The Alpha Centauri Express

Our nearest stellar neighbour, Alpha Centauri is still a long way away. It would be great to send a probe to study the neighbourhood, but the practicalities are nightmarish – relativistic flight over that distance would be difficult and hideously expensive. Unless, of course, we sent something very small and light with no instruments, and just some simple way of signalling home – the modulations of that signal by the environments encountered could provide invaluable data, and the logistics of powering the mission would become much more manageable.