91É«ÇéƬ

Sending tightly focused laser-beam signals to a satellite has big advantages
over using radio waves. Lasers are more secure, require less power, have a wider
bandwidth and don’t interfere with other transmissions. The snag is that light
is blocked by clouds. But in WO 01/52453, the Applied Physics Laboratory at the
Johns Hopkins University in Maryland suggests floating a balloon to an altitude
of 20 kilometres—way above the clouds—and anchoring it with a
lightweight tether. Optical fibres woven into the tether carry signals up to the
balloon, where a solar-powered amplifier retransmits the pulses as a laser beam
to a satellite in orbit.