Sub-nanosecond ground-to-space clock synchronization for nanosatellites using pulsed optical links

Abstract

Here we present the design and ground testing for a nanosatellite mission that will demonstrate terrestrial-to-space clock synchronization using a pulsed optical link to a low Earth orbiting nanosatellite. The 1kg, 1L nanosatellite payload comprises fully redundant chip-scale atomic clocks, microprocessor-based clock counters, picosecond event timers, and avalanche photodetectors. During flight operations, an experimental satellite laser ranging facility, located at the Kennedy Space Center in Florida, will emit nanosecond optical pulses of infrared laser light towards the nanosatellite. By reflecting the emitted pulses off of a retroreflector array mounted on the nadir face of the nanosatellite and returning the pulses back to the ground, the laser ranging facility will record the round-trip light-travel time of the laser pulses. At the same time, one of the avalanche photodetectors will record the arrival time of the pulses at the nanosatellite. By combining these data, the discrepancy between the ground and space clocks can be determined, in addition to the range to the satellite. Laboratory testing of the space instrument indicates a short term time-transfer precision of less than 200ps, equivalent to a range accuracy of 6cm. This flight instrument will comprise roughly 1U of a 3U CubeSat mission manifested for launch in the Fall of 2017 through NASA’s CubeSat Launch Initiative program.