Optomechanical Design and Analysis for Nanosatellite Laser Communications

The CubeSat Laser Infrared CrosslinK (CLICK) mission is a technology demonstration of a 1.5U laser communications terminal for an intersatellite link. The terminal is deployed on a pair of 3U CubeSats in Low Earth Orbit (LEO). The pointing, acquisition, and tracking (PAT) approach includes both coarse and fine systems. The coarse tracking system uses a beacon laser transmitter and receiver camera. The fine tracking system uses a fast steering mirror and quadrant photodiode. The communications transmit and receive paths include a refractive telescope, transmit laser collimator, and avalanche photodetector (APD) receiver. The communications laser full-width, half maximum (FWHM) beam divergence angle is 14.6 arcseconds, and the beacon laser FWHM divergence is 0:75° (2700 arcseconds). The opto-mechanical design process includes prediction & verification of assembly alignment & calibration, thermoelastic effects, structural modes & static loading, and fastener analysis. The opto-mechanical assembly has the sensors and laser transmitters kinematically mounted to enable on-ground calibration to less than 25.4 mm decenter, or 0.1° tip/tilt. The thermoelastic alignment error between the payload and bus star tracker is estimated via finite element analysis to be less than 9 arcseconds. The payload optical bench is designed with custom thermal isolation and control to maintain 20 ± 10 ° C. The thermal modeling of the payload is described in detail. Structural static loading and fastener analyses of the CLICK payload under launch loads of 30 G verify margins of safety are greater than 10 and above the recommended values. Modal analyses predict the first resonant frequency to be 888 Hz, above typical vehicle structural vibration ranges with a factor of safety greater than 3.5

Influence of shear thinning and material flow on robotic dispensing of poly(ethylene glycol) diacrylate/poloxamer 407 hydrogels

Robotic dispensing of hydrogels offers a direct way for generating complex hydrogel shapes. For this, there is a general need for hydrogel formulations with suitable rheological properties. In this contribution, hydrogel formulations containing poly(ethylene glycol) diacrylate (PEG-DA) and Poloxamer 407 are characterized regarding their flow behavior during robotic dispensing. Formulations contain between 15% and 20% PEG-DA and 22.5% and 25% Poloxamer 407. All formulations show shear thinning which can be described using a power law with a power law index between 0.10 and 0.11 and calculated shear rates at the wall of the dispensing needle of 379 s−1 with a dispensing speed of 8 mm s−1 and a dispensing needle inner diameter of 0.51 mm. Thus, facilitating the generation of smooth hydrogel strands, three-dimensional hydrogel objects can be prepared without flow after robotic dispensing and can be cured afterward to elastic hydrogels, retaining the shape of the dispensed object

The CubeSat Laser Infrared CrosslinK Mission (CLICK)

© COPYRIGHT SPIE. 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

Optical Communications Crosslink Payload Prototype Development for the Cubesat Laser Infrared CrosslinK (CLICK) Mission

The Cubesat Laser Infrared CrosslinK (CLICK) mission is a technology demonstration of10 Mbps downlink. On the second flight, with two identical 3U CubeSats, CLICK-B/C, a \u3e20 Mbps crosslink will be demonstrated in addition to downlinks. In this paper representative link budgets for the crosslink are presented, including both communications and beacon lasers. The payload Pointing, Acquisition and Tracking (PAT) system is introduced, and the performance of the second stage closed loop tracking signal processing is assessed. Errors below 1 urad are reported from test and simulation. The communication detector of the payload is a 200 um InGaAs Avalanche PhotoDetector (APD), with a 1 GHz bandwidth and a dynamic range of more than 40 dB provided by programmable gain amplifiers. The APD performance enables a data rate of 17.7 Mbps at a range of 520 km. The timing accuracy of the detector is better than 130 ps