NTS-3 Signals Experiments – Overview
Joanna Hinks, Air Force Research Laboratory and Jon Anderson, Canyon Consulting
Date/Time: Tuesday, Aug. 24, 1:50 p.m.
Navigation Technology Satellite – 3 (NTS-3) is an Air Force Research Laboratory flight experiment that will explore new ways to incorporate resiliency into the positioning, navigation, and timing (PNT) enterprise. From its geosynchronous orbit, NTS-3 will investigate a number of technologies to evolve and augment GPS, including a steerable phased array antenna, advanced timekeeping system, and automated ground operations. Rather than focusing just on the spacecraft, NTS-3 experiments encompass the space, ground, and user segments. PNT signals are what bind all three segments together and both enable and constrain the capabilities of any satellite navigation system, or system of systems. Enabled by a reprogrammable waveform generator, the NTS-3 Advanced Signals Team endeavors to develop and implement innovative new signals and system concepts to address current and future military PNT needs. This presentation will describe the major categories of signals experiments planned for the NTS-3 mission, as well as the challenges of incorporating reprogrammable signals across all three segments.
The history of GPS modernization has been the history of GPS signal modernization. From L2C to M to L5 to L1C, each new signal introduces new capabilities and addresses new challenges. Increasingly, space is recognized as a contested environment and the greater reliance of warfighters on GPS has led to challenges, especially those caused by jamming and spoofing. Some of these challenges can be ameliorated by new signal designs that protect against specific threats. More generally, the advent of software-defined receivers and transmitters enables the PNT endeavor as a whole (including the dedicated GPS constellation and potential future assets, ground-based or in other orbits) to be more responsive as new threats arise in the future. When the next challenge is identified, it should not take decades to deploy a signal-based solution!
The NTS-3 signals experiments fall into two categories: Signal concepts that would be broadcast from every satellite in the constellation (as are today’s signals) to provide an enhanced capability, and signals that are well-suited for transmission from an augmentation payload (potentially in GEO or some other non-GPS orbit) that might only have one satellite at a time in view for a particular location. Some potential experiments include civil authentication, signal acquisition aids, modulation schemes to improve transmitter efficiency or multipath performance, and high data rates to provide auxiliary information such as GPS clock and extended ephemeris.
As NTS-3 moves towards greater signal flexibility and agility in space, one cannot ignore the ground and user segments. Without a ground segment to command new signals responsively and fielded user equipment to take advantage of new capabilities, new signal development efforts are wasted. In order to move towards true reprogrammability, it is necessary to develop new processes to specify, disseminate, and implement signals across the satellite navigation enterprise.
Approved for public release; distribution is unlimited. Public Affairs release approval #AFMC-2020-0030.