Slow Space Elevator

[Zeropoint]

Re: Slow Space Elevator

 

But if we have rockets that good, what do we need a space elevator for?

 

With airplanes, why do we need ships?

[Kristopher]

Re: Slow Space Elevator

 

Pick a standard. If "it's just a hypothesis until we actually do it' date='" then SSTO is just as much handwavium as the beanstalk. In both cases, the technology needs work. In both cases, we are unaware of any reason why it cannot work.[/quote']

 

Based on what I've read, SSTO is a lot closer to reality than beanstalks (I cannot even begin to explain how appropriate I find the fairy-tale-sounding name given to the space elevator concept). Delta Clipper, X-33, etc, were at least at the experimental prototype stage -- much of what they found was that we pretty much know what we need to do to make it work, we just aren't there yet. Beanstalks, not so much -- even if nanotubes as a building material turn out to be more than a dream, there's plenty else that might not work and quite a bit we don't know how to do yet.

 

Straw man! You're the one who brought up SSTO' date=' no one was mentioing it, much less taking shots, until you did. [/quote']

 

Going back to previous discussions on the matter of the beanstalk, the absolute disdain some people expressed for even the hint of SSTO in the discussion was a little stunning.

[Lawnmower Boy]

Re: Slow Space Elevator

 

Not to mention that any developments in material technology going towards making beanstalks will make SSTOs more cost-efficient first.

At the end of the day, would-be developers may still discover what urban transit authorities already know. Busses are often more cost-efficient than separate grade rail, just because of capital costs.

[McCoy]

Re: Slow Space Elevator

 

Not to mention that any developments in material technology going towards making beanstalks will make SSTOs more cost-efficient first.

*Visualizes a carbon-fiber re-entry vehicle*

 

We'll let you and Kristopher take the first ride.

[Nyrath]

Re: Slow Space Elevator

 

The kind of materials that would make the spacevator possible would reduce the amount of weight taken by the structure of an SSTO drastically' date='[/quote']

Not necessarily. A space elevator needs materials that make strong tension members, a SSTO needs materials that make strong compression members. A material that is good under tension is generally pretty poor under compression, and vice versa.

[Nyrath]

Re: Slow Space Elevator

 

Going back to previous discussions on the matter of the beanstalk' date=' the absolute disdain some people expressed for even the hint of SSTO in the discussion was a little stunning.[/quote']

It is simple math.

 

The difference in potential energy between an object on Earth and an object in GEO is a mere 15 kilowatts per kilogram. The Space Shuttle takes gigawatts per kilogram to put an object in LEO, it cannot even reach GEO.

 

Chemical rockets like the proposed SSTO are getting pretty close to the theoretical maximum. To get better performance out of a rocket, you need more energetic fuel. Unfortunately this means nuclear. And that means zillions of environmentalists on your lawn waving torches and pitchforks.

 

You have to make a chemical rocket out of gossamer and cobwebs in order to make it a single-stage-to-orbit. All of our current heavy lift vehicles are multi-stage-to-orbit because of this. The DC-X SSTO prototype cracked its fiberglass skin with a hard landing on test flight #8

 

Nuclear is no prize either. A solid core nuclear thermal rocket isn't that much better than chemical. To get the sort of performance to boost huge payloads into orbit, you need something like an open-cycle gas core nuclear enegine. Or Project Orion.

 

Orion involves setting off about one thousand nuclear bombs at regular intervals to boots into orbit. Just think about the fallout. Open-cycle gas core is even worse. It is the equivalent of vaporizing the entire reactor and blowing it out the exhaust nozzle. The environmentalists will have a conniption fit.

 

Space elevators, on the other hand, have a much better theoretical maximum performance. The early models will be only slightly better than rockets, but it has much more potential for improvement.

 

Another advantage is that a rocket cannot "rest." If it wants to stop for some reason at 100 kilometers, it has to burn propellant just to keep from falling back to Earth. Payload on the space elevator, on the other hand, can be stopped indefinitely (except for all the payload canisters behind it).

