Session
Weekday Session 6: Advanced Technologies II
Location
Utah State University, Logan, UT
Abstract
Since the launch of the Optical Communication and Sensor Demonstration (OCSD) Mission in November 2017, The Aerospace Corporation has relied upon a manually operated optical terminal in El Segundo, CA to support optical communications downlinks. Scaling our constellation of laser communication capable small satellites and resulting increase in data volume has necessitated multiple geographically dispersed optical ground stations. In 2021, The Aerospace Corporation developed and deployed two remotely operable optical terminals in Maui, Hawaii and Albuquerque, New Mexico, demonstrating up to 200 Mbps downlink communication rates with Forward Error Correction. The station is comprised primarily of commercial off-the-shelf (COTS) components to reduce cost and enable short assembly time. Upgrades to support greater than 200 Mbps downlink rates are in-work. To the best of the authors’ knowledge, this newly deployed optical communication terminal network is the lowest cost operational system of its type worldwide. Each ground station is comprised of a 7ft clamshell dome housing a 17-inch telescope equipped with two short wave infrared (SWIR) imagers - the narrow field of view (NFOV) and the wide field of view (WFOV). The telescope is mounted on a gimbal articulated by two rotary stages (azimuth and elevation) and their associated drive electronics. Hardware is commanded with servers housed in a separate temperature-controlled cabinet, connected to the dome via conduit. The Optical Communication Terminals are passive receive only. Satellite tracking is achieved by ingestion of high precision GPS based ephemeris downloaded in advance of the laser communication pass via radio from the spacecraft. Tracking software translates spacecraft ephemeris to telescope azimuth and elevation until acquisition of laser signal, typically at twenty degrees elevation. At this point, incoming NFOV frames are run through custom image processing algorithm to determine the region of interest (ROI) and pixel coordinates of the satellite. The algorithm is optimized to limit false positives on noise and atmospheric phenomena while maintaining the ability to locate dim targets. Target coordinate information and associated frame timestamp are then forwarded to centroid processing software which commands the gimbal with azimuth and elevation offsets to center the target on the avalanche photodiode’s (APD) field of view. In the absence of centroids due to clouds, Laser Clearing House closures, or space segment related pointing errors, the tracking system defaults to pre-loaded ephemeris-based tracking. The Aerospace Corporation has integrated lasercomm modems targeted for data rates greater than or equal to 622 Mbps. The system is designed to be expandable for higher data rates and additional capability by incorporating an FPGA frontend with real-time software processing using CPU servers. Docker has been used to containerize and orchestrate the various software modules, including the FPGA controller, real-time CPU apps, and post-processing software. Remote commanding of all components is orchestrated by high level Python application programming interface (API) accessible via representational state transfer (REST) interface. The software and hardware architecture supports fully automated capability which is being actively developed for the terminals. Results are presented showing acquisition and tracking performance, as well as bit error rate characterization and metric tracking for the receive modem.
Development and Deployment of Remotely Operable Optical Communication Terminals
Utah State University, Logan, UT
Since the launch of the Optical Communication and Sensor Demonstration (OCSD) Mission in November 2017, The Aerospace Corporation has relied upon a manually operated optical terminal in El Segundo, CA to support optical communications downlinks. Scaling our constellation of laser communication capable small satellites and resulting increase in data volume has necessitated multiple geographically dispersed optical ground stations. In 2021, The Aerospace Corporation developed and deployed two remotely operable optical terminals in Maui, Hawaii and Albuquerque, New Mexico, demonstrating up to 200 Mbps downlink communication rates with Forward Error Correction. The station is comprised primarily of commercial off-the-shelf (COTS) components to reduce cost and enable short assembly time. Upgrades to support greater than 200 Mbps downlink rates are in-work. To the best of the authors’ knowledge, this newly deployed optical communication terminal network is the lowest cost operational system of its type worldwide. Each ground station is comprised of a 7ft clamshell dome housing a 17-inch telescope equipped with two short wave infrared (SWIR) imagers - the narrow field of view (NFOV) and the wide field of view (WFOV). The telescope is mounted on a gimbal articulated by two rotary stages (azimuth and elevation) and their associated drive electronics. Hardware is commanded with servers housed in a separate temperature-controlled cabinet, connected to the dome via conduit. The Optical Communication Terminals are passive receive only. Satellite tracking is achieved by ingestion of high precision GPS based ephemeris downloaded in advance of the laser communication pass via radio from the spacecraft. Tracking software translates spacecraft ephemeris to telescope azimuth and elevation until acquisition of laser signal, typically at twenty degrees elevation. At this point, incoming NFOV frames are run through custom image processing algorithm to determine the region of interest (ROI) and pixel coordinates of the satellite. The algorithm is optimized to limit false positives on noise and atmospheric phenomena while maintaining the ability to locate dim targets. Target coordinate information and associated frame timestamp are then forwarded to centroid processing software which commands the gimbal with azimuth and elevation offsets to center the target on the avalanche photodiode’s (APD) field of view. In the absence of centroids due to clouds, Laser Clearing House closures, or space segment related pointing errors, the tracking system defaults to pre-loaded ephemeris-based tracking. The Aerospace Corporation has integrated lasercomm modems targeted for data rates greater than or equal to 622 Mbps. The system is designed to be expandable for higher data rates and additional capability by incorporating an FPGA frontend with real-time software processing using CPU servers. Docker has been used to containerize and orchestrate the various software modules, including the FPGA controller, real-time CPU apps, and post-processing software. Remote commanding of all components is orchestrated by high level Python application programming interface (API) accessible via representational state transfer (REST) interface. The software and hardware architecture supports fully automated capability which is being actively developed for the terminals. Results are presented showing acquisition and tracking performance, as well as bit error rate characterization and metric tracking for the receive modem.
