The future of the space elevator

Transcription

1 1 The future of the space elevator JOSÉ GERARDO CHÁVEZ ROSAS Introduction The Space Elevator is the most promising Space Transportation system on the drawing boards today, combining scalability, low cost, qualify of ride, and safety to deliver truly commercial-grade space access - practically comparable to a train ride to space. Rocket-based space launch systems are inherently limited by the physics of rocket propulsion. More than 90% of the rocket's weight is propellant, and the rest is split between the weight of the fuel tank and the payload. It is very difficult (if not impossible) to make such a vehicle safe or low cost. A target cost of $1000 per kg is proving to be impossible to reach. In comparison, airliners charge us about $1 per pound, and train transportation is in cents per pound. The Space Elevator is based on a thin vertical tether stretched from the ground to a mass far out in space, and electric vehicles (climbers) that drive up and down the tether. The rotation of the Earth keeps the tether taut and capable of supporting the climbers. The climbers travel at speeds comparable to a fast train, and carry no fuel on board - they are powered by a combination of sunlight and laser light projected from the ground. While the trip to space takes several days, climbers are launched once per day. The first "baseline" design will use 20 ton climbers, but by making the tether thicker (which can be done using the Space Elevator itself) we can grow the Space Elevator to lift 100, or even 1000 tons at a time. In addition to launching payloads into orbit, the Space Elevator can also use its rotational motion to inject them into planetary transfer orbits - thus able to launch payloads to Mars, for example, once per day. Imagine the kind of infrastructure we can set up there, waiting for the first settlers to arrive... Looking back from the year 2100, the construction of the Space Elevator will be considered to mark the true beginning of the Space Age, much like the advent of the airplane or steamboat heralded the true commercial use of the air and sea. The above is taken from an ISEC (International Space Elevator Consortium) document which explains the basics of the current draft of the space elevator. The document states that the projects are based on a vertical tether stretched thin from the ground to a mass far out in space, and electric vehicles (climbers) that drive up and down the tether. The rotation of the Earth keeps the tether taut and capable of supporting the climbers. The climbers are powered by a combination of sunlight and laser light projected from the ground. However, my proposals do not incorporate laser beams, although two of my projects are based on photocells. I think that, in practice, laser beams may not have sufficient capacity to carry a heavy load (100 or 1000 tons.); even photocells do not have that power conversion capacity. It is for this reason that my proposals are not based on laser beams but on existing techniques we use every day. Below are my proposals for an alternative space elevator. I believe that in all cases they could be used alone or in combination with my other proposals for the best performance of the space elevator. The challenge is not easy but I think it's absolutely possible! Clarification: In all cases, I present a very simple design for the cabin of the elevator, without radiation protection. This is for reasons of illustration; obviously there must be modifications in the real projects.

2 2 Project 1: Space elevator with chain of nanotubes and space electric motors Explanation: in this project we need only solar panels placed in geostationary orbit large enough to lift the desired weight and electric motors that will raise either a chain or a tether made of nanotubes. The electric motor powered by photocells would be situated close to the photocells. The chains or tethers may have a counterweight at the other end similar to that used in building elevators to enhance the efficiency of its operation. A second elevator could even be used as a counterweight so as one moves up the other goes down.

3 3 Project 2: Space elevator with helium balloons and photocells Explanation: to raise the platform, along with the cabin and solar panels, liquid helium is released from a tank which serves at the same time as a support base and lifting platform for the cabin and solar panels. Balloons are filled with helium gas and these balloons will raise the platform the first 50 km into space. The cabin is independent of the base so, after reaching the height of 50 km, the photocells will begin to provide the necessary power to the electric motors allowing the cabin to continue its trip into space, driving up the tether. To lower the cabin from space the cabin is left to fall down the tether in controlled fashion until reaching 50 km altitude where the platform is waiting with helium balloons. The compressors begin their work to get gaseous helium back into the tank (by making it liquid) and the whole device continues its descent to the earth. Perhaps this is the most complicated of my proposals, but the idea is to use the height provided by the balloons to improve the efficiency of the photocells as the radiation is greater at that altitude (50 km).

4 4 Project 3: Space elevator with low speed rocket or power The basic idea is this: To get into orbit a spacecraft needs to develop a very high speed in a very short time. In this case that huge speed is not necessary as the cabin cannot fall because it is supported by or hung from the tether or cables of nanotubes. Therefore, a low speed rocket (which represents a huge saving of fuel, weight and size) will be able to put into "orbit" the cabin or anything else at a very low cost. To get down de cabin to earth, the rocket is put upside down.

5 5 Project 4: Space elevator with electric conductive cables or tether of nanotubes The basic idea is this: Can electrically conductive nanotubes be manufactured? If so, then nanotubes could not only support the cabin but could also feed the lifting system of electric motors and the problem would be solved. That is to say: an electrically conductive cable made of nanotubes could serve the same way we use cables in a trolley but also serving as a support at the same time.

6 6 Project 5: Endless belt space elevator The main idea of this project is to use a lifting endless belt to raise the space elevator from the ground with the help of a pulley and using a large electric motor (as many as required) here on earth. The elevator would be attached to the lifting endless belt or tether made of nanotubes. The pulley would be located at the desired height, perhaps 300 kilometers or more. The chains or tethers may have a counterweight at the other end as we use in building elevators to enhance the efficiency of its operation. You could even use a second elevator as a counterweight so as one moves up the other goes down, as in my project number 1. The great advantage of this proposal is that all the energy is provided from the earth and the cabin only carries the payload or passengers into space which represents a huge energy savings. This technology is very simple and practical. It is in fact the one which I consider the most practicable.

7 7 CONCLUSIONS Hello, my name is Gerardo Chavez, I am a 58 year old Mexican inventor and I'm very happy to collaborate on this fantastic project. At first I thought it would be impossible to develop the proposed space elevator, but then I realized that it was not only possible but practicable in a few years with the technology we have today. The results of these ideas are five projects that I present to you today. Using the techniques I propose the only problem would be in the construction and positioning of the cable, rope, tether, band, etc. made of nanotubes and the launching of the geostationary satellite. The other needed devices are made with today's technologies. I think it's definitely possible to build a space elevator in the short term. On the other hand I think that in this particular case the laser beam system is not the best option because if we want to put into orbit 100 or tones imagine the size of the laser beam to perform this task. That is why my proposals are conventional techniques currently used and much more powerful. Thank you very much for your attention and I hope some of these proposals contribute to the realization of the space elevator. 1. Introduction 1 2. The development-process of the Climber 2 3. Conclusions 7 With the kind support of ICYT (Institute of Science and Technology) of Mexico City and Jorge Ramirez Thanks also to Brian Kelly José Gerardo Chávez Rosas México D.F. México gerardochav@yahoo.com.mx Web site: Tel: + 52 (55)