 

This is why we have such disdain for SSTO.

 

Here's an analogy:

 

What if the Battleship New Jersey in the US Navy was constructed by assembling it in Nevada, and equipping it with huge caterpillar tractor treads so it could travel over the desert to the Pacific Ocean.

 

Pretty silly, isn't it. Much better to ship all the girders and materials by train to the ocean-side dock and assemble it there. The battleship will not be capable of traveling to Nevada, but that's what trains are for.

 

In the same way, it makes no sense to build a huge space-going battleship on Earth, then having it lift into orbit. It makes far more sense to transport the girders and stuff into orbit by a space elevator and assemble the battleship in orbit. The battleship cannot go to Earth but why would it want to?

[Lawnmower Boy]

Re: Slow Space Elevator

 

There's plenty of use for high tensile-strength materials in a rocket. For example, the fuel tank. These are pretty complex structures, after all.

 

And there's no question about the superiority of the energetics of a space elevator. It's just that the economics doesn't reduce to the energetics. You have to build the darn thing. And, apparently, support the nontrivial costs of long transit times.

[Nyrath]

Re: Slow Space Elevator

 

And there's no question about the superiority of the energetics of a space elevator. It's just that the economics doesn't reduce to the energetics. You have to build the darn thing. And' date=' apparently, support the nontrivial costs of long transit times.[/quote']

Agreed. It seems to me the controversy is over short-term vs. long-term benefit.

 

SSTO can probably be made viable more quickly (i.e., short-term). It is just that it's a dead end. There is no way that one can make huge space stations, lunar colonies, and large space fleets by boosting a few tons into orbit every month or so.

 

The analogy is that most cargo in the US is shipped by train or by truck. Not by airplane. Like rockets, cargo aircraft have to be fragile and lightweight, gulp down huge amounts of fuel, have comparatively limited cargo capacity, and if they turn off their engines they fall to the ground.

 

Trucks and trains needed to have the huge infrastructure of roads and train tracks built first. And they are not as quick as air freight. But they were far cheaper in terms of fuel expended, have huge cargo capacity, and the prime movers do not need all the fragile and high tech engineering that a plane requires.

 

Take your pick.

[Kristopher]

Re: Slow Space Elevator

 

Agreed. It seems to me the controversy is over short-term vs. long-term benefit.

 

SSTO can probably be made viable more quickly (i.e., short-term). It is just that it's a dead end. There is no way that one can make huge space stations, lunar colonies, and large space fleets by boosting a few tons into orbit every month or so.

 

The analogy is that most cargo in the US is shipped by train or by truck. Not by airplane. Like rockets, cargo aircraft have to be fragile and lightweight, gulp down huge amounts of fuel, have comparatively limited cargo capacity, and if they turn off their engines they fall to the ground.

 

Trucks and trains needed to have the huge infrastructure of roads and train tracks built first. And they are not as quick as air freight. But they were far cheaper in terms of fuel expended, have huge cargo capacity, and the prime movers do not need all the fragile and high tech engineering that a plane requires.

 

Take your pick.

 

Depends on what I'm shipping. I'm not going to ship an organ for transplant by UPS Ground.

 

Similarly, there are going to be things for which you can't wait around for a few weeks while the spacevator trundles its way up a handwavium thread.

[Nyrath]

Re: Slow Space Elevator

 

Depends on what I'm shipping. I'm not going to ship an organ for transplant by UPS Ground.

 

Similarly, there are going to be things for which you can't wait around for a few weeks while the spacevator trundles its way up a handwavium thread.

Yes, as per my analogy, you'll use emergency overnight air express for that.

 

For everything else you send it by rail.

[McCoy]

Re: Slow Space Elevator

 

And' date=' apparently, support the nontrivial costs of long transit times.[/quote']

 

Depends on what I'm shipping. I'm not going to ship an organ for transplant by UPS Ground.

