In June 1962, a little more than a year after President John F. Kennedy put the U.S. on course for the moon, NASA's piloted spaceflight organizations agreed that Lunar Orbit Rendezvous (LOR) should be the Apollo lunar landing mission mode. LOR would employ two spacecraft; a Command and Service Module (CSM) for carrying three astronauts from Earth to lunar orbit and back again; and a small Lunar Excursion Module (LEM) for landing two of them on the moon and returning them to the CSM in lunar orbit. Both the CSM and the LEM would include two modules: the Command Module (CM) and Service Module (SM) in the case of the CSM, and the Descent Module and Ascent Module in the case of the LEM.
On July 11, 1962, NASA Administrator James Webb made public NASA's mode choice. He told newsmen that LOR Apollo would leave Earth on a Saturn C-5 (as the Saturn V rocket was known at the time) capable of launching 45 tons to the moon, and that the agency would also study a two-man Direct Ascent Apollo lunar landing mission launched on a Saturn C-5. In Direct Ascent, a single spacecraft would carry the astronauts from Earth to the lunar surface and back again. Webb did not provide a justification for the two-man Direct Ascent study, though it soon became clear that it was a concession to Jerome Wiesner, chairman of the President's Science Advisory Council (PSAC). Wiesner, a Massachusetts Institute of Technology professor who had also served as PSAC chairman for Kennedy's predecessor, Dwight Eisenhower, did not trust LOR's complexity.
While NASA moved ahead with LOR, it hired McDonnell Aircraft Company and TRW Space Technology Laboratories to study Wiesner's preferred mode. For McDonnell, manufacturer of the one-man Mercury and two-man Gemini spacecraft, the study had three aims. The company would develop a conceptual Direct Ascent moonship design incorporating a two-man Command Module similar to the three-man North American Aviation (NAA) Apollo CM. When NAA contracted with NASA to build the Apollo CSM in November 1961, it had assumed that Apollo would use either Direct Ascent or Earth-Orbit Rendezvous. In both of those mission modes, the CSM would have had the honor of landing on the moon. NAA did not welcome NASA's choice of LOR.
McDonnell would also look at using Gemini for the Direct Ascent moon landing mission. At the time it conducted its study, Gemini's Earth-orbital maiden flight was scheduled for launch in 1964. Known initially as "Mercury Mark II," the spacecraft, which was meant to reach Earth orbit atop a Titan II rocket, was meant to provide NASA with experience with spacewalks and rendezvous and docking ahead of Apollo. From aft to front, the Gemini spacecraft consisted of the Adapter, Service, and Command Modules. The Gemini Command Module, which measured 8.7 feet across its heatshield and weighed 5775 pounds, had two hatches (one per astronaut) with one forward-facing window each. Gemini could carry enough supplies for a 14-day Earth-orbital mission.
Finally, McDonnell would determine modifications the two-man Apollo and Lunar Gemini spacecraft would need to serve as unpiloted "rescue" vehicles. NASA expected that a rescue lander, if one flew, would be landed unmanned at the target landing site ahead of the crew's arrival. If the piloted lander became unable to return its crew to Earth through either damage or irreparable malfunction, the astronauts would transfer to the dormant rescue lander and blast off for Earth.
The company proposed four possible two-man Direct Ascent Command Module designs. The company's conical two-man Apollo would measure 8.8 feet tall and 10.4 feet across its heatshield. (For comparison, the three-man Apollo was 10.6 feet tall and 12.8 feet across.) Interior volume would total 185 cubic feet, of which 73 cubic feet would be available for the crew.
The astronauts would enter and leave the module through a hatch containing two windows located above the pilot's couch. A blow-out hatch with one window located above the co-pilot's couch would provide emergency egress. During Earth launch and reentry, lunar liftoff, and while sleeping on the moon, the astronauts would recline in their couches facing the nose and main control panel. This would place the windows above and behind their heads. For lunar landing, they would sit upright on their couch backs facing landing controls and view the surface through the windows. Following Earth atmosphere reentry, the two-man Apollo Command Module would lower to a gentle land landing on three 71-foot-diameter parachutes.
Lunar Gemini I modifications would include a beefed-up heat shield so that it could withstand reentry at lunar-return speed, improved radio systems for communication between moon and Earth, lunar landing controls, and life support consumables stocks for an eight-day lunar mission. The spacecraft would also include two systems for viewing of the lunar surface during landing. The right-side astronaut would recline in his couch normally (back toward heatshield and lunar surface) and deploy an external mirror for an "over-the-shoulder" surface view. The left-side astronaut would roll over in his couch and view the surface directly through a transparent "viewing dome" built into his hatch. The Lunar Gemini I Command Module would weigh 6802 pounds.
Except for its Earth landing system, Lunar Gemini II would closely resemble Lunar Gemini I. Until June 1964, NASA planned a land landing for its Earth-orbital Gemini spacecraft. The Gemini Command Module would deploy an steerable delta-winged paraglider during descent to Earth and glide to a touchdown on skids or wheels. McDonnell retained this system in its Lunar Gemini I design, but decided to trim weight from Lunar Gemini II by substituting a single 84-foot-diameter parachute and splashdown at sea. Land landing in the Lunar Gemini II capsule would be not survivable; if emergency land landing became necessary, the astronauts would eject from the falling capsule after reentry and descend on personal parachutes. The Lunar Gemini II Command Module would weigh 6376 pounds.
