Bridging the 1970s: Lunar Viking (1970)

NASA's lunar soft-landers: in the background, the Apollo 12 Lunar Module Intrepid; in the foreground with Apollo 12 Commander Charles Conrad, Surveyor 3. Image credit: NASA.

In the 1960s, U.S. space assets included two spacecraft designed to soft-land on the Moon. These were automated three-legged Surveyor, of which seven were launched on Atlas-Centaur rockets between June 1966 and January 1968 (five Surveyors landed successfully), and the piloted four-legged Apollo Lunar Module (LM), which landed at six sites between July 1969 and December 1972.

Even as Surveyor 7 successfully soft-landed near the great ray crater Tycho, NASA, science advisory groups, Congress, and President Lyndon Baines Johnson considered plans for a project to soft-land spacecraft on Mars. Originally conceived in late 1967/early 1968 as "Titan Mars 1973," Project Viking, as it became known, received new-start funding in the Fiscal Year (FY) 1969 budget.

NASA's Langley Research Center (LaRC) managed Viking. LaRC, located in Hampton, Virginia, contracted with Martin Marietta in Denver, Colorado, to build two new-design Viking Landers. Meanwhile, the Jet Propulsion Laboratory (JPL) in Pasadena, California, began work on two Viking Orbiters based on its Mariner flyby spacecraft design first flown in 1962. The twin Viking spacecraft would each comprise a Lander and an Orbiter, and each Lander-Orbiter combination would leave Earth atop a Titan rocket with a Centaur upper stage.

NASA at first planned to launch the Vikings in July 1973, when an opportunity for a minimum-energy Earth-Mars transfer would occur. In January 1970, however, tight funding planned for FY 1971 forced a slip to the August-September 1975 minimum-energy Earth-Mars transfer opportunity.

For NASA's piloted space program, 1970 was eventful even though only a single mission took place. The mission, Apollo 13 (11-17 April 1970), was intended to build on the experience gained through the Apollo 11 (16-24 July 1969) and Apollo 12 (14-24 November 1969) landings. The Apollo 11 LM Eagle landed long, but the Apollo 12 LM Intrepid set down close by derelict Surveyor 3 on the Ocean of Storms, demonstrating that the LM could successfully reach a predetermined target.

Landing accuracy was important for planning geologic traverses, the first of which was to have taken place at Fra Mauro during Apollo 13. An explosion in the Service Module of the Apollo 13 Command and Service Module (CSM) Odyssey scrubbed the landing and put off the first lunar geologic traverse to Apollo 14 (31 January-9 February 1971), which also was directed to Fra Mauro.

The Apollo 13 accident and postponement of subsequent missions meant that much of the activity in NASA's piloted program in 1970 concerned planning and budgets. President Richard Nixon saw no cause for a large-scale Apollo-type goal in the 1970s; NASA Administrator Thomas Paine begged to differ. Nixon appointed the Space Task Group (STG) in February 1969 — less than a month after his inauguration — and made his Vice President, Spiro Agnew, its chair. Paine, a Washington neophyte, misjudged Agnew's importance in the Nixon White House, so believed that he had scored big when Agnew declared at the Apollo 11 launch that he believed NASA should put a man on Mars before the end of the 20th century.

Paine took Agnew's statement as an endorsement of the Integrated Program Plan (IPP), NASA's proposal for its future after Apollo. The IPP included a large Earth-orbital "Space Base," nuclear rockets, lunar orbital and surface bases, a piloted Mars landing mission, and Mars orbital and surface bases. At Paine's insistence, the STG's September 1969 report The Post-Apollo Space Program: Directions for the Future offered the White House only the IPP with three different timetables for carrying it out. Nixon's aides, more cognizant of their boss's thoughts on spaceflight, added an introduction outlining a future with no major goals and no target dates.

This NASA Marshall Space Flight Center illustration from 1970 displays Integrated Program Plan hardware elements planned to be operational in the 1990s. 

Paine largely ignored this clear message, instead focusing his efforts on making a permanent Earth-orbiting Space Station NASA's 1970s goal. In addition to a host of Earth-focused uses, the Station would permit astronauts to live and work in space for long periods. This would enable aerospace physicians to certify that humans could remain in space long enough to reach and return from Mars, a voyage that might last three years. A reusable piloted logistics resupply & crew rotation spacecraft — a Space Shuttle — would economically service the Station.

