While the design is cool, it actually appears to be overbuilt for the mission. By overbuilt, I mean it appears that the structure is more than would be required for the expected loads which would be a waste of weight. The stylishly streamlined cockpit looks pretty but a spherical design would be lighter and stronger. On top of that, those big engines at the rear really aren't needed. If you're going to have landing engines with enough power for a soft touchdown, why not use the same engines for all phases of the flight similar to what they did with the Apollo Lunar Module? Sure, the cockpit is offset from the center of mass and the crew would have to look out of the top when docking, but that's the same situation that exists when the Shuttle docks with the ISS.
My design concept has some similarities with the Eagle. It would consist of a truss with a spherical cockpit at one end and landing pads mounted on outriggers. There would be 3 or 4 rocket engines mounted at the center of gravity, with each engine being powerful enough to compensate for the loss of 1 engine and still make a safe landing. By that, suppose the vehicle had 4 engines and each engine was designed to produce 6,000 pounds of thrust at the moment of touchdown for a total of 24,000 pounds of thrust. If one engine failed, the remaining engines would have to each produce 8,000 pounds of thrust to allow a safe touchdown. If two engines failed, you'd have to jettison your payload to have a chance at a safe landing or abort to orbit. Asymetric thrust vectors can be handled by mounting the engines as close together as possible, using some thrust vectoring, and by putting fairly strong attitude control thrusters on those outriggers.
The propellant would be carried in 2 or 4 spherical tanks on the truss. Like the CH-54, external payloads would be attached to the structure and hung below. This would require some careful loading to keep everything in balance and it would probably require some shielding on the payloads to make sure they aren't eroded by the engines or dust kicked up on landing.
The cockpit would be big enough to carry perhaps 6 people per trip. It'd have to serve as cramped living quarters until the first habitation module is set up and operational.
My idea is for this to serve as a reusable shuttle between lunar orbit and the surface. The initial design would probably use hypergolic propellants because they're storable. If water ice does exist on the surface, the design might be able to be reengined with LH/LOX engines using propellants produced from the ice. This would really reduce the cost of operations and would also have the benefit of allowing for greater payload capacity due to higher Isp.
For the job of flying between LEO and lunar orbit, I'd like to see a dedicated vehicle designed for that mission. It would use aerobraking if possible for LEO insertion, otherwise it'd use thrusters to slow down to orbital velocity. I think this would be a lot more efficient than trying to design a single vehicle to fly from Earth orbit to the lunar surface and back.
As a side note, I just picked that 24,000 pound thrust number for the sake of example. Lest anyone thing 24,000 pounds of thrust would be insufficient for putting a heavy payload on the surface, remember that the moon's gravity is only 1/6th that of Earth. 24,000 pounds of thrust at touchdown would be capable of landing a vehicle on the moon that would weigh over 144,000 pounds on Earth. Take a look at the Apollo Lunar Module numbers:
Descent stage mass: 10,149 kg
Ascent stage mass: 4,547 kg
Descent stage propellant: 8,165 kg
Descent stage thrust: 4,491 kgf
At the moment of touchdown, the LM's mass consisted of the ascent stage mass, descent stage dry mass, and residual propellant mass. These numbers are approximately:
Descent stage dry mass: 1,984 kg
Ascent stage mass: 4,547 kg
Est residual propellant: 600 kg
Approx landing mass: 7,131 kg
Notice how the descent engine thrust is less than the ascent stage mass by itself. The descent engine was throttled back considerably from full thrust at touchdown or the vehicle would not have been descending. I estimate the LM descent engine was only producing about 1188 kgf at touchdown.
Space/Science » in reply to The utimate lunar tug
Re: The utimate lunar tug
