A 1990s iMac Processor Powers NASA’s Perseverance Rover

A 1990s iMac Processor Powers NASA’s Perseverance Rover
A high-res image showing Perseverance seconds before reaching the Martian surface. (Image: NASA/JPL-Caltech)

As we watched NASA put a rover on Mars last month, it definitely seemed like the agency had to be using some sort of high-tech processor in its machine. Surely the rover is built on something much more powerful than the components in devices us civilians use, right? But while NASA is technically using a specialised processor to power the Perseverance rover, it’s not far removed from the world of consumer electronics — about 23 years ago.

NewScientist reports that the Perseverance rover is powered by a PowerPC 750 processor, which was used in Apple’s original 1998 iMac G3 — you remember, the iconic, colourful, see-through desktop. If the PowerPC name sounds familiar, it’s probably because those are the RISC CPUs Apple used in its computers before switching to Intel. (Although now the company is back on the RISC train with its homegrown M1 processor.)

The PowerPC 750 was a single-core, 233MHz processor, and compared to the multi-core, 5.0GHz-plus frequencies modern consumer chips can achieve, 233MHz is incredibly slow. But the 750 was the first to incorporate dynamic branch prediction, which is still used in modern processors today. Basically, the CPU architecture is making an educated guess on what instructions the CPU is going to process as a way to improve efficiency. The more information that’s processed, the better the chip gets at predicting what it needs to do next.

However, there’s a major difference between the iMac’s CPU and the one inside the Perseverance rover. BAE Systems manufactures the radiation-hardened version of the PowerPC 750, dubbed RAD750, which can withstand 200,000 to 1,000,000 Rads and temperatures between −55 and 125 degrees Celsius. Mars doesn’t have the same type of atmosphere as Earth, which protects us from the the sun’s rays, so one flash of sunlight and it’s all over for the Mars rover before its adventure can begin. Each one costs more than $US200,000 ($256,980), so some extra protection is necessary.

Motorola PowerPC 750 processor with off-die L2 cache on the CPU module from a Power Mac G3. (Photo: Henrik Wannheden, Other) Motorola PowerPC 750 processor with off-die L2 cache on the CPU module from a Power Mac G3. (Photo: Henrik Wannheden, Other)

“A charged particle that’s racing through the galaxy can pass through a device and wreak havoc,” James LaRosa at BAE Systems told NewScientist. “It can literally knock electrons loose; it can cause electronic noise and signal spikes within the circuit.”

But why use a processor old enough to remember when Eve 6 released its first album? It has nothing to do with cost — those old processors are the best ones for the job because they are reliable. NASA’s Orion spacecraft, for instance, used the same RAD750 processor.

“Compared to the [Intel] Core i5 in your laptop, it’s much slower…it’s probably not any faster than your smartphone,” Matt Lemke, NASA’s deputy manager for Orion’s avionics, told The Space Review back in 2014. “But it’s not about the speed as much as the ruggedness and the reliability. I need to make sure it will always work.”

Taking that into consideration, it’s reasonable that NASA would choose older technology over the new stuff. After all, when you’re spending $US2.7 ($3) billion to land a robot on Mars, it’s important that your tech is reliable enough to stand the test of time — down to the tiniest soldered circuits. Currently, the RAD750 powers around 100 satellites orbiting Earth, which includes GPS, imaging, and weather data as well as various military satellites. Not one of those has failed, according to LaRosa.