After Venus: Pioneer Mars Orbiter with Penetrators (1974)

Pioneer Venus Orbiter (PVO) in Venus Orbit. The Pioneer Mars Orbiter (PMO) would have been based on this design. Image credit: NASA.

The name "Pioneer" was applied to several different spacecraft designs, all of which were meant to spin to create gyroscopic stability. The first U.S. Moon probe, launched by the Air Force in August 1958, bore the name. Though Pioneers 0 through 3 failed, Pioneer 4 flew by the moon at a distance of about 58,000 kilometers in March 1959. It became the first U.S. spacecraft to escape Earth's gravity and enter orbit around the Sun.

Pioneer 5 (March 1960), a unique design, was a pathfinder for future NASA interplanetary missions. Managed by NASA's Ames Research Center (ARC), it set a new record by transmitting until it was 36.2 million kilometers from Earth.

The Pioneer series seemed to draw to a close. In 1965, however, NASA ARC applied the name to its drum-shaped interplanetary "weather stations." The first, Pioneer 6, entered solar orbit between Earth and Venus in December 1965, where it monitored magnetic fields and radiation. Pioneers 7, 8, and 9 performed similarly prosaic (and generally little noticed) missions.

The first Pioneer design included a solid-propellant rocket motor on top; this was intended to slow the spacecraft so that the moon's gravity could capture it into lunar orbit. Pioneer 0, launched under U.S. Air Force auspices, was lost when its Thor-Able booster exploded 77 seconds after launch. Pioneers 1 and 2, launched under NASA auspices, also failed to reach lunar orbit, though the former attained a record altitude of 113,781 kilometers and returned useful data before falling back to Earth (October 1958). Image credit: NASA.

NASA's Pioneer 3 and 4 lunar flyby spacecraft were launched on Redstone-derived Juno II rockets. Booster failure doomed Pioneer 3, but Pioneer 4, shown here attached to its small solid-propellant upper stage, performed a distant lunar flyby. Image credit: NASA.

Pioneer 5, intended originally as a Venus probe set for launch in June 1959, was launched instead in March 1960 as a pathfinder for subsequent NASA planetary missions. Image credit: NASA.

Pioneers 6 through 9 were drum-shaped spacecraft that measured "space weather" conditions in interplanetary space near Earth's orbit. Image credit: NASA.

The name regained star status when Pioneer 10 left Earth in March 1972. It became the first spacecraft to brave the Asteroid Belt and fly past Jupiter. Pioneer 11 launched in April 1973, bound for Jupiter and Saturn. It went silent in 1995. Pioneer 10 sent its last signal from beyond Pluto in 2003.

The final Pioneer launches occurred in 1978. The Pioneer Venus Multiprobe spacecraft dropped four instrumented capsules on Venus, while Pioneer Venus Orbiter (PVO) surveyed the planet until 1992. The latter was informally designated Pioneer 12 and the former Pioneer 13.

Pioneer 10 and Pioneer 11, the only nuclear Pioneers, were Earth's first probes to traverse the Asteroid Belt and voyage through the outer Solar System. Image credit: NASA.

Pioneer Venus Multiprobe deploys its one large and three small atmosphere probes. Against expectations, two probes survived landing and return data from the surface of Venus. No other U.S. spacecraft has landed intact on Venus. Image credit: NASA.

If NASA ARC, the Planetary Programs Division of the NASA Office of Space Science, and Hughes Aircraft had had their way, the Pioneer name might also have been applied to a Mars spacecraft. In a 1974 report prepared on contract to NASA ARC, Hughes described a Pioneer Mars Orbiter (PMO) derived from the Hughes PVO spacecraft design. The PMO mission, set for launch in 1979, was intended as a follow-on to the twin Viking missions, which were scheduled to leave Earth in 1975 and seek life on Mars in 1976.

Hughes described the PVO upon which the PMO would be based as drum 2.5 meters in diameter and 1.2 meters tall with a 3.3-meter antenna mast on top and a solid-propellant Venus orbit insertion motor on the bottom. The company then cited differences between the PMO and PVO designs: for example, PMO's orbit insertion motor would need to be larger since it would arrive at Mars traveling faster than PVO would at Venus. In addition, PMO would operate in Mars orbit, about twice as far from the Sun as Venus, so solar cells would entirely cover its sides so that they could make enough electricity to operate the spacecraft's systems. PVO would operate in Venus orbit, so it would need to be only partly covered with solar cells.

The most obvious difference between the PVO and PMO designs were the Mars spacecraft's six 2.3-meter-long, 0.3-meter-diameter penetrator launch tubes. These would replace PVO's science instruments; apart from unspecified instruments in the penetrators, PMO would carry no science payload.

PMO, like PVO, would leave Earth on an two-stage Atlas-Centaur rocket. Because PMO would weigh more than PVO (1091 kilograms versus 523 kilograms), however, it would need a solid-propellant third stage to complete Earth escape. To make room for the third stage and penetrators, PMO's conical launch shroud would be 0.8 meters longer than its PVO counterpart.

PMO would need to reach Mars on 7 September 1980 so that its Mars orbit insertion motor could place it in its planned Mars orbit. To reach the planet on that date, PMO would need to depart Earth during one of 10 consecutive daily launch opportunities starting on 28 October 1979. 2 November 1979 would be the nominal launch date. The launch opportunities would only last from 10 to 15 minutes each.

