# What would happen if a satellite took a direct hit from a coronal mass ejection (CME)?

I was wondering what would happen if the average satellite were hit by an average CME. According to wikipedia the average velocity of a CME is 20 to 3,200 km/s. In addition to this it's super-heated, electrically-charged and has various other destructive properties.

My question is, what would be the death sentence for a satellite getting directly hit?

Impact Force? Heat? Radiation? Magnetic interference? All of the above and more?

I know I state "average" satellite, we can assume that "average" means basic shielding from solar radiation as is "standard" on inter-planetary satellites (not an LEO satellite, assume Voyager, not that I know whether or not this shielding would make a difference). Where an average CME could be described by any CME that has occurred where significant enough data was recorded to make assumptions.

In addition to this, and to extend the question slightly, does the technology exist today to completely shield against coronal mass ejections at 20km/s? 100km/s? 3200km/s?

For instances, would The Parker Solar Probe be able to withstand a direct hit from a CME provided it was pointed in the correct direction?

We can look at what happened when this actually occurred.

The geomagnetic storm of March 1989 was caused by a Coronal Mass Ejection.

Here are just a few of the many effects on satellites.

• One satellite lost 3 miles in altitude (not 30 km! don't believe that legend).
• Another began uncontrolled tumbling.
• GOES 7 lost communications and imagery for a time.
• Japanese satellite CS-3B lost half its redundant command circuitry.
• Commercial GEO satellites had attitude control problems.

Some users couldn't acccess the document here so I added screenshots. (Starts on internal page number 1487)

• Commercial GEO satellites had attitude control problems. -- Do you mean altitude? – tonysdg Aug 2 '18 at 17:12
• No, I mean attitude. "Spacecraft attitude is briefly the angular orientation of a spacecraft body vector with respect to an external reference frame." spacealliance.ro/articles/view.aspx?id=200903060613 – Organic Marble Aug 2 '18 at 17:17
• @tonysdg No? en.wikipedia.org/wiki/Attitude_control .... – yeah Aug 2 '18 at 17:19
• Oh, cool! I don't know much about satellites -- was just browsing HNQs and thought it might be a typo. Thanks for the lesson! – tonysdg Aug 2 '18 at 17:20
• Welcome to space stack exchange @tonysdg! – Organic Marble Aug 2 '18 at 17:22

I spent a couple of years working in the Astrophysics and Space Physics Section of JPL. Working with the Space Physics folks taught me a lot about the solar wind and other space weather phenomena. Later on, working with Hank Garrett of JPL's Space Environments group taught me more, especially concerning effects on spacecraft.

I'll start out with a description of what is a CME.

A big, fast coronal mass ejection (CME) (also here) is not all that different from the regular solar wind, except that: it is more localized; it moves a lot faster away from the sun; and the entrained magnetic field can be very different, especially in direction, from that of the solar wind around the CME. A CME is a rapidly-moving blob of magnetoplasma: it is largely ionized hydrogen (just like the solar wind), so protons and electrons, with a sprinkling of heavier atoms, and it carries with it magnetic field that was entrained in the lower solar corona. Almost all the atoms are at least singly ionized; some of the heavier ones are multiply ionized.

Although the mechanism that generates the CME is largely irrelevant to this question I'll mention it. It has to do with the behavior of magnetic fields in the lower corona of the sun. The field lines get stretched, twisted, and "kinked", and just like stretching and kinking a rubber band, this stores energy in the field. Occasionally those fields snap to a lower-energy configuration (a process called magnetic reconnection) and the energy suddenly released powers the CME explosion.

NOTE: there is no net electric charge to a CME. It is electrically neutral. But it is a plasma, so all those charge carriers can move around, at least a little.

