FUTURE generations of planetary rovers could leave today鈥檚 vehicles trailing in the dust, thanks to the revival of an idea that pre-dates the space age by a quarter of a century. But despite its benefits, many experts at NASA have never heard of the revolutionary design.
According to a team from Kingston University, London, the elastic loop mobility system (ELMS) should be lighter and more agile than its competitors. And because it has few moving parts, it should be reliable enough to handle remote missions.
ELMS was patented in 1933 by a British inventor, one J. G. K. Kitchens. The drive track of today鈥檚 modified version is a continuous band wrapped around drive wheels at the front and back of the vehicle and held in place by two smaller 鈥渓oad鈥� wheels. The band is made from a titanium-based shape-memory alloy. Before fitting it is circular, curving in at the edges. When fitted onto the rover, it is forced out of its preferred shape by the wheels and the weight of the vehicle. The lower part of the track loop flattens against the ground to provide a large area of grip. In between the drive wheels and the ground the belt acts as a spring, providing suspension for the delicate instrumentation on board the vehicle. And because the wheels are high off the ground, they are protected from clogging with rocks and dust.
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Conventional tracks have interlocking sections held together with pins, but this system is too unreliable when the nearest engineer is on another planet. Wheel-based systems such as the rocker bogie used on NASA鈥檚 Sojourner rover in 1997 are simpler, but each wheel has only a small area of contact with the ground, so they are less sure-footed over difficult terrain.
Alex Ellery and Nildeep Patel at Kingston University鈥檚 astronautics and space systems research group used computers to simulate the performance of rovers propelled by a variety of drive systems. The simulations show that ELMS rovers can climb 35-degree slopes, while vehicles riding on rocker bogies will only manage 20 degrees before they start to slip. They also showed that ELMS should be able to clamber over obstacles twice as big as those that a rocker bogie could negotiate.
Being so nimble is a distinct advantage on Mars鈥檚 rocky surface. An ELMS rover should be able to travel up to 1 kilometre. In 1997, Sojourner had to stay within 100 metres of the landing vehicle throughout its mission.
An ELMS system is barely two-thirds the weight of a rocker-bogie design 鈥� a vital advantage for space flight. And an ELMS-driven rover could go 500 kilometres between services. On the downside, ELMS consumes more power than other systems. 鈥淭he greater range more than makes up for it,鈥� says Patel.
Yet these results largely confirm what NASA scientists discovered back in the 1970s, when Nick Costes, then at the Marshall Space Flight Center, and Stein Sture from the University of Colorado started to develop an ELMS-based system for a third Mars lander.
Martian exploration was suspended before the NASA project took off. By the time the agency sent the Sojourner rover to Mars on the Pathfinder mission, Costes had retired and the ELMS research had been forgotten. A NASA spokesman said that the agency鈥檚 current robotics experts had not heard of the design.
The European Space Agency is reviewing the Kingston group鈥檚 report and may be the first to benefit from ELMS. 鈥淚t鈥檚 unlikely that this concept would be used in the first Mars mission,鈥� says Michel van Winnendael, a robotics engineer in ESA鈥檚 Aurora technology development programme. 鈥淏ut we need to keep it in the picture for future missions, especially for vehicles that can go further at higher speeds.鈥�
