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Star Cores: Computers in space

Posted on 3 Sep 2008 at 14:26

Martin James discovers why computers aboard spacecraft ten billion miles from home are less powerful than a Commodore 64.

The first American in space, Alan Shepherd, said: "It's a very sobering feeling to be up in space and realise that one's safety factor was determined by the lowest bidder on a government contract." It must be even more sobering for some of today's astronauts that some of the computers up in space are older than they are.

You might think the likes of NASA's Phoenix Mars Lander - which touched down on the red planet in May - would feature staggeringly powerful computing hardware and some of the most highly advanced software.

But conditions beyond the Earth's atmosphere mean the computers on board space missions, whether manned or unmanned, are designed to survive rather than to impress. The tiniest design fault or software glitch could spell disaster - truly life or death.

Temperature variations, radiation, shock and vibration all put a greater strain on components than they will ever be subject to on Earth. The vacuum means that air-cooling isn't an option, and normal storage methods simply don't work. Combine that with a requirement for equipment to last ten times longer than your home PC ever will (the still-operational Voyager mission, for example, launched back in 1977), and you start to realise the enormity of the challenges faced by the scrupulous engineers that design the computer hardware and software inside shuttles and other space-bound vehicles.

Keeping up with the space race

Down to Earth

The world of science fiction bandies around concepts such as robots and warp drives with an ease only afforded by the unconstrained imagination. By comparison, the reality is positively arcane. The twin Voyager spacecraft are the two furthest man-made objects from Earth - Voyager 1 is in the region of ten billion miles from the sun, but to get there has been a journey of 31 years. Think back to what passed for computing technology in 1977 and you'll start to get a picture of how dated Voyager's equipment actually is.

Processing power on board each craft is provided by three RCA 1802 chips running at a pedestrian 6.4MHz, while RAM is limited to a paltry 12KB. But when Voyager 2 sent back groundbreaking data in December last year suggesting that the Solar System is asymmetrical, the age of the components didn't matter a jot.

Voyager's project scientist Ed Stone described the Voyager missions as "the most romantic and beautiful project ever attempted by NASA" and, thanks to the reliability of its on-board systems, that project survives to this day - almost 20 years after it achieved its primary mission objective of a flyby of Jupiter and Saturn. And, partly thanks to the low power drain of those limited processors, the twin Voyager craft are expected to continue to feed us priceless data about our solar system until at least 2020.

With spacecraft, the "bottom line" is reliability: reducing faults to an absolute minimum through exhaustive and meticulous testing, built-in redundancy and sticking to tried and tested methods. And, while the computing equipment on the likes of the Voyager craft and the famous Apollo 11 mission that took Neil Armstrong to the moon is pitifully basic compared with even something as humble as an Eee PC, that doesn't mean it isn't essential to the success of those missions.

For Apollo 11, engineers on the ground calculated the real-time trajectory to the moon and back based on information fed to Earth by the shuttle's 30kg on-board computer. They also devised three separate solutions for the all-important lunar descent and compared reams of data transmitted from space with predicted values to detect potential problems. As Apollo 13 commander Jim Lovell is quoted as saying: "Space flights are not miracles, but are directly related to technological engineering on the ground."