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

One of many contractor proposals for piloted flyby spacecraft put forward in the mid-1960s — this one by Douglas Aircraft Company, c. 1966. The small-diameter section is a modified Apollo Command and Service Module (CSM) spacecraft. Automated Mars probes depart the probe compartment in the large-diameter section. Image credit: Douglas Aircraft Company/San Diego Air & Space Museum (
From 1962 to 1967, NASA and its contractors studied piloted Mars/Venus flybys as a possible interim step between Apollo lunar missions in the 1960s and piloted Mars landing missions in the 1980s. Many of the conceptual flyby spacecraft designs were based on planned or proposed Apollo and Apollo Applications Program technology.

Starting in February 1967, the flyby concept fell into disfavor following criticism by the President's Science Advisory Committee (PSAC). President Lyndon Johnson's PSAC, which had previously supported the piloted flyby concept, declared that piloted flybys made unwise use of astronauts, and that NASA should reassess its plans for using of humans and robots in space. NASA substituted the word "encounter" for "flyby" and continued to task Bellcomm, its Washington, DC-based Apollo planning contractor, with studies of various aspects of piloted flyby missions.

In August 1967, however, Congress eliminated all funds for piloted flyby studies and other advanced mission planning from the Fiscal Year 1968 NASA budget. The lethal AS-204/Apollo 1 fire (27 January 1967) was a key factor in the decision to cut funding designed to give NASA a post-Apollo future. Writing in the aftermath of these cuts, Bellcomm cautioned that its February 1968 report on experiments and observations to be conducted during a 1977 Venus-Mars-Venus encounter mission "should be considered as illustrative of feasibility rather than a plan for the future."

The four-man piloted flyby spacecraft would leave Earth orbit on 23 January 1977. During an Earth-to-Venus transfer spanning mission days one through 148, the spacecraft would pass asteroid 1566 Icarus at a distance of 4.46 million miles (11 May 1977). The astronauts would use the spacecraft's one-meter telescope to measure the asteroid's albedo (reflectivity). At opportune times throughout the mission, they would conduct other astronomical observations, including studies of fluctuations in the radiation from quasars (now known to be the active cores of galaxies), zodiacal light (sunlight reflected off interplanetary dust), faint stars, the planet Mercury, and galaxy redshifts (evidence for an expanding universe).

A piloted flyby spacecraft — this time a 1967 NASA Manned Spacecraft Center design — releases a probe as it flies past the sunlit side of Venus. Visible on the spacecraft are a rectangular radar antenna for probing through the planet's dense clouds; a one-meter optical telescope; a large dish antenna for transmissions to Earth; and a small dish antenna for receiving probe data. Image credit: NASA.
On 16 June 1977, the piloted flyby spacecraft would release a 2.88-ton orbiter for relaying to Earth radio signals from the probes it would release during its first Venus flyby. The orbiter would fire rocket motors to slow down so that Venus's gravity could capture it into a 4000-kilometer-high circular orbit.

The piloted flyby spacecraft would zip past Venus for the first time on mission day 149 (21 June 1977), releasing 10 automated probes. These would include four "rough" landers, four bomb-shaped "photo sinker" probes, and two meteorological balloon probes, each containing six balloons with small instrument packages. The automated landers would be designed to survive the planet's heat and pressure for one hour after touchdown, while the sinkers would drop through the thick Venusian atmosphere for about 30 minutes and be destroyed on impact with the surface. The balloon probes would drift among the hot clouds of Venus for one month.

The flyby astronauts, meanwhile, would study Venus using their telescope and a cloud-penetrating radar. Closest approach would occur in sunlight 680 kilometers above the southern hemisphere, at which time the astronauts would fire the flyby spacecraft's rocket motors briefly to help to bend its course toward Mars.

