# How could we hear back from Breakthrough Starshot? [duplicate]

The Breakthrough Starshot concept is to send a swarm of tiny spacecraft on a flyby mission to Proxima Centauri b. These are tiny spacecraft (on the scale of centimeters). Given how miniscule the arriving signal is/has been from any of the much larger probes sent to the outer planets, how could we possibly receive what must surely be a much less powerful signal from a vastly greater distance? The Voyager spacecraft, for example, could transmit at several watts from about 40 or 50 light-minutes away, requiring a big dish to capture a usable signal; the tiny Starshot probes would surely be transmitting not more than a few milliwatts from over 4 light-years away.

Is the idea for them to form up into a phased array to send their data back to Earth? And even so, would that really help the situation much? How has the project planned for data downlink?eh

EDIT: Seems this question has already been asked before: How are the tiny spacecraft proposed by Project Starshot supposed to communicate with Earth?

That "1000m" is obviuosly a typo. A 4m sail at 400nm wavelength (blue) gives a beam width of about $$10^{-7}$$ radians, and so a spot at 4ly of about $$4\times 10^9m$$. A kilometer sized receiving array (they propose to adapt the laser array used for propulsion would receive about $$10^{-14}$$ of the beam, which should allow a data rate of a a few kb/s.