Space elevators? how about tubes??

Originally posted by djmolecular
5 mile long tube horizonatally on the ground, near the end of the line it changes to a short distance vertical tube????

non living cargo.

Also same priciple as the plane. Launch payload in accelrated tube... After launch, then use boosters to make it the rest of the way to orbit. Less fuel costs. I think the plane would be a better idea.

You don't mention the velocity you expect when it exits the tube, and the altitude. Based on the altitude we can look at the atmospheric density and from the velocity we can calculate the heat generated from frictional forces.

I remember reading about some of the design challenges of the mach 3+ SR-71 involving finding materials that would withstand the extremely high temperatures involved when traveling so fast.

As a general rule you can go faster at higher altitudes because the atmosphere is less dense there resulting in less drag/heat problems. High launch velocities too close to the ground will encounter a dense atmosphere, where drag and heat buildup and loss of velocity will be big. The people who thought of the idea that Phage posted seem to have some awareness of these issues:

Originally posted by Phage
You mean something like this?

In the abstract, they propose a 100 km long evacuated tunnel within which a magnetic levitation system would accelerate a spacecraft to orbit speeds. Upon reaching the end of the tunnel, which would be roughly 5 kim above sea level, the craft would coast into orbit, using a small rocket thruster to even out its orbital path.

www.gettingtherefromhere.info...

The additional acceleration forces involved in going in a circle could prove to be very uncomfortable.

The fact that the tube is evacuated means the densest part of the atmosphere, the first 5 km above the ground, won't be encountered.

Maybe a hybrid system would result in some cost savings, where you build an initial loop closer to the ground where construction costs are cheaper, and just make it so that the G-forces don't exceed some reasonable value. Then transition from the loop into the straight maglev evacuated tube described.

If you want to launch cargo only with it the g-force are less of a concern but keep in mind that designing a payload to accept 70 G-s can pose challenges of its own, like added wright to make the packaging sturdier to withstand the extra G's. One of the biggest needs we have now is to get fuel to the ISS so finding a cheaper way to launch this fuel would be great. That article claims $1/kg for the maglev instead of $10,000/kg now, quite an impressive savings.


[edit on 12-4-2010 by Arbitrageur]

A linear accelerator that started at sea level and accelerated up the side of mount everest could work, even for humans.

Mount everest with a 8850 meters of height would provide a great point for launch. This would equal in something like a 13 kilometer linear accelerator. Accelerating at 4G would result in an exit velocity of roughly 1000 m/s.

The high exit point and thin atmosphere from that 8,8km height onward both help tremendously.

so yes, a "space catapult" would be really clever and cost effective.

reply to post by above


Yeah, but what is the likelyhood of a linear elevator being built up the side of mt everest? Nobody could fund that...ever. Not to mention the fact that it would be nearly impossible to get the material there, and nearly impossile to bulit the thing anyway.

Linear accelerator at standard atmosphere = fail
Linear accelerator at atm 5 miles up = not gonna happen.

Originally posted by LeeTheDestroyer
reply to post by above

 

Yeah, but what is the likelyhood of a linear elevator being built up the side of mt everest?

The link Phage posted mentions the estimated cost and I'm not sure using Mt Everest would make it any cheaper, it might cost more:

www.gettingtherefromhere.info...

Initial construction costs are projected to be high (~$20 billion), which puts this kind of system out of reach unless a major corporating wants to stake its future on the project or a coalition of governments decides to get involved. Without seeing the plan, I cannot say whether there are opportunities to reduce the estimated costs. It is somewhat likely that the costs would increase. Plus, finding a 100 km long stretch of land where you would be able to construct the tunnel would be challenging.

It doesn't seem to take the US government long at all to spend $20 billion, but I tend to think that cost estimate is low.

The other problem with Mt. Everest is, that it's not close to the equator. If you notice, most launch sites are built closer to the equator (Florida, Texas, New Mexico) because the equator is already moving at about 1000 miles an hour due to the Earth's rotation. This is over 5.5% of the 18,000 miles an hour needed to reach Earth orbit, so the further from the equator you launch, the more of that 5.5% you have to add to the launch. That may not sound like a lot but if we can get that 5% for free, we'll take it.

Regarding finding a 100km stretch of land to build it, New Mexico might be a good place to start looking for that.