Paine expected that NASA would use a two-stage version of the Saturn V rocket to launch the core Station and other large IPP hardware elements. In January 1970, however, he found himself obliged to announce that Saturn V production would end with the fifteenth rocket in the series. Apollo missions through Apollo 19 would occur at six-month intervals, ending in 1974, and Apollo 20 would be canceled so that its Saturn V, the last of the original Apollo buy, could launch the Skylab Orbital Workshop. Skylab was the last remnant of President Johnson's post-Apollo piloted program, the Apollo Applications Program (AAP), which aimed to apply successful Apollo technology to new space goals; that is, to squeeze the U.S. investment in Apollo for all it was worth.

NASA advance planning developed a split personality in 1970. Some planners assumed that Saturn V rockets would be available indefinitely; others, that the Space Shuttle would launch all IPP hardware.

For example, even as Paine announced the end of Saturn V production, NASA piloted spaceflight planners studied a versatile reusable chemical-propellant Space Tug which could double as a Saturn V fourth stage. As early as 1980, a four-stage Saturn V would launch a Lunar Orbit Space Station (LOSS). The Saturn V S-IVB third stage would boost the LOSS/Space Tug toward the Moon and detach; the Space Tug would then correct the LOSS's course en route to the Moon and slow it so that the Moon's gravity could capture it into lunar orbit.

Subsequent Saturn V missions would build up a propellant farm and fleet of Space Tugs in lunar orbit. Astronauts in Space Tugs with crew cabins and landing legs would then descend from the LOSS to resume piloted lunar surface exploration and build a Lunar Surface Base (LSB).

Space Tug outfitted for piloted lunar landings. Image credit: NASA.

In June 1970, five planners with Bellcomm, the NASA Headquarters planning contractor, completed a multi-part memorandum in which they bemoaned the "prolonged gap in the lunar program. . .of at least six years" that NASA's Space Tug/LOSS/LSB plans would create. They argued that the gap would threaten the multidisciplinary community of lunar scientists Apollo and its robotic precursors had created. The gap also meant that Apollo exploration would make discoveries that could not be followed up until at least 1980. Construction of the LSB could not proceed immediately after the LOSS was established; piloted Space Tug missions to check out prospective LSB sites would need to take place first.

The Bellcomm team proposed a novel method of filling the gap after Apollo 19 and hastening construction of the LSB. They sought to repurpose spacecraft designs expected to become available in 1975: namely, the robotic Orbiter and Lander of the Viking Mars exploration program.

At the time they wrote, neither the Viking Orbiter nor Viking Lander designs were final. The Lander, for example, would eventually carry three biology experiments and two scanning cameras, but the Bellcomm team assumed only two biology experiments and one camera. They saw this as an advantage, for it meant that the Mars Viking design was not so far along that it could not to some degree take into account anticipated Lunar Viking needs.

Lunar Viking Lander. The design depicted includes a pair of scanning cameras.  Image credit: NASA/Russell Arasmith.

The most obvious modification to the Mars Viking design for lunar missions would be replacement of the Lander aeroshell, heat shield, and parachutes with a solid-propellant landing rocket. The Lunar Viking Orbiter would expend liquid propellants to slow itself and the Lunar Viking Lander so that the Moon's gravity could capture the combination into lunar orbit, then would perform maneuvers to adjust its orbit ahead of Lander release. The Lander would then detach and, at the proper time for a landing at its target site, ignite the solid-propellant rocket.

After its propellant was expended, the motor casing would fall away. The Lunar Viking Lander would then complete descent and soft-landing using liquid-propellant vernier rockets.

The Bellcomm team outlined six basic Lunar Viking missions; some included several variants. For example, the first Lunar Viking mission, the Orbital Survey Mission, would have three variants. None would include a Lander and all would use only instruments planned for the Mars Viking Orbiter. All three would complete their main objectives a month after capture into lunar orbit.

The Orbital Survey Mission variant #1 would see a Viking Lunar Orbiter map the entire Moon in visual wavelengths at eight-meter resolution from 460-kilometer-high lunar polar orbit. Variant #2 would map the entire lunar surface in stereo at 12-meter resolution. For variant #3, a Lunar Viking Orbiter would operate in 100-kilometer orbit. This, the Bellcomm planners explained, would enable it to image potential Lunar Viking Lander and Space Tug landing sites at two-meter resolution.

The Mars Viking Orbiter was meant to transmit data at a rate of just 1000 bits per second over a distance ranging from tens of millions to hundreds of millions of kilometers (that is, from Mars to Earth). The Lunar Viking Orbiter, on the other hand, would transmit from only about 380,000 kilometers (that is, from the Moon), so in theory could transmit about 75,000 bits per second. The Viking Orbiter data recorder could, Bellcomm estimated, store up to 100 images. The Lunar Viking Orbiter would use these capabilities to image the Moon while it was out of radio contact over the farside hemisphere and transmit the farside images to Earth while it passed over the Nearside hemisphere.