The Centaur second stage would place PMO into a low-Earth orbit, then would ignite again 30 minutes later to begin pushing the spacecraft out of Earth orbit. The third-stage motor would then ignite to place PMO on course for Mars. PMO would weigh 1069 kilograms after third-stage separation. Launch on 2 November 1979 would yield a 310-day Earth-Mars transfer.

Following third-stage separation, PMO would use hydrazine thrusters to set itself spinning at 15 revolutions per minute (RPM) for stabilization. The antenna mast bearing the high-gain, low-gain, and two penetrator data reception antennas  would revolve in the opposite direction at the same rate, so would appear to stand still. Controllers on Earth would use the thrusters to carefully target PMO so that it would not accidentally hit Mars and introduce terrestrial microbes. They would perform a final course correction 30 days before Mars arrival.

One day out from Mars, on 6 September 1980, PMO would orient itself for its Mars orbit insertion burn and increase its spin rate to 30 RPM. The spacecraft's high-gain antenna would not point at Earth during the insertion burn. Controllers on Earth could, however, send PMO commands through the low-gain antenna.

Candidate PMO orbits. Image credit: Hughes Aircraft Company.

PMO would reach Mars late in northern hemisphere summer, when the planet's south polar cap would be near its maximum extent. Hughes Aircraft proposed two possible elliptical Mars orbits — south polar and north polar — each with a period of 24.6 hours (one martian day) and a periapsis (low point) of 1000 kilometers. South polar orbit periapsis would occur above a point on Mars's surface 72° south of the equator, while north polar orbit periapsis would occur above a point at 37° north latitude. The spacecraft's high periapsis altitude would serve to forestall orbital decay, helping to ensure that PMO would not drop living terrestrial microbes on Mars. PMO would have a mass of 741 kilograms after orbit insertion.

The PMO mission's Mars orbit phase would last one martian year (686 terrestrial days). During this mission phase, PMO would deploy its six 45-kilogram penetrators singly and in pairs using a penetrator deployment system based on the Hughes-built TOW missile launcher. Before Earth departure the penetrators would be sealed inside their launch tubes and heated to kill hitchhiking microbes.

PMO deploys its first penetrator. The departing penetrator is at center right, while the exhaust plume from its small solid-propellant rocket motor gushes from the bottom end of the penetrator launch tube at lower left. On the bottom (left) side of the spacecraft, the Mars orbit-insertion engine bell is visible, as are the bottom ends of the six penetrator tubes. One tube is partly obscured by the exhaust plume, one by the orbit-insertion engine bell, and another by a neighboring penetrator tube. The top ends of three tubes are visible; one obscures the base of the counter-spun antenna mast mounted at the center of PMO's top (right) side. The high-gain dish antenna (center), two penetrator antennas, and the low-gain antenna are attached to the mast. Image credit: Hughes Aircraft Company/DSFPortree.

Penetrator deployment would occur near apoapsis (orbit high point), when the spacecraft's orbital velocity would be at its slowest. Hinged covers would open at both ends of the launch tube, then the penetrator's solid-propellant deployment rocket motor would ignite to launch it from the tube. Launching the penetrator in the direction opposite PMO's orbital motion would cancel out its orbital velocity and cause it to fall toward Mars. The dome-nosed penetrator, a Sandia Corporation design, would drop through the martian atmosphere and implant itself in the surface up to 15 meters deep.

After impact, the penetrator would extend its antenna and begin transmitting data from its science instruments. PMO would record the penetrator data for relay to Earth through its high-gain dish. Chemical batteries in the penetrators would enable each to collect and transmit data from Mars for about eight days.

For their weak signals to be received, the penetrators would need to impact the surface not far from PMO's periapsis point. The orbiter could maintain radio contact with a given penetrator for at least eight minutes at a time. A PMO in south polar orbit would initially place its penetrators between 63° and 87° south; a north-polar-orbiting PMO would place them between 56° and 80° north. Periapsis would gradually shift north or south, however, permitting placement at other latitudes. With all six penetrators deployed, PMO would have a mass of 412 kilograms.

Viking 1 and Viking 2, each of which comprised a three-legged lander and an orbiter bearing cameras, were designed with certain assumptions in mind; for example, that microbial life on Mars would be ubiquitous, so that a scoop of surface dust and a jury of three biological experiments would readily reveal its presence. Unfortunately for the proposed 1979 PMO mission and NASA Mars exploration planning in general, the Viking biology experiments yielded equivocal results that were generally interpreted as indicative of a lifeless world. This, combined with the loss of the Mars Observer spacecraft as it attempted capture into Mars orbit in 1993, helped to create a two-decade gap during which no new U.S. spacecraft explored Mars.

Sources

Pioneer Mars Surface Penetrator Mission: Mission Analysis and Orbiter Design, Hughes Aircraft Company, August 1974.

Pioneer Mars 1979 Mission Options, A. Friedlander, W. Hartmann, and J. Niehoff, Science Applications, Inc., 29 January 1974, pp. 61-99.

Solar System Log, Andrew Wilson, Jane's, 1986, pp. 12-13, 16-17, 21.

More Information

The Russians are Roving! The Russians are Roving! A 1970 JPL Plan for a 1979 Mars Rover 

Prelude to Mars Sample Return: the Mars 1984 Mission (1977)