So it might be surprising to hear that the most exciting new frontier in space exploration starts a mere 2,000 km above the terrestrial surface. We aren't talking about manned missions, automatic rovers or even probes. We're talking about satellites. Even more prosaically, we're talking about communications satellites, in low Earth orbit. Yes, they'll be fitted with precision laser equipment that sends and receives particles of light ?" photons ?" in their fundamental quantum states. But the missions will be an essentially commercial proposition, paid for, in all probability, by banks eager to protect themselves against fraud.