Skip to comments.The Cold Equations Of Spaceflight
Posted on 09/09/2005 5:26:35 AM PDT by nuke rocketeer
In the past month, we have been blessed with numerous leaks from NASA of various study documents relating to the new boosters that will be needed to carry out the new manned moon program. I've been monitoring the large volume of Web chatter about these plans, and have noticed a disturbing theme therein. Many Space Cadets are expressing dissatisfaction with these leaked NASA plans. They say that the Shuttle-derived boosters are too primitive, too expensive to develop, too expensive to operate, and not inspiring enough. They can't understand why we will be returning to the Moon with rockets and space capsules that look like minor variations of those used in the Apollo program 40 years ago.
(Excerpt) Read more at spacedaily.com ...
Has anyone figured out how they are going to get through the Van Allen Radiation belt alive?
Let private enterprise do it. They're already doing brilliantly in near space.
We can't even keep the insulating foam from coming off of the shuttle's external fuel tank. Space technology will advance ONLY when it become profitable and private industry starts paying more of the bills.
Can't find enough dilithium crystals?...........or melange......
So the problem seems to be that of being able to carry enough fuel. Which has to be of the conventional kind.
I can't imagine nuclear power driving a space ship and especially a manned one. The mass of fat-nucleus atoms needed to shield it would render it literally impossible.
You mean I'm stuck here???
I fully agree, but try telling some other Freepers that Burt Rutan does not have the ability to reach orbit, and given his budget never will, and you will need asbestos underwear.
An Orion could, but the Atmospheric test ban Treaty puts a legal bar to this vehicle, and the fact that it puts all kids of fallout in the atmosphere puts an ethical and environmental bar in front of it.
The Apollo astronauts got through it alive. The key for that is to go through it quickly.
Predestination is an ugly thing, Harley.... ;-)
Is private enterprise somehow immune to the Cold Equations of Space? They're not.
And they're also not immune to the Cold Equations of Return on Investment. Aside from the fabulously profitable comsat market, private enterprise hasn't got much incentive to go into space right now.
Yep. Anything we do in space is going to be hard AND expensive. TANSTAAFL. I would like to see us substitute a modernized Dyna-Soar for the modernized Apollo in the new launch vehicle.
Oh well, back to Traveller.
Basically an atom bomb with wings??
Would there be some way to get around this by keeping some of the propulsion system earthbound? Like a humongous slingshot or catapult?
Yes. See my post #10.
10K isn't THAT rarefied. Even if you mean miles.
Rail gun, pshaw. I wanna see a giant coil spring compressed and go SPROI-OI-OI-OING up a tube.
Distance is also a shield.
Once you get to Low Earth Orbit via conventional means, you can hook up to a nuke power section via tether (we can make long and very strong strings these days) and have it pull you to Mars orbit via high-efficiency ion drive
It has been determined that the first man made object to truly leave the earth's bounds was a man hole cover from a nuclear test detonation tunnel. High speed imagery was used to calculate velocity.
Most of our satelites are well below 10,000 miles up. Care to reconsider?
The world's longest extension cord, huh. Someone oughtta do the math for how heavy it would need to be in order to carry the requisite current... shoot, even to support itself against high atmospheric winds.
Nope, A HUGE thick hemisphere of steel with a crew compartment on top and injection ports to squirt a hydrogen bomb under it to detonate a few microseconds later. See this site
Not if you use the best fat-nucleus element available - the nuclear fuel itself. Design a ship whose uranium or plutonium can double as shielding. There will need to be some additional shielding against radiation from the fuel itself, but that's minimal.
Why don't I have to duck those pesky things while on the Albuquerque Tramway?
If you brought together a layer of fissionable uranium heavy enough to stop the radiation of some presumably localized reaction, the shield would itself be well over criticality and so couldn't even be built. Plutonium? Same thing, except it's also a devil of a material to deal with structurally (goes through something like five phases in the solid state depending on temperature).
Tunnels have been dynamited and bored for roadways much further than 2 miles.
We're still stuck using Chemistry.
Hyrdogen and Oxygen burn fast. Controlled-explosion gets you off the ground. Gliding, friction and parachutes get you back.
