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The space elevator - could it be a reality?

01 December 2008

Space elevator. It sounds like something from a science fiction novel, but in fact it is a very real structure proposed by very real scientists, engineers, and space enthusiasts. Current work is concentrated on the development of super-strong tethers, which have to be tested, and that’s where Bosch Rexroth’s machine frame system has come in very handy

Essentially, a space elevator is a fixed structure that uses a climbing mechanism to transport material from the earth's surface into space. Realising such a structure may seem a daunting task, but organisations like the Spaceward Foundation are hoping to advance the technology with contests like the Space Elevator Games. One technique of erecting the fixed structure of the space elevator is by using a form of tethering method. The Space Elevator tether is a thin ribbon, with a cross-section area roughly half that of a pencil, extending from a ship-borne anchor to a counterweight well beyond geo-synchronous orbit. The climbing mechanism can then travel along the tether beyond Earth's gravitational pull without the use of rocket propulsion. Theoretically, the space elevator could then deliver cargo and people into orbit at a fraction of the cost of traditional launching methods. Aerospace engineer and co-founder and leader of the executive crew of the Spaceward Foundation, Ben Shelef takes up the story.

"Right now the technology to complete a space elevator does not exist. The purpose of the Space Elevator Games is to get the right people in industry and academia thinking about how we can make this work and to stimulate the development of new technologies to make the structure a reality."

The Strong Tether Competition, a $2m technology challenge backed by NASA, is just one of the Games events to develop a new class of super-strong tethers. Starting with a commercially available tether, the competition requires a 50% improvement in breaking force from year to year, and a tether pull machine has been built to measure the tensile strength of each of the team's proposed elevator tethers.

“The tether pull machine is designed to run a comparative test between two tether samples,” explains Mr Shelef. "One of the decisions made early on in the programme was that we wanted to make tether testing an exciting business to watch, so we created a head-to-head strength competition.” The ‘tug-of-war’ tether pull machine grabs two tether samples at their respective ends, and then pulls their free ends towards each other. Since the pulling mechanism floats, the resultant force on the tethers is equal, and as the force increases, one will break first. The remaining tether, along with the pull mechanism, will lunge the other way and clearly indicate a winner.

Rexroth's aluminium structural framing system was chosen for the machine build. Using bolt-together connectors, the tether pull structure was quickly assembled without special tools or skills and no additional painting or other finishing was required. The team could also choose from a broad selection of Rexroth accessories to extend the machine beyond a simple frame and base, to a complete multi-functional structure. And, every aluminium structural framing component is reusable, which made it simple for the team to change the configuration at every design iteration.

The Strong Tether challenge is conducted in two rounds. The first round pits tethers from two teams directly against each other to determine the team with the strongest tether. The second round then determines if the first-round winner is at least 50 percent stronger than a ‘house’ tether that represents off-the-shelf materials. If it is, that team will win the competition.


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