Meeting Nasa’s Rovers
By: Andrew Webb
Tags: Jpl, Making, Mars Rovers, NASA, Mars

To showcase some of the potential uses for pi-top [4], we designed and built two mini Mars rovers whose movements were remotely controlled by it. The idea being this is exactly the sort of project a club, society or school could work on. It combines various skills and technologies, from coding and 3D printing to environmental studies and photography.

We’ve travelled around the world with these rovers, and recently had the privilege of visiting NASA’s Jet Propulsion Labs (JPL) at the California Institute of Technology, to see what the real Mars rovers are capable of.

When we arrive, we’re greeted by our friendly NASA liaison, Brandon, who sorts us out with security passes. The first stop is a fantastically detailed exhibition room full of models of previous rovers, landers and probes that JPL have designed and built over the decades.

We get a chance to meet scale models of household names like Sojourner, Spirit and Opportunity, and there’s even a model of the (surprisingly enormous) Voyager spacecraft. Voyager is currently the farthest-travelling man-made object ever to have existed, having journeyed about 21,691,691,000 km. It’s fascinating to see these models, but I’m itching to see real rovers.

The next stop on our tour is the enormous Spacecraft Assembly Building. As we enter the viewing platform, the scene below takes my breath away. I gawp excitedly through the airtight windows down onto an enormous, sparkling white factory floor like no other I’ve ever seen. Years working with manufacturers in China has taken me through a lot of busy factories that makes pieces of metal and plastic for consumer goods. This factory makes spacecraft.

The far wall of the room proudly displays the mission emblems of every spacecraft that JPL have constructed. It forms a sort of trophy cabinet; over 30 spacecraft have been constructed here, now dotted around our solar system and beyond. The emblems are an exciting and profound reminder that the secrets of our solar system, and the wider universe, are being slowly unlocked in no small part by the things constructed in the room in which I’m now standing.

The floor is divided into six areas, each dedicated to a different aspect of the mission. As well as the rover itself, the cruise stage (the part that’s responsible for actually getting to Mars), and the Entry, Descent and Landing (EDL) stage that takes the rover to the surface, are all made here. They sit in various states of completion, some little more than lightweight metallic scaffolds, others like the imaginatively named ‘Powered Descent Vehicle’, already completed.

The chassis of the Mars 2020 rover

My eyes immediately go straight to the most exciting thing in the room — there in the far corner, the chassis of the 2020 Mars rover is almost complete. It’s about the same size as a small car, but its shape is unmistakable, a design derived from its predecessor, the Curiosity rover. It’s this rover that we based our own pi-top rover on. I can’t quite believe that the vehicle I’m looking at is the very same vehicle that will touch down on the surface of another planet in less than two years.

Although our rovers were made on a small budget with mostly 3D printed and laser-cut parts, each pi-top rover has many design elements that were directly inspired by the Curiosity rover, and work almost as well on a home-brewed miniature as they do on the real rover… sort of.

On our little rovers, each of the six wheels is driven by its own independent DC motor, attached to a ‘rocket-bogie’ suspension system to give the rover good traction and stable footing in uneven terrains. A suite of environmental sensors monitor air quality, temperature, humidity, and an ultrasonic sensor on the front mimics the functionality of the obstacle-avoiding ‘hazcams’ mounted to the front and back of Nasa’s rovers.

A mast in the middle of the rover supports a high-resolution camera, as well as the pi-top [4] itself, which process all the data and sends it back to base over WiFi. We even use a robot arm, made of six servo motors, to acquire ‘samples’ just like the real rover — although ours lacks the suite of highly sophisticated lasers, drills and spectrometers present in the real thing, as apparently it’d be dangerous to give kids lasers strong enough to cut rock. Who knew?

Speaking of dangerous equipment, there are other two major aspects of the real Mars rovers we didn’t attempt to replicate, one predictable and one a little surprising. You might guess the first — we didn’t attempt to recreate the spectacular system of rockets and parachutes used to get the rover on Mars (more on that in a minute). But you might not guess that the hardest part to authentically replicate is the battery.

Power is a tricky thing on Mars. Traditional batteries won’t last long enough, and solar panels don’t work well in Mars’ long winter months (or at night for that matter) are liable to slowly get covered in Martian sand over time until they are all but useless, which has been the fate of most landers and rovers before Curiosity. With Curiosity, JPL has gone with something radically different, and this car-sized rover runs on a nuclear battery, or more formally the ‘Radioisotope Thermoelectric Generator’ (RTG). Sitting in the ‘trunk’ at the back of the rover is a 5 kg block of plutonium, wrapped in thermo couplings and slowly decaying. This gives off enough heat energy to keep things ticking over on the rover for at least 14 years. The system does use a couple of Lithium-Ion (Li-Ion) batteries to make sure power is steadily available when it’s needed most. Li-Ion batteries are ubiquitous in almost all consumer electronic devices now, so we had no trouble acquiring some for our rover. At least we could have something in common with the real thing!

Artist’s concept of the Mars 2020 Rover (NASA/JPL-Caltech)

The Mars 2020 mission will use the same ambitious (and successful) landing sequence used for Curiosity in 2012, sometimes affectionately referred to as the ‘7 Minutes of Terror’. The Entry, Descent and Landing stage is responsible for slowing the rover from a blistering 13,000mph through space to a complete stop, safely on the surface of Mars. Its heat shield uses the Martian atmosphere to slow to just (!) 1000mph, at which point an enormous supersonic parachute deploys to further slow things down. At 370mph the heat shield is jettisoned, and cameras are used to carefully guide the rover towards the landing zone. Retro rockets slow the descent even more until the rover is just 10 meters above the surface of the planet, then things get really sci-fi. The remaining spacecraft now consists of just the rover itself and a rocket-powered ‘sky crane’, responsible for hovering in position while the rover is slowly lowered down, on cables, to touchdown on the Martian surface at gentle 2mph. Once all that has been successfully completed, the sky crane explosively cuts its support cables and flies off to a safe distance to a dramatic crash landing. Being dramatic isn’t a requirement of the mission, but the ‘7 Minutes of Terror’ is, to my mind, one of the most dramatic, ambitious and outright sci-fi aspects of these Mars missions.