A Robotic and Piloted Planetary Exploration Program for the 1970s and Early 1980s (1968)

Leaving home: Earth as viewed from Apollo 4 on 9 November 1967. Image credit: NASA.
It was the best of times. It was the worst of times. (With apologies to Charles Dickens.)

For NASA, the year 1967 began with the promise of a bold start for the Apollo Applications Program (AAP), the planned successor to the Apollo lunar program, which would see space station missions in low-Earth orbit and advanced lunar exploration missions. Top NASA officials briefed the press on their ambitious AAP plans on 26 January 1967 (see "More Information" below). 

Barely a day later, fire raged through the crew cabin of the Apollo 1 Command and Service Module (CSM) spacecraft during a test on the launch pad, killing astronauts Gus Grissom, Ed White, and Roger Chaffee. The resulting investigation angered Congress — NASA had failed to report persistent problems in its relations with North American Aviation (NAA), the CSM prime contractor. Affronted legislators, already eager to cut government expenditures because of the soaring cost of U.S. military involvement in Indochina, responded in August-September 1967 by slashing President Lyndon Baines Johnson's Fiscal Year (FY) 1968 NASA budget request by nearly half a billion dollars. 

The cuts mostly affected projects aimed at giving NASA a post-Apollo future; AAP, of course, but also the Voyager robotic Venus/Mars exploration program (see "More Information" below) and advance planning for piloted missions beyond the Moon, including piloted Mars/Venus flybys. Members of the NASA Office of Manned Space Flight (OMSF) Planetary Joint Action Group (JAG) had hoped that major funding for piloted flybys could begin in FY 1969, with the first in a series of piloted flybys — a Mars flyby with sample return — leaving Earth in late 1975 (see "More Information" below).

Even as OMSF had sought piloted flybys, the scientific community had continued its perennial quest for an expanded robotic program. In a February 1967 report to the Johnson White House, the President's Science Advisory Council (PSAC) disparaged piloted flybys and urged a 1970s program that would see robotic spacecraft begin a wide-ranging reconnaissance of the entire Solar System. Scientists were outraged when instead the FY 1968 budget cuts threatened to end U.S. robotic exploration entirely after the twin Mariner '69 Mars flybys.

In October and November 1967, NASA Administrator James Webb spoke out in favor of new robotic planetary missions in the 1970s. He urged members of Congress to take note of Soviet plans for robotic exploration beyond the Moon. Talks began with White House budget officials and Congressional leaders aimed at salvaging a 1970s planetary program from the wreckage of the FY 1968 budget process.

Meanwhile, in Florida, components of AS-501, the first flight-ready Saturn V rocket, came together with an Apollo CSM in the giant Vertical Assembly Building (VAB) at NASA Kennedy Space Center (KSC). Without the three-stage behemoth an Apollo Moon landing was impossible.  The testing and assembly process had begun months before the Apollo 1 fire with the aim of a launch in the first quarter of 1967, but preparation for the automated test mission — which NASA designated Apollo 4 — hit one snag after another. 

Following the fire, NASA subjected the CSM NAA had delivered to KSC for the Apollo 4 mission to enhanced scrutiny. The spacecraft, designated CSM-017, was found to contain more than 1400 wiring errors. Fixing them required months. Welding errors in the NAA-built Saturn V S-II second stage also needed correction. 

Troubled assembly: the Apollo 4 CSM and Saturn V rocket in the Vertical Assembly Building at NASA Kennedy Space Center, Florida. Image credit: NASA.
The giant rocket was at last rolled out to Launch Pad 39A on 26 August 1967, but its troubles were not over, for Apollo 4 was also a test of launch pad hardware and pre-launch procedures. As the launch team struggled to make pad and rocket function together, the press, the public, and the Congress became increasingly impatient.

Apollo 4 lifted off at last on 9 November 1967. Rocket, spacecraft, launch facilities, and world-wide tracking & communications network operated together almost flawlessly.

The Apollo 4 Saturn V and CSM climb toward orbit. Image credit: NASA.
About three hours after insertion into a 190-kilometer-high (118-mile-high) low-Earth orbit, the AS-501 Saturn V S-IVB third stage restarted to boost CSM-017 into an elliptical orbit. It was the first orbital restart of the stage, which would boost Apollo missions out of Earth orbit to the Moon. 

Near orbital apogee CSM-017 separated from the S-IVB. The spacecraft fired its Service Propulsion System (SPS) main engine to increase its altitude to 18,092 kilometers (11,242 miles), then fired it again for 4 minutes and 30 seconds to hurl itself at Earth at a lunar-return speed of 24,911 miles (40,090 kilometers) per hour. 

