Epoxy-based shape memory composite for space applications

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 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.

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11180/111800Y/The-CubeSat-Laser-Infrared-CrosslinK-Mission-CLICK/10.1117/12.2535953.pdf

The CubeSat Laser Infrared CrosslinK Mission (CLICK)

This article presents an innovative mechatronic design of a high-accuracy pointing mechanism for orbital laser communication terminals.The system is based on a dual-stage architecture and is miniaturized to fit nanosatellite-class spacecraft, aiming to enable optical communication on small-size space platforms. The focus is on control design aspects and on the performance assessment of an experimental prototype under emulated external environmental disturbances.

High-Precision Dual-Stage Pointing Mechanism for Miniature Satellite Laser Communication Terminals

Small satellite launch opportunities are rapidly expanding and technical capabilities are improving. Several commercial constellations of small satellites for Earth observation and communications are making their way onto orbit, increasing the need for high bandwidth data downlink. Laser communications (lasercom) has the potential to achieve high data rates with a reduction in power and size compared to radio frequency (RF) communications, while simultaneously avoiding the significant regulatory burden of RF spectrum allocation. The primary challenge for lasercom is aligning a narrow beam between the transmitter and receiver. High-precision pointing must be achieved by both the space terminal and the ground station. While existing lasercom ground stations have primarily utilized professional telescopes at observatory-class facilities, making optical ground stations more affordable and transportable is a key enabler for expanding lasercom to small satellites and new applications, as well as establishing networks to mitigate the effects of weather. We describe the development of the Massachusetts Institute of Technology Portable Telescope for Lasercom (MIT-PorTeL) utilizing an amateur telescope augmented with an externally mounted receiver assembly. The ground station has a 28 cm aperture and utilizes a star tracker for automated calibration. The ground station reduces mass by at least 10x and cost by at least 100 x over existing optical ground stations. We present a ground station architecture that enables deployment in less than one hour and that is capable of tracking satellites in low-Earth orbit. We describe the receiver assembly and fine pointing system that enables arcseconds-level pointing accuracy. Finally, we present results from testing the ground station on the roof of an MIT building tracking a star and tracking the International Space Station.

A portable optical ground station for low-earth orbit satellite communications

We describe techniques developed to optimize beam pointing control for a CubeSat laser downlink demonstration mission being developed at the MIT Space Telecommunications, Astronomy, and Radiation Laboratory. To fine-point its downlink beam, the mission utilizes an uplink beacon signal at 976 nm captured by an on-board ±5-deg field-of-view detector and tracked by a 3.6-mm commercial, off-the-shelf MEMS fast steering mirror. As these miniature actuators lack feedback sensors, the system design is augmented with an optical calibration signal to provide the mirror’s pointing feedback. We describe the system and introduce calibration algorithms utilizing the feedback signal to achieve higher fidelity beam pointing control. A demonstration in the laboratory is conducted to obtain a quantitative performance analysis using quasi-flight hardware with simulated spacecraft body pointing disturbances. Experimental results show that beacon tracking errors of only 16  μrad root-mean-square are feasible for both axes, significantly exceeding the mission pointing requirement of 0.65 mrad and indicating the feasibility of narrower beams and higher data throughputs for next-generation downlink demonstration missions.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-58/issue-4/041605/On-orbit-beam-pointing-calibration-for-nanosatellite-laser-communications/10.1117/1.OE.58.4.041605.pdf

On-orbit beam pointing calibration for nanosatellite laser communications

The nanosatellite optical downlink experiment (NODE) implements a free-space optical communications (lasercom) capability on a CubeSat platform that can support low earth orbit (LEO) to ground downlink rates>10  Mbps. A primary goal of NODE is to leverage commercially available technologies to provide a scalable and cost-effective alternative to radio-frequency-based communications. The NODE transmitter uses a 200-mW 1550-nm master-oscillator power-amplifier design using power-efficient M-ary pulse position modulation. To facilitate pointing the 0.12-deg downlink beam, NODE augments spacecraft body pointing with a microelectromechanical fast steering mirror (FSM) and uses an 850-nm uplink beacon to an onboard CCD camera. The 30-cm aperture ground telescope uses an infrared camera and FSM for tracking to an avalanche photodiode detector-based receiver. Here, we describe our approach to transition prototype transmitter and receiver designs to a full end-to-end CubeSat-scale system. This includes link budget refinement, drive electronics miniaturization, packaging reduction, improvements to pointing and attitude estimation, implementation of modulation, coding, and interleaving, and ground station receiver design. We capture trades and technology development needs and outline plans for integrated system ground testing.

Nanosatellite optical downlink experiment: design, simulation, and prototyping

Free space optical (FSO) communications have the potential to outperform traditional radio frequency data rates by orders of magnitude using comparable mass, volume, and power. The Nanosatellite Optical Downlink Experiment (NODE) is a 1.2U, 1 kg, 15 W, 1550 nm CubeSat downlink transmitter that uses a master-oscillator power amplifier configuration with a modest 1.3 mrad half-power beamwidth (HPBW) enabled by a microelectromechanical system (MEMS) Fast Steering Mirror (FSM) [1],[4]. NODE is designed to be compatible with the Portable Telescope for Lasercom (PorTeL) ground station [3],[6],[19], which has successfully demonstrated tracking of low Earth orbit objects to better than 5 arcseconds RMS. The flight-like opto-mechanical NODE engineering model has successfully passed vibration testing at qualification levels specified by NASA GEVS [9]. The engineering model has also passed thermal testing in vacuum under worstcase expected environmental loads, and component operational temperatures remained within limits. Tests of the optomechanical alignment and control algorithms meet +/0.05 mrad (3-sigma) for the space and ground terminals. We present results from the NODE engineering unit and flight unit development, integration, and testing, as well as interface test results with PorTeL.

/pdf/integration-and-testing-of-the-nanosatellite-optical-nqvr5vaant.pdf

Integration and Testing of the Nanosatellite Optical Downlink Experiment

A controllable shape memory alloy (SMA) hinge apparatus comprises multiple SMA elements to effect a first angle of rotation and a second angle of rotation between a first object and a second object. In one example, respective SMA elements are independently activated by Joule heating to rotate the first object and/or the second object. SMA elements undergo a three-dimensional transformation (e.g., bending or torsion), and a pair of elements may undergo antagonistic transformations so as to provide for a multiple-use bidirectional non-continuous rotary actuator. SMA elements may be trained to achieve different angles of rotations between the objects (e.g., zero degrees and 90 degrees). SMA elements may be nitinol, and may be formed as wires, rectangular sheets, or coils. In some examples, the first object may be a spacecraft (e.g., a satellite) and the second object may be a deployable structure (e.g., a robotic appendage, a deployable solar panel, a deployable aperture, a deployable mirror, a deployable radiator, and at least one actuator to steer an antenna dish).

Shape memory alloy (sma) hinge apparatus, and systems and methods employing same

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-55/issue-11/111610/Nanosatellite-optical-downlink-experiment-design-simulation-and-prototyping/10.1117/1.OE.55.11.111610.pdf

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Nanosatellite optical downlink experiment: design, simulation, and prototyping

Integration and Testing of the Nanosatellite Optical Downlink Experiment

Shape memory alloy (sma) hinge apparatus, and systems and methods employing same

Nanosatellite optical downlink experiment: design, simulation, and prototyping