# What's the point of building a space elevator?

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1. Mar 12, 2015

### 1832vin

i don't get it, people say that it would be a god sent, but i don't get it,

even if you are in space, you still need to travel at escape velocity, so you would still need to accelerate, and building a station on geostationary location is EXTREMELY FAR (i thin it was X3 the diameter of earth....

so what's the point in building a space elevator? you are still putting the same amount of energy to be in escape velocity....

and if you are going to a geostationary point, it requires much more energy?

2. Mar 12, 2015

### Quantum Defect

I am not a rocket scientist, but...

(1) You do not need to reach escape velocity, you can plod along, as you would climbing a mountain. A person ascending to the top of Everest does not need to be launched from the surface with the velocity required to make it to the top, no?

(2) Energy for climbing can be supplied from the ground, and you need only supply the energy requred to move the cargo up -- most of the mass of a rocket is fuel.

(3) You do need to reach orbital velocity, but this is achieved in the same way that you achieve "orbital velocity" when you walk from the center of a merry go round out to the perimeter.

3. Mar 12, 2015

### phyzguy

The point is that rockets are an extremely inefficient way of transferring energy to a payload. The current cost of putting an object into geosynchronous orbit using rockets is about $20,000 / kg. Let's look at the energy cost of doing this if you could use an electrically powered elevator. The energy per kg required to achieve escape (almost the same as geosynchronous orbit)is given by $\frac{G M_{Earth}}{R_{Earth}}$, and is about 6E7 Joules/kg, or about 16 kWh/kg. For electric energy cost of about$0.10/kWh, this means you could lift an object to geosynchronous orbit for \$1.60 / kg, more than 10,000 times cheaper than using rockets.

4. Mar 12, 2015

### litup

The key is getting into orbit. Right now you can see the giant rockets with their million horsepower + power motors spewing out thousands of tons of propellant to get a few tons into orbit.

If you can just climb a rope at say 200 Km per hour you will reach orbit without that incredible waste of energy. You get up to geo orbit with just a few bucks worth of electricity and the line doesn't just stop at geo level. It keeps going up, something like 100,000 km with a weight on the end to stabilize the whole assembly and you can just keep pedaling up that rope till you are 100,000 km (60,000 miles up). You will then be doing about 17,000 mph (27,000 Kph) which is way past Earth's escape velocity AT THAT ALTITUDE. So you just need to add additional velocity which means a lot less propulsion needed to get you to the target planet or asteroid or whatever.
Earth is tilted at 23.5 odd degrees from the plane of the rest of the planets you can choose an angle of departure that will bet you most anywhere in the solar system, a free thrust away from Earth.

The only bad part is the fact you will be going up at maybe 200 Km/ hr and so to get to 100,000 km will take about 3 weeks. So you cool your heels for a few weeks while you get your more or less free ride to space.

They would have to protect you from solar flares and so forth because it can be dangerous for humans taking weeks to get up there.

5. Mar 12, 2015

### Drakkith

Staff Emeritus
I don't know too much about space elevators, but I'd bet just getting a hundred miles or so above the ground would drastically increase the efficiency of a rocket engine since it doesn't have to deal with that pesky dense atmosphere. You might be able to use something like an ion drive to reach even better efficiency, assuming the technology improves enough to use that close to the Earth.

6. Mar 12, 2015

### Bob600

A space elevator is the only way to ultimately get into space. Think of it as a train going up and down. Problem is that any materials currently created would be to heavy and collapse under their own weight before getting anyway near space. Nano tubes may be getting close but can't be created in the volume required. But all that said eventually should mankind survive long enough he will not be going into space sitting on a tube filled with explosives.