Preliminary Results from the CHOMPTT Laser Time-Transfer Mission

CubeSat Handling of Multisystem Precision Time Transfer (CHOMPTT) is a demonstration of precision ground-to-space time-transfer using a laser link to an orbiting CubeSat. The University of Florida-led mission is a collaboration with the NASA Ames Research Center. The 1U optical time-transfer payload was designed and built by the Precision Space Systems Lab at the University of Florida. The payload was integrated with a NASA Ames NOdeS-derived spacecraft bus to form a 3U spacecraft. The CHOMPTT satellite was successfully launched into low Earth orbit on 16 December 2018 on NASA’s ELaNa XIX mission using the Rocket Lab USA Electron vehicle. Here we describe the mission and report on the status of this unique technology demonstration. We use two satellite laser ranging facilities located at the Kennedy Space Center and Mount Stromlo, Australia to transmit nanosecond, 1064 nm laser pulses to the CHOMPTT CubeSat. These pulses are timed with an atomic clock on the ground and are detected by an avalanche photodetector on CHOMPTT. An event timer records the arrival time with respect to one of the two on-board chip-scale atomic clocks with an accuracy of 200 ps (6cm light-travel time). At the same time, a retroreflector returns the transmitted beam back to the ground. By comparing the transmitted and received times on the ground and the arrival time of the pulses at the CubeSat, the time difference between the ground and space clocks can be measured. This compact, power efficient and secure synchronization technology will enable advanced space navigation, communications, networking, and distributed aperture telescopes in the future

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

CubeSat Handling of Multisystem Precision Time Transfer

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

Here we present the evolution of a student satellite mission: CHOMPTT (CubeSat Handling of Multisystem Precision Time Transfer), from its original concept as a candidate for the University NanoSatellite Program 8 (UNP8), to a spacecraft ready for launch in Fall of 2017 on ELaNa XIX (Educational Launch of Nanosatellites). 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 EDSNNODeS-derived bus from NASA Ames Research Center. The OPTI payload comprises of: 1) a supervisor board that handles payload data, power regulation, and mode settings, 2) an optics assembly of six 1 cm retroreflectors and four laser beacon diodes for ground-tracking; and 3) two fully redundant timing channels, each consisting of: a chip-scale atomic clock, a microprocessor with clock counter, a picosecond event timer, and an avalanche photodetector (APD) with band-pass filter. Several iterations of OPTI have been developed, tested, and designed to achieve its current functionality and design a laboratory breadboard design, a 1.5U high altitude balloon design, engineering unit design, and its current flight unit design. In-lab testing of the current OPTI design indicates a short-term precision of 100 ps, equivalent to a range accuracy of 3 cm necessary to achieve our primary objective of 200 ps time transfer error, and a long-term timing accuracy of 20 ns over one orbit (1.5 hours). After the spacecraft reaches its nominal 500 km orbit at a 85 degree inclination, an experimental laser ranging facility at Kennedy Space Center in Florida, will track and emit 1064 nm nanosecond optical pulses at the CHOMPTT spacecraft. The laser pulses will then reflect off the retroreflector array mounted on the nadir face of CHOMPTT, and return the pulse to the laser ranging facility where the laser ranging facility will record the round-trip duration of the laser pulses. At the same time the pulse arrives at the spacecraft and is reflected by the array, an APD will record the arrival time of the pulses at the nanosatellite. By comparing the arrival of the pulse at the CubeSat and the duration of the round-trip of the laser pulse, the clock discrepancy between the ground and CubeSat atomic clocks can be determined, in addition to the CubeSats range from the facility. 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

A Novel, Low Power Optical Communication Instrument for Small Satellites

The Miniature Optical Communication Instrument is a NASA-sponsored compact, pulsed optical communication system for distant, power-constrained small satellites. The primary motivation for this system is to reduce the power required for the laser transmitter and to enable variable repetition rates in order to produce a versatile instrument for small satellites down to the CubeSat scale. A differential pulse-based scheme is driven by an FPGA-based Software-Defined Pulse Modulator. This not only improves the reach of the system but also reduces the size and principally the power required, with only a small reduction in data throughput. In addition to optical communication, the MOCI also has potential capabilities in precision clock synchronization and navigation beyond Earth orbit

Deep Space Laser Communication Transmitter and High Precision Timing System for Small Satellites

The Miniature Optical Communication Transmitter is a NASA-sponsored compact, pulsed optical communication system for distant, power-constrained small satellites. A pulse-based scheme is driven by an FPGA-based Software-Defined Pulse Modulator. In addition to optical communication, the MOCT also has potential capabilities in precision clock synchronization and navigation beyond Earth orbit. This work is a continuation of results presented at the 2015 SmallSat conference.1 A novel combinatorial delay generation technic allow a 10-fold increase in timing resolution and a similar improvement for delay uncertainties compared to previously reported results. The Laser system prototype is now complete and can operate with some amplification

The Miniature Optical Communication Transceiver—A Compact, Power-Efficient Lasercom System for Deep Space Nanosatellites

Optical communication is becoming more prevalent in orbit due to the need for increased data throughput. Nanosatellites, which are satellites that typically weigh less than 10 kg, are also becoming more common due to lower launch costs that enable the rapid testing of technology in a space environment. Nanosatellites are cheaper to launch than their larger counterparts and may be a viable option for communicating beyond Earth’s orbit, but have strict Size, Weight, and Power (SWaP) requirements. The Miniature Optical Communication Transceiver (MOCT) is a compact optical transceiver designed to provide modest data rates to SWaP constrained platforms, like nanosatellites. This paper will cover the optical amplifier characterization and simulated performance of the MOCT amplifier design that produces 1 kW peak power pulses and closes three optical links which include Low Earth Orbit (LEO) to Earth, LEO to LEO, and Moon to Earth. Additionally, a benchtop version of the amplifier design was constructed and was able to produce amplified pulses with 1.37 W peak power, including a 35.7% transmit optics loss, at a pump power of 500 mW. Finally, the modulator, seed laser, amplifier, receiver, and time-to-digital converter were all used together to measure the Bit Error Ratio (BER), which was 0.00257 for a received optical peak power of 176 nW. Keywords: optical communication; laser; nanosatellite; CubeSat; EDFA; transceiver; PPM; BERUnited States. National Aeronautics and Space Administration (Grant NNX14AO53G

Optical time transfer for future disaggregated small satellite navigation systems

Precision time-keeping is a critical requirement of any satellite navigation system, including GPS. Even the most stable space qualified atomic clocks drift over time to the point where they can significantly degrade navigation precision. Periodic re-synchronization of these clocks with respect to terrestrial time standards is therefore required. Time transfer through Earth’s atmosphere using optical frequencies offers improved accuracy due to reduced time delay uncertainties relative to radio frequencies. In this paper we describe the design and laboratory testing of the Optical Precision Time Transfer Instrument, a compact device for real-time terrestrial-to-space clock corrections, using existing satellite laser ranging facilities. This instrument will comprise roughly 1U of a 3U CubeSat mission, sponsored by the Air Force’s University Nanosatellite Program and slated for launch in the 2017 time-frame. The instrument will demonstrate time transfer with a short term accuracy of 100 psec, equivalent to 3 cm of position error, and a long term timing error of 6 nsec over one orbit, limited solely by the frequency stability of the on-board miniature atomic clocks. Future missions using this time transfer technology and equipped with higher stability clocks will enable disaggregated navigation systems, with precision time-keeping components separated from other functionality