CSM-017 split into its component modules — Command Module (CM) and Service Module (SM) — then the former reoriented itself with its bowl-shaped heat shield forward so that it could withstand fiery atmosphere reentry. The SM burned up as planned. The CM's heat shield, meanwhile, reached a temperature of nearly 2760 C (5000° F). Crew cabin temperature did not exceed 21 C (70° F). Just eight and a half hours after liftoff, the Apollo 4 CM deployed three parachutes and lowered to a splashdown in the Pacific. 

The unmanned Apollo 4 Command Module (right) bobs in the Pacific Ocean near Hawaii at the end of its eight-and-a-half-hour test flight. One of its three main parachutes remains attached; it would be retrieved for analysis along with the spacecraft. Image credit: NASA.
The trade magazine Aviation Week & Space Technology reported that, ironically, on the very day of NASA's Apollo 4 triumph, NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, had laid off workers as a result of the FY 1968 budget cuts. NASA MSFC was the home of the Saturn family of rockets. 

On 12 December 1967, a little more than a month after Apollo 4, President Lyndon Baines Johnson toured NASA's Michoud Assembly Facility near New Orleans, Louisiana, where Saturn rockets were assembled and tested. His visit was meant to reassure local and state officials and to raise worker morale. Whether he succeeded is open to interpretation. Standing before a partially complete Saturn V S-IC first stage, Johnson told the workers

. . .that man will make space his domain is inevitable. Whether America will lead mankind to that destiny does not depend on your ability, but depends on our vision, our willingness, and our national will and determination. This great pilgrimage of man — like all his adventures — costs money. Christopher Columbus spent more years trying to find money for his voyage than he spent discovering the New World. In the modern world, we can no longer depend on Queen Isabella pawning her jewels. We have to depend on taxes. We must have revenues that only Congress can grant. . . So we will advance in space to the extent that our people and their representatives are prepared for us to advance and are prepared to pay the cost of that advance. We may not always proceed at the pace we desire. I regret — I deeply regret — that there have been reductions and there will be more. There have been interruptions. . . But I do have faith and confidence in the American people.

This background may help to explain why two engineers at Bellcomm, NASA's Washington, DC-based advance planning contractor, responded as they did when NASA invited them in late November-early December 1967, to state their opinions on the course U.S. planetary exploration should take in the 1970s and early 1980s. In a report completed and distributed to relevant NASA facilities on 26 February 1968, J. P. Downs and W. B. Thompson were cautiously optimistic. 

Downs and Thompson explained that their report reflected "the authors' thinking at. . . [a] particular time" and that it was "a reflection of a long term point of view." They assumed that the deep FY 1968 budget cuts were a short-term, temporary setback, not a sign of a long-term trend. In fact, they anticipated an annual NASA budget of between $5 billion and $6 billion by FY 1971 or FY 1972, when, they expected, NASA would start development of a piloted planetary program.

At the same time, the Bellcomm engineers cautioned that "[a]s more information becomes available on technical details and resources, the program may change." They added, however, that "the rationale expressed. . . is expected to remain much as it is now."

Downs and Thompson described a NASA planetary program containing 21 missions to 11 Solar System bodies between the years 1969 and 1984. Missions would occur in three "branches." The first branch would comprise missions to Venus and Mars that would serve as precursors to at least three piloted Mars and Venus missions. Missions in the second branch would explore Mercury, Jupiter, and the other "major planets" (Saturn, Uranus, and Neptune), a task they called "the major challenge to the unmanned program." The third branch would include missions to explore two comets and two asteroids. 

Their program would begin with the twin Mariner '69 Mars flybys already on NASA's schedule and continue in 1970 with a Mariner Venus/Mercury dual flyby mission launched on an Atlas/Centaur rocket. The Atlas/Centaur was already in early 1968 the workhorse of the NASA robotic lunar and planetary program. 

The Venus/Mercury mission, which would form part of both the first and second of Downs and Thompson's three branches, would seek gaps in Venus's cloud cover in the hope of glimpsing its mysterious surface. In addition, as the spacecraft flew past the planet, it would transmit radio signals to Earth through the Venusian atmosphere in an attempt to chart its structure.

Mariner Mars '69 engineering model. Note the large steerable camera "pod" mounted below the hexagonal bus body, the high-gain dish antenna on top, and the four solar arrays. Image credit: NASA.

Space workhorse: an Atlas-Centaur rocket launches the Surveyor 1 lunar lander on 30 May 1966. Image credit: NASA.
During the flyby, Venus would give the spacecraft a gravity assist that would reduce by between 50% and 75% the amount of propulsive energy it would need to reach Mercury. Downs and Thompson explained that the innermost planet is, by dint of its proximity to the Sun, often lost in glare when viewed from Earth and hence mysterious; orbiting close to the Sun also means that its orbital speed is high, making it difficult for spacecraft to reach.

