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Will The Next Generation of Spacecraft Land In the Water?
Posted by
Zonk
on Fri Dec 14, 2007 01:01 PM
from the splashdown-for-the-future dept.
from the splashdown-for-the-future dept.
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."
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Thought about something like this (Score:3, Interesting)
Re: (Score:2, Insightful)
Re:Thought about something like this (Score:5, Funny)
Parent
Re:Thought about something like this (Score:4, Funny)
Adam [discovery.com]? Is that you?
Parent
Re: (Score:3, Insightful)
Re: (Score:3, Funny)
Re: (Score:2, Informative)
Re: (Score:3, Interesting)
Re:Thought about something like this (Score:4, Interesting)
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.
Parent
Re:Thought about something like this (Score:5, Interesting)
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.
Parent
Re: (Score:3, Interesting)
To use that to escape Earth gravity, though
Simple Answer (Score:2, Insightful)
Re:Simple Answer (Score:5, Informative)
Parent
Re:Simple Answer (Score:4, Insightful)
There are some very good reasons for building an all-American rocket beyond mere politics. It has everything to do with developing domestic expertise in the field, and encouraging R&D in the country for these technologies, which can only serve as a foundation for developing even more.
Beyond what the other posters have mentioned, brute forcing the problem is also rarely a good solution. Instead of spending tens of million each launch to lift a huge, heavy spacecraft into orbit, its weight should be optimized, both for the sake of proper engineering and for the sake of cost cutting. I won't presume to know the specific technical difficulties of a project as complicated as the CEV, but there's a balance between more lift power and reducing spacecraft weight.
Parent
Stupid Answer Re:Simple Answer (Score:3, Insightful)
And of course, you overlook the many domestic alternatives that *actually exist*. Like EELVs (Delta and Atlas). Or those that could be restarted since they just quite making them a few years ago (Titan IV - ro
Re: (Score:3, Insightful)
Re: (Score:3, Informative)
The Apollo program that sent men to the moon had a much better safety record than the Shuttle, which lost two crews, one on takeoff and another on re-entry.
It also had a much smaller crew module and in part, was built to scare the crap out of the Soviets.
Part of the goal with Ares is to use what worked from the man-rated Shuttle program (inexpensive and expendable main tank, reusable, recoverable SRBs) and what worked from Apollo (updated and enlarged crew module) with refinements that mean the vehicle will be flexible and have room for growth. Saturn V was a nice rocket, but didn't meet these goals. You have to build a whole new one every time.
Re: (Score:3, Informative)
Here's a quote from http://www.space.com/news/spacehistory/saturn_five_000313.html [space.com]:
"There is no point in even contemplating trying to rebuild the Saturn 5. Having a complete set of Saturn 5 blueprints wo
Water or land? (Score:5, Informative)
Re: (Score:2)
Breaking the water (Score:3, Interesting)
I don't think it's the surface tension that gets you, it's the inertia. Still, the mobility of water means that you're decellerating from 200 MPH to zero in 0.2 seconds instead of 0.1, so it's a big reduction of force.
Missing Option: Cowboy Neal (Score:3, Informative)
Sorry, had to get that in there. I couldn't help but feel the summary was asking us for our uninformed opinion.
It sounds to me like you're talking about the requirement that has been with the system from the beginning that it be able to ditch in the ocean, regardless of the nominal landing profile. What NASA is trying to decide now is if it should normally land in the ocean and face the added recovery hassle and risk, or on land and need to accomodate
Theyy could always ask Paul Revere ... (Score:5, Insightful)
"One if by land, two if by sea ..."
Seriously, why not just do the moon mission, then pick up the landing bags as the ISS on the way home. Better yet, why not have a specialized vehicle just for orbit-to-moon-and-back, and transfer to a special-use re-entry vehicle at the ISS?
Re:Theyy could always ask Paul Revere ... (Score:5, Insightful)
Just put whatever you want to rendezvous with in whatever orbit is convenient, it won't go anywhere.
Parent
Re:Theyy could always ask Paul Revere ... (Score:5, Informative)
You put the package in whatever orbit is convenient (as opposed to the ISS, which isn't convenient), and you know its position as surely as you know that of the ISS, or any other sattelite. Space navigation doesn't involve any "finding", ever.
Parent
Re: (Score:3, Insightful)
Because that would actually _increase_ the mass boosted towards the moon by a factor of a thousand of more. (It takes a lot of fuel to brake into Earth orbit, and yet more to change orbital planes to match up with the ISS.)
