The simplified architecture is a minimal system for a deep-space optical communications transceiver. For a deep-space optical communications link the simplest form of the transceiver requires (1) an efficient modulated optical source, (2) a point-ahead mechanism (PAM) to compensate for two-way light travel, (3) an aperture to reduce the divergence of the transmit laser communication signal and also to collect the uplink communication signal, and (4) a receive detector to sense the uplink communication signal. Additional components are introduced to mitigate for spacecraft microvibrations and to improve the pointing accuracy.
The Canonical Transceiver implements this simplified architecture (see figure). A single photon-counting “smart focal plane” sensor combines acquisition, tracking, and forward link data detection functionality. This improves optical efficiency by eliminating channel splits. A transmit laser blind sensor (e.g. silicon with 1,550-nm beam) provides transmit beam-pointing feedback via the two-photon absorption (TPA) process. This vastly improves the transmit/receive isolation because only the focused transmit beam is detected. A piezoelectric tip-tilt actuator implements the required point-ahead angle. This point-ahead mechanism has been demonstrated to have near zero quiescent power and is flight qualified. This architecture also uses an innovative 100-mHz resonant frequency passive isolation platform to filter spacecraft vibrations with voice coil actuators for active tip-tilt correction below the resonant frequency.
The canonical deep-space optical communications transceiver makes synergistic use of innovative technologies to reduce size, weight, power, and cost. This optical transceiver can be used to retire risks associated with deep-space optical communications on a planetary pathfinder mission and is complementary to ongoing lunar and access link developments.
This work was done by Gerard G. Ortiz, William H. Farr, and Jeffrey R. Charles of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Physical Sciences category. NPO-46073
This Brief includes a Technical Support Package (TSP).
Simplified Architecture for Precise Aiming of a Deep-Space Communication Laser Transceiver
(reference NPO-46073) is currently available for download from the TSP library.
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Overview
The document from NASA's Jet Propulsion Laboratory presents a Technical Support Package detailing a simplified architecture for a deep-space communication laser transceiver. This innovative system is designed to enhance the precision and efficiency of optical communications in space, addressing the challenges posed by high power density and the need for effective transmit/receive isolation.
The architecture is built upon three key technological advancements:
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Single Photon Counting Imaging Focal Plane Array: This component features a "smart" readout circuit that allows for simultaneous acquisition, tracking, and data detection. It is designed to be nominally blind to the transmit laser wavelength, enabling accurate measurement of the transmit beam angle through a process known as Two Photon Absorption (TPA). Each pixel in the array is sensitive to single photons, producing an electrical output pulse for each incident photon, which facilitates noise-free digital signal processing.
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Improved Passive Isolators: These isolators are mounted to the spacecraft body and operate at sub-Hertz resonant frequencies, effectively eliminating the need for a virtual star line of sight reference subsystem. This enhancement significantly reduces the impact of high-frequency vibrations from the spacecraft, allowing for a more stable communication system.
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Near-Zero Quiescent Power Mechanism: This mechanism is employed for point-ahead control, utilizing a two-axis tip-tilt piezoelectric actuator. The design minimizes power consumption, size, and mass, making it suitable for deep-space applications.
The document emphasizes the novelty of this architecture, which simplifies the overall system by eliminating unnecessary subsystems, thereby maximizing performance while minimizing size, mass, and power requirements. The combination of these technologies allows for efficient use of received Earth beacon power and enhances the sensitivity of the communication system.
Additionally, the architecture addresses the challenge of transmit/receive isolation by selecting an Earth beacon wavelength that is distinct from the transmit wavelength, allowing for effective detection without interference. This is achieved by using semiconductor detectors that are not sensitive to the transmit wavelength, ensuring high sensitivity and performance.
Overall, this document outlines a significant advancement in deep-space communication technology, with the potential to support future missions by providing reliable, high-data-rate communication capabilities essential for exploring distant celestial bodies.