In 1971, NASA would launch on a Titan III-C rocket its first new-design Mars orbiter and surface probe. Downs and Thompson suggested that the new orbiter might be based on the Boeing Lunar Orbiter design. The Titan III-C, a U.S. Air Force rocket, was meant to replace the Saturn IB-Centaur rocket formerly emphasized in NASA planetary mission plans. Use of the Titan III-C in the Downs and Thompson program was a response to a statement by NASA Administrator James Webb that the Saturn IB would be phased out to save money. 

18 June 1965: the first Titan III-C rocket stands on the pad at Launch Complex 40, Cape Canaveral Air Force Station, Florida. Image credit: U.S. Air Force.

Boeing-built Lunar Orbiter spacecraft. Image credit: NASA.
The 159-kilogram (350-pound) battery-powered survivable surface impactor probe would include an atmosphere entry shell, a parachute, a protective impact shell carved from soft, lightweight balsa wood, and 13 pounds of science instruments. These might include a life detection device. Instruments on the entry shell would  chart atmospheric structure as it plummeted toward the surface after separation from the impactor. These data would enable engineers to design heavier, more sophisticated Mars landers. 

NASA would launch in 1972 its first new-design Venus orbiter and atmospheric probe on a Titan III-C. In addition to "a concentrated search over the entire planet for visible access to the surface," the orbiter would employ an imaging radar to chart surface topography. The probe would measure the thermodynamic properties of the atmosphere to enable design of meteorological balloon probes suited to Venusian conditions.

In 1973, NASA would ramp up the pace by launching on three Titan III-Cs a pair of Mars orbiter/impactor probe missions and a second Mariner-derived Venus/Mercury flyby spacecraft. The latter would resemble that launched in 1970 but would add a Venus survivable surface impactor probe. The prime objective of the Mars impactor probes would be to search for life. 

The 600-pound Venus impactor probe would attempt to return data on the planet's harsh surface conditions for at least an hour. The dense Venusian atmosphere would, Downs and Thompson wrote, enable a survivable landing without a parachute.

The following year, NASA would launch its first flyby mission to Jupiter on a Titan III-C augmented with a Centaur upper stage. Dubbed a "galactic Jupiter probe," it would be the first NASA spacecraft designed for an operational lifetime of up to 10 years. It would survey interplanetary particles and fields and aid future spacecraft designers by surveying the interplanetary meteoroid environment with particular emphasis on the Asteroid Belt between Mars and Jupiter. A Jupiter gravity-assist would make it the first spacecraft to escape the gravitational grip of the Sun.

NASA would ramp up the planetary exploration pace in 1975 by launching four rockets — probably Titan III-Cs with Centaur upper stages. An orbiter and surface probe would leave Earth for Mars. Two orbiters with impact lander probes would launch to Venus. The space agency would also launch a clone of the 1974 galactic Jupiter probe mission.

The year 1976 would see NASA's first mission to a comet. After launch on an Atlas/Centaur, a Mariner-derived spacecraft would race past Comet d'Arrest. Downs and Thompson explained that the small size of the comet nucleus and the rapid speed of the flyby would require NASA to develop a sophisticated new tracking system for its comet spacecraft cameras.

In 1977, the first Mariner-derived "Grand Tour" spacecraft would depart Earth on a Titan III-C/Centaur. A series of gravity-assist flybys would speed it across the outer Solar System, enabling it to explore all four planets beyond the Asteroid Belt in the space of a decade. That same year, NASA would launch on two Titan III-C/Centaur rockets a Mars orbiter with an impactor and a Venus orbiter with a pair of impactors. The Venus impactors might be targeted to land on high-elevation surface features; these might, Downs and Thompson suggested, have cooler temperatures than lower elevations, and thus be more likely to support life.

The year 1978 would see launch of NASA's first asteroid mission (a flyby of asteroid Icarus using a Mariner-derived spacecraft launched on a Atlas/Centaur) and the second "Grand Tour" mission (a clone of the 1977 mission). It would also see an significant shift in the character of the U.S. planetary program as astronauts joined the action. 

Thompson was a veteran of the NASA OMSF Planetary JAG piloted flyby studies. The NASA budget seemed unlikely to stretch far enough to support development in time to carry out the Planetary JAG's 1975 piloted Mars flyby mission, so the Bellcomm engineers opted instead to take advantage of an opportunity to launch a piloted Venus/Mars/Venus flyby mission in late 1978. 

