Van Allen Probes

Our Mission: Search for Greater Understanding Twin spacecraft, designed to withstand an incredibly harsh environment, are following nearly identical paths through the radiation belts, solving mysteries about a critical region of near-Earth space.

What Are The Radiation Belts? The radiation belts are two donut-shaped regions surrounding our planet, where fast moving, electrically charged particles are trapped by Earth’s magnetic field. We've known about the radiation belts for a long time, in fact they were one of the first space-age discoveries. But until recently we thought they didn't change very much. Now we know how much they change, and just how critical those changes are. They are known as the Van Allen belts, named for the man who discovered them in 1958, Dr. James Van Allen.

When the Sun Sneezes the Earth Catches a Cold Earth and the space around it are affected by the activity of the Sun. Events on the Sun, such as solar flares and coronal mass ejections, can cause drastic changes around Earth called geomagnetic storms. They also cause changes to the size, content and energy of the radiation belts. Just like weather on earth is driven by the Sun, our space environment also experiences storms, (a little different than the storms we are familiar with), but these storms can affect life here on the ground. The intensified radiation is dangerous to our satellite technology within the radiation belts and can even wipe out power grids if it gets intense enough.

Strange Behaviors of the Radiation Belts Entirely new radiation belts sometimes appear. Slower moving particles can suddenly accelerate to near the speed of light. Reds and Oranges indicate increased particle intensity. Blues and Greens indicate decreased particle intensity. Images courtesy of G. Reeves, Los Alamos National Laboratory Following a solar event, sometimes the energy and number of particles inside the radiation belts increases, sometimes decreases, and other times stays the same.

Why Should We Care? Astronauts and the satellites that we depend upon for communication, navigation, and our modern way of life operate in the Van Allen radiation belts. Changes in the belts can pose a serious threat to the wellbeing of both people and technology.

Protecting People and Technology When high energy particles collide with human tissue they can damage DNA which may lead to cancer-causing mutations within cells. When high-energy particles – those moving with enough energy to knock electrons out of atoms – collide with human tissue, they alter the chemical bonds between the molecules that make up the tissue’s cells. Sometimes the damage is too great for a cell to repair and it no longer functions properly. Damage to DNA within cells may even lead to cancer-causing mutations. and Disrupted radio frequency transmissions caused by geomagnetic storms could mean no GPS, radio, or satellite TV. Dmitry Lovetsky / AP

More Study is Needed We know that changes in the belts are linked to the geomagnetic storms caused by solar activity, but we don’t know enough to be able to accurately predict the behavior of the radiation belts during these space weather events.

Harbor from the Storm When severe weather is predicted here on Earth we are able to take precautions to protect our homes and lives. Harbor from the storm In the same way, prediction of severe space weather helps astronauts take precautions. Our satellites can be put in a “safe mode” in order to protect them before the “storm” hits.

Designing for an Extreme Environment Van Allen Probes don’t switch into “safe mode” when the going gets rough like satellites often need to do. Talk about aluminum coating- glass shielding on solar panels. copyright © ONERA 1996-2006 The probes were designed to operate in the harshest of environments, to monitor the conditions that could destroy other spacecraft.

Each probe will carry an identical set of instruments. RBSPICE RPS EC ECT-MagEIS EFW EMFISIS Some of these will measure number and energy of particles, others will measure electric and magnetic waves and fields ECT-REPT ECT-HOPE

Why are There Two Identical Spacecraft? An analogy: Imagine you are on a raft in the ocean. You are alone. You feel the raft rising and falling with the motion of the ocean. Is the entire ocean rising and falling? Is it just a wave passing by? Without having something else to compare your motion to, it would be difficult to know for sure.

Greater Understanding With Comparison: Measuring Over Space and Time Now imagine there is another raft a short distance away. That raft is rising as yours is falling, just as the ducks are in this picture. Would this additional information be helpful in determining why your raft was moving and help you more clearly understand your surroundings? Why?

Measurements over Space and Time Together, the Van Allen Probes will measure over space and time: the speed, number, and type of particles; the strength and direction of electric and magnetic fields; the properties and behavior of waves of plasma.

Unsolved Mysteries: Part One What We Know: Particles inside the radiation belts are sometimes accelerated to nearly the speed of light. This is called "relativistic." The Mystery: How does this happen? What is speeding them up? Where do these high energy electrons and ions come from?

Unsolved Mysteries: Part Two What We Know : The particles normally travel in certain ways, following paths associated with Earth's magnetic field lines. Sometimes, they don't follow their normal path, and they may even leave the radiation belts. The Mystery: How are the particles lost? What is it that knocks them out of their normal paths and sends them careening into the atmosphere, and out of the belts?

Unsolved Mysteries: Part Three What We Know: There is a system of electric currents flowing through the same region as the belts called the ring current. The Mystery: Do changes in the ring current affect the behavior of the radiation belt particles? If so, how?

The Result: Practical Uses New knowledge will bring new innovation and protection It will enable engineers to design radiation-hardened spacecraft better suited for this severe environment. It will help forecasters to more easily predict the response of the radiation belts to geomagnetic storms so alerts of potential hazards can be sent out to technology operators and astronauts. Now we guess at the protection a spacecraft needs, and usually add 2-3 times more protection. Sometimes it enough, and other times its not and we lose a satellite. With more knowledge, we would know how to get it just right every time. The risk of losing a craft would be decreased AND we would save money by not possibly over protecting the craft and therefore adding extra unnecessary weight

This Mission is Important to All of Us Understanding the mysteries of the radiation belts is key to our modern way of life. Protecting our current technologies and the health of the people who work with them Exploring a poorly understood region of near-Earth space Influencing future technologies and innovations

Van Allen Probes http://vanallenprobes.jhuapl.edu/