Space elevator. Dream, hoax or reality?

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...the safety margin goes to well over 100%. The bottom few thousand kilometers (the only part that is likely to fall DOWN) is literally only centimeters across. In the event of a break it would fall mostly on and around the anchor point. Parts of it would burn up during re-entry. The remainder COULD cause some damage if any pieces hit something.
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And if the break occurs anywhere there is going to be an imbalance in the centripetal force holding the cable up and the rest of the elevator is going to start moving outward into space to balance the released tension that was formerly holding it in place. Is the platform going to have gigantic retro rockets to keep it in position? And even if it did the rest of the hanging cable would continue to move outward. That's quite a mess to repair, especially when the launch section on Earth is toast from the part that dropped.

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As for Orion. If Dr. Dyson truely thinks that Orion is a practical way to move stuff from Earth's surface to outer space, well, I guess I'm not as impressed with him as I was. I hope he has been misunderstood.
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As far as I know, Dyson is speaking as an engineer. He has stated that Orion is the only case he knows of, of a modern technology completely suppressed for political motives only.

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NO ONE is going to let you set off a couple hundred atom bombs in the sky above their least favorite national park, or even their least favorite city. If you try to take off from the middle of the Pacific Ocean the countries situated downwind would probably launch a pre-emptive strike to stop you. And be treated as heros by the world community.
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I never suggested anything other than an ocean launch, you are getting a little melodromatic here. We are not talking about spectacular Hiroshima scale blasts here. Gigantic death dealing clouds of radioactivity would not rain down upon Pacific countries. You may well be right about the political cowardice of our leaders, that is not an engineering problem but a human one. Bush walked out of the Kyoto agreements, that's all it takes.

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Chemical rockets obviously work, but are VERY EXPENSIVE and not really practical outside of cislunar space.
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Right, that's why we should move on to something with more BANG for the buck - heh heh.

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So I guess my point is - why waste time thinking about a technology that can/should never be used (in the way you have advocated here)?
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Should NEVER be used? Why? Because I used the dreaded NUCLEAR word?

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Orion is technically feasible, *IF* you ignore that landing thing (which means it really isn't).
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Throwaway designs can be quite economical. There is no reason that the rocket can't be designed more cheaply for a single launch. It is not at all clear that the non-payload part couldn't come back.

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People will shoot you if you try to fly an Orion from the surface.
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They won't be able to shoot anyone if they are anywhere near it when it lifts off. One of the best features of the design.

Are there any possibilities in generating electricity on earth and beaming it to a rocket powered with an ion drive using microwaves or something? That way we dont nuke anyone accidently

Mark Vitrone

you will have to lose alot of energy on sending the beam up. why would we launch a nuclear accident?

The intuitive mind

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>Is the platform going to have gigantic retro rockets to keep it in position?<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

Rockets?!!! We don't need no stinking rockets!

Consider a beanstalk that is 100,000,000 meters total length with an orbital station at geosync altitude, about 36,000,000 meters, a main counter balance mass at 100,000,000 meters and "tuning" masses at various locations along the length of the cable. One way to handle the broken cable scenario is to move some of these vibration tuning masses up and down the cable to keep the cable at a constant altitude and maintain its 24 hr rotation period and absorb the transients from the break. Mass can also be released from various locations along the cable, including the main counter balance, if necessary.

You would have to keep track of where the released mass would go at all times, and be prepared to delay release if it posed a danger to other objects in space. Alternately, the release mechanism could be designed to add an arbitrary delta v to the released mass to steer it into a safe orbit. Most released masses would end up in Earth-orbit, and would have to be retrieved fairly soon to keep them from hitting the beanstalk.

NOTE: The station at geosync does NOT have to be attached to the cable. Stations at other altitudes do.


<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>Should NEVER be used? Why? Because I used the dreaded NUCLEAR word?<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

No. There are some some reasons that actually make sense. BTW, my complete objection here was (to pick a moderate sized nit : Should never be used *near the atmosphere of an inhabited planet*. For interplanetary missions I have only minor objections to Orion. See below.