A Titan III-C rocket would be sufficient to place the Lunar Viking Orbiter into a 100-kilometer circular lunar polar orbit with plenty of propellant remaining on board for additional maneuvers. An Atlas-Centaur SLV-3C rocket would suffice if after lunar-orbit capture no other maneuvers were planned.

The second type of Orbiter-only Lunar Viking mission would use a Titan III-C-launched Orbiter outfitted with a scientific instrument suite tailored specifically for lunar investigations. The Bellcomm team modeled their specialized Lunar Viking Orbiter science payload on instruments expected to be mounted in the Service Module of the advanced Apollo 16, Apollo 17, Apollo 18, and Apollo 19 CSMs.

The Bellcomm team's third Lunar Viking mission would establish twin Farside Geophysical Observatories. A Titan III-D/Centaur rocket - the rocket intended in 1970 to launch the 1975 Mars Vikings - could, they calculated, place a stripped-down Lunar Viking Orbiter with two Lunar Viking Landers attached into a 600-kilometer circular equatorial orbit. The twin Landers would then detach and land at two different Farside sites, out of direct radio contact with Earth. The Orbiter would serve as a communications satellite for retransmitting radio signals from the twin Landers. Landing site selection would be based on Orbital Survey Mission images.

The Farside Geophysical Observatory payload on the twin Landers would comprise instruments similar to those in the Apollo Lunar Scientific Experiment Package (ALSEP) the Apollo astronauts first deployed during Apollo 12. This would extend the exclusively Nearside Apollo seismic monitoring network to the farside hemisphere.

Unfortunately, a Lunar Viking Orbiter in 600-kilometer equatorial orbit could receive signals from each Lunar Viking Lander only about 10% of the time. The Bellcomm planners noted that an Orbiter in a 5000-kilometer circular equatorial orbit could communicate with a Lander at Tsiolkovskii crater (23° south latitude) 26% of the time. Launching on the Titan III-D/Centaur would, they explained, enable the stripped-down Lunar Viking Orbiter to carry enough propellants to capture into 600-kilometer orbit and, after it released the Landers, maneuver to a 5000-kilometer communications orbit for the remainder of the mission.

Bellcomm's fourth Lunar Viking mission, the Farside Geochemical Mission, would see a Lunar Viking Orbiter/augmented Lunar Viking Lander combination leave Earth atop a Titan III-D/Centaur and capture into a 2000-kilometer circular equatorial orbit. The augmented Lunar Viking Lander would detach and ignite its chemical-propellant motors to place itself into a 2000-kilometer-by-100-kilometer elliptical orbit, then would ignite them again to reach a 100-kilometer circular equatorial orbit.

Finally, it would use its solid-propellant motor to deorbit and chemical-propellant verniers to soft-land at a geologically interesting Farside site. The Bellcomm team proposed that it transport to the surface a rover weighing up to 2000 pounds. Neither the augmented Lunar Viking Lander nor the rover was described. The Orbiter, again stripped down to serve mainly as a communications satellite, would remain in its initial 2000-kilometer orbit throughout the mission.

The Polar Mission, fifth on Bellcomm's list, would see the Lunar Viking Orbiter and Lander perform science together much as the Mars Viking Orbiter and Lander were meant to do. The Orbiter would again serve as a relay, but would also carry a suite of scientific instruments. The Lunar Viking Orbiter would capture into a 100-kilometer lunar polar orbit. As it passed over the Moon's poles, it would search permanently shadowed polar craters for ice deposits.

If ice were found, the Orbiter would release the Lander and maneuver to a higher orbit to improve communications. The Lander, meanwhile, would touch down in cold darkness and use an arm-mounted scoop or perhaps a drill to collect surface material for analysis in an on-board automated lab.

The sixth and most complex Lunar Viking mission, the Transient Event Mission, would aim to find and study Transient Lunar Phenomena (TLP). The Bellcomm team, which devoted an entire appendix of their report to TLP studies, noted that TLP had been recorded for decades at many sites on the Moon by telescopic observers. Appearing as bright spots, color changes, and hazes, TLP were generally interpreted as volcanic gas releases tied, perhaps, to the tides Earth raises in the solid crust of the Moon.

According to the Bellcomm planners, about half of all TLP recorded by 1970 had occurred in and around 40-kilometer-wide Aristarchus crater, located just west of Mare Imbrium in one of the most geologically diverse areas of the Moon. The Lunar Viking Orbiter would thus spend as much time as possible within sight of Aristarchus. This requirement would, along with the need for good image resolution, dictate Lunar Viking Orbiter altitude and maneuvers.