The piloted flyby spacecraft and its Earth-orbit departure booster stack would be assembled in Earth orbit using components launched on two-stage Saturn V rockets. After leaving Earth orbit and discarding its boosters, it would follow a free-return heliocentric path that would end at Earth. Only minor course corrections would be required after Earth-orbit departure.

In 1979, the crew of the piloted flyby spacecraft would deploy automated meteorological balloons and impactor probes as they passed Venus for the first time and automated sample returners as they passed Mars. The balloons would drift the Venusian atmosphere for a long period. They would seek evidence of life in cool atmosphere layers. 

Astronauts would examine in a sealed lab the Mars dirt and air the sample returners launched to the flyby spacecraft to determine whether they could be safely returned to laboratories on Earth. The following year (1980) would see the mission carry out its second Venus flyby — a clone of the first — followed a few months later by a direct Earth-atmosphere reentry.

The years 1979 and 1980 would also see the last two Mariner-derived comet/asteroid flyby missions on the Downs and Thompson schedule. The first, the last mission launched on an Atlas/Centaur, would visit asteroid Eros, while the second, launched on a Titan III-C/Centaur, would race past Comet Encke.

A second piloted flyby mission would depart Earth in 1981. During its Venus flybys in that year and in 1983 it would deploy a pair of balloon-borne "several thousand pound" Buoyant Venus Stations of a type proposed by the Martin Company in 1967, as well as an unspecified number of long-duration Venus landers. All would look for life. The Mars flyby in 1982 would see more surface sample collection and observations tailored toward selecting sites for eventual piloted Mars landings.

Downs and Thompson expected that their 1984 piloted planetary mission, the last on their schedule, would probably take the form of a Venus orbiter. A piloted Venus mission would, they wrote, "serve to pace the development of a high energy space storable propulsion system." After proving that it could slow the piloted Venus spacecraft so that Venus's gravity could capture it into orbit and accelerate it out of Venus orbit back toward Earth, the compact, powerful, long-lived rocket stage would propel piloted Mars orbiter and landing missions and boost out of Earth orbit large new-design robotic outer planet and "deep space" spacecraft.

The Bellcomm engineers' report landed on desks across NASA in late February. Their timing could have been better — barely a month ahead of its distribution North Vietnam attacked South Vietnam on the eve of Tet, the Chinese New Year, leading to greatly expanded U.S. involvement in the Vietnam War. The Tet Offensive created new pressure on the Federal purse, helping to ensure (among other things) that NASA's budget slide would continue in FY 1969 and beyond.  

Despite the war and other national challenges, in the period covered by the Downs and Thompson plan NASA managed to fly a dozen planetary missions, of which 11 reached their targets. In large part, these were justified in terms of heading off new Soviet space victories and providing an avenue for the development of new technology with defense implications. 

All the flown missions were directed toward major planets; none would visit asteroids or comets and (of course) none would include astronauts. Italicized initial dates given below are launch years.

  • 1969: The Mariner '69 Mars flyby spacecraft were designated Mariner 6 and Mariner 7 after launch; they left Earth atop Atlas/Centaur rockets.
  • 1971: The Mariner '71 Mars orbiter spacecraft were designated Mariner 8 and Mariner 9 after launch; Mariner 8's Atlas/Centaur rocket malfunctioned but Mariner 9, the first planetary orbiter, was a great success, mapping all of Mars until late 1972.
  • 1972: Pioneer 10, launched on an Atlas/Centaur rocket with a solid-propellant kick stage, became the first spacecraft to traverse the Asteroid Belt;  in 1973, it became the first spacecraft to fly past Jupiter. The gravity-assist kick it received made it the first spacecraft placed on a path to escape the Solar System.
  • 1973: Pioneer 11 followed Pioneer 10 through the Asteroid Belt to Jupiter; in 1979 it became the first spacecraft to fly past Saturn.
  • 1973: Mariner 10 left Earth on an Atlas/Centaur rocket and flew past Venus in early 1974; later that year it became the first spacecraft to fly past Mercury. It flew past Mercury twice more in 1974-1975.
  • 1975: Viking 1 and Viking 2, each of which comprised a lander and a Mariner-derived orbiter, launched atop Titan III-E rockets, arriving in Mars orbit in June 1976 and August 1976, respectively. Viking 1, which touched down on 20 July 1976, was the first successful Mars lander; Viking 2 landed successfully on 3 September 1976. Their life detection experiments yielded equivocal results.
  • 1977: The Mariner Jupiter-Saturn '77 spacecraft were renamed Voyager 1 and Voyager 2. They left Earth atop Titan III-E rockets. Voyager 1 flew past Jupiter in 1979 and Saturn in 1980; Voyager 2 flew past Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989.
  • 1978: Pioneer Venus Orbiter and Pioneer Venus Multiprobe (PVM) launched atop Atlas/Centaur rockets. Though not designed to survive landing, one PVM small probe continued to operate after striking the surface, becoming the first (so far only) successful U.S. Venus lander.

