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.


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)


  1. ESA had made similar study in 1980s (1981 to 1988)
    for spin stabilized Mars Orbiter called "Kepler"
    to be launch with Ariane 3 the probe would go in elliptical orbit around Mars.

  2. I remember Kepler - though just barely! Was it intended to deploy a lander or landers?


  3. nope, simply a low cost Mars Orbiter

  4. Very interesting the criteria that made a pioneer, a pioneer. Never knew that before. Was there anything after Pioneer Venus that might have otherwis taken on that famous name?

  5. Galileo had some Pioneer heritage, or so I've heard it said. I'm not aware of any others.


    1. I corrected and fleshed out some of the Pioneer mission details. I should learn that I cannot rely on my memory for specific mission information.


  6. i know New Horizons came out of the NASA “New Fronteers” mission projects but were back when would it have been a Pioneer under the definition in the article.

  7. U:

    That's a tough question to answer. I suppose if we'd kept the Pioneer label alive - the way we've retained the "Explorer" label - then it could have been applied to just about any mission. One thing to consider, though - Pioneer became associated with NASA Ames Research Center early on. All the Pioneers starting with Pioneer 5 were NASA ARC-managed. So, if that trend had continued, then New Horizons would probably not have been a Pioneer mission.


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  9. I remember being intrigued when I first read about this plan at Beyond Apollo, so it's nice to read a bit more information about it on this post, that's the most interesting stuff, proposals that were actually feasible, although never realized. It was stupid of NASA to sell Viking simply as a mission about finding life on Mars, although I never understood why if life indeed doesn't exist on Mars we should view that as something bad. Hardly the only stupid thing NASA ever done though.

    1. Anon:

      My policy is rescue and revise. Sometimes I don't change much - other times it's an extensive rewrite. I've even merged some posts. Some of my posts have been around since the 1990s, but if you put the original version next to the latest version, you'd see few similarities beyond the basic topic. And, of course, I am writing new posts. I won't count the "toy spaceships" post - the most recent wholly new post I've written is the Chrysler space pod post.

      How NASA sold Viking - that's a complicated topic. Mars has a mystique attached to it that will come back at you if you're not careful. We're steeped in Percival Lowell's Mars even now, I think. The planet is, however, a truly harsh place. In the 1968-1975 period, when Mariner 9 and the Vikings were prepared and launched, we truly did not understand that. We designed Viking for a world like Earth, where life is ubiquitous. That made sense based on what we knew at the time, which wasn't nearly enough.

      NASA didn't make its Mars decisions on its own - planetary scientists, working with the best data they had, shaped the NASA Mars Program in the 1960s-1970s, just as they do now. Politicians looked at NASA's plans and made funding decisions, just as they do now. The media looked at NASA's activities and reported them badly to NASA's stakeholders, U.S. taxpayers, just as they do now.

      Viking didn't show that Mars is lifeless. It showed that working out whether life exists on Mars or not would be a complicated process. The penetrator mission - and Mars 1984, which I wrote about here - - were conceived withe the scientific method in mind. The first set of hypotheses we formed concerning Mars were (possibly) disproved, so it was time to go at it with a new set of hypotheses. Unfortunately, we weren't funding many robotic missions, in part because of Shuttle budget overruns. Galileo and HST grew out of the late 1970s epoch, but missions to more fully characterize Mars had to wait.

      There was a sense that Mars had had its turn. Also, Viking and Voyager crushed stated Soviet plans to explore and sample the Solar System using robots. And, robotic missions were more costly than they are now.

      I don't think one can characterize NASA planning as "stupid" in this instance. Not to sound too corny, but is a child learning to crawl stupid? Is a person arriving unexpectedly in a new city in a new country without a map or phrasebook stupid? Was Galileo, pointing a lousy telescope at the moon and rolling metal balls down inclined planes, a stupid man?

      What has happened since 1997 is we've learned things about Earth that apply to Mars and we've ramped up our Mars exploration capabilities and knowledge. Here's where we are now, I think. (continued in next reply)


    2. (continued from last reply)

      We know that life on Earth can take some pretty weird forms and live in some pretty inhospitable places. We believe that the earliest life formed near (or even in) hot springs. We know that life formed very early. We know that, by some estimates, Earth has more biomass under its surface than it does on its surface. Much of that life appears to resemble the earliest forms of life that formed on Earth.

