Space Environment Basics

Introduction

Space can be a pretty boring place to fly around in for months or even years at a time. Then, suddenly, you’re hit with a piece of dust that blasts a hole in your solar panels. Or a helium atom from hundreds of light-years away zips into a wire and shorts everything. Or a solar storm hits the Earth’s atmosphere you’re flying through, energizing and expanding it, creating more drag than you expected which makes you burn more propellant. 

The types of chaos you find in space can be lumped into a few categories outlined below. However, there are dozens (maybe hundreds) of different ways these things can ruin all your hard work.

Vacuum Effects

Space is a pretty empty place, especially when you’re not near a chunk of material such as a planet, moon, or star. Outside of those places, you could travel for hundreds of thousands of years and not hit anything.

There are a few major problems all the emptiness creates for spacecraft:

Overheating

Thermal conduction and convection are great ways to move heat around and keep things at a constant temperature. Since there are marginal densities of fluid or gas in space, we’re left with just radiation to dump all the heat created by electronics, thrusters, the sun, and so on. This means we need radiators, heat pipes, special paints, and more to stay comfortable.

Outgassing

On Earth, we can smell things like air fresheners and plastic bags because they release their molecules easily. It’s even easier for materials to release molecules in space. Materials venting their molecules in space are a big problem because they land on other surfaces like optics, solar panels, and radiators. Even a thin layer of the wrong kind of molecules can make a big difference in performance.

No Shielding

Atmospheres around bodies like Earth and Venus block radiation and destroy meteoroids. Some satellites try to fly as close to Earth as possible, for instance, to minimize the chance of damage from everything zipping around above them.

Atmospheric Effects

The thin atmosphere above Earth helps spacecraft by blocking radiation and burning up bits of trash, but it also hurts spacecraft. (You win some, you lose some).

Atomic Oxygen

Oxygen likes to pair with itself to create O2, but this molecule can be split up by the sun and other radiation sources to create single atoms of oxygen.The single atoms react with just about anything that has free electrons available. When it finds them, the parent material “oxidizes”, which can dramatically change its appearance, strength, ductility, and more. For example, rust is oxidized iron. 

In the lower atmosphere, this atomic oxygen quickly recombines with something, but in the thin upper atmosphere, they can fly around for longer periods before hitting something (like your spacecraft). Vulnerable spacecraft materials that can oxidize include paints, leftover flux inside welds, lubricants, insulation, optic coatings, wire coatings, and so much more. A lot of hardware and materials you buy for space nowadays take this into account, but be sure to check. Another trick is to put thin oxide coatings (like silicon oxide) on parts like solar panels since you can’t oxidize something that’s already oxidized!

Drag

Any spacecraft below about 2,000 km (depending on things like the solar cycle) will run into enough molecules of the atmosphere to create drag. The slowdown lowers the orbit of the spacecraft until it eventually crashes and burns. The International Space Station, for instance, has to be boosted to higher speeds a few times a year so it doesn’t crash. Another effect, for noncircular orbits, is to turn your orbit into a circle anyway since you slow down the most at the perigee nearest the atmosphere, which drops your apogee point.

Sometimes, you want this drag. It prevents low earth orbit from getting too jammed up with dead systems, for instance. There’s also a “sweet spot” around 400 km that is dense enough to clear out a lot of space junk and block some radiation, but low density enough that your thrusters can add the speed you lose back. NASA and other space agencies also like to use drag in deep-space missions to planets like Mars since they lose speed without having to burn a lot of propellants.

Side note: You’ll sometimes hear about the “Ballistic Coefficient” of satellites. Tiny, heavy spacecraft have higher coefficients than big, light spacecraft. Higher coefficients lose less speed so you can stay in your orbit longer. 

Plasma

Plasmas are a soup of electrons and atoms missing electrons (e.g. ions). Plasmas can have particles with a range of energies. Danger can come from ion reactivity (like atomic oxygen) and from spacecraft charging.

In space, plasmas are assumed to be overall neutral with an equal amount of positive and negative charge carried by the ions and electrons. However, because there are more electrons than ions and because they move faster, spacecraft flying through plasmas build up a negative charge faster than the positive ions can react. The result is that your spacecraft surface can build up a charge like a capacitor within a few milliseconds.

