In 1938, the BIS Technical Committee decided to go the full distance and produce a conceptual design of a vessel that would carry a crew of three safely to the Moon, permit them to land for a stay of fourteen days, and provide for a safe return to the Earth with a final payload of half a tonne. The object of the exercise was to demonstrate that, within the capabilities of propellants that could be specified (at least theoretically) at the time, such a mission was not merely possible but would be economically viable – in so far as the vehicle lift-off mass from the Earth would be no more than one thousand tonnes. The conceptual design that resulted came to be known as the BIS Lunar Spaceship, and for all its flaws and misconceptions it must be regarded as one of the classical pioneering studies in the history of astronautics.
At this point it is appropriate to review the nature of the problem and the arguments put forward by more objective critics against the feasibility of its solution. The mission proposed for the Lunar Spaceship would involve total velocity changes in excess of 16 km/s, a figure that would be significantly increased by certain losses. The best available propellants were not expected to achieve rocket motor efflux velocities of one quarter of that figure. This enormous disparity implied that, if one attempted to achieve the entire mission with a simple single-stage vessel, 99% or more of its initial lift-off mass would have to consist of the propellant. (In the more common parlance of rocketry this required a mass ratio exceeding100.) The most enthusiastic proponents of Space flight were at one with their critics in dismissing this as inconceivable.
To circumvent this, the pioneers of astronautics invented the Step Rocket, in which the vessel consisted of a series of stages of diminishing size, fired in sequence. As each successive stage completed firing, its engines and other redundant structure would be discarded leaving the higher stages to continue the flight. In this way it would be possible to obtain a high mass ratio without invoking the need to achieve impossible structural factors. Looked at in another way, the total velocity change required of the overall vessel would be shared between the stages. Thus in the case in point, four equal stages would each need to contribute little more than 4 km/sec to the total velocity change. That would be possible with the performance of known propellants. The proportion of the stage mass taken up by propellant would assume a reasonable level (say, 75%, corresponding to a mass ratio of 4). However, a penalty would be incurred in the final payload, which would be reduced in inverse proportion to some number raised to the power of the number of stages. Optimistically, at the time, that number might have been taken as 10. Thus, with four stages, the final payload might be expected to be only one ten-thousandth of the lift-off mass. The nub of the argument of the more informed critics of such a lunar flight would have been that such a mission would probably have required as many as five stages, perhaps more, so that the initial vessel would have had to match an ocean liner in size to carry an ultimate payload of one tonne. Such a mission could not be viable.
In 1919 Robert Goddard, in his classical paper “A Method of Reaching Extreme Altitudes”, went a stage further than the step rocket principle in suggesting a firing procedure that amounted to the continuous discarding of redundant structure. This procedure, in principle, could result in a significant improvement in payload ratio compared to the step rocket. The BIS, in its design concept, adopted a cellular construction that, in essence, conformed to Goddard’s suggestion. The BIS Space Ship was de- scribed in the January 1939 Journal by H.E. Ross. The vessel was divided into six tiers (steps) of equal hexagonal cross-section and the six sections were made up of an array of tubes each consisting of a separate rocket motors. Each of the lowest 5 steps was made up of 168 motors, intended to impart sufficient velocity to achieve escape from the Earth’s gravitation. The remaining stage consisted of 45 medium motors and 1200 smaller tubes intended to land the remainder of the vessel on the Moon; allow for subsequent escape from the latter (leaving redundant structure on the surface of our satellite), and for reduction in velocity prior to entering Earth’s atmosphere.
Perhaps the most important lasting achievement of the Lunar Spaceship study, however, came from their conclusions regarding the landing upon, and lift-off from, the lunar surface. R.A. Smith developed the concept after the War in an article – “Landing on an Airless World” – published in the August 1947 BIS Journal; accurately depicting the procedure that was to be adopted with the Apollo Lunar Excursion Module. The only notable difference between the two cases was, perhaps, that Smith’s design was more elegant than the actual LEM.
The Technical Committee decided that its activities should embrace an experimental programme to support its Lunar Spaceship concept. From the outset, it rejected the experimental “firing of free rockets” as valueless on account of their small scale and lack of control over the many parameters involved in such flights. It made no attempt, therefore, to emulate the VfR or later American groups. The BIS workers considered that the development of rocket motors for their proposed lunar mission would have to proceed in stages, beginning with literature and experimental studies of possible propellants, followed by the design of chambers and nozzles on the best theoretical basis – the work of Sänger was cited as noteworthy in this respect. The resulting motors and selected propellants would then be brought together in static proving stand firings in which all the variables could be systematically controlled and measured. The intention was correct and logical, but even the over-optimistic members of the Technical Committee were bound to note that such a programme was far beyond their resources. Nevertheless, largely under the supervision of Janser, who was a research chemist, they embarked on the preliminary stages of the propellant survey hoping that eventually they would solicit sufficient support from public benefactors, convinced by the evidence emerging from the Lunar Spaceship study, to proceed with serious development. Undaunted, R.A. Smith designed a basic test stand that was actually constructed.
Despite some shortcomings, the programme of the Technical Committee was a laudable endeavour. The BIS Lunar Space Ship mission was a “bridge too far” for the technology at the time. There was never any possibility that the cellular vehicle could have performed as required. In retrospect the critics in the Society, who asserted that attention should have been devoted to lesser targets, were right. If the Technical Committee had set its sights, for example, on an orbiting spacecraft they could have produced a convincing case for its feasibility and, perhaps, succeeded in soliciting support for a strong research and development programme.
In the event, war came and the development of the rocket was to depend upon purely military considerations with astronautical achievements a fortuitous spin-off.
Information used with kind permission from Dr Bob Parkinson, Editor of the book “Interplanetary – the History of the British Interplanetary Society”, published by the BIS.
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