A little improvement in technology gets you a little better rocket ship. But you're still stuck using the Chemistry of Hydrogen and Oxygen (and the various solid fuel-based ways of storing the two elements to get a controlled explosion later.)
Nuclear doesn't sound like the next wave except for deep space exploration satellites. Plasma engines give you a good boost in deep space over a long period of time but it doesn't get you off the ground or the moon or Mars.
Until we get a new form of Energy (not based on Chemistry or dangerous Nuclear), we're stuck doing what we're doing now. Slightly better crafts as slight technology improvements come on stream.
New physics, anti-gravity, something else is needed to make the next step.
I read an article in Discover a few months ago about space elevator plans. Very compelling if we can overcome materials restrictions. Once we get out of the Earth's Gravity well moving around gets a lot cheaper.
The climb-up-a-ribbon stuff?
Chewing down the middle of an equatorial mountain would require the same thing.
No. It would require digging and building up to create the required exit angle. An angle that could be much less at 20,000 ft than at sea level. But not anything close to trying to dig that deep. The pressure and heat would not be anything like 5 miles deep. You sure are argumentative about a simple concept.
The biggest hurdles for that approach have to do with the fact that any ground-based boost method will induce high accelerations; and after that, the payload ends up having to go very fast in thick atmosphere.
The only way to handle the first problem is by adding length to your booster system. You'd have to handle the second by adding sheilding (heavy!), or somehow keep the atmosphere in the launch system at low density.
There is potentially a lot of merit in developing an air launch capability, although that's got to deal with other issues.
An ablative shield possibly? Cast a shield from a material that carries away heat when vaporized? (Ice?)
Again, see my post #10. A rail gun, with a mountain top terminus solves both problems. Shooting a vehicle into space while keeping acceleration structural loads below 7 G. Atmospherics are greatly helped by not entering the atmosphere until the vehicle is already above the thickest part of the atmosphere (higher is better). And high energy beams may be able to split the flight path, thus decreasing resistance even more.
Does this involve large amounts of cabbage , beans and beer?........
First off is the fact that even at 29,000 feet (the top of Mt. Everest) you've got a hell of a lot of atmosphere to deal with, and you're going to hit it at well over 8 km/sec (you have to account for drag losses in your exit velocity). You can't be going straight up -- your velocity has got to take you in a ballistic trajectory that forces you to remain in the sensible atmosphere (which lasts up to ~400,000 feet) for quite a long time -- several minutes, at least. Note that the Shuttle sheds most of its orbital energy, and thus gains most of its atmospheric heating, above 200,000 feet. Bottom line is that there are tremendous heating issues to deal with, even with a rail gun.
In essence you're reversing the ballistic missile re-entry problem. (Harvey Allen's famous work on re-entry body shapes is summarized here, with a good assessment of the heating issues involved.)
An alternative is to use a railgun to boost the vehicle to a "respectable" speed to get it up high, and then use rockets to finish the job. The problem there is that the power overhead for the railgun probably increases tremendously due to the vastly increased launch mass.
You've also got to deal with the problem of how to move your great big mass through the long tunnel. You've got probably surmountable alignment and smoothness issues, but you've also got to deal with holding the payload in the center of the gun. Do you put it on rollers?
Finally, you've got to figure out a way to pull the air out of your tunnel, but still allow the payload to get out safely. This means a door of some sort that has to be big and heavy enough to keep air out, but must be nimble enough to open quickly, when the payload is close to the exit. Unfortunately, the act of opening the door will let the air come cascading in, which will lead to severe turbulence, buffeting, and shock waves as it rushes down the tunnel and comes into contact with the hypervelocity payload. Your tolerances are shot at that point, and you'd be in significant danger of hitting the wall, which would be a disaster.
So there's a huge design issue there that can probably only be addressed by adding "non-propulsive" length and width to your tunnel, and/or by making a faster door. Note that if it takes one second to open the door, then you've got to ensure that your payload is at least 8 km away when you start to open it. If you've got any experience with supersonic wind tunnels, you'll recognize the likelihood that there will be a large shockwave coming down the tunnel toward your payload.