Good Spaceships

To sustain a thriving Lunar transportation system in the future, we will need good spaceships. And a good spaceship, by definition, is one that is fully reusable. As we have seen, the best way to make an Earth orbital spaceship reusable is to give it wings. It has to be a spaceplane. Also, as we have seen, the SSTO spaceplane has large propellant tanks, making it the ideal space tanker. The conclusion is that among the best spaceships of the future will be winged space tankers. This automatically makes them a part of the infrastructure needed to refuel other good spaceships. As for good spaceships operating near the Moon, the situation is different. The Moon has no atmosphere, so good Lunar spaceships do not need wings, as long as they stay there. Also, Lunar gravity is only one sixth that at the surface of Earth, and so good spaceships need far less fuel, but to be good spaceships, they have to refuel. This means that some other ship has to bring the fuel, unless fuel is found on the Moon. If propellants are found on the Moon, then they will have to be transported, in some form, to LEO, as we will see. What does all this have to do with the Lunar spaceplane? The answer is obvious. Spaceplanes are uniquely qualified to ship propellants both to and from the Moon.

For any good spaceship to operate between Earth and the Moon, it must be able to use the Earth's atmosphere for aerobraking. This means that all good spaceships returning from the Moon must be designed aerodynamically. Using blunt body capsules is one solution, but an inefficient one, because they are modular and therefore incomplete. The spaceplane, whether it sports a double-delta wing, a lifting body, or a blended wing-body, is far superior to any kind of reentry capsule. Spaceplanes are simple, complete, self-contained, in-space refuelable, fully reusable, and versatile. They are good spaceships, rather than piece-meal spacecraft.

A comparison of the modular Moon mission to the Lunar spaceplane reveals some interesting facts in terms of mission complexity. As every engineer knows, complexity often leads to failure; so the simpler a system is made, the more reliable it will be. And yet, the modular concept is complex, because it involves so many components. Furthermore, the modular mission is inefficient, because it repeats the same things over and over. For example, modules first use one set of propellant tanks and one engine, then (after they throw those away) they use another completely different set of propellant tanks and another engine, each with its complex pressurization system, piping, valves, nozzles, gimbals, etc. Of course, the reason they do this is because they do not refuel in space. Ironically, by using multiple modules to keep mass and propellant usage down, total mass is actually driven up. Table 10.1 shows a simple comparison of three Lunar spacecraft, the Apollo, Orion, and spaceplane, as they prepare to leave Earth orbit. The spaceplane, good spaceship that it is, has just refueled, and so it is equipped with refueling ports, which the other two spacecraft lack. This is the only area in which the good spaceship is more complex than the modular vehicle. Trans-Lunar insertion occurs well after the modular spacecraft has lost much of its complexity during staging, yet still the Lunar spaceplane is over twice as simple, and therefore twice as efficient, as the competition.

Table 10.1 Comparison of modular and spaceplane mass complexities at trans-Lunar insertion

Apollo

Orion

Spaceplane

Fuel tanks

4

4

1

Oxidizer tanks

4

4

1

Engines

4

l

3

Attitude control systems

4

4

1

Crew cabins

2

2

1

Hatches

4

4

2

Docking ports

2

2

1

Refueling ports

G

G

2

Coupling mechanisms

4

3

G

Total

2S

30

12

Assuming that Lunar spaceplanes are feasible, what is their real value? Once again, the answer lies in their inherent strengths as tankers and in their winged reusability. Lunar spaceplanes will transport propellants to the Moon if necessary, and from the Moon if the required resources are found. This indicates that spaceplanes will be valuable no matter which of these futures unfurls. Let us look at each aspect of this.

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