The Space Development Agency (SDA) is developing the Proliferated Warfare Space Architecture (PWSA) – a constellation of hundreds of satellites in low earth orbit delivering space-based capabilities to the joint warfighter. The PWSA is a mesh network of optically connected satellites providing low-latency data transport and missile warning/tracking capabilities. SDA capitalizes on a unique business model that values speed and lowers costs by harnessing commercial development. The Optical Communications Terminal (OCT) standard was created to provide optical interoperability specifications, enable a strong marketplace, and to drive advancements in optical communication capabilities to terrestrial, maritime, and airborne warfighting elements. As part of the spiral development process, the OCT standard evolves with PWSA deployment phases. SDA has incorporated feedback as well as advancements to the OCT standard, resulting in the release of version 3.1.0. In this paper we discuss key aspects of the OCT standard, such as wavelength, modulation, data rates, polarization, link distance, error correction coding, pointing, acquisition and tracking, and position, navigation, and timing.
As lasercom transitions from individual demonstrations to wide-spread deployment, diverging standards and proprietary implementations will impede interoperability between terminals from different suppliers. In this environment, there is an urgent need for a universal lasercom translator terminal capable of supporting multiple acquisition sequences and communication waveforms in order to connect disparate networks. Development of such a generalized terminal is a key goal of the DARPA Space-Based Adaptive Communication Node (Space-BACN) program. Pointing, Acquisition, and Tracking (PAT) are crucial aspects of interoperability, and multiple styles of PAT sequences have emerged. Even within a given category of beacon generation (e.g., synthesized, in-band, out-of-band), multiple parameters must be specified to define specific entry/exit criteria for each PAT stage, requiring detailed pre-coordination to ensure that terminals from different suppliers can establish a link between them. In addition, extra hardware must be incorporated into the terminal design to accommodate a superset of PAT requirements. Finally, verification testing of multiple PAT sequences in a common testbed drives the testbed implementation requirements. Here, we examine the implications of attempting to accommodate a generalized PAT sequence with a single lasercom terminal. First, we consider the performance of different styles of PAT sequence, and the trades between pointing uncertainty, maximum acquisition range, and allowable scan time. Next, we consider potential hardware requirements for terminals that support multiple PAT sequences. Finally, we consider the testing of such a terminal, and present a testbed architecture intended to accommodate multiple PAT sequences by highly flexible emulation of the remote terminal PAT behavior.
The DARPA Space-Based Adaptive Communications Node (Space-BACN) optical terminal will be a low-cost reconfigurable optical intersatellite link (OISL) terminal capable of supporting up to 100 Gbps low-earth-orbit (LEO) links. Rapid and reliable pointing, acquisition, and tracking (PAT) is critical to OISL performance, especially in cross-plane LEO links, where contacts can be short. The Space-BACN optical terminal will demonstrate a novel reconfigurable acquisition implementation, which can be dynamically configured to operate in one of three acquisition modes: in-band, out-of-band, and synthesized beacon. Here, we review the features, implementation, performance analysis, and verification approaches for each of the three acquisition modes.
The Panoptic Astronomical Networked OPtical observatory for Transiting Exoplanets Survey (PANOPTES, www.projectpanoptes.org) project is aimed at identifying transiting exoplanets using a wide network of low-cost imaging units. Each unit consists of two commercial digital single lens reflex (DSLR) cameras equipped with 85mm F1.4 lenses, mounted on a small equatorial mount. At a few $1000s per unit, the system offers a uniquely advantageous survey eficiency for the cost, and can easily be assembled by amateur astronomers or students. Three generations of prototype units have so far been tested, and the baseline unit design, which optimizes robustness, simplicity and cost, is now ready to be duplicated. We describe the hardware and software for the PANOPTES project, focusing on key challenging aspects of the project. We show that obtaining high precision photometric measurements with commercial DSLR color cameras is possible, using a PSF-matching algorithm we developed for this project. On-sky tests show that percent-level photometric precision is achieved in 1 min with a single camera. We also discuss hardware choices aimed at optimizing system robustness while maintaining adequate cost. PANOPTES is both an outreach project and a scientifically compelling survey for transiting exoplanets. In its current phase, experienced PANOPTES members are deploying a limited number of units, acquiring the experience necessary to run the network. A much wider community will then be able to participate to the project, with schools and citizen scientists integrating their units in the network.
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