Recent advances by groups at MIL Lincoln Labs and the Jet Propulsion Laboratory have demonstrated that it is possible to detect single photons emitted by lasers from very large distances. The current record holder is the LADEE Laser Communication system, which was able to operate from lunar distances. The technique uses cryo-cooled nanotubes. The current performance is of order 2 bits per photon. That system uses a 10cm optics on the spacecraft, and a 1-meter telescope on the ground. As the StarChip cruised out, it would rely on communications from earth to update its clock and its estimation of the stars’ ephemeris (orbital position at specific times).
The ground system and the StarChip transmitter will implement forward error correction, matched filtering, and other contemporary approaches to increasing the gain of this transmission through signal processing, beyond the direct detection of single photons that has already been demonstrated in existing systems. The Starshot light beamer would be used in reverse, as a receiving array to receive the laser communications from the nanocraft. Using it as a phased array telescope would offer a sufficient collecting area to receive the signal.
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