On the feasibility of putting fuel sources in LEO
Several companies are building and testing lunar lander engines that use LOX/Liquid methane implying that lunar landers can be launched from Earth with empty tanks and fueled onorbit or stored fully fueled or refueled many times.
http://www.aviationweek.com/search/arti ... 13,%202009
If they can be fueled up in orbit, then they can be refueled and potentially reused anywhere and anytime. This opens up a lot of new and potentially better ways to get to and from the Moon in case something bad happens along the way. If you don’t look at what happens when something fails before you write requirements and design an engine, you paint yourself in the corner when an engine fails like it did on Apollo 13. Fortunately, they had a backup engine system completely separate from the stage that failed.
There also is no such thing as a requirement that an engine cannot fail for any reason. Instead, we use the phrase “increase reliability” as a replacement for such a requirement. Reliability is simply a statistic that can only be calculated based on the number of previously successful engine burns and not measured. The more the engine is reliable, the more the company can charge the customer for it since customers demand the most reliable engine.
Refueling and reusing a lunar lander lowers cost and improves safety when engines fail. It also makes it safer for the outpost crew’s personal well-being, especially during their return trip during the ascent phase from the lunar surface. They don’t have to worry all of the time about their precious fuel, especially if they are going to be there for 6 months in a very inhospitable environment. It also opens up lunar surface access to competition for others with engines that burn or supply the same fuel.
If you could refuel a spent descent engine on the lunar surface and use it again, then the descent engine transforms into the ascent engine. You could also use it to hop around on the Moon like divers do in a similar fashion exploring caves that are several miles long.
If you lift off of the lunar surface with a fully refueled descent engine, you now have a backup engine stage in the form of the part of the lunar lander configuration which houses the crew and the return cargo. You have 2 systems capable of getting into lunar orbit instead of 1. So, if the primary refueled stage fails, you ignite the backup stage and proceed to lunar orbit. Without two stages with two sets of separate tanks and engines, you crash on the lunar surface if your engines fail. This risk was present during the Apollo program. If their ascent engine failed, they were doomed. It took some very brave and courageous heroes to accomplish Kennedy’s goal. Two stages are always better than one, especially in this instance. If you don’t believe an Astronaut, just ask any Navy pilot.
So onorbit fuel depots make good sense no matter if they are in low Earth orbit or low Lunar orbit. The other advantage of having a refueling station in low Lunar orbit is the ability to provide this type of engine failure redundancy by landing an unmanned lander with cargo and fuel needed during the stay and return trip. You land the unmanned cargo and fuel before you send the crew to the surface. Their job would be to get and use the cargo and fuel during their trip. You delay sending the crew in case the unmanned lander fails to land intact.
Sending crew, cargo, and fuel into low Earth orbit and onto the Moon and back in one shot is how we did it in the Apollo program. Notice, we have altered this approach to one that assembles transfer vehicles together before embarking on the trip to the Moon and now, we are now considering having fuel in space somewhere ready for the crews when they get into space. Sounds like a natural progression of things are happening where one shot deals that are extremely risky are a thing of the past.