The Pioneer Venus Multiprobe bus (lower right) is shown deploying three small probes (center) and one large probe (upper left). In reality the large probe was deployed on 16 November 1978 and the small probes were deployed on 20 November 1978. The bus and probes entered the Venusian atmosphere on 9 December 1978. Image credit: NASA.
In their report, Downs and Thompson anticipated that NASA would be given the go-ahead to start a new piloted planetary program in FY 1971 or  FY 1972, and after a fashion they were correct. In January 1972, President Richard Nixon called on Congress to fund the winged Earth-orbital Space Shuttle. 

Originally proposed as a low-cost fully reusable Space Station crew rotation and resupply vehicle, the Shuttle became instead a multi-purpose spacecraft after Nixon refused to fund a Space Station. It would be only semi-reusable, which lowered its development cost but dramatically increased its operations cost. Among its goals was to launch all U.S. robotic planetary spacecraft.

Downs and Thompson's NASA budget prediction — $5-6 billion annually by about FY 1972 — entirely missed the mark. In terms of buying power in an inflationary time, NASA's budget remained at about half that amount throughout the 1970s and early-to-mid 1980s. Funding scarcity adversely impacted both Shuttle development and planetary exploration. 

Shuttle development problems traceable to funding shortfalls, lack of successful new Soviet planetary missions, tight planetary science budgets, and the Challenger accident (28 January 1986) came together to create an 11-year hiatus in new U.S. planetary launches following the 1978 Pioneer launches. The stoppage ended at last with the launch of the Magellan Venus radar mapper on board the Shuttle Orbiter Atlantis on 4 May 1989. 

By the time Magellan flew, NASA had announced that it would cease Shuttle planetary launches after it launched the Galileo Jupiter orbiter and probe and Europe's Ulysses solar polar orbiter in favor of resuming planetary launches on expendable rockets. Galileo launched on board the Orbiter Atlantis on 18 October 1989 and Ulysses launched on board the Orbiter Discovery on 6 October 1990. 


The first two sentences of this post are based on the first sentence of Charles Dickens' 1859 novel A Tale of Two Cities.

The Space Program in the Post-Apollo Period: A Report of the President's Science Advisory Committee, "Prepared by the Joint Space Panels," The White House, February 1967.

"Science Advisers Urge Balanced Program," Aviation Week & Space Technology, 6 March 1967, pp. 133-137.

"Orbiters Studied for Planetary Missions," W. J. Normyle, Aviation Week & Space Technology, 23 October 1967, pp. 30-32.

"Washington Roundup: NASA Thanks You," Aviation Week & Space Technology, 20 November 1967, p. 25.

"Apollo 4 Closes Gaps to Lunar Mission," W. J. Normyle, Aviation Week & Space Technology, 20 November 1967, p. 26-27.

"NASA Pushes Planetary Program," W. J. Normyle, Aviation Week & Space Technology, 27 November 1967, pp. 16-17.

"Remarks Following an Inspection of NASA's Michoud Assembly Facility Near New Orleans," President Lyndon Baines Johnson, 12 December 1967 (https://www.presidency.ucsb.edu/documents/remarks-following-inspection-nasas-michoud-assembly-facility-near-new-orleans — accessed 30 August 2022).

"A Feasible Planetary Exploration Program Through 1980 — Case 710," J. P. Downs and W. B. Thompson, Bellcomm, Inc., 26 February 1968.

Astronautics & Aeronautics 1967, NASA SP-4008, 1968, pp. 43-45, 246, 248, 255-256, 282-284, 295-296, 314, 320, 323-324, 333, 336-343, 352-353, 373-375.

Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, NASA SP-4206, Roger E. Bilstein, NASA, 1980, pp. 351-360.

More Information

"Essential Data": A 1963 Pitch to Expand NASA's Robotic Exploration Programs

NASA's Planetary Joint Action Group Piloted Mars Flyby Study (1966)

Missions to Comet d'Arrest & Asteroid Eros in the 1970s (1966)

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)

The First Voyager (1967)

Triple Flyby: Venus-Mars-Venus Piloted Missions in the Late 1970s/Early 1980s (1967)

Things to Do During a Venus-Mars-Venus Piloted Flyby Mission (1968)

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