Space Optical Communications Using Laser Beams

communications
Space Optical Communications Using Laser Beams (TOP2-248)
New method for optical data transmissions from satellites using laser arrays for laser beam pointing
Overview
NASA has developed a new laser beam pointing technology for use in space optical communications. With further development, possible applications include communications from the Earth to spacecraft in Earth orbit and in deep space, such as at the moon and Mars. A possible application is to the Artemis Program for CubeSats in low-Lunar Orbit (LLO). Current architectures use dynamical systems, (i.e., moving parts, e.g., fast-steering mirrors (FSM), and/or gimbals,) to turn the laser to point to the ground terminal and possibly use vibration isolation platforms (VIP). This patented technology from NASA Ames uses a combined lens system and a vertical-cavity surface-emitting laser (VCSEL)/Photodetector Array. This static system has the potential to replace the current dynamic systems and VIP, dependent on studies for the particular application. Laser beam pointing is very challenging for low-Earth Orbit (LEO), including science missions. Computer simulations using this design have been made for an application to a CubeSat in LEO.

The Technology
This invention provides a new method for optical data transmissions from satellites using laser arrays for laser beam pointing. The system is simple, static, compact, and provides accurate pointing, acquisition, and tracking (PAT). It combines a lens system and a vertical-cavity surface-emitting laser VCSEL)/Photodetector Array, both mature technologies, in a novel way for PAT. It can improve the PAT system's size, weight, and power (SWaP) in comparison to current systems. Preliminary analysis indicates that this system is applicable to transmissions between satellites in low-Earth orbit (LEO) and ground terminals. Computer simulations using this design have been made for the application of this innovation to a CubeSat in LEO. The computer simulations included modeling the laser source and diffraction effects due to wave optics. The pointing used a diffraction limited lens system and a VCSEL array. These capabilities make it possible to model laser beam propagation over long space communication distances. Laser beam pointing is very challenging for LEO, including science missions. Current architectures use dynamical systems, (i.e., moving parts, e.g., fast-steering mirrors (FSM), and/or gimbals) to turn the laser to point to the ground terminal, and some use vibration isolation platforms as well. This static system has the potential to replace the current dynamic systems and vibration isolation platforms, dependent on studies for the particular application. For these electro-optical systems, reaction times to pointing changes and vibrations are on the nanosecond time scale, much faster than those for mechanical systems. For LEO terminals, slew rates are not a concern with this new system.
ISS Left: Space Optical Communications using a Lens System with a Vertical Cavity Surface Emitting Laser (VCSEL)/ Photodetector Array

Right: Irradiance of three overlapping laser beams after 500 Km of propagation from LEO. Computational results
Benefits
  • Minimal maintenance required
  • Components are simple, static, and reliable
  • Increase in communications performance
  • Compact, with no moving parts
  • Does not need a vibration isolation platform

Applications
  • CubeSat communications - Artemis Program, CubeSats in LLO
  • Spacecraft industry
  • Space communication: - Deep space optical communications (DSOC) - Optical multiple access (OMA)
  • Communication between a constellation of close satellites
Technology Details

communications
TOP2-248
ARC-17122-1B ARC-17122-1C
Peter M. Goorjian, "A new laser beam pointing method using laser arrays", Paper 10910-51, Conference 10910, Free-Space Laser Communications XXXI, SPIE Photonics West 2019, San Francisco, California, February 2-7, 2019

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10910/109101F/A-new-laser-beam-pointing-method-using-laser-arrays/10.1117/12.2506303.full

Goorjian, P. M., "A New Laser Beam Pointing Method Using Laser Arrays" NASA/TM-2018-58815, November 2018

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190002843.pdf
Similar Results
Satellite
Fine-pointing Optical Communication System Using Laser Arrays
A new method is described for optical data transmissions from satellites using laser arrays for fine pointing of laser beams that use body pointing. It combines a small lens system and a VCSEL/Photodetector Array in a novel way to provide a fine pointing capability for laser beams that are pointed by body pointing of a CubeSat. As Fig. 1 shows, an incoming laser beam (green or blue, with rightward arrows), transmitted from a ground terminal, enters the lens system, which directs it to an element of the pixel array (gray rectangle). Each element, or pixel, consists of a VCSEL component/photodetector pair. The photodetector detects the incoming beam, and the VCSEL component returns a modulated beam to the lens system (green or blue, with leftward arrows), which sends it to the ground terminal. As the incoming beam changes direction, e.g., from the blue to the green incoming direction, this change is detected by the adjacent photodetector, and the laser paired with that photodetector is turned on to keep the outgoing laser beam on target. The laser beams overlap so that the returning beam continues to point at the ground terminal. The VCSEL component may consist of a single VCSEL or a cluster of VCSELs. Figure 2 shows the propagation of two overlapping laser beams. The system can very accurately point finely focused diffraction-limited laser beams. Also, simultaneous optical multiple access (OMA) is possible from different transceivers within the area covered by the laser array. For this electro-optical system, reaction times to pointing changes and vibrations are on the nanosecond time scale, much faster than mechanical fine pointing systems.
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