DSCOVR and the impacts of space weather
NASA, NOAA and the US Air Force recently launched DSCOVR a satellite with the mission of monitoring solar activity. To find out a bit more about space weather we spoke to Richard Dyer, EUMETSAT Metop spacecraft operations engineer, and Ed Trollope, spacecraft operations engineer from Telespazio Vega working at EUMETSAT.
Q) What’s the most common type of problem space weather can cause for our satellites?
There are a variety of different types of problem our satellites can encounter, which are caused by space weather.
The most common problem is what we call a Single Event Upset. The computer (or phone) you’re reading this on has stored the webpage in memory as a series of 1’s and 0’s, called ‘bits’.
If one of the charged particles we see in space hits our computer’s memory, one of these values can change so instead of reading “hello” you read “fello”. We call this a ‘bit flip’. In fact, if you find any spelling mistakes in any of our web pages, they were probably caused by space weather ;).
Computers onboard our satellites can spot single errors and correct them, but when too many bits become corrupted and “hello” reads “fwdgl”, the computer simply can’t work anymore and will crash. In this case, we have to re-boot them, just as you would a smartphone or a PC.
Single Event Upsets can be caused by high energy particles from the Sun, or by Galactic Cosmic Rays which are even more energetic. The biggest risk for Metop is when it flies through the inner Van Allen radiation belts, over what is called the South Atlantic Anomaly, or through the polar radiation belts.
Q) What are Galactic Cosmic Rays?
Galactic Cosmic Rays are high energy particles coming from somewhere else in the galaxy outside of our solar system, but the risk they pose to our satellites is still dependent on what our Sun is doing at the time.
Just as the Earth’s magnetic field helps to shield us from the Sun’s radiation, the Sun’s magnetic field helps to protect us from the rest of the galaxy!
But the Sun’s magnetic field isn’t always the same, and it gets stronger and weaker in an 11-year cycle. So when the Sun’s field is weaker, our satellites are more at risk of being hit by a Galactic Cosmic Ray.
Q) What are the other problems space weather can cause?
A more serious problem for geostationary and Low Earth Orbit satellites are Single Event Transients – these are much rarer than Single Event Upsets and impact small switches called transistors in power supplies, or on the computer’s processor chip itself.
As with Single Event Upsets, only very severe Solar Storms or particularly energetic Galactic Cosmic Rays are likely to cause Single Event Transients.
In extreme cases, the switch can become permanently set in one position, and this is called a Latch-up. This happened to a transmitter system on Metop-A which sends the real time data down to ground stations all over Earth.
We now use the redundant transmitter, but only have it switched on when we are below the Inner Van-Allen Belts which protect us from Solar Storms and Galactic Cosmic Rays. On Metops B & C, this component has been upgraded so we can leave the transmitter on all the time.
Something that tends to be more of a problem for Geostationary satellites is sudden discharging of electric charge.
As Meteosat orbits around the outer radiation belts which are full of electrons and protons, it can travel into an area where the relative numbers of protons and electrons changes suddenly causing a discharge event on our satellite, like a small lightning bolt.
This can send spurious signals through the satellites, cause bit flips in computers or even burn through circuitry. Again, Solar Storms just increase the risk of something happening.
Long term exposure to radiation in space is known to degrade the solar panels which are used to power our satellites.
The power output from the arrays falls gradually over time and they are built bigger than needed at the beginning of life so that they can provide enough energy all the way through the satellite’s lifetime.
Big solar storms can accelerate this process a lot – we saw a 3% drop in the power produced by the solar arrays of all our Geostationary satellites on 28th October 2003.
Finally, In Low Earth Orbit, satellites can experience more atmospheric drag during Solar Storms due to the expansion of a part of the atmosphere called the ionosphere.
This means we may have to perform more manoeuvres to boost the orbit, but this doesn’t need to be done instantly and doesn’t use much more fuel so it isn’t a big problem.
However, a potentially more serious problem is that Metop flies in an area with a lot of space debris which we have to dodge occasionally. This requires incredibly precise measurements of the orbits of both the satellites and the debris, but the increased drag makes the exact behaviour of the orbits unpredictable.
If you wish to know more about collision avoidance, check out our web page on Satellite Manoeuvres.
Q) How do you protect the satellites against the problems space weather can cause?
Normally all the components on board are “radiation hardened” to help prevent such problems, but this can be difficult and there are limits to what is possible.
If we know there is an increased risk then switching off sensitive systems can protect them, which is why we switch off the Metop-A redundant transmitter each time the satellite flies over the South Atlantic Anomaly.
Of course, there are some systems you can’t switch off without risking the safety of the satellite, and switching something off may lose or impact on valuable data for our users – so switching anything off isn’t something we do lightly.
Q) So, Solar Storms don’t usually impact our satellites?
Generally, they don’t – however, several other satellite operators have suffered problems on Geostationary Spacecraft due to discharge events during Solar Storms.
Also, we have never experienced a big Solar Storm in the entire history of the space age, so we mustn’t get complacent.
For example in 1859, the so called “Carrington Event” was about 30 times bigger than any Solar Storm Metop has experienced, and about 6 times bigger than the one in 2003 which caused the solar arrays on our Meteosat satellites to lose power.
Although solar storms produce lots of high energy particles that can cause SEUs, both our Polar and Geostationary Satellites are designed to cope with much higher energy Galactic Cosmic Rays.
Metop has to routinely fly through the lower Van Allen Radiation belt in an area called the South Atlantic Anomaly, and this is much harsher than all but the worst Solar Storms.
So, Solar Storms increase the risk of something happening, but are usually benign.
Q) Will DSCOVR mean better warnings of bad conditions?
DSCOVR is designed to monitor the solar wind, and to provide a 15-60 minute lead time for geomagnetic storm warnings.
These storms cause the upper atmosphere to expand, and increases the risk of problems related to charging for our geostationary satellites. DSCOVR will also help us to better understand the Sun and its processes in general, which are not yet fully understood.
If you have any questions you would like to ask to our experts please send an email to firstname.lastname@example.org
Featured image credit: NOAA