Photos: Competitors prepare for lift-off

Members of the Spaceward Foundation, which is hosting the competition with funding from NASA, prepare the light source that will be beamed from a transmitter to a receiver on the robot climber.

A close-up shot of the Space Miner team's climber, which is a wheelchair frame powered by "super cells" that can produce at least 2.5 amps of current each.

A graduate student from the University of British Columbia holds up his team's solar-cell-powered robot, which will climb the tether in competition with six other bots this weekend.

Robot climbers get three chances to ascend a 50-meter ribbon carrying a payload and traveling at a minimum speed of 1 meter per second. That's similar to climbing a 20 story building in one minute.

A member from the Starclimber team assembles a parabolic reflector, which is designed to focus light on the hot end of the robot's engine. Starclimber incorporates a Stirling engine, which can convert heat into mechanical energy with an efficiency of 30 to 40 percent, on par with gas engines.

Team Speco works on its climber, which uses a roller friction drive and triple junction photovoltaic cells.