Earth-orbital Gemini astronauts would rely on ejection seats for escape if their Titan II booster malfunctioned. Lunar Gemini I and II would retain this system. For its Lunar Gemini III design, McDonnell opted for a launch escape tower similar to the one on Mercury capsules. In the event of a Titan II malfunction, the tower's solid-rocket motor would blast the Lunar Gemini III Command Module to safety. Couches with shock absorbers would replace the ejection seats, and three 71-foot-diameter parachutes would provide a slower, gentler descent than Lunar Gemini II's single parachute. These modifications would restore the land landing capability lost in Lunar Gemini II. The new couches would be configurable so that the astronauts could sit upright relative to the moon's surface (feet toward heatshield) during lunar landing. New hatch windows would provide direct views of the lunar surface for both astronauts. The Lunar Gemini III Command Module would weigh 6453 pounds minus its launch escape tower. All three Lunar Gemini versions could return up to 85 pounds of scientific equipment and lunar samples to Earth.
McDonnell proposed that both the two-man Apollo and the Lunar Gemini Command Modules should reach the moon atop a stack of three propulsion/service modules. The cylindrical, 21.6-foot-diameter, 16.4-foot-tall Retrograde Module would weigh 26.9 tons with a full load (23.8 tons) of liquid hydrogen/liquid oxygen propellants. Its bottom would rest atop the Saturn C-5 rocket and its top would attach to the bottom of the Terminal Landing Module. The Retrograde Module would perform course corrections during flight to the moon, lunar orbit insertion, de-orbit, and descent to 6000 feet above the moon, then would detach from the Terminal Landing Module and tumble away to crash on the surface (image at top of post).
The Terminal Landing Module, which would perform descent to the lunar surface following Retrograde Module separation, would weigh three tons with a full load (1.7 tons) of ignite-on-contact hydrazine/nitrogen tetroxide propellants. It would measure 21.6 feet across its base, which would attach to the top of the Retrograde Module, and 19.3 feet across its top, which would attach to the bottom of the Service Module. It would measure only 6.5 feet tall; this low profile would keep the Direct Ascent lander's center of gravity near the surface, helping to ensure that it would not tip during landing on its four spindly legs. The legs would fold against the Retrograde Module's sides under ejectable streamlined fairings during ascent through Earth's atmosphere. A compartment in the module's underside would hold 165 pounds of scientific gear for exploring the lunar surface.
The top of the Service Module would measure 10.4 feet across if attached to a two-man Apollo CM and 8.7 feet across if joined to a Lunar Gemini Command Module. It would stand 8.5 feet tall and measure 19.3 feet across its base, where it would attach to the top of the Terminal Landing Module. The Service Module would perform lunar liftoff and course corrections during the flight home to Earth. It would weigh 11.7 tons with a full load (9.7 tons) of hydrazine/nitrogen tetroxide propellants. In addition to propulsion systems, the Service Module would carry 1148 pounds of Command Module support equipment, including Gemini fuel cells to provide electricity and drinking water, a surface-mounted radiator for cooling, life-support oxygen tanks, and two boom-mounted radio dish antennas.
McDonnell found that both the two-man Apollo and the Lunar Gemini could both serve a "rescue" function. The rescue spacecraft would fly to the moon ahead of the piloted mission, land (perhaps homing in on a radio beacon mounted on a pre-landed automated Surveyor lander), and remain dormant awaiting the crew for up to 30 days. The piloted spacecraft would land near the rescue spacecraft. If it became damaged during landing or malfunctioned after touchdown, the astronauts would walk to the rescue spacecraft and use it to return to Earth. Rescue modifications would include a guidance system similar to that under development for the automated Surveyor lunar soft-lander; additional liquid oxygen/liquid hydrogen fuel cell reactants (5.7 pounds per day) for powering electric heaters in the Command Module during the 14-day lunar night and additional water (6.5 pounds per day) for evaporative cooling during the 14-day lunar day; and a propellant-saving Surveyor-type "direct descent" landing profile with no stop in lunar orbit before descent to the lunar surface.
NASA/PSAC differences over the Apollo mode choice became public midway through the two-man Direct Ascent study, when Wiesner and Webb argued in front of President Kennedy and reporters during a presidential tour of Marshall Space Flight Center (September 11, 1962). Soon after McDonnell submitted its report, NASA reaffirmed its decision to go with LOR (October 24, 1962). Webb threatened to resign if NASA's choice were overruled, and Wiesner, sensing that Kennedy would back his NASA Administrator, acquiesced. On November 7, the agency finalized its LOR decision by awarding the contract to build the LEM to Grumman Aircraft Engineering Corporation in Bethpage, Long Island.
Reference:
Direct Flight Apollo Study, Volume I: Two-Man Apollo Spacecraft and Volume II: Gemini Spacecraft Applications, McDonnell Aircraft Corporation, October 31, 1962.
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