 

Similarly, there are going to be things for which you can't wait around for a few weeks while the spacevator trundles its way up a handwavium thread.

Again, transit times. I asked before, but didn't see an answer. How long does it take to assemble, fuel, and preflight the Space Shuttle for launch? Assuming the weather cooperates. Aren't there months at a time when it's too cold or too windy to launch the shuttle?

 

SSTO, even in an emergency, is going to involve more prep time than taking a car out of a garage.

[Nyrath]

Re: Slow Space Elevator

 

How long does it take to assemble' date=' fuel, and preflight the Space Shuttle for launch?[/quote']

Space Shuttle Columbia was once launched twice within 56 days, but that was the shortest turnaround time of any shuttle.

[Zeropoint]

Re: Slow Space Elevator

 

I don't think anyone is saying that we WON'T need launch capacity any more once we have a space elevator; obviously there are time-sensitive shipments (but as some other people have pointed out, just how fast is a spacecraft launch, from recognition of need to actual liftoff?)

 

What we're saying is that there are some projects that are only possible with cheap lift capacity, and the space elevator provides that.

 

Also, I'm unsure why people get stuck on the idea of SINGLE stage to orbit. Yeah, it sounds cool and science-fictiony, but what other benefits does it have over, say, an air-breathing first stage to carry the orbiter to the upper atmosphere? Or how about using a big balloon to carry the orbiter up there before it fires?

[McCoy]

Re: Slow Space Elevator

 

Or how about using a big balloon to carry the orbiter up there before it fires?

Only if you have a steerable baloon. Rocoons were used in the 50's, and I believe maybe even back to the 40's, when altitude was all that mattered, but they introduce an element of positional uncertainty to the launch that would have to be paid for later in delta-v if you destination was anything other than "up."

[Nyrath]

Re: Slow Space Elevator

 

Also' date=' I'm unsure why people get stuck on the idea of SINGLE stage to orbit. Yeah, it sounds cool and science-fictiony, but what other benefits does it have over, say, an air-breathing first stage to carry the orbiter to the upper atmosphere?[/quote']

Or any other multi-stage rocket with recoverable stages.

No, one gets the distinct impression that people get stuck on the idea of SSTO because Tom Corbett Space Cadet did not ride a disintegrating totem pole into space.

[Tom Carman]

Re: Slow Space Elevator

 

Or any other multi-stage rocket with recoverable stages.

No, one gets the distinct impression that people get stuck on the idea of SSTO because Tom Corbett Space Cadet did not ride a disintegrating totem pole into space.

 

I'm stuck on it because "just gas it and go" is the simplest way to operate. Not the most efficient, granted, or the best way to move massive loads (or massive quantities of small loads). But for low-orbit/suborbital passenger operation and priority couriers I expect you will get better service from this model than from any other "some assembly required" approach.

[Vondy]

Re: Slow Space Elevator

 

Also, I'm unsure why people get stuck on the idea of SINGLE stage to orbit. Yeah, it sounds cool and science-fictiony, but what other benefits does it have over, say, an air-breathing first stage to carry the orbiter to the upper atmosphere? Or how about using a big balloon to carry the orbiter up there before it fires?

 

Spaceship One used an airplane based launch to achieve orbit. It was just a proof of concept prototype, but it worked. The only problem I see with balloons, which have amazing lift capacity and airborne time, is the one already mentioned: accurate position.

[Sundog]

Re: Slow Space Elevator

 

Spaceship One used an airplane based launch to achieve orbit. It was just a proof of concept prototype' date=' but it worked. The only problem I see with balloons, which have amazing lift capacity and airborne time, is the one already mentioned: accurate position.[/quote']

 

 

So you just change "Balloon" to "Zeppelin". Modern designs are entirely controllable, and stable in winds up to speeds that would preclude a launch anyway.

