North American Aviation (NAA) was the prime contractor for the Apollo Command and Service Module (CSM). In December 1965, the company's engineers briefed NASA's Office of Manned Space Flight (OMSF) and Bellcomm, OMSF's planning contractor, on results of a preliminary feasibility study of a one-man CSM mission to rescue Apollo astronauts stranded in lunar orbit.

The NAA engineers did not describe specific lunar-orbit rescue scenarios, though the CSM modifications they outlined offer clues about the types of rescues they envisioned. The normal CSM docking unit was an active probe system that could dock only with a passive drogue system. The Apollo Lunar Excursion Module (LEM) moon lander carried the drogue system. (The LEM was later called the Lunar Module, which was abbreviated LM and pronounced "lem.") The special docking unit on the rescue CSM's nose would be configurable as either an active probe or active drogue, so could be used to dock with either a LEM or a passive CSM. The rescue CSM pilot could reconfigure the docking unit in flight, implying that the situation in lunar orbit might be unknown or in flux when he departed Earth. The rescue CSM would also carry a dish-shaped LEM docking radar on an extendible boom to facilitate rendezvous and docking with a disabled CSM.

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NAA expected that a lunar-orbit rescue might require a spacewalk, so provided the rescue CSM pilot with a tether and a life support umbilical extension, a compressed-gas-propelled maneuvering device, and a protective "meteoroid garment" of the type Apollo moonwalkers would wear over their suits. In addition, the rescue CSM would carry an Expandable Structures Space Rescue System (ESSRS) device. ESSRS was an inflatable pole meant to serve as a handrail for astronauts spacewalking between two spacecraft.

Other rescue CSM modifications would include new crew couches to accommodate four astronauts, a fourth umbilical so that all crewmembers could link their suits to the rescue CSM's life support system, added breathing oxygen, and new rendezvous and docking computer software. Modifications and additions would add a total of 445 pounds to the rescue CSM. Removal of science equipment and other unneeded systems would, however, reduce the rescue CSM's mass by 415 pounds, for a net mass gain of only 30 pounds.

The rescue CSM would be a "Block II" spacecraft, much like the Apollo lunar CSMs. In late 1965, NAA expected to build a total of six Block I and Block II CSMs per year beginning in late 1966. Block I CSMs would be used in Apollo testing and Apollo Extension System (AES) Earth-orbital missions. AES, a proposed program intended to apply Apollo hardware to new missions, became a predecessor of the Apollo Applications Program, which subsequently evolved into the Skylab Program. In the event, only Block II CSMs carried astronauts; work on Block I CSMs ceased following the deadly AS-204 (Apollo 1) fire of 27 Jamuary 1967.

The company offered two plans for building the six rescue CSMs it expected would be needed for the Apollo Program. Rescue Vehicle Program "A" would see CSM-110 and CSM-113 converted into rescue CSMs; that is, diverted from lunar exploration missions. They would be flight-ready in early 1969 and mid-1969, respectively. Starting in mid-1970, one of the six CSMs produced annually would be a rescue CSM; this would, NAA noted, further reduce the number of Block II CSMs available for lunar exploration.

Lift off of Apollo 8, the only manned lunar mission that did not include a Lunar Module. Image: NASA. Lift off of Apollo 8, the only manned lunar mission that did not include a Lunar Module. A Saturn V bearing a rescue CSM would have been similarly configured. Image: NASA

Rescue Vehicle Program "B" would see NAA produce nine CSMs per year. The company's representatives told NASA that this would guarantee "non-interference with basic Apollo or AES." The first rescue CSM of Program "B," designated CSM R-1, would be ready for flight at the end of 1968, between AES CSM-109 and lunar CSM-110.

NAA assumed that during every Apollo lunar mission a rescue CSM would stand by atop a three-stage Saturn V rocket on one of the Launch Complex 39 pads at Kennedy Space Center, Florida. The rescue CSM Saturn V would be outwardly identical to the lunar mission Saturn V. The rocket would, however, carry no LEM in the tapered Saturn Launch Adapter shroud that linked bottom of the rescue CSM to the top of its S-IVB third stage.

The rescue CSM and Saturn V would stand by until the Apollo lunar CSM safely departed lunar orbit and began the fall back to Earth, then would be rolled back to the cavernous Vehicle Assembly Building for storage until the next Apollo lunar mission. A single rescue CSM could stand by during three lunar missions, then would need to be replaced. NAA did not explain what would be done with disused rescue CSMs; presumably they would be scrapped.

The company assumed that in most cases the rescue CSM would launch as soon as NASA learned that a crew had become stranded in lunar orbit. This would mean that it probably would not be able to rely on launch geometry to match orbits and rendezvous with the stranded spacecraft.

NAA found that, in theory, the lone pilot would be able to fire the rescue CSM's Service Propulsion System (SPS) main engine to achieve an elliptical "catch up" orbit around the moon; then, at apolune (lunar orbit high point), he would ignite the SPS again to line up his spacecraft's orbital plane with that of the stranded spacecraft. At perilune (lunar orbit low point), the pilot would fire the SPS a third time to lower the rescue CSM's apolune, thus circularizing its orbit and placing it near the stranded spacecraft.

In practice, launching immediately could create complications. It might, for example, increase the rescue mission's duration. NAA calculated that the time needed to reach a stranded spacecraft and return to Earth could in fact exceed the Block II CSM's anticipated 240-hour (10-day) operational lifetime by up to 52 hours. NAA recommended that, in such cases, NASA should delay rescue CSM launch until its mission duration would remain less than 10 days.

NAA estimated that its Rescue Vehicle Program "A" would add a total of $86 million to the cost of the Apollo Program. Of this, $50 million would be spent on an 18-month program of development and testing, $6 million on modifying two Apollo lunar CSMs, and $38 million on building four new rescue CSMs. The company provided no cost estimate for its Rescue Vehicle Program "B."

The NAA engineers did not discuss how astronauts stranded in lunar orbit might eke out their limited supplies of consumables – for example, breathing oxygen – while they awaited rescue. Consumables would be particularly worrisome in the case of a LEM stranded in lunar orbit by a catastrophic CSM failure: At the time of the NAA study it was expected that the LEM would be able to keep two men alive for only one or two days. Neither did they mention the risks of a one-man lunar voyage, nor the problems associated with keeping a rescue CSM, Saturn V rocket, launch pad, and launch team on standby.

Perhaps because of these difficulties (and probably many others), NASA chose not to prepare for astronaut rescue in lunar orbit. This did not stop Bellcomm from considering the problems of lunar orbit survival three years later, in December 1968, shortly after the Apollo 8 CSM became the first piloted spacecraft to return from lunar orbit.

Reference:

4-Man Apollo Rescue Mission, AS65-36, M. W. Jack Bell, et al, North American Aviation, November 1965; presentation at NASA Headquarters, 13 December 1965.