Space radiation has to do with the flow of energy through space. This energy flow can be in the form of waves such as sunlight or in the form of particles such as electrons, protons and elements in the Periodic Table. Sunlight is a form of electromagnetic radiation produced by the sun. Electromagnetic radiation in general includes gamma rays, x-rays, ultraviolet radiation, visible light, infrared radiation (or heat), microwaves and radio waves.
Particle radiation in space can travel at very high speeds. One type is solar particles that are emitted in a burst of energy from our sun called a solar flare or a coronal mass ejection. Another type is extremely energetic particles that originate outside of our solar system called galactic cosmic rays. The origin of galactic cosmic rays is not entirely understood but it is known that one source of them is explosions of stars called supernovas. These particles can travel at speeds so high that a single particle can be equal, energy-wise, to a tennis ball traveling 250 kilometers per hour, faster than professional tennis players can hit! Another important type of space particle radiation is found in the “radiation belts” around the Earth.
Earth is surrounded by a magnetic field that looks something like the field you see around a bar magnet when you use iron filings to make it stand out better. You may have seen this demonstrated in a science class. The Earth’s magnetic field helps protect us from space radiation such as solar flares and galactic cosmic rays by deflecting many of the particles before they reach us. This magnetic field also traps charged particles within it like an invisible magnetic prison. The trapped particles are so numerous that they form into donut-shaped clouds with the Earth at the center, and stretch thousands of miles above Earth's surface at the equator. Scientists call these the “van Allen Radiation Belts” because they were discovered by Dr. James van Allen using one of the first satellites launched by NASA in 1958. The radiation in the van Allen Belts consists mainly of electrons and protons. More information about the radiation belts can be found at http://radbelts.gsfc.nasa.gov/.
Earth isn't the only place where radiation belts exist. The planet Jupiter has belts that are much larger that ours. Radiation belts can also be found around exotic stars called pulsars.
Space radiation can have serious effects on satellite operation. Some particle radiation is so energetic that it can penetrate to the interior of a satellite and interact with its electronic circuitry. This can cause a wide variety of effects that range from unimportant ones to the shutdown of a vital system. For example, if the circuitry controls the way the satellite is pointing its antenna, the satellite can veer out of contact with ground-based receivers and be temporarily “lost”.
It is important to understand the space radiation environment so that reliable satellites can be designed at a reasonable cost. Underestimating the radiation environment leads to excessive risk for the satellite. This can result in degraded performance and a shorter mission lifetime. On the other hand, overestimating the radiation environment can result in over-design by engineers. This can increase the cost of the satellite and even limit its capabilities.
Radiation effects in the interior of satellites are often grouped into three categories: total ionizing dose, displacement damage and single event effects. Total ionizing dose effects in electronics are the result of damage that usually builds up over a long period of time in an insulating region of an electronic device. This changes the device properties, which results in performance degradation and eventually can cause the device to fail completely. Displacement damage is also a cumulative effect but this occurs in the electronic device’s semiconductor material. These effects also cause the device to deteriorate at first and possibly fail if it is exposed to enough radiation. Single event effects are caused by the passage of a single particle through a sensitive region in an electronic device. There are many types of single event effects, which can be either non-destructive or destructive to the device. The severity of the effect can be so small that it can go unnoticed. At the other extreme it could cause a system in a satellite to shut down.
Space radiation can create other kinds of damage in satellites as well. For example, it can cause electric charge to build up in an insulating material to the point where a discharge can occur that damages something. This discharge is the same type of thing that would happen if you walked across a carpet, touched an object and were shocked by a static discharge.
Since space radiation can affect our satellites it can also adversely affect our society by causing problems in communication systems, GPS navigation systems and other high technology systems in space. It can also affect air travel in the Earth’s polar regions, which are less protected by the Earth’s magnetic field than the equatorial region. A large coronal mass ejection from our sun can also cause serious effects in electric power grids. The particle radiation ejected from the sun disturbs the Earth’s magnetic field, causing a “magnetic storm”. This in turn can induce surges in power lines and in an extreme case cause a blackout. A dramatic event of this sort occurred in March 1989, when the resulting power surge shut down an entire system at a power station and caused a blackout in a large portion of Quebec. Due to our growing dependence on high technology systems, an extreme radiation event like this can now potentially cause more economic hardship than other extreme events on our planet such as hurricanes and earthquakes.