Sure it seems you can do it all with these plans, but at what cost? SLS doesn't promise to be economical. It will take several launches of SLS to make the Moon plan work. It will also take several (at least 2) launches of the same rocket to make the Mars plan work even after the EMLP has been established. The only reusable part of the SLS are its solid rocket boosters. At least in the moon plan a reusable moon lander is called for, and the EMLP is designed to be a multi-mission asset. These plans call for many in-space and landing assets to be built. This is not cheap. I am also skeptic about this Mars lander that is supposed to land and launch astronauts on to and from the Martian surface. How big does that thing need to be? How much fuel does it need? Mars is about one third of the gravity of Earth. Sp they seem to need one third of the energy of a Earth based rocket to get to orbit. Like a third of a Falcon 9. I'm just guessing here, the details I'm sure are different due in part Mars' gravitational field's profile (gravity is not linear with altitude). Yet, it gives you an idea of the problem. Think of all that hardware and fuel launching from Earth, in parts, and sending off to Mars. Its huge! The Mars plan seems to imply that the large transfer vehicle is for only one use, and one mission. So if we want to make another go at it, we need to spend a lot of money to do so.
Apollo used all throw away assets to do its 7 moon landings. It was canceled due to cost. I hold the philosophy that space assets should and ought to be reusable, that is used for more than one mission. The trans-lunar injection was performed by Saturn V's third stage. That function can be made by a reusable space tug. A reusable space tug would be equipped with propulsion (chemical, ion, and/or plasma), communication, and power (solar or nuclear). They would dock with a manned capsule or cargo capsule/canister and take them to their destination. I don't see why NASA does not pursue this route rather than majoring on throw away assets. A reusable space tug can take crew, cargo, and/or modules from Earth orbit to Lunar or Martian orbits and return to Earth orbit. Then they could be refueled and loaded up with a payload and do the next mission. The only thing that has not been mastered in this sequence is an unmanned tug returning to Earth orbit. Yet, space programs do have experience getting into Mar's orbit and using aerobraking to do it. Similar techniques could be used with the tug. Of course, when its taking a capsule back to Earth, the capsule would disengage the tug before the tug maneuvers to Earth orbit because it could take weeks for the tug to get to low orbit. NASA could make its own, or a company can make its own and sell the services to NASA. I wonder if some company out there is doing just that? I don't know. I did think up this reusable tug idea back in 2004 when SpaceShipOne was making its historical flights. I posted this idea on Space.com forums at the time. It seems that NASA thought of the Space Tug concept too in 1969. These tugs could be of variable sizes for a variety of missions for many customers. They could go to Moon, Mars, Venus, Mercury, the Asteroid Belt, and even the gas giants. They could form an effective fleet for space exploration and commercial exploitation such as mining. I imagine that reusable in-space assets, such as the space tug, could bring down the cost of traveling to the Moon and Mars significantly since the commercial launch companies can also leverage their launch capabilities.Yes, the Boeing plans are cool. I believe they will be too costly for Congress to flip the bill. Making good use of the new commercial space approach with reusable assets could make the missions cheaper and help keep them going for a long time.