The most common effect is basically nothing: the charge balances back to neutral or the charge levels are low or the spacecraft is designed well and you sail on undisturbed. Some sensors, though, can be sensitive to the charge build-up and give you false readings. For instance, if you were trying to measure the charge in a space plasma while your sensor carried a charge then you’d get bad readings.

There are situations where plasmas can destroy hardware. This can happen if you put two charged surfaces near each other without a conduction path, for instance. The charge can arc or break down materials between the buildup zones, causing a rapid discharge event that can pop chunks of material off, create conduction paths, melt wires, and more. The other situation that can occur is to get particularly energetic electrons that can influence sensitive electronics below the surface. These types of events can occur with galactic cosmic rays and solar events.

One more note: your orbit matters. Low inclination, low altitude orbits have almost no charging concerns because the energies tend to be low and the plasma density high so you get lots of very small charging that balances quickly. On the other hand, orbits in geosynchronous, the radiation belts, and high inclinations can see much higher energies and lower densities so the charge builds up quickly and takes longer to dissipate.

Spacecraft Glow

Chemical reactions between the spacecraft and the atmosphere create a visible glow that can be picked up by optical and other sensitive sensors. The materials you choose, the way you’re facing, your altitude, and more affect how much glow you’ll see. (It’s better to choose materials not susceptible to oxidation.)

Most of these chemical reactions are related to atomic oxygen combining with things that release photons as part of the chain reaction, but there are other ways to create plasmas in space. 

Scintillation

Scintillation generally means there’s a variation in a signal as it passes through something. In this case, it’s the change in communication signals as they pass through the ionosphere part of the atmosphere. You’ll see the effects as commands and data being too “fuzzy” or corrupt to interpret correctly.

The ionosphere has a charge to it (e.g. “ion”-osphere) and the path of a photon can be bent by these charges. The lower the energy of the photon, the greater the path change. So some radio frequencies can have their signals corrupted in both phase and magnitude when the ionosphere is particularly active. On Earth, this happens at night as the atmosphere settles from its sun-induced inflation. You can also get corruption when flying through auroras at the poles.

There isn’t much control you have over the path, you can only control the frequencies you use and the time windows you send data. This tends to not be a problem for high-end space missions, but CubeSats and low-cost radios can be affected.

Radiation

There are three primary sources of radiation and one secondary source. Regardless of the source, radiation can degrade solar panels, short electronics, and alter material properties. They’re also the source of “Single Event Errors” (also called Single Event Upsets) which can change the value of data bits or even permanently alter circuit performance. 

Despite the chaos potential, a lot of radiation goes right through a spacecraft or human without interacting with it in an appreciable way. Because there’s a significant amount of chance involved in radiation, most analyses deal with probabilities and teams make tough engineering decisions about where to use heavy shielding or choose to gamble.

Galactic Cosmic Rays

These are high-energy particles zipping through the solar system from far-off cosmic events like supernovas. Some of the most dangerous particles, even though they’re just atoms, can be like dropping a bowling ball on your spacecraft. That would be a rare event, but it has and will happen and there’s not much you can do to protect yourself. The Earth and the Sun, though, both provide material and magnetic shields that block many of the particles so mission designers consider things like solar cycles and orbit altitude when trying to avoid being blasted by these rays.

Solar Events

The sun can spit and spew particles in flares and coronal mass ejections. The particles don’t tend to have the same energy as galactic cosmic rays, but there are a whole lot more of them. They can overwhelm spacecraft, shorting out electronics, cause arcing within lubricants, and disrupt communications. They can also inflate the atmosphere, creating significantly more drag.

Trapped Radiation and the South Atlantic Anomaly

Earth’s magnetic field can trap radiation from all sources as long as they have the right energy and approach the field lines at the right angle. Once trapped, they bounce back and forth between the magnetic poles until they collide with something. These belts, also called Van Allen Belts, are famous for their high density of particles that can disable spacecraft and harm humans. Most missions avoid these areas.