      We know that water flowed on a warm Mars until about a billion years ago, by which time life on Earth had been established for more than two billion years. We know that the environment changed on Mars, just as it has on Earth. Earth grew more cozy for multicellular forms in large part because of the actions of single-celled forms. Mars, on the other hand, developed a harsh surface environment and appears to have never made the jump to multicellularity (but we can't know for sure). Life never took charge of the surface environment as it has on Earth, in any case. Changes in the surface environment of Mars had other causes that were inimical to life.

      So, what we've done is pretty much what the Mars 1984 planners wanted to do - we've just spread it out. Which to me means that the real search for life on Mars can soon begin. We might have to stop thinking of Mars as a place for bigger and bigger rovers - or at least a place for those plus more missions with other capabilities. Insight should tell us a lot about subsurface heat-flow.

      If we find that, say, Mars are Earth have a same sort of environment a kilometer or so down, then it's time to drill with a mind toward planetary protection. I predict that that is when we'll find life *in* Mars. The technology for robotically drilling into Mars will, incidentally, also apply to places like Europa, Titan, and Enceladus.


  10. I am neither American or former Soviet to have even the most minimal nationalistic element in my thinking, and exploration of other worlds, which is what space exploration really is about as I see it, is a gain for all humanity no matter which nation conducts it. However, the nationalistic element was there during the cold war, but I don't understand what is meant by saying that Viking and Voyager programs destroyed Soviet planetary exploration ambitions. Between August 1978 and November 1989, a period of more than 11 years, the US didn't launch even a single planetary probe, or a lunar for that matter, while the USSR launched 10, definitely narrowing the gap that existed during the '60s and the '70s, when the US did have a certain lead in planetary exploration. There were indeed some even more ambitious Soviet plans, like MSR missions, that were not realized, but it's doubtful that they could ever have been successful, give the state of the technology of the time.

  11. A:

    I might not have expressed myself well on that point. During Apollo, the USSR declared that it would explore everywhere using robots, not placing cosmonaut lives at risk and saving lots of money. Let the decadent capitalists endanger lives and blow tens of billions of dollars. They them proceeded to launch the Lunokhod rovers and the Luna 16, 20, and 24 sample-returners to the moon, and announced plans for robotic Mars and Venus exploration in the 1970s. The US responded with Mariner 9 and 10, the twin Voyagers, and the twin Vikings. All succeeded magnificently, while all the Soviet Mars missions failed (or at least underperformed). The Soviet Mars program ended in the mid 1970s and would not start up again until the late 1980s. The Soviets then shifted their attention to Venus until the late 1980s.

    The US did an end run around the Soviets, essentially. US spacecraft outperformed Soviet ones at Mars and visited Mercury, Jupiter, Saturn, Uranus, and Neptune and their moon systems before the Soviets could launch missions to those worlds. This gave the Soviets very little scope for impressive firsts.


  12. Regarding planetary exploration, and that means flights beyond the Earth-Moon system, the US took an early lead with the Mariner 2 mission in 1962, and has essentially retained that since, although of course there is no longer USSR. Specifically regarding the Soviet Mars missions, we must always make the distinction between orbiter and lander missions. The orbiter missions, naturally in regard to those ones that actually made it to Mars, were reasonably succesfull, returning lots of data and photos, while the lander missions were a failure, however despite unimaginably superior technology to that available to the Soviets at the time, no nation or consortium of nations has ever succeeded in landing a spacecraft on Mars (see Beagle 2 and Schiaparelli) apart from United States, somethng that puts the problems faced by the Soviet Mars exploration in some perspective and it takes a lot of Cold War bias in order to characterise those missions failures without first making a distinction between orbiter and lander ones. During the 1978-89 period, the US planetary program was not entirely dead, since spacecraft launched by 1978 did a lot of exploration (the Voyager flybys took place during that period after all), however the gap in planetary exploration was smaller then during any other period, for the very simple reason that the US no longer launched planetary probes while the USSR did, and achieved some important first during that period, like the first use of balloons on another world, the first use of SAR (synthetic aperture radar) and the first ever images from a cometary nucleus. There was scope for even more impressive firsts, had for example the 5NM Mars Sample Return mission been realized, so the true limit for the Soviets was not a lack of potential firsts but rather the limitations of their technology.

    1. A:

      All that you say makes sense, though it's telling that when the Soviets published popular-audience pamphlets on their Mars program they nearly always used Mariner and Viking images. Soviet planetary spacecraft just weren't all that good. They've abandoned the field now.



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