June-September 1981:Mars rover proposals

The Langley Rovers

Studies into ways of seeing beyond the Martian horizon date to 1972. Five concepts were developed at NASA's Langley Research Center, each one with increasing range and sophistication. The most elementary was the cable-controlled rover. It had a range of 164 ft (50 m) and carried a sampler scoop and an X-ray fluorescence spectrometer. The most complex was the autonomous rover having a range of 62 miles (100 km), on-board sampling equipment and direct communications with Earth. In between was the small rover,battery-powered, 328 ft (100 m) range, camera and scoop. The medium rover had a 0.62 mile (1 km) range, stereo camera,drill, scoop, and was nuclear powered. And lastly, the advanced rover— 6.2 mile (10 km) range, nuclear and battery-powered, scoop, drill, stereo camera, communications via the orbiter rather than through the lander.

The autonomous rover was further refined during the next two years. In this later version, the rover would be carried aboard a Viking lander, necessitating the removal of one camera. The vehicle would have a range of 28 miles (45 km) and weigh 2381 lbs (108.2 kg). Of this, 891 lbs (40.5 kg) would be scientific equipment. It would carry a camera, a RTG nuclear generator, a scoop, an X-ray diffractometer and an alpha backscatter spectrometer. Its mission was photo and geochemical survey. It would look for sub-surface water using on-board equipment and the basic Viking science package. It would also perform rock sampling, locating and cataloging interesting areas such as rock niches.

Post-Viking Rovers

The Jet Propulsion Laboratory, shortly after the Viking landings, announced a study of advanced Lunar and Planetary explorations. It was called the Purple Pigeons — bright birds of the future. For Mars, they planned two orbiter/landers. Each lander would carry two rovers. Once on the surface, they would be controlled via relay satellite in synchronous orbit. Each rover would weigh 441 to 551 lb (200 to 250 kg) and carry a TV camera, manipulator arm for picking up samples, as well as geological, chemical and meteorological equipment. X-ray and gamma-ray spectroscopes and multi-spectral photo systems. It would also look for signs of life. To perform soil studies, the rovers would each carry an optical microscope and a seismic 'thumper'. The science packages would be complementary. If one should run into difficulties, the other could assist.

The rovers would be 3.28 ft (1 m) wide and 9.84 ft (3 m) long and ride on 6 wire mesh wheels like those used on the Apollo lunar rovers. The rovers could cover 621 to 932 miles (1,000 to 1,500 km) in one Martian year — moving at 1.86 to 2.5 miles (3 to 4 km) a day. Using lights, they could work during the night and in craters. Later studies, however, indicated that it would be preferable to have the two rovers working separately,surveying different areas. Another proposal was to convert the Viking lander itself Into a roving mobile laboratory. The hardware would be spare flight qualified vehicles. To provide mobility, each footpad would be replaced by an elastic loop similar to caterpillar tracks but lighter and less complicated. It would provide uniform low ground pressure giving a smooth ride over rocks and soft soil. The tracks would swivel for course changes. The rover would move 328 ft (100 m) at a time, two bumpers extending out from the side. Its range would be about 90 miles (150 km). Tests indicated that it could climb 30° to 40° slopes.

Martin Marietta had been studying a mobile Viking since 1974. The Viking 3 would be equipped with a new unified biological instrument. It had 11 test cells for analysing Martian soil. An Alpha-Proton X-ray experiment, similar to that used on Surveyor, would be used to determine elemental composition of the surface and an X-ray diffractometer used for mineral studies. It would also carry a crusher/grinder so that a wider variety of surface samples could be analysed. The increased power requirements meant that a more efficient RTG nuclear power source would be required.

Mars Ball Probe

Another unusual post-Viking concept is the Mars Ball probe. This rover is a beach ball-like device; it would roll across the Martian surface using either on-board systems or the Martian winds. It carries science and guidance equipment and can be stopped and started. The concept had been studied by both JPL and the French Space Agency. One wind-blown rover had a 44 to 61 lb (20 to 30 kg) science package and would inflate and deflate on command.

By the second anniversary of the Viking landing, it had been agreed that the next US Mars probe would involve some type of rover system. After several years of study, two basic ideas developed — the autonomous rover having a long range to carry out exploration away from the lander and/or a teleoperated mini-rover. The autonomous rover would be about the size of a large desk. It would use the same kind of elastic loop treads as the Viking 3 proposal. It would travel about 61 miles (100 km) in one Martian year. The science package would weigh between 220 and 352 lbs (100 and 160 kg). It would carry stereo cameras and a manipulator arm. and small science packages could be dropped off at selected locations. Power would come from a 250 watt RTG. Unlike previous concepts, the vehicle would be self-navigating without detailed instructions from Earth. The autonomous rover would survey the terrain, detect any obstacles, remember them and plot a course to avoid them. It would have a proximity sensor, laser ranging instruments,stereo cameras and a computer to evaluate the data. A self-navigation capability would avoid the bottleneck caused by the many-minute delay required to get a signal from Mars to Earth.

The teleoperated mini-rover, on the other hand, would be a very simple vehicle with none of the sophisticated systems of the autonomous rover (one drawing shows a box on two wheels and a tail skid). Equipped with a camera and drill, it would act as an extension of the lander. Its function wpuld be as a sampler and to deploy science packages.