The South Atlantic Anomaly is a region off the east coast of South America that is part of the belts that dip low enough for even low earth satellites to fly through. The belt reaches as low as they do because the magnetic poles do not align with the Earth’s spin rotation poles. Satellites that fly through this region often turn off sensitive electronics and astronauts take special precautions to shelter. 

Secondary Radiation

Secondary radiation happens when radiation particles hit other particles, either transferring energy or even splitting into other particles. This cascade of particles can be more dangerous than the original particle because there are now more high-energy particles, which increases your chances of being hit by them. One reason why spacecraft designers don’t just wrap their systems in lead is that, while you would stop the first particle, it’s hard to make the shielding thick enough to also stop all the secondary particles. It’s better to take your chances and hope the first particle doesn’t hit you.

Material Degradation from Radiation

Pictures on Earth fade if they’re in the sunlight for too long because photons hit the color molecules and either destroy, displace, or alter them. The problem is much worse in space where nothing blocks the highest energy photons from colliding with your spacecraft. This can hurt your solar panels, your thermal paint, make your insulation brittle, darken your optic lenses, and more. 

Some materials, like metals and ceramics, are not typically affected by this type of damage because of their abundance of energy-absorbing electrons or because of the way they tightly bind their molecules. However, polymers and glasses do have problems, but for different reasons. Check the curated links below for more information.

Micrometeoroids/Orbital Debris

These are little bits of trash and rocks and other stuff flying around at high speeds. A lot of the junk flying around Earth is smaller than your pinky nail, but the high speeds it hits you with are like throwing baseballs or shooting bullets at your spacecraft. Some of the relative speeds can be 5 km/s to 20 km/s while a bullet shot by a rifle is about 1 km/s, so we’re talking very fast speeds.

Different agencies track hundreds of thousands of bits of debris, but they can’t see the very small stuff. Like radiation, you’re essentially hoping you’re not unlucky. If you do get a warning that something is coming, you can burn propellant to get out of the way, rotate your spacecraft to a less sensitive direction, and/or hope it misses you anyway.

Although many people have warned for decades that human-created space junk is a growing concern, it’s difficult to clean up. Space is huge and you need something large that can absorb the collisions or slow things down enough to reenter the atmosphere. It’s likely that we’ll hear more stories of spacecraft being disabled by debris over the next decade.

Wrapping up

Whole textbooks have been written about the space environment. And companies hire people whose sole responsibility is to understand just the radiation part of things. There’s so much to know and (my personal opinion is) it’s all fascinating. Consider that somehow all of humanity has thrived for so long despite being Earth being surrounded by all manner of things hostile to us. Understanding at a deep level what we need to get through to survive out there is a worthy use of our time.

Curated Videos

1. https://www.youtube.com/watch?v=LIqPxnoprqY
   The National Security Space Institue (NSSI) has put together a series of polished and animated videos explaining space concepts, including this one on the space environment. It’s packed with good information and visual aids.
   
   
2. https://www.youtube.com/watch?v=snv1SnxcSbM
   The US Air Force Academy has produced a series of videos for college lectures, including this overview on the space environment. This isn’t as polished as the link above but does provide a good overview.
   
   
3. https://www.youtube.com/watch?v=lvDYYRhoNOE
   This is a college lecture. It’s slow-paced and more in-depth than the overviews. It’s not for everyone, but if you want some details then this is a good resource. The channel has other videos on this topic as well.
   
   
4. https://svs.gsfc.nasa.gov/825
   This page hosts a short video of atomic oxygen interacting with other atoms. It may help you understand more about what’s going on.
   
   
   

Curated Links

1. https://ieeexplore.ieee.org/document/8758870
   This academic paper by Yifan Lu provides an excellent overview of the space environment with statistics, plots, and images of damage to highlight points.
   
   
2. https://uvsolutionsmag.com/articles/2019/uv-degradation-effects-in-materials-an-elementary-overview/
   As the link suggests, this is an overview of how ultraviolet light can damage optics and polymers.
   
   
3. http://assets.press.princeton.edu/chapters/s9500.pdf
   This book chapter covers space plasmas in a mix of plain language and specific scientific notation. It’s a handy reference you can grow with as you learn more about the topic.