How Does a Space Elevator Work?

Nanotube
Nanotube | Source

Introduction

In an age where space travel is moving towards the private sector, new innovations begin to surface. Newer and cheaper ways to get into space are being pursued. Enter the space elevator, a cheap and efficient way to get into space. It is like a standard elevator in a building, but with the exit floors being low-Earth-orbit for tourists, geo-synchronous orbit for communication satellites, or high-Earth-orbit for other spacecraft (Lemley 34). The first person to develop the space elevator concept was Konstantin Tsiolkovsky in 1895, and over the years more and more have surfaced. None have come to fruition because of technological shortcomings and lack of funds (34-5). With the invention of carbon nanotubes (cylindrical tubes that have a tensile strength 100 times that of steel at 1/5 its weight) in 1991, the elevator took a step closer to reality (35-6).

Cost Projections

In an outline created by Brad Edwards in 2001, the elevator would cost $6-$24 billion (36) with each pound lifted to cost about $100 compared to the space shuttle’s $10,000 (34). This is merely a projection, and it is important to see how other projections panned out. The shuttle was estimated to cost $5.5 million per launch and was actually over 70 times that amount, while the International Space Station was projected at $8 billion and actually cost over 10 times that amount (34).

Platform
Platform | Source

Cables and Platform

In Edward’s outline, two cables will be spooled into a rocket and launched into geo-synchronous orbit (about 22,000 miles up). From there, the spool will unwind with both ends extending to high-orbit and low-orbit with the rocket being the center of gravity. The highest point the cable will reach is 62,000 miles up with the other end extending to the Earth and being secured to a floating platform. This platform will most likely be a refurbished oil-rig and will serve as a power-source for the climbers, aka the ascent module. Once the spools have fully unfurled, the rocket- housing would then go to the top of the cable and be the basis for a counterweight. Each of these cables would be made of fibers that are 20 microns in diameter that will be adhered to a composite material (35-6) The cable would be 5 cm thick on the Earth side and about 11.5 cm thick in the middle (Bradley 1.3).

Climber
Climber | Source
Counterweight
Counterweight | Source

Climber

Once the cables have fully unfurled, a ”climber” would go from the base up the ribbons and fuse them together using wheels like a printing press does until it got to the end and joined the counterweight (Lemley 35). Every time a climber goes up, the ribbon's strength increases by 1.5% (Bradley 1.4). Another 229 of these climbers would go up, each carrying two additional cables and cross-linking them at intervals with polyester tape to the growing main cable until it would be about 3 feet in width. The climbers would remain at the counterweight until the cable is deemed safe, then they can safely travel back down cable. Each of these climbers (about the size of an 18 wheeler) can carry about 13 tons at 125 miles per hour, can reach geo-synchronous orbit in about a week, and will receive their power from “photovoltaic cells” that receive laser signals from the floating platform as well as solar power as a backup. Other laser bases will exist around the world in the event of inclement weather (Shyr 35, Lemley 35-7).

Problems and Solutions

At the moment, many aspects of the plan require some technological advances that have not materialized. For example, a problem with the cables is actually creating them. It is difficult to make carbon nanotubes in a composite material like polypropylene. A roughly 50/50 mix of the two is required. (38). When we go from the small scale to the large, we lose the properties that make the nanotubes ideal. Also, we can barely manufacture them in lengths of 3 centimeters, much less the thousands of miles that would be needed (Scharr, Engel).

In October of 2014, a possible replacement material for the cable was found in liquid benzene put under large pressure (200,000 atm) and then slowly released into normal pressure. This causes the polymers to form tetrahedral patterns much like a diamond and thus give it an increase in strength though the threads are currently only 3 atoms wide. The Vincent Crespi Laboratory team at Penn State came up with the find and is making sure that no defects are present before further exploring this option (Raj, CBC News).

Another issue is space junk colliding with the elevator or the cables. To compensate, it has been proposed that the floating base can move so that the debris can be avoided. This will also address oscillations, or vibrations in the cable, which will be countered by a dampening motion at the base (Bradley 10.8.2). Also, the cable can be made to be thicker in higher-risk area and regular maintenance can be done on the cable to patch tears. Additionally, the cable could be made in a curved fashion rather than flat strands, thus allowing space junk to be deflected off the cable (Lemley 38, Shyr 35).

Another problem facing the space elevator is the laser-power system. Currently, nothing exists that can transmit the 2.4 megawatts required. Improvements in that field are promising, however (Lemley 38). Even if it could be powered, lightening discharges could short out the climber, so building it in a low-strike zone is the best bet (Bradley 10.1.2).

To prevent the cable from breaking because of meteor strikes, curvature would be designed into the cable for some strength and reduction in damage (10.2.3). An additional feature that the cables will have to protect them will be a special coating or a thicker fabrication to face erosion from acidic rain and from radiation (10.5.1, 10.7.1). A repair climber can continually replenish this coating and also patch the cable when needed (3.8).

And who will venture into this new and unprecedented field? Japanese company Obayashi is planning a 60,000 mile long cable that would be capable of sending up to 30 people at 124 miles-per-hour. They feel that if the tech can finally develop they will have a system by 2050 (Engel).

Benefits

That being said, many practical reasons exist for having the space elevator. Currently, we have limited access to space with a select few actually making it. Not only that but it is hard to recover objects from orbit, for you must rendez-vous with the object or wait for it to fall back to Earth. And let's face it, space travel is risky and everyone takes their failures poorly. With the space elevator, it is a cheaper way to launch cargo per pound, as mentioned earlier. It can be used as a way to have manufacturing done in zero G easier. Also, it will make space tourism and satellite deployment a much cheaper venture and thus more accessible. We can easily repair rather than replace satellites, adding to further savings (Lemley 35, Bradley 1.6).

In fact, costs for various activities would decrease 50-99%. It will give scientists the ability to perform meteorological and environmental studies as well as allowing for new materials in microgravity. We can also clean up space debris easier. With the speeds achieved at the top of the elevator, it will make any craft released at that point able to travel to asteroids, the Moon or even Mars. This opens up mining opportunities and further space exploration (Lemley 35, Bradley 1.6). With these benefits in mind, it is clear that the space elevator, once fully developed, will be the way of the future to space horizons.

Works Cited

Bradley C. Edwards. "The Space Elevator". (NIAC Phase I Final Report) 2000.

CBC News. "Diamond Thread Could Make Space Elevator Possible." CBC News. CBC Radio-Canada, 17 Oct. 2014. Web. 14 Jun. 2015.

Engel, Brandon. "Outer-space an Elevator Ride Away Thanks to Nanotech?" Nanotechnology Now. 7th Wave Inc., 04 Sept. 2014. Web. 21 Dec. 2014.

Lemley, Brad. "Going Up." Discover June 2004: 32-39. Print.

Raj, Ajai. "These Crazy Diamond Nanothreads Might Be The Key to Space Elevators." Yahoo Finance. N.p., 18 Oct. 2014. Web. 17 Nov. 2014.

Scharr, Jillian. "Space Elevators On Hold At Least Until Stronger Materials Are Available, Experts Say." The Huffington Post. TheHuffingtonPost.com, 29 May 2013. Web. 13 June 2013. http://www.huffingtonpost.com/2013/05/29/space-elevators-stronger-materials_n_3353697.html?utm_hp_ref=spaceflight

Shyr, Luna. "Space Elevator." National Geographic July 2011: 35. Print.

© 2012 Leonard Kelley

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