Considering Possible Ideas :
There are several possibilities for sending people and materials to the Moon. Presently the best way to transport anything to the Moon is by sending a spaceship. The technical potential nowadays offers a wide variety of possibilities ranging from quick but expensive missions to the Moon to cheap but time-consuming missions (more than a year for the round trip). That is why it is important to find a compromise between the two resources – time and money – i.e. to design a spaceship which is not very expensive, but also allows comparatively frequent missions to the Moon.
Naturally the first idea that we had in mind was constructing a spacecraft similar to the Apollo mission spacecraft, i.e. launching a capsule from Earth using a multi stage propulsion system and then the capsule’s own engine to set it on a trajectory to the Moon. In this case however the price of the mission is very high, the mass ratio between fuel and payload is big, therefore we decided to abandon that idea.
One of the options is the “Lunar Elevator.” The “Lunar Elevator” is a spacecraft that moves constantly on an orbit between Earth and Moon, carrying cargo between the two. This design is inefficient, however, because it requires an adjustment of the velocity every time the spacecraft passes around the Earth, due to the rotation of the Moon around Earth. Such frequent adjustments are not effective and require a lot of fuel, which makes the operation of this spacecraft in orbit very expensive. This is the fastest of the methods considered – a round trip takes about 7 days.
Another option is using a propulsion system on a parking orbit around the Earth to move the cargo to the Moon, and then to return to Earth either with another cargo from the Moon or empty. The propulsion system itself is very heavy and its transportation to the Moon and back takes a lot of energy, at the same time serving no purpose. This is again a fast but expensive solution.
The alternative to the former two options is the “Lunar Kick.” The lunar kick is a system of two separate propulsion systems at constant parking orbits around the Earth and the Moon. When a cargo is launched from Earth it connects to the propulsion system orbiting around the Earth. The propulsion system then transfers the cargo to an elliptical orbit around the Earth and eventually ejects it to a translunar orbit by a “kick”. The kick is an explosion that separates the cargo and the propulsion system by giving them both opposite momentum, with the exact amount of energy thus bringing the propulsion system back to circular LEO (Low Earth Orbit) and accelerating the cargo towards the Moon. When cargo is launched from the Moon, the same process happens in the reverse direction. This method is most efficient considering the available time and money.
The “Lunar Kick”
A mass of 500 tons for the propulsion system is appropriate because this is roughly the mass of the International Space Station and the mass ratio between the cargo and the propulsion (1:25) is sufficient for a successful kick. Before the kick the whole system is transferred to an elliptical orbit through the use of ion engines. This takes about a month depending on the desired eccentricity of the orbit. Then an explosion takes place and, like a spring, and separates the propulsion system and the cargo. In about 3 days the cargo reaches the Moon.
a. Advantages
The “Lunar Kick” has several advantages. One is that the propulsion system itself does not move with the payload to the Moon and therefore no energy is spent on accelerating such a big mass on a translunar trajectory. Another is the time it takes to send one load of cargo to the Moon. This amount of time, although not the smallest possible, is acceptable because it is much more cheaper and effective than faster alternatives. The simplicity of the system is also one of the serious advantages. The only thing that has to be done is launch the cargo to LEO and attach it to the ‘cannon’ which will in turn do the work. Furthermore the cannon has enough fuel to complete several kicks (about 8) without refueling. Each kick brings to the Moon 20 tons of payload and thus achieving a very good price per kilogram of payload to the Moon (about USD 24000 for the Titan 4B and about USD 4000 for Proton 8K82K 11S861). This low price may open the door for the construction of lunar bases, unthinkable by now.
Through the use of plasma engines the work of the ‘cannon’ is made very economical. With one refueling it can perform up to 9 kicks, which would be impossible if chemical boosters were used. The time it takes to achieve the desired orbit is longer than it would be if chemical boosters were utilized but in this way it is much more efficient; furthermore the time loss is totally acceptable.
Finally, the use of explosives to act as a spring makes the system even more effective because it transfers the momentum gained by the ‘cannon’ to the cargo and while ejecting the payload to a translunar trajectory circularizes the orbit of the cannon thus bringing it back to where it started and it is ready for another kick.
b. Disadvantages
The method of the Lunar Kick also has some disadvantages. A relatively large explosion is necessary to produce the desired velocity changes, which causes a great acceleration (50-200 gees), which no human being can withstand. So this limits the types of materials that can be sent to the Moon (i.e. no experiments with harmless animals on a lunar station =). The explosion, although it theoretically works perfectly well, may in practice harm either the propulsion or the cargo itself if their structures are not firm enough.
