The CubeSat Laser Infrared CrosslinK Mission (CLICK)

Abstract

The CubeSat Laser Infrared CrosslinK mission is a joint Massachusetts Institute of Technology (MIT), University of Florida (UF), and NASA Ames Research Center effort to develop laser communications (lasercom) transceivers. The terminals demonstrate full-duplex intersatellite communications and ranging capability using commercial components to enable future large constellations or swarms of nanosatellites as coordinated distributed sensor systems.CLICK will demonstrate a crosslink between two CubeSats that each host a < 2U lasercom payload. Range control is achieved using differential drag in Low Earth Orbit (LEO), with attitude controlled using a three-axis reaction wheel assembly and attitude sensors, including star trackers.The lasercom terminals are direct-detect and rate scalable, designed to achieve a 20 Mbps crosslink at ranges from 25 km to 580 km and operate full-duplex at 1537 nm and 1563 nm with 200 mW of transmit power and a 14.6 arcscecond (0.07 milliradian) full width half max (FWHM) beamwidth. The terminals also use a 976 nm, 500 mW, 0.75 degree FWHM beacon and a quadcell for initial acquisition, and a low-rate radio crosslink for exchanging orbit information.The payload transmitter is a master oscillator power amplifier (MOPA) with fiber Bragg grating for pulse shaping and MEMS fast steering mirror (FSM) for fine pointing, modeled after the MIT Nanosatellite Optical Downlink Experiment. The transceiver leverages UF's Miniature Optical Communications Transmitter (MOCT) including a chip-scale atomic clock (CSAC). The receiver implements both a time to digital converter (TDC) as well as pulse recovery and matched filtering for precision ranging.

Laser Intersatellite Links in a Starlink Constellation: A Classification and Analysis

“…The ATP system in a laser terminal typically consists of a coarse pointing assembly (CPA) and a fine pointing assembly. The CPA provides coarse alignment of laser beams, and has a wide field of view and low precision while the fine pointing assembly has a narrow field of view and high precision, and aligns laser beams to achieve the desired pointing accuracy [17]. The CPA enables the ATP system to roughly point the laser beam in the desired direction without reorientation of the satellite.…”

“…Due to the low SWaP and cost requirements of small satellites like CubeSats, the ATP system design in CubeSat Lasercom Infrared CrosslinK (or CLICK) project [17] does not use a CPA and relies on satellite's attitude determination and control system for body pointing to achieve coarse pointing. Compared to CubeSats, the ATP system in SpaceX's Starlink satellites will have higher SWaP and cost.…”

Practical Limits on Nanosatellite Telescope Pointing: The Impact of Disturbances and Photon Noise

“…Many proposed solutions to the attitude control limitations of CubeSats have been in the form of second-stage correction (Beierle et al, 2018;Pong, 2018;Cahoy et al, 2019). ASTERIA (Arcsecond Space Telescope Enabling Research in Astrophysics) is the first sub-arcsecond imaging CubeSat (Pong, 2018).…”

“…The science telescope on ASTERIA operates at 20 Hz, reading out 50-ms exposures for science and pointing control, limiting the detectable stellar magnitude to m V < 7 since dimmer stars do not flip the detector's first analog-to-digital bit (Knapp et al, 2020a) in an exposure. Similarly, the CLICK free-space laser communications CubeSats (Cahoy et al, 2019), due for launch in 2021, will use microelectromechanical systems (MEMS)-based steering mirrors to achieve fine pointing, while the DeMi mission launched in 2020 is designed to use a MEMS deformable mirror for fine wavefront steering (Morgan et al, 2019).…”

Practical limits on Nanosatellite Telescope Pointing: The Impact of Disturbances and Photon Noise

“…Many proposed solutions to the attitude control limitations of CubeSats have been in the form of secondstage correction (Beierle et al, 2018;Pong, 2018;Cahoy et al, 2019). ASTERIA (Arcsecond Space Telescope Enabling Research in Astrophysics) is the first sub-arcsecond imaging CubeSat (Pong, 2018).…”