A CSM-Only Back-Up Plan for the Apollo 13 Mission to the Moon (1970)

The Apollo 13 crew of Commander James Lovell (left), Command Module Pilot John "Jack" Swigert (center), and Lunar Module Pilot Fred Haise (right). Image credit: NASA.

Launch of Apollo 13, the planned third Apollo Moon landing, was just two months in the future when NASA Manned Spacecraft Center (MSC) engineer Rocky Duncan proposed an alternate plan for the mission. He noted that Apollo 13 would mark the first flight of the Hycon Lunar Topographic Camera (LTC), a modified U.S. Air Force KA-74 aerial reconnaissance camera, which would be mounted in the Command and Service Module (CSM) crew hatch window for high-resolution overlapping photography of candidate future Apollo landing sites.

In Apollo Program parlance, this was dubbed "bootstrap photography." It took advantage of the piloted CSM, which had to loiter in lunar orbit anyway to collect the lunar surface crew after they completed their mission, to collect data useful for planning future Apollo missions.

Duncan noted that previous Apollo lunar missions had followed a "free-return" path that would enable them to loop behind the Moon and fall back to Earth if their CSM Service Propulsion System (SPS) main engine failed. The Apollo 13 CSM, on the other hand, would fire its engine during the voyage to the Moon to leave the free-return trajectory. This was necessary so that the mission's Lunar Module (LM) could reach its target landing site at Fra Mauro.

The Apollo 13 Saturn V rocket clears the tower. Image credit: NASA.

A day after launch from Earth, the Apollo 13 crew ignited the CSM Odyssey's Service Propulsion System (SPS) main engine to leave the free-return trajectory that would automatically return them to Earth in the event of an SPS failure. This was required to permit the mission to reach its destination, the scientifically significant Fra Mauro landing site. Image credit: NASA.

The MSC engineer then described a scenario in which the Apollo 13 LM was judged to be "NO-GO" soon after Trans-Lunar Injection (TLI), the maneuver that would boost them from low-Earth orbit and place them on course for the Moon. TLI would occur about two hours after launch; it would use the Saturn V S-IVB third stage with its single J-2 engine.

Following TLI, the CSM would separate from the segmented shroud — the Spacecraft Launch Adapter — linking it to the S-IVB stage; the shroud would then peel back to reveal the LM. The crew would dock their CSM with the port on top of the LM and separate it from the S-IVB stage. Presumably soon after maneuvering away from the S-IVB they would discover the fault that would render their LM unable to land on the Moon.

Apollo 13 would then become a "CSM-only lunar alternate photographic mission." The CSM would remain on a free-return path until it reached the Moon, then its crew would perform a standard two-impulse lunar orbit insertion (LOI) maneuver; that is, they would fire the SPS to slow their CSM so that the Moon's gravity could capture it into an elliptical lunar orbit, then would fire the engine again at perilune (the low point of its lunar orbit) to circularize its orbit.

Duncan noted that some "desirable photographic orbits with high inclinations. . .require a three-impulse LOI." He argued, however, that "since the crew has not been trained for this type of LOI. . .this type of profile [should] not be flown."

In Duncan's alternate mission, Apollo 13 would capture into a lunar orbit that would take it over the craters Censorinus and Mösting C. These were, respectively, ranked first and eleventh in priority on the Apollo 13 list of targets for lunar-orbital photography.

Censorinus was the leading landing site candidate for Apollo 15, which at the time Duncan wrote his memo was planned as an H-class mission similar to Apollo 13 (that is, its LM would not carry a Lunar Roving Vehicle and would remain on the Moon for only about a day and a half). Apollo 12 in November 1969 had been the first H-class mission, so had been designated H-1; Apollo 13 was H-2, Apollo 14 would be H-3, and Apollo 15 would be H-4, the final H-class flight.

Duncan advocated delaying the crew's scheduled sleep period by two lunar revolutions to enable them to photograph Censorinus and Mösting C. The photographic program would begin during Revolution 3 with vertical stereo photography using window-mounted Hasselblad cameras.

Revolution 4 would see the first high-resolution vertical Hycon LTC photography, then the astronauts would conduct high-resolution oblique (side-looking) LTC photography during Revolution 5. They would perform "landmark tracking" using the CSM's wide-field scanning telescope (a part of its navigation system) during Revolutions 6 and 7, then would begin their delayed sleep period.

The Apollo 13 crew would awaken during Revolution 12 and fire the SPS to change their spacecraft's orbital plane (that is, the angle at which its orbit crossed the Moon's equator). They would do this so that, beginning with Revolution 14, they would pass over Descartes, a suspected volcanic site in the Moon's light-colored central Highlands, and Davy Rille, a chain of small craters of suspected volcanic origin. The astronauts would repeat the five-revolution photography sequence they used to image Censorinus and Mösting C. Duncan noted that Descartes ranked second on the Apollo 13 list of photographic targets, while Davy was fourth.

