How a Spacecraft Like Orion Survives the Harsh Radiation of Orbit

​Today NASA sent its new space capsule Orion on a test flight around Earth for the very first time. It's a multi-purpose crew vehicle that the space agency believes is our best shot at returning to the moon–and hopefully, one day, onwards to Mars.

But amongst the challenges Orion faces—a successful launch and re-entry are especially key—NASA scientists are keeping a close eye on another variable: how well the spacecraft's computers weather the often dangerous and unpredictable levels of radiation of space.

This isn't a problem unique to Orion. Radiation affects everything from satellites in low Earth orbit to deep-space probes—highly energized ions that wreak havoc with computers and make it difficult for computers to do their jobs. But unlike, say, the laptops on the International Space Station (which aren't expected to last for very long) or myriad communications satellites (whose ancient processors are by now tried and true), Orion's electronics are new, and NASA needs to make sure that they work as expected for years and decades to come.

"We have a lot of systems that go out to geosynchronous orbit … so we kind of know what this radiation band looks like," said Mark Geyer, Orion's program manager, during NASA's pre-flight briefing on Tuesday. "The difference is these particular computer chips, we've tested them on the ground in certain conditions … but you really need to fly."

Radiation in space can affect electronics in two ways. On the one hand, you have transient faults or errors—short bursts of naturally occurring high energy ions that come from solar activity or from deep space, and can disrupt electrical charges when they penetrate an integrated circuit.

"In RAM what happens is these particles can flip bits and so therefore they can change stored memory. They can change programming. They can cause all sorts of transient failures," explained Lloyd Massengill, professor of electrical and computer engineering at Vanderbilt University, and director of engineering in the Institute for Space and Defense Electronics. "And then in microprocessors, they can generate signals that are … erroneous, that can propagate through the processor and cause it to execute incorrectly its programming."

In other words, radiation can corrupt data. It can turn a 1 into a 0. It can make a processor think that 2+2=5.

"They're pretty dastardly things, because if you have a satellite system, if it's a mission critical kind of process that's running, then these errors, these transient errors can cause a satellite to do all sorts of erroneous things," Massengill continued. "The worst case would be, for example, shutting down a system for communications, or firing a thruster when it shouldn't be fired."

The number of transient faults that occur can vary depending on where the spacecraft is in space—radiation is extremely dangerous around Jupiter, for example—and in a worst case scenario, faults can occur on a minute by minute basis. In some instances, vehicles such as the Hubble Space Telescope are shut down entirely when passing through high-radiation zones such as the Earth's Van Allen radiation belt. NASA shut off Orion's cameras as it passed through the belt too.

Radiation Area Monitor aboard Expedition 26. Image: ​NASA

And that's just the everyday threat that radiation poses. Secondly, there are also the long-term effects of radiation to consider—the degradation to circuits that occurs over time. The more high-energy ions an integrated circuit is exposed to, the less effective it becomes at storing information or performing calculations. Eventually a component can fail. Engineers try and anticipate this failure in part thanks to manufacturer ratings that estimate how much short and long term radiation an electronic component can withstand.

You can shield electronics to some extent from the threat of radiation, both short and long-term. Lockheed Martin's Orion program manager Mike Hawes explained in an earlier NASA briefing that there is actually a research payload onboard Orion that will measure radiation levels and test the effectiveness of various shields. But shielding is also heavy, and size, weight and cost constraints make using it in satellites and other spacecraft difficult unless absolutely necessary. Often, engineers will attempt to compensate for the effects of radiation in the design of an electronic component itself.

One option is to build a chip that has been radiation hardened from the ground up, physically designed in such a way that it is less susceptible to the effects of short and long-term radiation. In other words, if throwing an Intel chip in your expensive satellite isn't good enough, you're left with no choice but to design and manufacture a processor of your own—no small feat, and one that takes considerable money and time.

(A curious side note: One popular processor that is still sold and used today is a radiation hardened Power PC 750 manufactured by BAE. It has a clock speed of up to 200 MHz. Its commercial equivalent was used in many Apple Mac models from the late 1990s to early 2000s.)

Because not everyone can afford or needs radiation hardened electronics, the most common coping strategy according to Massengill is called Triple Modular Redundancy (TMR). Instead of using special electronics, you can use more readily available, non-hardened parts—but three of them in tandem, all doing the same thing at the same time. If one of them throws an error, the other two will outvote it and correct it.

Curiously, modern day space technology is actually more susceptible to radiation than it was the last time we went to the Moon.

"The interesting things about computers now, is although they are much more powerful, they are also more susceptible to radiation than the earlier computers," said Geyer during NASA's Tuesday briefing. "We have a more powerful system, but it's susceptible to different kind of environments than the Apollo system."

Massengill explains that this isn't actually all that surprising. As electronics become more complex—as we shrink down transistors and pack more and more of them into smaller packages, pushing technology to its limits—interference is more likely to occur. It's a matter of scale.

Software certainly helps too. Algorithms are helping solid state storage and flash memory last longer in space, and there are ways for processors to re-configure themselves to adapt to their environment.

But all we can really do is buy the hardware time. Computers, much like the astronauts who operate them, can only survive in space for so long.