Space Technology

You may have heard quips about how primitive the electronics used in space technology are compared to what you can buy as a consumer. This can be a puzzling fact given that space exploration is a very technical (and expensive) enterprise.  If we're going to spend hundreds of millions or billions of dollars to send a spacecraft out into the solar system (most of which just goes to getting to your destination), why give it old brains?

In fact, the example of the computers in the lunar landers isn't a very good one to illustrate the point I am trying to make.  While the computing power available is very small compared to devices today, it was actually quite advanced for the time.  So why would I mention an example that doesn't fit with the norm?  There are a couple reasons why technology in the early days of space exploration was more up-to-date than it is today.  The first is easy:  We were engaged in the "space race" with the Soviet Union.  NASA had an enormous budget compared to today, and was given the directive to take whatever steps (and often, risks) were necessary to win the race.

Core rope memory

The second reason takes a bit more explanation. The picture to the left is of a massive 128 byte (wow!) memory module from the Apollo Guidance Computer.  This is what is known as core rope memory, which means that a person sitting in a factory literally wove the wire into a pattern encoding the data.  So...how does that explain why Apollo-era technology could be sent into space easier than today's electronics?  If a human being put the memory modules together, that means the wires must have been at least a minimum workable size.  But consider current generation CPUs.  The size of transistor gates is 22nm.  For comparison, a human hair is about 50,000nm across and a silicon atom (which microchips are made of) is 0.11nm.

A Solar Flare

Both core rope memory and new computer components work fine on Earth, so why not in space?  The difference is that outer space is constantly flooded with radiation from the solar wind and cosmic rays, but (luckily for us) Earth's magnetic field protects us from most of this.  When enough highly energetic particles are passing through your spacecraft, one is bound to hit something important and transfer that energy into whatever it hits.  In old electronics that wasn't a big deal - the components were big enough that the energy could spread out and cause few problems.

Newer components are a different story.  As you may have noticed above, the current generation of computer parts have die features on the scale of a few atoms.  This means that it doesn't take very much energy to flip a digital bit from 1 to 0 or back. That's good when you need to power a CPU with over a billion transistors but very bad when you're being bombarded by high-energy radiation.  Then again, I'm not sure that's ever a good situation to find yourself in...  When a bit flips in a memory chip (usually causing a crash or data corruption), that's called a soft error.

Clearly, electronics on spacecraft must be different than personal computers to function in their environment. Any component that leaves Earth's protective magnetic bubble must be radiation hardened.  There are many techniques for accomplishing this, but they fall into 2 general categories. First, the components are often manufactured using different materials and surrounded by radiation shielding to prevent errors.  Second, there can be error correcting codes for memory and redundant calculations to check for errors that have already occurred.  All of this adds complexity to the design, which then must undergo multiple rounds of testing before it has a chance of seeing spaceflight.  This testing process, which is essential to ensuring spacecraft systems continue functioning after we hit "launch," is why these systems are less powerful than what you can buy at any electronics store.  So rather than making fun of NASA's newest Mars rover, Curiosity, for having a camera with less resolution than your cell phone (it's 2 MP), just enjoy the images it takes and remember that it survives being bombarded by radiation every day.