A document discusses an architecture of a spaceborne laser communication system that provides for a simplified control subsystem that stabilizes the line of sight in a desired direction. Heretofore, a typical design for a spaceborne laser communication system has called for a high-bandwidth control loop, a steering mirror and associated optics, and a fast steering mirror actuator to stabilize the line of sight in the presence of vibrations. In the present architecture, the need for this fast steering-mirror subsystem is eliminated by mounting the laser-communication optics on a disturbance-free platform (DFP) that suppresses coupling of vibrations to the optics by ≥60 dB. Taking advantage of microgravitation, in the DFP, the optical assembly is free-flying relative to the rest of the spacecraft, and a low-spring-constant pointing control subsystem exerts small forces to regulate the position and orientation of the optics via voice coils. All steering is effected via the DFP, which can be controlled in all six degrees of freedom relative to the spacecraft. A second control loop, closed around a position sensor and the spacecraft attitude-control system, moves the spacecraft as needed to prevent mechanical contact with the optical assembly.
This work was done by Chien-Chung Chen and Hamid Hemmati of Caltech for NASA’s Jet Propulsion Laboratory. NPO-42693
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Simplified Optics and Controls for Laser Communications
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Overview
The document titled "Simplified Optics and Controls for Laser Communications" from NASA's Jet Propulsion Laboratory outlines advancements in laser communication (lasercom) technology, which promises higher data return rates while minimizing the size and weight of telecommunications systems for deep space missions. The key innovation discussed is the use of a Disturbance-Free Platform (DFP) developed by Lockheed Martin Space Systems, which significantly simplifies the architecture of lasercom systems.
Traditional lasercom systems rely on high-bandwidth control loops to stabilize the optical line of sight against platform disturbances, which can complicate the design and increase mass and power consumption. The DFP isolates the optical components from high-frequency vibrations of the host spacecraft, eliminating the need for fast steering mirrors and associated relay optics. This isolation allows for longer integration times for the optical focal plane array, enabling the use of faint celestial objects (like stars) as pointing references, which is particularly beneficial for deep space applications where strong beacons are impractical.
The document emphasizes that the narrow beamwidth of lasercom systems, while advantageous for efficient signal delivery, poses challenges for pointing control due to the larger attitude uncertainties and vibrations of spacecraft. The DFP's ability to mitigate these issues allows for a more straightforward system architecture that can be applied to both deep space and near-Earth missions.
Additionally, the document discusses the operational complexities associated with deep space lasercom, such as the limitations imposed by atmospheric turbulence on ground-based beacon uplinks. The DFP's design addresses these challenges, making it feasible to communicate effectively without relying on strong beacons.
Overall, the document presents a compelling case for the DFP-enabled lasercom system as a transformative approach to optical communications in aerospace, highlighting its potential to enhance mission capabilities while reducing system complexity and weight. This innovation could pave the way for more efficient and reliable communication in future space exploration endeavors.