Flight from Venus to Mars would span mission days 150 through 344. The astronauts would measure the albedo of Mars-crossing asteroid 132 Aethra from a distance of 35.9 million miles on 5 December 1977, and would study radio emissions from Jupiter in collaboration with radio astronomers on Earth. The crew would release three 2.36-ton Mars Surface Sample Return (MSSR) landers on 30 December 1977, five days before closest Mars approach.

On 3 January 1978 (mission day 345), the flyby spacecraft would pass 3960 kilometers above the martian night hemisphere at a speed of 5.6 kilometers per second. As they approached the planet, the astronauts would photograph the martian moons Deimos and Phobos.

The MSSR landers would touch down between two and four hours before flyby spacecraft closest approach. Each would deploy a drill to collect a subsurface sample and an aerosol filter to gather airborne dust. Mortars would launch other collection devices at least 100 feet to sample beyond the zone contaminated by the MSSR probe landing rockets. Each lander would then load its samples into a "rendezvous rocket" and launch it to the passing flyby spacecraft. Geophysics and exobiology experiments on the MSSR landers would then radio data to Earth for up to two years.

The Mars-to-Venus leg of the mission would span days 346 through 573. The astronauts would use the flyby spacecraft's biology laboratory to analyze the Mars samples the MSSR landers collected. They would also measure the albedo of three asteroids: 1192 Prisma, in the Main Belt between Mars and Jupiter, at a distance of 49.5 million miles (14 April 1978); 887 Alinda at 11.5 million miles (25 April 1978); and 1566 Icarus (again) at 62.3 million miles (5 August 1978). On 15 August 1978, the flyby spacecraft would release a second Venus radio-relay orbiter.

The flyby spacecraft would pass by Venus for the second time on mission day 574 (20 August 1978), releasing the same types and number of probes as during the first Venus flyby. They would be directed to targets identified using data obtained from the first flyby. Closest approach would occur in darkness over Venus's southern hemisphere at an altitude of 700 kilometers.

The Venus-to-Earth leg would span mission days 575 through 716. The astronauts would reenter Earth's atmosphere with their cargo of samples and data in a modified Apollo Command Module on 9 January 1979.


"Experiment Payloads for Manned Encounter Missions to Mars and Venus," W. Thompson, et al., Bellcomm, 21 February 1968.

The Space Program in the Post-Apollo Period, President's Science Advisory Committee, The White House, February 1967, p. 18.

"Science Advisors Urge Balanced Program," Aviation Week & Space Technology, 6 March 1967, p. 135.

Humans to Mars: Fifty Years of Mission Planning, 1950-2000, Monographs in Aerospace History #21, NASA-SP-2001-4521, David S. F. Portree, NASA History Division, NASA Headquarters, February 2001, pp. 23-32 ( - Accessed 28 March 2017).

More Information

EMPIRE Building: Ford Aeronutric's 1962 Plan for Piloted Mars/Venus Flybys

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

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


  1. Do i read it right ?
    4 astronauts put in a confinement smaller as a Salut Space station for 1.9 years round trip ?
    probably in classic work schedule - 2 men work - while 2 men sleep
    and NO woman onboard (why sound that more like Prison ?)

    You need psychological well balanced Astronauts
    to do this mission, other wise they kill each other on day 120.
    and what about Family father send on this mission ?
    the chance is high on return he face not his family on Aircraft carrier
    but a lawyer with divorce papers...

  2. This post doesn't say anything about the number of crewmembers, the gender balance of the crew, or the size of the habitable volume of the spacecraft. Nor does it report on the duty schedule. As I indicate, there were many piloted flyby designs. I can't think of any off-hand that were meant to be smaller than a Salyut. Crew numbers ranged from three to eight. There were many kinds of mission profiles; some missions lasted as little as a year. The triple-flyby mission described here is one of the longer ones. NASA was almost certainly fly a short mission first, then longer missions after that.

    This post is about how busy the crew would be during their flight. They'd have a suite of science instruments they could use between planets, either independently or in conjunction with Earth-based researchers. During flybys, the entire crew might be awake for 24 hours or longer. Studying the fresh Mars surface samples would keep the biologists and geologists busy. Plus, there'd be "space station-type" experiments to perform. It's perhaps best to think of a flyby spacecraft as an interplanetary space station.