But only a little, at least for movements perpendicular to the mag field lines. The matter (ions and electrons) and mag field in the solar wind and in a CME are tied together, so large-scale relative motion of one with respect to the other is inhibited. If an ion or electron tries to move with respect to the local mag field, the Lorenz force, F = q (V X B), where q is the charge on the particle, V is the particle's velocity, B is the mag field strength and direction, and X is the vector cross product, makes the particle spiral around the local mag field lines. It has a tough time crossing a lot of those field lines, because it keeps getting turned back by that Lorentz force. Conversely, if the mag field tries to change (which moves the field lines) this sets up a relative V with respect to the charged particles, and they begin their gyrating. I know this sounds like magic, but the physics of the situation has those gyrating charged particles generate their own mag fields (current loops generate mag fields, per the Biot-Savart law) that resist the change in the magnetic field. So the particles and mag field are "joined at the hip"!

Things get interesting at shock waves. Fast CMEs move at 2,000-3,200 km/s, while the fastest normal solar wind is about 1,000 km/s. This difference in speed is far faster than the "magnetosonic" velocity, the speed at which waves travel in the mag-field-plus-ions soup. So a shock wave forms at the front of such a CME. Shock waves compress things. In the case of a CME shock front, it's compressing the magnetoplasma, so the particle density increases and the mag field strength increases, rapidly. In the solar wind in front of the shock the mag field can be in one direction, and just behind the shock it can be in a completely different direction. Turbulence behind the shock front lends chaos to this transition and compression, so the mag field can be all over the place, both in magnitude and direction.

I mentioned the particle density increasing. But it's still what we would consider a hard vacuum. The "blast wave", the sudden impulse of momentum due to impact of the particles in the wave, is insignificant in a CME at 1 AU kinds of distances from the sun. There's just not enough mass involved. But a proton going 3,000 km/s has a kinetic energy of ~4.7 X $10^{4}$ eV (electron volts), which qualifies as ionizing radiation.

And changing mag fields generate electric fields, per Maxwell's equations. Rapidly changing mag fields generate strong electric fields. You see this in some of the earthly effects of CMEs: blown power transformers, power grids brought down, etc. There are fascinating descriptions of the 1859 Carrington Event, the largest CME impact on record, setting fires in telegraph stations and electrically shocking (some severely) the operators.

Now, to the meat of the matter: effects on spacecraft.

These kinds of electromagnetic things can happen on spacecraft. Spacecraft are just full of conductors, in the electronics, in the power systems, even in the spacecraft structure. In the face of rapidly changing magnetic fields (remember the telegraph lines of 1859!), long conductors, especially ones that form loops (they don't have to be circular loops) can generate voltages larger than the spacecraft's electronics are designed for, and can cause latch-ups and other damage. Even smaller voltages, in data lines, can corrupt data being transmitted between spacecraft systems, causing various kinds of problems from corrupted commands or table entries (such as in star trackers) to operating system crashes.

The multi-kV radiation burst at the shock front can cause any of the problems associated with radiation at such energies, such as single-event upsets (SEUs) and bit-flips.

Most modern spacecraft are designed to handle these kinds of events, and those designs are generally successful. I'm not sure if their margins are large enough to handle another Carrington Event.

But there are some effects these designs can't handle, and those involve the wildly varying magnetic field, and heating of Earth's upper atmosphere. Many spacecraft operating within the lower parts of Earth's magnetosphere use magnetic torque rods, also called magnetorquers, for attitude control, since they require no propellant or moving parts, just electric power. They depend on Earth's magnetic field behaving "normally", i.e. predictably. When a CME hits Earth's magnetopause the magnetic chaos propagates into the magnetosphere and the usually-predictable mag field becomes quite unpredictable. Satellites with no secondary attitude control systems to back up magnetorquers will lose attitude control.

A fair fraction of the energy a CME delivers to Earth winds up in Earth's upper atmosphere, heating it. This makes the gas expand, so it moves outward, occupying more volume. This makes the average density go down. But spacecraft don't move outward with the atmosphere, they stay at their orbit altitude—for a while, anyway. At a given, fixed altitude, the heating causes the air density to increase, causing more drag and thus more energy loss and altitude loss. Dropping ~3 km in a day or so of a magnetic storm's duration is a lot.

I hope this is useful!

