Precursor task team (1989)

 "MARS ROVER SAMPLE Return (MRSR) is widely perceived as too expensive." Thus began the first of two February 1989 memoranda by Brian Wilcox, a Jet Propulsion Laboratory (JPL) rover engineer. MRSR was a robotic mission jointly studied between 1983 and 1989 by JPL and NASA's Johnson Space Center in Houston, Texas. By late 1988, MRSR had evolved into a mission of great complexity with an estimated price tag topping $10 billion.

Wilcox explained that the purpose of his memo was to "contribute to the debate about ways to reduce the cost of such a mission." In the aftermath of MRSR's September 1988 pre-Phase A review, MRSR management had solicited inputs aimed at cost reduction. Wilcox wrote that his approach was to "eliminate as many mission elements as possible, and to reduce the reliance of those that remain on unproven. . .technology."

At the time he wrote his memorandum, the baseline MRSR mission included four spacecraft, all separately launched from Earth. These were a lander with a Mars Ascent Vehicle (MAV) for launching one kilogram of samples from the surface of Mars to Mars orbit; an 850-kilogram nuclear-powered rover capable of a 200-kilometer sample-collection traverse; a two-part Mars orbiter comprising an imaging system capable of 25-centimeters-per-pixel resolution for making rover traverse maps and an Earth Return Vehicle (ERV) for performing rendezvous and docking with the MAV in Mars orbit, taking the Mars sample, and transporting it to Earth; and a communications orbiter for relaying radio commands between Earth and the rover.

Whereas others suggested that MRSR's cost be reduced by eliminating or postponing its rover, Wilcox made a rover even more crucial to the mission. He argued for a slow-moving 2500-kilogram rover bearing an ascent vehicle capable of returning 100 grams of Mars samples directly to Earth. Martin Marietta Corporation proposed a similar Viking-based rover-with-MAV mission in 1975.

Such a rover would, he explained, be capable of rolling over obstacles a smaller rover would have to avoid. This would eliminate the need for traverse maps of sub-meter features. The mission could thus get by with an imaging orbiter no more capable than the 1960s Lunar Orbiters.

Because the rover would move slowly, controllers on Earth would not need to continuously monitor and pilot it. This, Wilcox contended, would eliminate the relay orbiter requirement. The rover's size - eight meters long by three meters wide - would mean that it could carry the eight square meters of solar cells needed to supply its electricity needs. It could thus avoid costly, politically problematic nuclear power.

Wilcox envisioned that his MRSR spacecraft would be assembled in Earth orbit by Shuttle or Space Station astronauts and launched to Mars orbit as a single unit. The rover would then separate from the imaging orbiter and descend to the surface. Because the rover would carry the MAV, it would not need to rendezvous with it on Mars. Because its sample arm would not be used to transfer samples to the MAV, it could get by with simple core drills for sample collection. The direct-return MAV would also, of course, remove the need for the ERV and a complex and risky automated rendezvous and docking in Mars orbit.

Wilcox's second memo, written less than a week after his first, defended his assumption that a rover could carry a MAV sufficiently large to launch 100 grams of samples directly to Earth. He proposed a three-stage solid-propellant MAV with "radial squibs" (small solid-propellant thrusters) on its spin-stabilized third stage for course corrections during Earth return. His six-meter-long MAV would, he estimated, have a mass of 1453 kilograms at launch from Mars. Of this, propellant would account for 1280 kilograms. The sample capsule for Earth atmosphere entry and landing would have a mass of 15 kilograms. Wilcox noted that trimming sample capsule mass to five kilograms might allow a MAV mass of less than 1000 kilograms.

The rover-with-MAV concept exerted little obvious influence on the MRSR Project. Six months after Wilcox wrote his memoranda, the MRSR Project was subsumed into the Precursor Task Team, an element of planning for President George H. W. Bush's abortive Space Exploration Initiative (1989-1993). Wilcox would subsequently propose a rover with a solid-propellant MAV as part of JPL's Mars Surveyor Program Mars Sample Return architecture in 1998.