Return to the Moon Lunar Landers - Opening the High Frontier

Return to the Moon Lunar Landers (low lunar orbit)

The initial Return to the Moon lunar landers that will operate from the low lunar orbit space station will consist of 3 different vehicles, a 2-person crewed vehicle that will look like the ascent stage of the lunar lander used in the Apollo program but with landing gear legs added,

a cargo lander that will look like the descent stage of the Apollo lunar lander that will be capable of landing 7,000 kg payloads on the Moon, and a tanker based on the cargo lander but with oversized propellant tanks.

The tanker will be able to land 7,000 kg of propellant that will be used to refuel the crewed lander, the cargo lander, and still have enough propellant leftover that it will be able to return to the Lunar Orbiting Space Station in low lunar orbit. After returning to the lunar orbiting space station, all three landers will be refueled and prepared for another mission. These landers will use the same storable propellants that were used for the Apollo lunar lander and that are used in the service module of the Orion spacecraft.

A typical landing using the three Return to the Moon lunar landers will start with the landing of the tanker at a landing site near the lunar South Pole. Once the tanker is successfully on the lunar surface, the cargo lander will land nearby. After that, the crewed vehicle will land. It is assumed that the cargo lander will carry a pressurized rover and two small propellant tank trailers for the first landing. The rover will use the trailers to refuel both the cargo lander and the crewed lander for their return trips to low lunar orbit with propellant from the tanker. Once that is done, the crew will use the rover to explore the lunar South Pole area for easily accessible ice deposits that are near an area in permanent sunlight that is large enough for building a lunar base.

For missions requiring only an unmanned rover, the tanker with a partial propellant load can land a 4,700 kg rover on the surface of the Moon and still have enough propellant on board to return to the low lunar orbit space station.

Another way to use this system will be to remove the landing gear from the crewed lander, attach it to the top of the cargo lander, and operate the combination like the original Apollo Lunar Module. Assuming the cargo lander is not damaged when the crewed lander takes off, it can be refueled and sent back to the lunar orbiting space station at a later date.

A second way to use the crewed lander will be as a sub-orbital hopper for sending astronauts to other parts of the Moon on exploration missions from the Moon base. For this type of mission, the lander will use 1/4^th of its propellant to head to a site of interest, 1/4^th to land, and the remaining half to return to the Moon base.

The crewed lander will have a space station departure mass of 4,700 kg and will use 2,300 kg of propellant to land on the Moon. It will require an additional 2,300 kg of propellant from the tanker to return to the low lunar orbit space station. The cargo lander and tanker will both have a space station departure mass of 18,000 kg and will use 8,500 kg of propellant to land on the Moon when fully loaded. They will need 2,300 kg of propellant each for the return to the low lunar orbit space station (no payload). The total amount of propellant required for these three vehicles to land on the Moon and return to the low lunar orbit space station is 26,200 kg. The amount of propellant required for the tanker to land a 4,700 kg unmanned rover on the Moon and return is 10,800 kg.

The advantages of the three Return to the Moon lunar landers are many; the landers are reusable, they build on our experience with the Apollo Lunar Module, they use existing propulsion systems that use storable propellants, they are small enough that they can be sent to the Lunar Orbiting Space Station with existing launch vehicles, and their propellant needs are manageable. Propellant resupply will be discussed in more detail in the article Return to the Moon Space Tug.

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Lunar Surface Exploration

All the articles about the Return to the Moon program show the first mission staying on the lunar surface for 2 weeks. If we are to make effective use of this time on the Moon, the astronauts will need some type of habitat to stay in. Camping out for 2 weeks in a crewed lander that lacks an airlock is not an option. This habitat can be a small inflatable structure, a structure that is designed to fit on top of a cargo lander,

or some kind of pressurized rover that can also be landed by the cargo lander. All of these solutions have been studied many times since the 1960s and the majority of them are within the payload capacity of the proposed cargo lander. One pressurized rover concept that is particularly well suited for this mission is the Space Exploration Vehicle with wheeled chassis. This vehicle is designed to support 2 astronauts for 2 weeks on the lunar surface. Prototypes of this vehicle have already been built and tested on Earth. If the SEV can be ready in time to meet the 2024 deadline, we will not only be returning to the Moon, we will be returning in style. The SEV with chassis and supplies has a mass of approximately 5,000 kg.

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Gateway Station Lunar Lander (L2 Halo orbit)

By comparison, a lunar lander designed to operate from the Gateway Space Station in an L2 Halo orbit is a much larger and more expensive vehicle. Lockheed Martin has proposed a single-stage reusable lander for this that carries a crew of four, a payload of 1,000 kg, has a surface stay time of 2 weeks, and uses a LOX/LH2 propulsion system. According to Lockheed Martin, this lander has a departure mass of 62,000 kg when it leaves the Gateway Space Station, and a dry mass of 22,000 kg when it returns at the end of the mission. The total amount of propellant required for each landing is 39,000 kg.

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Storable versus Cryogenic Propellants

Before the Moon Base is built and cryogenic propellant production using lunar water begins, all the propellants used by the Return to the Moon program will need to be brought up from Earth. The problem with using cryogenic propellants for the initial phases of this program will be the need to develop a cryogenic propellant storage system that can keep the propellants cold and recompress the boil-off gasses. Developing and testing such a system and getting it in place in lunar orbit in time for a 2024 lunar landing adds additional risk to not being able to meet the deadline. If the propellant losses due to boil-off are considered part of the cost of using cryogens then it will be necessary to send enough extra propellant with every shipment to account for this. Unfortunately, if a mission is delayed, the amount of propellant remaining at the lunar space station for the landing could become an issue depending on how long the delay is. Using storable propellants for the first landing, the lunar exploration phase, and the lunar base construction phase of the program eliminates these issues and provides a backup system for when the transition to cryogenic propellants begins in the future.

Ad Astra! (To the Stars)

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