• I added a few links, hope you don't mind. Speaking of nearly neutral plasmas, do you have any thoughts on Are there measurements of, or experimental limits to the residual charge of the Sun? – uhoh Aug 2 '18 at 3:14
• Wow! Tons to look into, thanks again as always. I'll have to look into some of these terms and get back later today if I have follow ups, and thanks @uhoh for the additional links, always helpful. – Magic Octopus Urn Aug 2 '18 at 12:50
• Not going to lie, I got out of my depth very quickly when I started reading more on photons. en.wikipedia.org/wiki/Lorentz_transformation is a doozy of a mathematical mind-dump; how do you guys do this stuff haha! I'll keep reading though, this is cooler than anything I've found on Earth recently :). – Magic Octopus Urn Aug 2 '18 at 14:59
• Do you have more of an explanation why atmospheric heating causes the local density to increase? I am puzzled: do I just have the mass balance wrong in my head? Should it be a separate question here or at earthscience.SE ? – Qsigma Aug 2 '18 at 17:02
• @MagicOctopusUrn Tom's Q&A – Qsigma Aug 3 '18 at 8:09

Inside of the Earth's magnetosphere, which includes all spacecraft in orbit (pedantically, all satellites), a Coronal Mass Ejection (CME) can not directly hit a spacecraft. The charged particles are captured by Earth's magnetic field.

However, solar flares and CMEs do still have measurable impacts on our spacecrafts, which is why in the US the National Oceanographic and Atmospheric Association (NOAA) (among other nations' organizations) keep track of Space Weather.

Space weather is reported using 3 metrics: R, S, and G -- or Radio Blackout Effects, Solar Radiation Storms, and Geomagnetic Storms.

Radio blackouts are caused by solar flares directly, and affect satellites (and many Earth-based radio systems) nearly as soon as we observe the flares in X-Ray light. Since all satellites typically talk to ground stations, and sometimes rarely talk to each other, each satellite has 3 general tactics to deal with this: Increase broadcast power (usually not worth it), store-and-retry in case the ground station doesn't confirm receipt of some packets, or just consider the information as lost and forget it even tried sending anything in the first place (most economical choice).

Solar Radiation Storms might shorten the life of solar panels on a spacecraft, but solar panels are typically designed to outlast the expected lifetime of a spacecraft anyways. The most important effect, though, is that it shortens the lives of satellites in Low Earth Orbit (LEO). As the Earth's atmosphere heats up, it expands, slowing spacecraft very near the planet, reducing their orbits, causing them to use up their maneuvering engines more quickly.

But, a larger factor for heating up the atmosphere comes from the CMEs and Coronal Holes, which are areas where the solar wind coming from the photosphere is higher than normal, ejecting high energy plasma over a long period of time, compared to CMEs that eject high energy plasma in rapid bursts. When the plasma interacts with Earth's magnetic field, they are either deflected or entrapped (depending on the orientation of the polarity of the particles), disturbing the field's normal equilibrium, creating a Geomagnetic storm, which create auroras, and induce currents on a global scale. The Geomagnetic Storm of 1989 is the first such event that comes to people's minds. The Carrington Event (solar storm of 1859) is the second event that comes to mind, being far greater than anything recorded, or even imaginable with modern technology.

Fortunately, few, if any, satellites were lost from that event. <./sarcasm>

Outside of Earth orbit -- and outside of the realm of satellites entirely, our space probes are designed to withstand the might and destructive power of our closest fusion reactor's fickle temper.

Here is SOHO's view of a direct hit from a X-17.2 class flare in October, 2003, one of the largest recorded, from the warm and toasty location of L1, about 1,500,000km closer to the sun than we are. During this, two of SOHO's instruments had to temporarily shut down, as described in the linked article, but were able to start back up relatively quickly. Despite taking such beatings, SOHO is on year 22 of its 3 year mission.

Such large X-class flares do also manage to directly impact Earth-orbiting satellites, despite what I generalized in the first paragraph. During the October 2003 flares, 46 satellites had failures, a large portion of the 70 total satellites with failures in 2003, as stated in the Wikipedia article on Space Weather.