CHOMPTT (CubeSat Handling of Multisystem Precision Timing Transfer): From Concept to Launch Pad

Here we present the evolution of a university nanosatellite mission, demonstrating state of the art ground-to-space clock synchronization. The CHOMPTT (CubeSat Handling of Multisystem Precision Time Transfer) mission will be presented from its original concept as a candidate for the University NanoSatellite Program 8 to a spacecraft ready for launch in Fall of 2017 on ELaNa XIX (Educational Launch of Nanosatellites). This technology may be used in the future for precision navigation beyond the GPS sphere, networking of satellite swarms, synchronization of terrestrial time standards over continental distances, and verification of new space atomic clocks. The 3U CubeSat houses a 1 kg, 1U OPTI (Optical Precision Timing Instrument) payload, designed and built at the University of Florida, and a 1.5U EDSN/NODeS-derived bus from NASA Ames Research Center. The OPTI payload comprises 1) a supervisor board that handles payload data, power management, and mode settings, 2) an optics assembly with six 1 cm retroreflectors and four laser diodes used as a beacon for ground-tracking, and 3) two fully redundant timing channels, each consisting of a chip-scale atomic clock (CSAC), a microprocessor with clock counter, a picosecond event timer, and an avalanche photodetector (APD) with band-pass filter. Several iterations of OPTI have been designed, developed, and tested leading to its final configuration – a laboratory breadboard (v1.0), a 1.5U high altitude balloon design (v2.0), an engineering unit (v3.0), and the flight unit (v3.1). In-lab testing of OPTI indicates a short-term precision of 100 ps, equivalent to a range accuracy of 3 cm, which is below the primary mission objective of \u3c 200 ps. The long-term timing accuracy is 20 ns over one orbit (1.5 hours), limited by the frequency stability of the on-board CSACs. After the spacecraft reaches its nominal 500 km, 85 deg inclination orbit, an experimental laser ranging facility at the Kennedy Space Center in Florida will track CHOMPTT and emit 1064 nm nanosecond optical pulses toward it. The laser pulses will then reflect off the retroreflector array mounted on the nadir face of CHOMPTT, returning the pulses to the laser ranging facility, which will record the round-trip time-of-flight. An APD will record the arrival time of the pulses at the nanosatellite. By combining the arrival time of the pulse at the CubeSat and the transmit and receive times of the pulse at the laser ranging facility, the clock discrepancy between the ground and CubeSat atomic clocks can be determined. The design and verification of the flight version of CHOMPTT will be reviewed and an overview of the lifetime development and progression of CHOMPTT from the inception to launch pad will be presented