I hope, and expect, that we will be using nuclear power in our spaceships within 20 years. And some of them may well be Orion class. There are some missions where speed and maximum payload are Really Important. But Orion is inherently wasteful of nuclear fuel. The amount of plutonium ejected as reaction mass from EACH bomb (on average, since they aren't all the same size) would power a fleet of 5 NTRs for several hours of continuous 1 g thrust. The NTRs wouldn't be as big, powerful or fast as an Orion, but they would still be big, powerful, and fast compared to chemical rockets and do a lot more work with a given amount of fuel.

A 10 kiloton launch mass Orion transport would need to process bombs at the rate of about 6 kilotons explosive yield per minute for 8 to 10 minutes to achieve orbit from the Earth's surface. This processing includes a LOT of water or styrofoam that is vaporized to provide the *fabulous* combination of thrust and specific impulse that Orion can produce. We could quite literally have sent a small town - people, houses, cars, etc. - to Mars in the early 1970s with just two or three of these machines, for about the same cost as the moon missions. We could still do it today.

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About half of these exhaust products would be deposited in the atmosphere and the ocean. When the Orion project was active we (all countries with nuclear capability) were doing atmospheric bomb testing at the rate of about 10 to 40 megatons per year, so an Orion launch at that time would have been insignificant by comparison.

It would eventually take hundreds of launches a year (assuming a 50% payload fraction and an elegant solution to the landing problem - sorry, no parachutes) to compete with the cargo capacity of a beanstalk system ...

Orion might be able to compete on the basis of construction cost (throw-away components help here) and cargo capacity, but it would never be competative in terms of operating cost (throw-away components really hurt here) or environmental impact.

The average person can tolerate an amazing amount of environmental radiation, but some of us have "manufacturing defects" that make us less hardy in this respect. These "defective" individuals began to have health problems of all sorts that were suspected, and in some cases proven, to be caused by the fallout. And of course if the radiation gets high enough even "non-defective" individuals start having problems. So we decided to stop.

It can be argued that the Human race in general would benefit <b>SO MUCH</b> from cheap access to space that sacrificing a few of of us in this way is justified. (IMO these benefits will turn out to be much much larger than even the most liberal of current estimates.) We wouldn't even have to say which individuals should be volunteered, because Nature would pick them for us.

Sigh. I may be short sighted, but I guess that's a line I'm just not able to cross.

"The good of the many outweighs the good of the few, or the one." ??? This is patent b*llsh*t most of the time, but consider how things can change when you throw in a zinger: an asteroid 200 or 300 km in diameter *IS* going to hit Earth in 17 years 5 months and 5 days. A rock like this would sterilize the planet within a few days if it hit deep water. NO ifs, ands or buts. Some life would probably survive a dry land or shallow water impact.

Suddenly (and briefly) Spock's philosophy makes sense. All significant objections to Orion (even for ground launch missions) and NTRs would disappear, or be suppressed, since it represents our only realistic option for survival. A fleet of ground launched Orions might be the only tool we could put together soon enough with the speed and raw power needed to save our beautiful planet. And us.

No need to worry about the landing problem, either.

Even in such dire circumstances we might still choose to use chemical rockets to lift stuff to orbit, so we could build and (especially) launch the Orions out there. A (pre-existing) beanstalk would allow this to happen faster and at much lower cost. Yes, even with no balancing mass comming back down.

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Hmmm. It looks like we'll end up with all three devices:

Beanstalks and space bolos for fast and very low cost travel and shipping along established trade routes, especially the surface to low orbit part of the trip. (But we still have to make that cable, first.)

Nuclear Thermal Rockets for faster but slightly more expensive travel and shipping. Especially to destinations where no elevators exist, and for initial exploration of new destinations.

Orion Nuclear Rockets for very high speed and relatively expensive (but still much cheaper than chemical rockets) transport. The military will probably own most Orion class machines. They should also be useful for rescue work ("Coast" Guard?), certain scientific missions (up-close, extended observation of the Sun or the gas giants?, or long range exploration out to maybe a light year or so?) and for other missions where power and speed are critical.

Regards,
LB