged particles – is trapped by our planet’s magnetic to predict space weather events. field. Later space missions revealed that the radiation occurs in two swaths around Earth, now called the Van The Van Allen Probes are part of NASA’s Living With Allen Radiation Belts. The inner, relatively stable belt, a Star (LWS) program, designed to improve the composed mainly of protons, extends from the top of science necessary to understand those aspects of the the atmosphere out to an altitude of some 4,000 miles. connected sun-Earth system that affect life and society. The outer belt, composed mainly of high-energy, fast- moving electrons, extends from about 8,000 miles to more than 26,000 miles above Earth’s surface.

We now know that intense particle radiation occurs around other planets and in other regions of our solar system, and throughout the universe. But how this radiation is created and behaves remains a mystery. Earth’s radiation belts can respond in unexpected ways, often quite suddenly and dramatically swelling and shrinking in response to dynamic changes in the sun.

Artist’s rendering showing a cutaway of Earth’s radiation belts together with two (not to scale) spacecraft representing the Van Allen Probes. www.nasa.gov Dual Spacecraft for an Extreme Environment Managing Success The Van Allen Probes are two identical spacecraft The Van Allen Probes will make critical contribu- studying the radiation belts, making it the first mis- tions to the research efforts of NASA’s Heliophysics sion to measure simultaneous belt events with identi- Division, which is within the Science Mission cal comprehensive instrumentation from different Directorate. This division manages flight programs locations. This method of study will provide important that carry out the exploration of the sun, its effects new insights into the physical behavior of the belts on the planets within the solar system, and space during geomagnetic storms. environmental conditions and their evolution. Specifically, it seeks to understand the transfer of Gathering this data is no easy task. Most space- energy from the sun to Earth, and the interaction craft in Earth orbit operate at least partly within the of solar plasma and radiation with Earth, the other radiation belts, and during periods of intense space planets and the galaxy. weather, sensitive electronics on board the space- craft may be hit by a charged particle, which can The Johns Hopkins University Applied Physics overwhelm sensors and degrade electronic devices. Laboratory (APL), in Laurel, Md., built and op- When conditions get especially active in the radiation erates the Van Allen Probes for NASA’s Living belts, some satellites switch to a “safe mode” to pro- With a Star program, which is managed by tect their systems. Not so for the Van Allen Probes; NASA Goddard Space Flight Center (GSFC), in these special probes and their instruments are Greenbelt, Md. “hardened” to work even in the most difficult condi- tions, and are built specifically to fly through the heart Key partners for the Van Allen Probes’ instruments of these storms. include Aerospace Corporation, APL, Fundamental Technologies, Laboratory for Atmospheric The Instruments and Space Physics/University of Colorado, For the Van Allen Probes to observe changes in the Los Alamos National Laboratory, National belts through both space and time, each probe will Reconnaissance Office, New Jersey Institute carry identical sets of five instrument suites: of Technology, Southwest Research Institute, University of California at Berkeley, University of Energetic Particle, Composition, and Thermal Iowa, University of Minnesota, University of New Plasma Suite (ECT): Hampshire and GSFC. NASA launched the space- Dr. Harlan Spence – The University of New craft in 2012 for a prime mission of two years. Hampshire

Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS):

Dr. Craig Kletzing – The University of Iowa NASA/ESA

Electric Field and Waves Suite (EFW): Dr. John Wygant – The University of Minnesota

Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE): Dr. Louis Lanzerotti – The New Jersey Institute of Technology

Proton Spectrometer Belt Research (PSBR) Relativistic Proton Spectrometer (RPS): Dr. David Byers – National Reconnaissance Office Dr. Joseph Mazur – Aerospace Corporation This SOHO image shows a coronal mass ejection leaving the Sun, with an artist’s rendition of the blast of material interacting with Earth’s magnetosphere. Van Allen Probes on the Web http://www.nasa.gov/vanallenprobes http://vanallenprobes.jhuapl.edu 11/2012