The LOR Decision

All of these events need to be understood in the context of the overall Apollo program and the engineering issue that preoccupied it during the year after Kennedy's speech: the famous ''mode decision.'' How would people fly to the moon? The obvious answer seemed to be to launch a spaceship from earth and have it land on the moon, then take off again and return to earth, which became known as ''direct ascent.'' Or one could launch several rockets into earth orbit and assemble them for the flight to the moon. These ideas drew on the famous Chesley Bonestell images published along with von Braun's articles in Colliers magazine in 1952. The landings featured large, sleek rockets landing fins-first on lunar terrain. This meant the astronauts would be at the top of a large stack, and would somehow have to control the rocket several stories below during descent. The initial MIT study even included a large periscope so the astronaut could see the surface as he landed from an awkward position at the top of a twenty-five-meter-tall vehicle.58

But as spaceflight matured and engineers became more familiar with the possibilities, other options emerged. A mathematician at NASA named John Houbolt began looking at an idea called ''lunar orbit rendezvous,'' or LOR. In this mode, NASA would send two spacecraft to the moon, and one would stay in orbit while the other descended to the surface. This scheme introduced a new kind of vehicle into the equation, and brought several advantages: the actual lunar landing craft could be a small, specialized machine, and all of the equipment and fuel required to return to earth could stay in orbit and need not be landed on the moon. It also gave the astronauts some leeway, for the critical lunar descent could be initiated from a relatively safe lunar orbit, rather than from a high-speed entry from earth. It provided some measure of redundancy, and had a better chance of meeting the end-of-the-decade schedule.

LOR also had costs, two of which became paramount. First, it required two spacecraft instead of one, doubling the complexity of the machinery and the project to get it off the ground (and possibly more than doubling the cost). Second, in order to return home, this new spacecraft would have to launch itself from the moon and rendezvous with the first craft in lunar orbit. This was a risky and unknown maneuver;launching a rocket from earth required weeks of preparation, numerous support personnel, and tons of specialized equipment. How would two astronauts perform this maneuver far from home, and find their way to a precise orbital rendezvous? Their lives would depend on getting it right.

The LOR decision and the controversy leading up to it is a rich and complex story and is still being examined by students of engineering decision making.59 We need not go into it in detail here, other than to explore its effects on the guidance system, which were significant.

LOR had two major, immediate implications. In November 1962 NASA selected Grumman Aircraft Corporation to build the Lunar Excursion Module or LEM (later shortened to ''LM'' but still pronounced ''lem''). The LOR decision gave the Gemini project its vision and relevance as a way to develop rendezvous practice and experience for the lunar mission. Needless to say, the astronauts had no problem with LOR—it put heavy emphasis on human flying skills.

Initially, it was not clear who would be responsible for the guidance system on the LM, but NASA immediately began thinking about sharing components of the guidance system between the two Apollo vehicles. LOR also required two additional radars: a landing radar device, which would measure altitude and velocity of the LM to the lunar surface, and a rendezvous radar device to track the LM back to the CSM (command and service module) for rendezvous. IL engineers wrote the specs for these because the Apollo computer would need to read their signals, and Grumman subcontracted the radars to RCA, which subcontracted the landing radar to Ryan Aeronautical.

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