The next poster posited simply leaving the required module in a convenient orbit not at the ISS. This is a little better as it only requires increasing the mass boosted towards
Re:Theyy could always ask Paul Revere ... (Score:4, Informative)
No, not really. The Apollos didn't preform any breaking maneuvers on the way back to Earth, they just hit the atmosphere at full speed and scrubbed off their speed there. If you enter shallow enough, you can burn off more speed in the upper atmosphere before you start getting into the thicker air, and a sufficiently durable heat shield turned out to be lighter then the fuel that would have been required to slow the ship down. In fact, even orbiting spacecraft generally burn as little fuel as possible to get themselves just bellow orbital velocity and then do the rest as atmospheric breaking.
Parent
Re:Theyy could always ask Paul Revere ... (Score:5, Informative)
Recall: Apollo's flight plan was an initial burn to get into earth orbit, another burn to leave orbit on course for the moon (trans-lunar injection), another burn to get in orbit of the moon, and another burn to leave orbit on course for earth (trans-earth injection). That's it. They didn't return to orbit after leaving the moon. They left the moon, coasted for a couple days, hit their entry interface, then hit the Pacific.
Why? Going back into orbit requires adding two more burns: one to enter Earth orbit, and another to leave it. Adding a rendezvous with the ISS (or any other floating payload) means an additional 1-2 burns to match the orbital planes, an additional burn to raise or lower your orbit, and God knows how long until the orbits of the two vehicles sync. Look at the space shuttle: even with matching the orbital planes and scheduling launch for an ideal rendezvous profile, it takes them 36-48 hours to catch up with the space station.
Trans-earth injection is complicated enough without adding all that. Extra burns means extra propellant, which means extra weight, which is exactly what you're trying to avoid. Not to mention, each of those steps is another opportunity for failure, and how do you abort if you don't have landing gear?
This is why they are Rocket Scientists(TM).
Parent
Actually... (Score:3, Informative)
Too bad. I thought that was a pretty good explanation, except that it's wrong.
Re: (Score:3, Informative)
Approaching the Earth from the Moon at a slight angle, ie aiming toward one pole or another rather than the equator, lets you use Earth's gravity to help change the orbital plane. You still need to shed a lot of velocity to establish Earth orbit, but
I understand NASA is on a short budget... (Score:5, Funny)
Bad Summary? (Score:2, Insightful)
"landing on land was preferred in terms of total life cycle costs for the vehicles."
Landing on land is cheaper, check.
"eliminating the 1500 lb airbags for landing has its appeal"
Landing on land lets it be lighter, check.
"A splashdown in water seems to be favored."
Huh? WTF? Am I supposed to go RTFA or something?
Re: (Score:2)
Lack of understanding. (Score:3, Informative)
"Landing on land lets it be lighter, check."
The airbags are used for landing on LAND.
They are not flotation devices. Any thing that can fly is going to light enough float on water if it doesn't leak.
The airbags are to reduce the impact.
surface of earth is mostly water (Score:3, Insightful)
Re: (Score:3, Informative)
Gotta give the carriers something to do... (Score:2)
Probably both, it turns out (Score:5, Interesting)
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 is the downside? (Score:3, Insightful)
Re: (Score:3, Informative)
One vote in favor of landing on land (Score:3, Insightful)
Re: (Score:3, Insightful)
What I don't get (Score:4, Interesting)
SpaceshipOne * 30 (Score:5, Informative)
Or you can stick to the simple way of doing it with rockets and parachutes.
Parent
Re: (Score:3, Insightful)
Remember that most of your energy is spent with energy in the direction of the orbit rather than going straight up, and thus why orbital flight is an order of magnitude more difficult that the suborbital fli
no! (Score:3, Insightful)
Because it's water, not land, DUH!
Skip water recovery weight (Score:5, Informative)
To use the ISS, the spacecraft would need to perform a complex aerobraking maneuver (basically, a partial re-entry), then have the fuel needed to circularize its new orbit so that it can rendesvous with the ISS. By the time this is done, the design for the capsule is far heavier than the 1,500lb penalty that airbags impose.
My idea, make the water landing a known 'capsule loss' scenario, the same way it is with the Shuttle. If things go _so wrong_ that a water landing is unavoidable (say, launch failure) then design the capsule for quick-egress after a water landing. Airplanes ditch in water and people have time to get out before they sink. My Piper Cherokee will float long enough for me to climb out onto the wing, and for a real shock look at the survival training that helicopter passengers go through in the military, that's some pretty intense worst case scenario stuff.
With Rogallo steerable parachutes, landfall should be available at all times except the first few minutes of launch. Skip the airbags, make the capsule so it stays afloat just long enough for egress, and train the astronauts on how to get out fast.
Re:Landing on a soft target (Score:5, Funny)
"Roger that. Approach the bean bag landing zone from 1 8 niner."
"Copy that Houston."
"You should see the Lava Lamps lighting your approach."
"Thank you Houston, Please prepare the after flight debriefing bong."
"grgrgrle"
Parent
Re: (Score:3, Informative)
dunno about that (Score:3, Interesting)
Figuring out exactly how and why a program craps out is a matter for endless debate among histori