    Crews would have to be selected with an eye toward mental stability. They'd also need to be physically healthy, though most of the piloted flyby plans included adequate medical facilities in case someone got sick. Personal lives would be impacted, of course. Crew selection would need to take that into account.

    Basically, the flyby spacecraft program would grow out of Space Station projects. Crews might live on board Earth-orbiting stations for 2-3 years, testing themselves and technology needed for long-duration flight. Then they'd launch what amounted to a station with a probe compartment on a more-or-less free-return voyage to Venus, Mars, or Mars-Venus.

    That would pave the way for Mars-Venus orbital missions and Mars landing missions. By the time this progression of missions was complete, NASA could have high confidence of success in interplanetary voyages.


  3. I love reading these proposals for Mars missions. What going to Mars have in common with tomorrow? It's always coming but never gets here. It is very fascinating to when you realize that most the science objectives in this mission were done by unmanned probes. The only we have yet to do is an unmanned Mars sample return. Did anyone see "Life" over the weekend?

    It's amazing to see how these studies come appear each decade and how they evolve as we learn more from unmanned exploration. In this particular one you can almost see the wheels grinding around the question "What kind of science could we do if we flew around Mars and Venus?" Then the wheels grind to a stop and roll in a different direction when they face the question "Why do you need people to do any of this?"

    1. In early 1968, when this report appeared, robotic exploration was at an early stage, as was, of course, piloted exploration. We had flown robotic Mars flyby and two robotic Venus flybys, plus a handful of successful robotic lunar missions. On the piloted side, we'd flown Gemini and were recovering from the Apollo 1 fire. It was by no means obvious that robots could accomplish all exploration (neither is it obvious today).

      The piloted flyby concept had among its early justifications human support for exploring robots. That is, robots were thought unlikely to survive an interplanetary journey, so sending astronauts along as caretakers seemed desirable. At the destination, the robots would need to operate independently for only a few days or hours.

      That justification ran aground on a couple of issues - first, it was assumed probes would be sterilized and sealed into individual canisters in the piloted flyby spacecraft probe bay. Servicing them would require human contact leading to contamination. Second, Mariner 2, 4, and 5 succeeded in reaching their targets (Venus, Mars, and Venus again) without human help, though not without some difficulties.

      The concept of Apollo-based piloted flybys grew from a desire to keep alive an option for piloted interplanetary voyages at a time when NASA was directed to based its future programs on Apollo technology. The hope was that flybys in the 1970s would "keep the dream alive," enabling piloted Mars landings in the 1980s. So there was a political side to this, as in all things involving humans.

      In its most advanced form, the piloted flyby concept was really a human/robot partnership. The sample-returner would set down and humans would direct some of its sample-return apparatus. It would then launch a sample capsule to the passing piloted flyby spacecraft. A biologist and a geologist would immediately open the capsule in a sealed lab. In theory, they might begin analysis of the sample within an hour of departure from Mars. This was thought to be important for biological analysis especially.

      It's interesting to note that the very first proposal for a robotic Mars sample-return spacecraft was a direct response to piloted flyby proposals. Robotic sample-return was expected to be cheaper, though perhaps not as effective because the sample would need months to return to Earth. During the voyage to Earth, it would be subjected to radiation, temperature changes, and possibly vacuum if the sample capsule leaked. The possibility that an unsealed sample capsule might land on Earth troubled people interested in planetary quarantine.

      Piloted flyby proponents - the few that existed - saw the sealed lab on the piloted flyby spacecraft as a means of maintaining planetary quarantine. After analysis, the sample would be sealed manually into a new sterilized capsule. If quarantine on the flyby spacecraft were breached, the crew would have potentially hundreds of days in which to become ill. In the worst-case scenario, the crew would simply not depart the piloted flyby spacecraft as it neared Earth - they would be lost.

