The last lunar outpost
by Dwayne A. Day
|The Space Exploration Initiative was dead virtually from the start, but for the next several years the National Space Council fought a running battle with NASA to get the agency to develop cheaper alternatives to returning to the Moon.|
By 1992 NASA finally scaled back its proposals. The agency proposed a series of small robotic precursor missions, starting with the Lunar Resource Mapper, a 900-kilogram spacecraft that would be launched atop a Delta launch vehicle and carry spectrometers to detect minerals and elements on the Moon. It would be followed by Lunar Geodetic Scout, which would make stereo images of the lunar terrain and map the Moon’s gravity field. But Congress removed the funding for the small spacecraft, which many agency critics viewed as the camel’s nose under the tent leading to bigger and more expensive follow-on missions.
In an effort to scale back the agency’s earlier plans for a permanently occupied lunar base, starting in 1991 NASA’s Office of Exploration had developed a different approach to a return to the Moon than the agency had initially proposed in summer 1989. This new approach was known as First Lunar Outpost and contained a number of key differences compared to the 1989 architecture. First, the goal was no longer to establish a permanent base on the Moon virtually from the start, but to begin with limited surface operations. Second, the mission did not rely upon either the space shuttle or reusable lunar transit vehicles. Third, the mission would completely bypass the space station. Finally, the plan did not rely upon unproven technology, such as reusable lunar transfer stages or the use of resources on the lunar surface.
FLO was formally unveiled by NASA in summer 1992. It was intended to serve as a detailed “baseline” proposal, not necessarily the final design. The purpose of such a proposal was to encourage engineers both inside and outside the space agency to develop alternative, preferably cheaper, methods of achieving the same goals. According to this proposal, Americans would return to the Moon by 2000.
FLO was in part a response to an outside study effort forced on NASA by the White House. NASA had been unable and unwilling to develop lower-cost alternative methods of achieving Bush’s goals. As a result, in 1990 the White House’s National Space Council had pushed the agency to create Project Outreach, which sought space exploration proposals from the general public. NASA then created the Synthesis Group to collate these ideas into a coherent final report. The Synthesis Group was headed by retired astronaut and Air Force Lieutenant General Thomas Stafford. The Synthesis Group produced its report in July 1991 and called for establishing waypoints along the way to the ultimate goal of a permanent lunar presence. One of the conclusions of Stafford’s committee was that a large launch vehicle was necessary for lunar missions in order to reduce the requirements for astronaut extravehicular activity and the number of interfaces between different parts of the spacecraft.
|FLO was intended to serve as a detailed “baseline” proposal to encourage engineers both inside and outside the space agency to develop alternative, preferably cheaper, methods of achieving the same goals.|
The First Lunar Outpost proceeded from the assumptions established by the Synthesis Group. The FLO spacecraft would be launched atop a new heavy lift launch vehicle bigger than a Saturn 5—124.4 meters tall vs. 110.6 meters for the Saturn 5. Some sources claim that NASA labeled this new vehicle “Comet.” The Comet core vehicle would be similar to the Saturn 5’s S-IC first stage, with five F-1A engines. On either side would be two smaller booster stages, each with two F-1A engines. The F-1A was an upgraded version of the Saturn 5’s F-1 engine, with 1.8 million pounds of thrust. This engine was ground-tested in the early 1970s, although never flown. The second stage would have six J-2S engines, and the third stage, or Trans Lunar Injection (TLI) stage, would have one J-2S engine. Unlike the Saturn 5, this massive booster would not taper gracefully from second to third stage, but would maintain its ten-meter diameter all the way to the slightly enlarged payload fairing. It would be a brute-looking monster.
There was a major difference between the First Lunar Outpost proposal and Apollo. Apollo used a clever and somewhat controversial method of reaching the Moon known as Lunar Orbit Rendezvous, or LOR. LOR used a separate landing craft that would descend from lunar orbit and then rendezvous to dock with the main spacecraft for the return to Earth. NASA had selected this method because it offered the greatest amount of payload weight placed on the lunar surface and also because the other alternatives, known as “direct ascent” and Earth Orbit Rendezvous, were considered more complex. Earth Orbit Rendezvous would have required more rocket launches and assembly of the spacecraft in Earth orbit. It also would have required a large landing craft. Direct ascent would have required a much larger rocket than the Saturn 5 to lift a massive landing craft and send it all the way to the Moon. LOR’s most vocal proponent, John C. Houbolt, had described the challenges of landing such a large vehicle as akin to backing an Atlas rocket down onto its launch pad.
NASA had acquired three decades of experience since the LOR decision and the First Lunar Outpost architects felt that direct ascent was a more viable approach in 1992 than it was in 1962. They called this “lunar direct mode.” A major drawback of Lunar Orbit Rendezvous is that the crew is restricted to landings primarily along the equator because the orbiting spacecraft would be out of range at various times. Earth Orbital Rendezvous would have required two or more launch vehicles to be prepared simultaneously, and also required on-orbit storage of cryogenic propellants. By selecting lunar direct mode for the First Lunar Outpost, the designers increased their mission flexibility and the abort modes in event of problems. In addition, if the vehicles spent little time in Earth or lunar orbit awaiting another vehicle, they could then utilize cryogenic propellants, thereby increasing their performance.