Aristarchus is the largest and brightest crater in this Apollo 15 image. Image credit: NASA.

In June 1970, the Mars Viking Orbiter was expected to operate during a six-month Earth-Mars cruise and then for at least three months in Mars orbit. This meant that — in theory — the Lunar Viking Orbiter could be expected to seek TLP for nine months in lunar orbit. In practice, the spacecraft would pass in and out of night several times each day as it orbited the Moon from very near the beginning of its mission, placing added stress on its solar arrays, batteries, and temperature-sensitive systems.

The Bellcomm team expected that the Lunar Viking Orbiter might not last for nine months, but that it would last long enough to detect a pattern in the occurrence of TLP events. Based on this pattern, the Lunar Viking Lander would be directed to a site where it would be likely to witness a TLP event up close.

If the Lunar Viking Orbiter could not spot enough TLP events to enable scientists to detect a pattern, the Lander would be dispatched to Aristarchus. There it would seek evidence of past TLP and stand by in the hope that it might witness a TLP event.

The Bellcomm planners lamented an expected six-year gap in U.S. lunar landings. One wonders how they would have greeted the news that NASA would soft-land no spacecraft on the Moon after Apollo 17 in December 1972 - that after almost 50 years, Apollo 17 remains the last U.S. lunar soft-lander. Three automated soft-landers followed Apollo 17: the Soviet Union's Luna 21, which delivered the eight-wheeled Lunokhod 2 rover (1973); Luna 24, which collected and launched to Earth a small sample of lunar surface material (1976); and China's Chang'e 3 lander (2015), which delivered the small Yutu rover.

20 August 1975: Viking 1 launch atop a Titan III-E/Centaur rocket. Image credit: NASA.

The Viking 1 and Viking 2 spacecraft exceeded all expectations. Viking 1 reached Mars orbit on 19 June 1976. The Viking 1 Lander separated from its Orbiter and soft-landed on 20 July 1976. Viking 2 reached Mars on 7 August 1976, and its Lander touched down on 3 September 1976. The Viking Landers performed multiple life-detection experiments (with equivocal results). Together, the four spacecraft of Viking 1 and Viking 2 transmitted to Earth more than 100,000 images.

The Viking 2 Orbiter suffered a propulsion system leak and was turned off on 25 July 1978; the Viking 2 Lander suffered battery failure and was switched off on 11 April 1980. The Viking 1 Orbiter depleted its attitude-control gas supply and was turned off on 17 August 1980. Though designed to operate on Mars for 90 martian days (Sols), the Viking 1 Lander transmitted from Mars until 13 November 1982 — a total of 2245 Sols. It might have lasted longer, but a faulty command caused it to break contact with Earth.

NASA and its contractors proposed many Viking-derived missions for the late 1970s and early 1980s. These included rover and dual-rover missions, sample-returners, and landers and rovers for the martian moons Phobos and Deimos. Their planning efforts in some ways resembled those of Apollo planners in AAP and its successor/remnant, the Skylab Program. The Earth-orbiting Skylab Orbital Workshop was staffed three times in 1973-1974. There was, however, no Viking Applications Program; despite Viking's success, its spacecraft designs saw no further application.

Sources

The Post-Apollo Space Program: Directions for the Future, Space Task Group Report to the President, September 1969.

America's Next Decades in Space: A Report for the Space Task Group, NASA, September 1969.

Internal Note: Integrated Space Program - 1970-1990, IN-PD-SA-69-4, T. Sharpe & G. von Tiesenhausen, Advanced Systems Analysis Office, Program Development, NASA Marshall Space Flight Center, 10 December 1969

"U. S. Space Pace Slowed Severely," W. Normyle, Aviation Week & Space Technology, 19 January 1970, p. 16.

"Presentation Outline [Space Tug]," NASA Manned Spacecraft Center, 20 January 1970.

"NASA Budget Hits 7-Year Low," W. Normyle, Aviation Week & Space Technology, 2 February 1970, pp. 16-18.

"Viking Spacecraft for Lunar Exploration - Case 340," R. Kostoff, M. Liwshitz, S. Shapiro, W. Sill, and A. Sinclair, Bellcomm, Inc., 30 June 1970.

On Mars: Exploration of the Red Planet, 1958-1978, NASA SP-4212, E. Ezell and L. Ezell, NASA, 1984, pp. 128-153, pp. 185-201, pp. 245-284.

More Information

"Assuming That Everything Goes Perfectly Well In The Apollo Program. . ." (1967)

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

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

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