Image: NASA.

In mid-1964, an in-house team of engineers at Marshall Space Flight Center (MSFC) in Huntsville, Alabama, became the first NASA group to study piloted Mars/Venus flybys based on Apollo Program hardware. They conducted their study because they wanted to see humans voyage to other planets, and because President Lyndon B. Johnson had made clear that, to contain spaceflight costs, the post-lunar landing space program should be based on hardware developed for Apollo lunar landings.

In public statements, NASA emphasized that LBJs vision called for a series of Earth-orbiting space stations based on Saturn rocket and Apollo Lunar Module (LM) components. Modified Apollo Command and Service Module (CSM) spacecraft would ferry scientist-astronauts, supplies, and new experiment apparatus to the low-cost stations, which would, it was hoped, provide concrete benefits to American taxpayers through research into biomedicine, new manufacturing processes, Earth and Sun observations, and advanced technology development.

The Johnson vision made no mention of piloted Mars/Venus flybys based on Apollo Program technology in its post-Apollo program. On the other hand, neither did it specifically forbid them.

Even before the MSFC engineers completed their study in February 1965, other NASA centers sensed that they might be left behind and got into the act. On 1 October 1964, North American Aviation (NAA), the Apollo CSM prime contractor, commenced a study for the Manned Spacecraft Center in Houston, Texas of piloted Mars/Venus flybys based on Apollo Program hardware. NAA presented results of its nearly nine-month study at MSC on 18 June 1965.

NAA proposed to exploit three main Apollo Program hardware elements for its piloted flyby missions: the CSM; Saturn V rockets; and the SLA (Saturn Launch Adapter), which in Apollo lunar missions linked the bottom of the CSM with the top of the Saturn V S-IVB third stage and housed the LM moon lander. NAA was SLA prime contractor.

The photo of Apollo 11 on the launch pad at the top of this post zeroes in on its conical Command Module under a white Boost Protective Cover, its drum-shaped silver-and-white Service Module, and, below that, its tapered, segmented white SLA. The black band below the SLA comprises the Instrument Unit, the Saturn V rockets electronic brain, and the top of the Saturn V rockets S-IVB third stage. Note workers on the launch pad gantry for scale.

Image: NAA/NASA.

The NAA study team included no good-quality drawing of all the engineering modifications it recommended for the piloted flyby SM. The most obvious of these was deletion of the modules single Service Propulsion System (SPS) engine and its replacement by three Apollo LM descent engines. The throttleable LM engines, each with independent propellant tanks and plumbing, would provide propulsion redundancy during the long voyage between planets.

The presentation to MSC did, however, include the above detailed cutaway line drawing of the CM. The bowl-shaped heat shield (denoted by the letter A) would work in tandem with the two outboard LM engines on the SM to protect the four-person crew during Earth-atmosphere reentry. Flyby mission reentry velocity could depend on many factors, including, for example, the flyby distance at Mars. In many cases, the CSM would approach Earth at the end of the flyby mission moving much faster than the planned maximum lunar-return velocity of about 37,000 feet per second. Hence, NAA proposed an end-of-mission retro maneuver to slow the CM for reentry.

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North American Aviations 1965 Mars/Venus Piloted Flyby Study (Part 1)