Will The Next Generation of Spacecraft Land In the Water?

Reservoir Hill writes "Work is progressing on the design of the new Orion Crew Exploration Vehicle (CEV), the next generation of NASA spacecraft that will take humans to the International Space Station, back to the Moon, and hopefully on to Mars. One major question about the spacecraft has yet to be answered. On returning to Earth, should the CEV land in water or on terra firma? After initial studies, the first assessment by NASA and the contractor for the CEV, Lockheed Martin, was that landing on land was preferred in terms of total life cycle costs for the vehicles. Getting the CEV light enough for the Ares rockets to be able to launch it, and therefore eliminating the 1500 lb airbags for landing has its appeal. A splashdown in water seems to be favored."

Comments

Thought about something like this

[pkadd]

Something i used to think of as a kid was: How about using the propulsion you get from the water for initial thrust of the spacecraft? Sort of like the effect you get from releasing a bottle of air under water, couldn't that be utilized in a cheap way of getting that initial upwards thrust, or would it be too cumbersome to make a vessel that is light enhough for it to actually float?

Re:Thought about something like this

[IdeaMan]

Actually the submersion idea is brilliant. The piece missing is the launch tube.
Build a 30 foot diameter tube 2 miles deep, with a piston on the bottom. Put brakes on the piston that will limit the acceleration down to about 5G. Empty the piston of water, lower spacecraft onto piston, when you launch just let the piston rise. The thousands of PSI of water pressure should give the spacecraft a significant amount of speed by the time it reaches the surface, light off rocket at a higher altitude than normal so the nozzle can be optimized for a higher altitude burn. I'll work on the math for this.

Re:Thought about something like this

[IdeaMan]

The setup:
30 mile long tube buried at a shallow angle, say 5-20 degrees. This lowers the pressure requirements at the bottom end of the tube.
Pressure (every 33 feet per 14.7 psi) Depth = sin(20)*length in feet = 24,100 psi
Acceleration = 5G, d = 1/2*a*t^2, therefore T = 44.5 seconds.
V = Acceleration * time, therefore V = 7110 ft/s
1 m/s = 3.28 ft/s
Delta-v to low orbit is 8600 M/s, or 28000 ft/s

So this method will give us 1/4 of the delta-v needed to get to low orbit.

If an ocean contour could be found that somewhat matched the angle involved, the tube buoyancy and alignment problem could be solved by anchoring it to the sea floor.

12G at 50 miles, 20G@30 miles give 14kft/s (1/2 low orbit delta-v)
50G @ 50 miles gives 29kFt/s, more than enough for LEO if you ignore drag.
This class of launch tubes would be suitable for refueling geo-synch shuttles.

62 mile tube @ 10 degrees (similar idea as the 100km launcher proposed for Antarctica) gives 25kPSI, 9k deltav @ 4 g.

I'm not sure if it would be easier to build a straight tube in Antarctica or in the Ocean.
One other problem is that once you surpass the speed of sound in a medium you no longer receive thrust from it. Speed of sound in water is 1482 m/s, or 4862 feet/s, so you would need to start pumping a hot gas, either rocket exhaust or hot hydrogen into the tube once you passed 4.8kft/sec.

Probably both, it turns out

[Thagg]

Lockheed, the Orion prime contractor, has expressed significant reservations about carrying the heavy airbags to the moon and back -- those 1500 lbs can better be used in other ways. On the other hand, there shouldn't be a problem with the weight on the more common missions to the space station and low-earth orbit, and the ability to reuse the capsule will be far greater if they put it down on land.

The speculation in this week's Aviation Week was that they would have bolt-on airbags for the earth-orbit flights, and would recover those missions on the land, and would recover at sea for the moon-return missions.

The reentry profile for the moon missions is really quite amazing. Recently Aviation Week had an article about it, describing how to get all the capsules to recover to the same spot on Earth. Do you recall way back in the Apollo days, they always described the narrow re-entry corridor? Too steep and you'd burn up, to shallow and you'd skip back into space forever? Well...

For Orion, they plan to use a skip back into space to bleed off some of the speed coming back from the moon, and to align the craft to re-enter at the correct place to land where they want, off the coast of California. It's an incredibly audacious plan, with tolerances that have to be measured in tenths of a degree of entry angle. Very cool.

Thad

What I don't get

[BorgDrone]

What I don't get is the continued use of rockets. Is going straight up (the brute force & ignorance method) really the most efficient method of getting up there ? Isn't an approach like SpaceShipOne uses more efficient in terms of amount of energy needed per kilo of launched mass and thus costs ?