      My aim with this response is to show that piloted flybys raised multiple issues. It wasn't as simple as choosing between humans and robots. The real choice was whether we would use piloted flybys as a bridge program that would see a human-robot partnership.


  4. Congradulations on another great post. You are by far the most accessible detailed source for the Manned Venus Flyby project. I had been under the impression that after the January 1967 report on the Wet Workshop spacecraft the project was shelved. Your post proves that it wasn't entirely. If I understand correctly the document assumes that it would be the Wet Workshop spacecraft on the alternative 1977 trajectory. Since Skylab can be considered as a prototype of the Manned Venus Flyby spacecraft though granted, a Dry Workshop, and back in 1968 Saturn V was still available, I am under the opinion that almost 50 years later MVF is still the most realistic interplanetary spacecraft proposed. All plans since talk about habitation and science modules which have never quite left the ground plus rockets and propulsion modules that have not quite flown MVF, with actual space flown hardware on an actual rocket looks most mature, with the possible exception of the 1987 Soviet Mars plan you mention in your book. Of course if anything SKylab proved the MVF spacecraft mass estimations were off, more equipment was necessary for a habitable station than what was planned at the time, which would have meant that Saturn V would have been insufficient, but still...

    1. I haven't written anything on the Wet Workshop Venus flyby proposal, I'm afraid. At least not yet. This post is related to the Planetary JAG piloted flyby scenarios, which enjoyed high-level support for a time. In my sources I posted a link to Chapter 4 of my NASA-published book HUMANS TO MARS. That chapter describes the Planetary JAG and its piloted flyby scenarios.

      I have written about a single-launch piloted Venus orbiter. I don't recall off-hand where I last posted it. This blog includes among its wholly new posts updated, corrected, combined, and expanded versions of posts from past blogs, just as those past blogs contained revised pages from my Romance to Reality website (1996-2006). This blog continues that tradition.


    2. I was under the impression that the EMPIRE and post EMPIRE studies listed at the bottom of this article relate to the MVF concept.

    3. Sorry to give you that impression. That's a well-known piloted flyby study, but it was on the fringes - NASA and NASA contractor work was more along the lines of the Planetary JAG studies.


  5. It seems that the manned flyby got tied with Mars-Voyager until August 1967 when Congress killed both.

    1. Piloted flybys would have mined Mars/Venus Voyager for probe technology - the minds behind the 1966 Planetary JAG study were very frank about that. JPL cared for that not at all - saw piloted flybys as competition, also something unlikely to ever occur that could drag Voyager down with it. It's probably overstating the case to say piloted flybys destroyed Voyager - it had never been a popular program and suffered its share of setbacks, some of which were JPL's fault - but linking the programs did contribute to the perception in Congress that Voyager was a costly foot in the door leading to (even more costly) piloted Mars missions. After the Apollo 1 fire, however, Congress was looking to cut (or at least not increase funding for) most everything in the NASA budget not related to reaching the moon before the Russians. So Voyager might have survived without the fire. It was rapidly resurrected as Viking in FY 1969, along with Mariner 8/9 in 1971 as a Viking precursor. Mariner 9/Viking was Voyager Light.


  6. On 3 January 1978 (mission day 345), the flyby spacecraft would pass 3960 kilometers above the martian night hemisphere at a speed of 5.6 kilometers per second. As they approached the planet, the astronauts would photograph the martian moons Deimos and Phobos. Yeah. They couldn't photograph anything else because the Martian hemisphere would be in darkness. Combined with an opaque Venus, this flight sounds like a tourist's dream. No wonder why a sane Congress wpuld never fund this crap

  7. It would've been interesting if the Soviets went with Venus flyby as a crazy propaganda move. The N-1 with the kinks hammered out somewhat a R-7 Soyuz crew vehicle could do a flyby with a 2/3-person flyby like the Zond lunar mission. That could've pushed the US to invest more in space...


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