LUNAR ORBIT RENDEZVOUS

Any journey in space is heavily influenced by the propellant available to achieve it. At the same time, the amount of propellant required is largely determined by the mass of the object that is to make the journey and how quickly the journey has to be undertaken. In simple terms, mass is everything. The alternative scheme, known as lunar orbit rendezvous (LOR) sought to limit the amount of mass that had to be propelled at each key point in the journey. A reduction in the quantity of propellant required for the Apollo spacecraft would also minimise the initial mass that would begin the journey, and thus bring the entire mission within the capability of a single Saturn C-5.

The advantages are best understood by working backwards through a mission. The only part of the spacecraft that could return to Earth was the heatshield – protected command module. To propel it out of lunar orbit required the propulsion capability of the service module and their combined mass defined the amount of propellant required for the task. Next, instead of taking a lot of redundant mass down to the Moon’s surface just to bring it up again, a dedicated lander would be designed specifically for the task, leaving the Apollo mothership, the CSM. in lunar orbit with the consumables and propellant to get home. This lander would only Lake two of the crew down to the surface, leaving the third to take care of the CSM. Moreover, there was no need for the engine, landing gear and the empty tanks that had enabled them to land on the surface, to come back up to lunar orbit. The crew with its gathered lunar treasures could return to the mothership in only the Lop part of the lander using a smaller engine and the propellant required for the task. As there would be no need to bring this remaining part of the lander back to Earth, it, too, could be discarded at the Moon. Therefore, the final propellant load for the CSM was made up by the fraction required to get the entire assemblage into lunar orbit, plus the fraction required to get itself to Earth. At each key point in the journey, the engines would work against only the mass that was absolutely necessary, and everything else would be discarded when its function had been fulfilled.

The cumulative weight savings made the LOR scheme highly attractive in engineering and cost terms, but it caused NASA to face certain operational realities which, in the early days of space flight, seemed daunting. As with EOR. having separate spacecraft meant learning how to rendezvous in orbit when both were travelling at what wrere then perceived to be incredible speeds. The ships would have to join together, or dock, to allow crewmen and cargo to transfer from one craft to the other. Neither of these techniques had yet been demonstrated in Earth orbit, but the LOR concept was calling for them to occur nearly half a million kilometres away in the lonely vicinity of the Moon. A failure of the rendezvous would doom the occupants of

the lander to certain death in lunar orbit, while a failure of the docking would require crewmen to don spaccsuits and move from one craft to another by going outside. At a time when no one knew what challenges the weightless environment would present to a crewman in a bulky pressure suit, this seemed to be a very risky thing to do.

Many in the burgeoning space community were aghast at the audacity of LOR. It seemed foolhardy and dangerous. However, convinced of the benefits, and with an almost religious /.cal, its leading advocate, John Houbolt. drove through layers of NASA bureaucracy and the entrenched positions of its various centres, in an effort to convince the organisation that there was little chance of getting to the Moon within the decade unless LOR was adopted.

NASA debated the mode issue for more than a year after Kennedy had laid dow n his challenge, during which Lime, direct ascent and its incredible Nova launch vehicle was largely discarded, leaving EOR, championed by von Braun, and LOR, which, because it included a specialied lander, had become Gilruth’s preferred option, as the competing schemes. As work on the spacecraft could not begin in earnest until the matter was settled, Joseph Shea from NASA headquarters asked each side to report on the other’s scheme – a management strategy that enabled von Braun to recognise the benefits of LOR. In June 1962, at a large meeting at Marshall, NASA acceded to Iloubolf s campaigning and chose LOR as the means by which they would get to the Moon.

With the mission mode settled, the definition, design and construction of the spacecraft could begin. The command and service modules would be built by North American Aviation. These craft were already well into their initial development, but their role could now’ be precisely defined; there being no need for a landing stage on the SM, for example. Major components for the SM had already been designed. It was decided to leave the thrust of its propulsion system at its original design value and Lake this capability into account in mission planning. Two versions of the CSM were to be built. The Block I spacecraft would be incapable of supporting a mission to the Moon, but w’ould allow experience to be gained in Earth orbit until the Block II became operational. The Block II would be the Moonship proper. Complete with fuel cells for power, hardware for docking, deep-space communications and a fully capable guidance and navigation system, the Block II CSM would be the linchpin in the Apollo story, ferrying a spidery landing craft to another w’orld. In a sense, the CSM was a mini-planet, providing everything three men w’ould need for Lw’o w’eeks in space during which they would undertake a journey that had been a dream of humans over the ages. In the event, the design of the Block II w’ould be forged in the lessons learned from the fatal flaw’s that would prevent the Block I from flying a manned mission.