[McCoy]

Re: Slow Space Elevator

 

So you just change "Balloon" to "Zeppelin". Modern designs are entirely controllable' date=' and stable in winds up to speeds that would preclude a launch anyway.[/quote']

Um, you are aware that the rocket launch on a rocoon usually destroys the baloon part?

[Zeropoint]

Re: Slow Space Elevator

 

I'm stuck on it because "just gas it and go" is the simplest way to operate. Not the most efficient, granted, or the best way to move massive loads (or massive quantities of small loads). But for low-orbit/suborbital passenger operation and priority couriers I expect you will get better service from this model than from any other "some assembly required" approach.

 

The required assembly could be as simple as using a crane to pick up the orbiter and put it on top of the first stage vehicle. That would take no more than a couple of hours, tops, and would make the engineering challenges and fuel consumption MUCH easier to deal with.

[Sundog]

Re: Slow Space Elevator

 

Um' date=' you are aware that the rocket launch on a rocoon usually destroys the baloon part?[/quote']

 

 

Sure. But there's no reason it HAS to. If you use a cold-gas thruster for initial impetus, then provided the Rocket doesn't physically impact the zeppelin, there's no reason for the launch procedure to damage the transport in any way.

[McCoy]

Re: Slow Space Elevator

 

Sure. But there's no reason it HAS to. If you use a cold-gas thruster for initial impetus' date=' then provided the Rocket doesn't physically impact the zeppelin, there's no reason for the launch procedure to damage the transport in any way.[/quote']

Interesting design challenge.

[Vondy]

Re: Slow Space Elevator

 

Um' date=' you are aware that the rocket launch on a rocoon usually destroys the baloon part?[/quote']

 

It occurs to me that modern zeppelins have greater endurance [flight time] and lift capacity compared to aircraft, and with favorable weather can be maneuvered to idea launch positions. If you aren't using a rocket, but a detachable interface craft (like spaceship one), then it could feasibly be dropped in such a way as to leave the zeppelin in tact - just as it is dropped from its traditional aircraft style "mother-ship." The lift capacity of a balloon would also allow for a larger interface craft (I believe) if need be. I'm not an engineer, of course, but it seems relatively feasible insofar as you aren't using traditional rockets.

[Nyrath]

Re: Slow Space Elevator

 

Sure. But there's no reason it HAS to. If you use a cold-gas thruster for initial impetus' date=' then provided the Rocket doesn't physically impact the zeppelin, there's no reason for the launch procedure to damage the transport in any way.[/quote']

What about using a system like this?

 

http://www.defenseindustrydaily.com/airlaunch-llc-performs-quickreach-test-01308/

 

http://www.airlaunchllc.com/News.htm

(scroll down to pictures at "DARPA, AIR FORCE AND AIRLAUNCH LLC DROP TEST SETS NEW C-17 RECORD")

[McCoy]

Re: Slow Space Elevator

 

What about using a system like this?

 

http://www.defenseindustrydaily.com/airlaunch-llc-performs-quickreach-test-01308/

 

http://www.airlaunchllc.com/News.htm

(scroll down to pictures at "DARPA, AIR FORCE AND AIRLAUNCH LLC DROP TEST SETS NEW C-17 RECORD")

 

It occurs to me that modern zeppelins have greater endurance [flight time] and lift capacity compared to aircraft' date=' and with favorable weather can be maneuvered to idea launch positions. If you aren't using a rocket, but a detachable interface craft (like spaceship one), then it could feasibly be dropped in such a way as to leave the zeppelin in tact - just as it is dropped from its traditional aircraft style "mother-ship." The lift capacity of a balloon would also allow for a larger interface craft (I believe) if need be. I'm not an engineer, of course, but it seems relatively feasible insofar as you aren't using traditional rockets.[/quote']

Yep, either the drogue chute or glider wings to get some seperation from the zeppelin before ignition. As I said, interesting design challenge.