On the Mars path

This summer’s hot destination is Mars, and few people know more about the logistics of getting there than Brian Muirhead, flight system designer for the Pathfinder and chief engineer at NASA’s Mars Science lab.

If the world’s design engineers were to get together to choose a figurehead, someone who embodies the finest qualities of their profession, then Brian Muirhead would be an ideal candidate.

A creative maverick who began his career repairing motorbikes in Greece, Muirhead was responsible for the design, development, test and launch of the Mars Pathfinder flight system. Pathfinder was the final mission to carry a rover to Mars in the 1990s.

While NASA’s only previous forays to Mars, the 1970s Viking missions, cost around $3bn (£1.8bn) in today’s terms, the Pathfinder team stayed within a total budget of $280m (£170m).

This was a watershed in space exploration, and only possible thanks to a pioneering use of design software. Muirhead received much of the credit for the achievement, and among other accolades was named 1997 Engineer of the Year by North America’s Design News magazine.

The lessons learnt by the Pathfinder team still resonate today, and in the hectic aftermath of NASA’s most recent Mars launch an excited Brian Muirhead shared his experience and vision of the roles software and hardware technology play in space exploration.

On 10 June a Delta 11 rocket carrying the Spirit rover successfully blasted off for the red planet, and at the time of writing another identical mission is sitting on the launch-pad.

These missions, which owe a heavy technological debt to Pathfinder, have, said Muirhead, been particularly tough. This was partly down to the logistics of managing a 900-person team, but also due to the reduced development time. For while the Pathfinder project took 36 months, the recent missions took 27. This timescale also made the mission more expensive – it cost $800m (£480m). ‘Time is money,’ said Muirhead, ‘and when you don’t have a lot of time you spend a lot of money.’

A chat with Muirhead is like a crash course in the salient points of late-20th century space exploration. Pathfinder, he explained, was an extremely important moment. ‘We stepped into the modern age in terms of computing,’ he said.

By this he means both hardware and software. For hardware, previous missions had relied on very old specialised processors with only around 1-3 mips (million instructions per second). By today’s standards Pathfinder’s processing power is pretty crude, but, said Muirhead, ‘with a 20 mips-class machine we thought we were in software heaven.’

In terms of software, one of the crucial new factors was the use of National Instruments’ Labview software. This ubiquitous test, measurement and control tool had already made its mark across a range of industries but using it on a high-visibility space mission was a radical move.

While previous missions had relied upon huge boards of written scribbled data, Labview, explained Muirhead, ‘has this beautiful graphic display that tells you in real time what’s going on. It gives you trend information and lets you know whether something may be diverging from your predicted performance.’

Perhaps one of the most dramatic applications of this clever tool is its use in environmental testing. Muirhead explained how Labview is used to control a new system at JPL (NASA’s Jet Propulsion Laboratory) that uses shaker tables to simulate extreme conditions. ‘We take our spacecraft and put them through the rigours of events like launch and Labview is used to control those systems.’

Apart from launch and touchdown, this test procedure is possibly one of the most exciting and nerve-racking times in the development of a spacecraft. ‘You put the entire thing on a shaker and apply 10 to 100s of Gs of force and if one of those shaker tables gets away from you, you can destroy your whole spacecraft. You sit there with a chicken switch and if something goes wrong you hit that switch. Labview controls and displays the data: you can see the input, see the output and response and then change the test in a matter of minutes.’

Pathfinder was also the first mission where solid modelling software was used extensively. This represented an enormous challenge, said Muirhead. ‘We were basically creating what we called our 900kg Swiss watch, and when you’re doing that kind of precision the potential for interferences and the quality of the interfaces really needed to be implemented using a solid modelling tool.’

Computer simulation also made a notable appearance on the Pathfinder project. ‘One thing we did that the teams on the new Mars exploration rover have carried further is what we called the ‘mother of all simulations’, where we linked the tools that defined and described and analysed the physics of entry with the deployment and performance of the parachute and the performance of solid rocket deceleration systems and airbags. All those different pieces of code were linked. Not in one system – we had to link them from one computer to another computer to another for them to run efficiently and that’s exactly how we designed the final airbag design.

‘In the case of the rover, we’re now able to simulate the terrain conditions and drive it over simulated terrain to assess its performance – particularly to determine how it will operate in the case of hazardous circumstances.’

To emphasise the degree to which Pathfinder’s success depended on these software tools, Muirhead harked back to the bad old pre-software days, and the 1976 Viking lander mission. ‘The Viking team didn’t have this kind of sophisticated analysis tool. Instead, they relied on very expensive test programmes. They ended up testing parachutes at high altitudes and it cost tens of millions of dollars. We don’t have to do that anymore. Instead we use computational fluid dynamics (CFD) and wind tunnel tests. That’s how we were able to do a Pathfinder mission for $265m (£160m) compared to over $3bn (£1.8bn) for Viking.’

One of the most recent examples of the use of CFD and wind tunnel tests was to characterise the parachute on the rover missions. ‘We had to make some changes to the parachute from the Pathfinder design,’ said Muirhead, ‘and after making these changes discovered that the parachute wouldn’t open.’ This discovery was made during a wind tunnel test, and with a quick change the team could get the parachute working properly again.

Until recently NASA has enjoyed a monopoly on missions to Mars. But now, in the form of the European Space Agency’s Mars Express (carrying Prof Colin Pillinger’s Beagle 2 lander) and the Japanese Nozumi mission, there are new kids on the block. Muirhead clearly relishes the challenges raised by this new-found competition, and Pillinger’s work in particular makes him nostalgic. ‘I’m impressed with what he’s done, and the commitment and talent of his people is a lot like what we did with Pathfinder.’

However, on the Beagle 2 lander’s chances of success he is less glowing. ‘I think Pillinger has stirred up quite a debate: he’s made assertions that I personally think he’ll have a hard time proving and I think he should take great pride in just getting to the launch-pad.’

In the search for Martian water Muirhead clearly backs NASA to find it first. ‘The Sojourner [Pathfinder’s rover] weighed 12kg, the new rovers weigh 180kg, and my next mission will weigh over 900kg. What we’re doing is progressively carrying more sophisticated science instruments to Mars, and the goal of the whole thing is searching for water.

‘Right now we’re looking at a mission called Mars Reconnaissance Orbiter which will give us a resolution 10 times better than anything we have now. If water’s there, we’re going to find it.’