Floating rovers

Ballooning was mankind's earliest step off the ground, and arguably marked the first chapter in the history of space exploration.

Now researchers at the University of Aberystwyth believe balloons could be at the heart of future planetary exploration missions.

The team, led by Dave Barnes of the university's intelligent robotics group, is devising aerobots — helium balloons with independent, AI-equipped payloads — that could be used on a forthcoming mission to Mars.

Three methods are available for surveying the surface of a planet, said Barnes: orbiters, static landers and rovers. He thinks aerobots will be the most useful because they can conduct surveys in their own right and improve the effectiveness of the other three.

'We can use them for high-resolution surface imaging but, unlike orbiters, aerobots can also touch the surface: they can land and deliver a science payload to allow surface science to be done. When they're flying, they can do atmospheric science. They can also be used for lander site selection, surface science, rover guidance, data relay and sample size selection.'

Also, he added, they can go where rovers cannot: 'To take Mars as an example, the southern hemisphere is very interesting from a scientific point of view, but it's not good terrain for rovers.'

Technically, there are two types of aerobots, Barnes said. The heavier-than-atmosphere types are UAVs that launch from an orbiter and deploy wings before they land. The Aberystwyth team is concentrating on the lighter-than- atmosphere type, which has two methods of deployment - inflation on descent, or landing followed by inflation.

There are two main challenges with using aerobots, Barnes said. The first is that, unlike landers and rovers, they are always in motion. 'You're in a constantly changing environment,' he said. 'A lander doesn't move at all and a rover, after you've stopped doing your traverse, ought to be in the same place the next day. An aerobot won't be.'

This leads to the second problem: if your aerobot is constantly moving, you have to know where it is. 'There's no GPS, you can't always see the stars, you can't commit orbiter resources full-time to track the aerobot and you can't commit terrestrial resources such as radio telescopes either,' Barnes said. The aerobot is on its own, so much of the Aberystwyth team's research focuses on onboard location technologies.

The gondola's computer is pre-loaded with a digital elevation model (DEM) obtained from the orbiter or from previous missions of the terrain over which it will fly. The DEM is relatively low resolution but includes features such as peaks, ridges, passes, plains, channels and pits. The gondola is equipped with a downwards-facing camera that takes a series of images and processes them in the same way to produce its own local DEM. 'We use various AI techniques to take account of scaling, orientation and gradients, and compare the global and local DEMs to figure out where the aerobot is,' said Barnes.

The team has tested two types of aerobot — a spherical balloon, and a hybrid balloon-kite system, known as a helikite, where the kite acts as a rudder, lending stability and improving lift from the prevailing wind. To manoeuvre the aerobot, the gondola is equipped with a series of small propellers.

The aerobot is being prepared for a possible ESA Mars mission in the next available launch window, which is 2009-2013. 'In simulations and demonstrations where we have flown actual aerobots at the European Space Research and Technology Centre (ESTEC) in Holland, we have shown that the aerobots are now able to spot and classify points of scientific interest in the surface,' he said. The ESTEC tests have confirmed that an aerobot weighing 3.5kg would need a balloon 7.2m in diameter to lift it.

Working with the project's software partner, SciSys, Barnes's team has also developed systems for autonomous aerobots to work together in a swarm or flock.

'It's far more efficient to get them to co-operate,' he said. 'Think of it like the police doing a fingertip search in a line.'

Trials of the technology in the Great Hall at Aberystwyth have demonstrated that an aerobot swarm can compensate for gusts of wind to keep in formation. 'I think in the next 50 years, certainly, aerobots will be used routinely for surface exploration of planets with atmospheres, such as Venus and Titan, as well as Mars,' said Barnes.

Follow this link to see an animation of an aerobot in action: http://www.scisys.co.uk/technologies/space/tech_aerobot2.asp