Duncan briefly considered a scenario in which the Apollo 13 LM was incapable of landing yet had a working descent engine which the crew could use to perform plane-change maneuvers in lunar orbit. He noted that the LM would block some CSM windows while it was docked. The astronauts might undock the CSM from the LM for photography and dock again for additional plane changes, or they might discard the LM after only a single plane change. Duncan favored a simpler approach: jettison the LM as soon as it was judged to be incapable of landing whether its descent engine was functional or not and use only the CSM SPS.

The astronauts would perform "target of opportunity" photography during Revolutions 18 and 19, then would sleep. They would wake during Revolution 24 and perform a plane change during Revolution 25 so that they could fly over Alphonsus crater, Gassendi West, and Gassendi East beginning with Revolution 27 and again carry out the five-revolution photography sequence. Alphonsus, where surface color changes and luminescence have been reported, was ranked ninth on the Apollo 13 target list, while the two sites in dark-floored Gassendi crater were ranked thirteenth and fourteenth, respectively.

Duncan estimated that, by the time the astronauts finished photographing the Alphonsus and Gassendi crater candidate landing sites, Apollo 13's cameras would likely have run out of film. He recommended that the crew fire the SPS to leave lunar orbit and return to Earth during Revolution 32 or two revolutions after the film ran out, whichever came first.

Apollo 13 left Earth on 11 April 1970. The LM Aquarius checked out as "GO" for a landing on the Moon, and on 12 April the crew performed the SPS burn to leave the free-return trajectory. The next day, CSM Odyssey suffered an oxygen tank explosion in its Service Module (SM).

Because the extent of the internal damage to the CSM was unknown, NASA wrote off Odyssey's SPS and looked to the LM for salvation. Astronauts James Lovell, Jack Swigert, and Fred Haise used Aquarius's descent engine to get back onto a free-return trajectory.

During their lunar flyby, the crew photographed the Moon through Aquarius's windows using hand-held cameras. The Hycon camera was not used. Odyssey blocked part of their field of view, but there could be no thought of discarding it: the crew needed the conical Command Module (CM), with its bowl-shaped heat shield, to re-enter Earth's atmosphere at the end of their voyage. With help from the world-wide Apollo mission team, the crew safely reentered Earth's atmosphere and splashed down in the Pacific Ocean in the Odyssey CM on 17 April 1970.

Inside the lifeboat: after the explosion in the Apollo 13 CSM Odyssey, the Apollo 13 crew shut down Odyssey's systems and relocated to the still-functional LM Aquarius. The LM was designed to support two men for 36 hours, not three for four days. This meant that exhaled carbon dioxide built up in the cabin air. With assistance from engineers on Earth, the crew built a system (image above) that allowed the CSM's carbon dioxide-absorbing lithium hydroxide canisters to be used in the LM. CSM Pilot Jack Swigert, who would have performed "bootstrap photography" in lunar orbit had the third lunar landing attempt gone ahead as planned, is visible at right. Image credit: NASA.

As Apollo 13 swung around the Moon and began its fall back to Earth, its crew used handheld cameras to photograph the lunar surface through windows in the LM Aquarius. This image, captured through one of the ceiling-mounted rendezvous and docking windows, shows parts of the Nearside and Farside hemispheres. Dominating the top half of the image is the crippled CSM Odyssey. To conserve electricity, its internal lights are off, making its windows dark. The out-of-focus lines on the rendezvous window were meant to enable the LM crew to gauge distance during rendezvous and docking with the CSM. Image credit: NASA.

Apollo 14 (31 January-9 February 1971) became the first (and last) lunar mission to use the Hycon LTC. By the time it flew, NASA had cancelled Apollo 15 and 19 as part of its efforts to preserve its proposed Space Station/Space Shuttle Program. It had renumbered the remaining Apollo flights so that they ended with Apollo 17. Apollo 14, H-3, became the last H-class mission. The camera's chief target was Descartes, which had moved to the top spot among Apollo 16 landing site candidates. Apollo 16, planned as a J-class mission, would include a two-seat Lunar Roving Vehicle, an LM capable of remaining on the Moon for three days, and a CSM with an ejectable subsatellite and a pallet of sophisticated sensors and cameras in its SM.

The Hycon camera captured 192 images, but malfunctioned while imaging the lunar surface about 70 kilometers east of Descartes. Though Apollo 14 returned no images of the site, Apollo 16 (J-2) landed at Descartes in April 1972.

Sources

Memorandum with attachment, FM5/Lunar Mission Analysis Branch to various, “Lunar alternate missions for Apollo 13 (Mission H-2),” Rocky Duncan, 13 February 1970.

"Scientific Rationale Summaries for Apollo Candidate Lunar Exploration Landing Sites – Case 340," J. Head, Bellcomm, Inc., 11 March 1970.

"Significant Results from Apollo 14 Lunar Orbital Photography," F. El-Baz and S. Roosa, Proceedings of the 1972 Lunar Science Conference, Vol. 2, pp. 63-83, 1972.

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