GPS as a Space Weather Monitor

GPS satellite orbits around the Earth.  Each satellite has a radiation sensor that can be used to learn more about the radiation belts.
GPS satellite orbits around the Earth. Each satellite has a radiation sensor that can be used to learn more about the radiation belts.

Big space weather news this week: measurements of the “radiation belts” made by the Global Positioning System satellites are now available to space weather researchers.  This is a huge deal for several reasons, but let’s start by unpacking that sentence:

Wait, what?

We’re talking about GPS satellites- the same satellites that your phone communicates with when you’re using Google Maps.  There are 31 of them up right now, and as they break down, they are replaced.  There have been many of these satellites up for a long time- starting in 1978, the United States has been launching GPS satellites into orbit.

Each one has a particle radiation sensor aboard in order to better understand the conditions around the satellite.  By particle radiation, we mean protons and electrons moving very close to the speed of light.  These can damage electronics and degrade satellite materials.  Compared to the types of sensors that are on scientific satellites, these are somewhat basic- they only get a rough idea of the particle energy and do not measure the direction of the particles, etc.  But for satellite operations, these details aren’t important.

An illustration of the radiation belts around Earth.  The satellites depicted are the Van Allen Probes, launched in 2012 to study the belts (from NASA).
An illustration of the radiation belts around Earth. The satellites depicted are the Van Allen Probes, launched in 2012 to study the belts (from NASA).

The GPS satellites are flying through the radiation belts, which are donut-shaped rings of high energy particles.  The radiation belts are a big problem for satellites and astronauts.  They’re also very dynamic: they change in size and shape as well as intensity.  A big challenge for space scientists is understanding how the radiation belts change and how the changes are tied to solar activity.  Understanding this will allow us to accurately predict where and when space radiation will be most dangerous.

Why is this a big deal?

To study the radiation belts, scientists launch satellite missions that fly through them with specialized instruments.  These missions have been very successful and give us very detailed information, but only at the satellite’s location.  Recently, the Van Allen Probes mission put up two satellites in order to better understand how the belts change over a large spatial scale.  

The GPS data is extremely useful because, even though the instruments are quite coarse, we’re now getting data at over 30 locations simultaneously!  This means that we can now create very large spatial maps of the radiation belts.  Combined with the dedicated science missions, researchers can now combine the detailed local measurements with the global GPS radiation maps.  This is a powerful combination.

What’s new?

Though GPS satellites have been around for a long time, this data has not been available to anyone besides GPS engineers and operators.  There are good reasons for this: the data could contain sensitive information and we didn’t know how reliable it would be.  Scientists at Los Alamos National Laboratory have been working to calibrate the data against other, independent measurements.  This shows that even though the GPS radiation instruments are more basic than scientific instruments, we can still trust the numbers.  They’ve also been working to put the data into a useable form and ensure there is no sensitive information included (raw satellite data is a mess of information, including satellite location info, system diagnostics, and communication logs).  They’ve finally reached the point where the data is ready to be released publicly, unleashing a powerful tool to researchers around the world.

For a deeper read, you can check out the article in Space Weather by Morley et al., 2017.