Patrick A. Taylor, National Radio Astronomy Observatory, Green Bank Observatory; Steven R. Wilkinson, Raytheon Intelligence and Space; Flora Paganelli, National Radio Astronomy Observatory; Ray Samaniego, Raytheon Intelligence & Space; Bishara Shamee, Raytheon Intelligence & Space; Aaron Wallace, Raytheon Intelligence & Space; Anthony J. Beasley, National Radio Astronomy Observatory
Keywords: radar, space situational awareness, cislunar ssa, space domain awareness, astronomy, imaging, instrumentation
Abstract:
In partnership with the National Radio Astronomy Observatory (NRAO) and Raytheon Intelligence & Space (RIS), the Green Bank Observatory (GBO) tested a multistatic radar configuration intended to expand the scientific reaches and capabilities of the Green Bank Telescope (GBT) and the Very Long Baseline Array (VLBA). The experimental effort installed an RIS Ku-band (13.9 GHz) transmitter on the 100-meter GBT and relied on the ten 25-meter VLBA stations to receive the returned signals from the Moon, space debris, and a near-Earth asteroid. The demonstration system had low power (700 W) and, when integrated into the GBT, had an effective isotropic radiated power (EIRP) of 109 dBW, providing very high signal-to-noise (SNR) returns from the Moon and enough SNR to make basic measurements of space-debris targets as well as detect an asteroid. Data was collected during two observations in November 2020 and March 2021. These experiments generated the highest resolution synthetic aperture radar (SAR) images of select locations on the Moon ever collected from Earth and detected ~500-meter asteroid (231937) 2001 FO32 at a 2.1 billion meters (~5.5 lunar distances) from Earth. Data was also collected from space debris, where the experiments show the systems potential to support the space situational awareness (SSA) mission. We will also present data from an October 2019 observation run against the space-debris targets, two derelict Russian satellites, Molniya 2-9 and 3-10, using the Arecibo Observatory planetary radar prior to its collapse. Both satellites are in highly elliptical orbits allowing the observations to occur when the geometry was favorable to receive returns at multiple VLBA stations. However, this is not required for collection against any specific target since most of the results shown will be from processing data from a single VLBA station. We discuss the differences between the Arecibo collection and both GBT collections, where the major difference was having 129 dBW with a narrowband signal at Arecibo versus 109 dBW with a tunable bandwidth of up to 200 MHz at GBT. We will also present the evolution of the SAR/ISAR processing of the lunar data. During the November 2020 experiments, we collected 50-meter and 5-meter resolution images of the Apollo 15 landing site. To achieve 50-m and 5-m resolution in azimuth at Ku band required collection durations of 5 minutes and 40 minutes, respectively. During the March 2021 experiments, we needed a 2-hour-and-40-minute continuous collection to produce the aperture required for a 1.25-m resolution image of the Apollo 15 site. We will also show the improvements in the SAR imagery of Tycho crater taken in March 2021. For the Tycho observation, we collected data to produce a 5-m resolution SAR image of the crater, and the latest imagery using our new techniques reveals interesting structure on the crater floor that was not initially visible in the first images produced. Our final topic is to present the next steps in the development of the 500 kW, Ku-band NRAO/GBO planetary radar system. The first step is to integrate a medium power, at least 10 kW, Ku-band transmitter to develop the end-to-end, real-time radar system with target characterization and imaging capabilities using the GBT transmitter and the VLBA receivers. This system will have a minimum EIRP of 123 dBW able to detect near-Earth asteroids well beyond the lunar orbit and collect high-resolution ISAR imagery and movies of the Molniya satellites used in the initial experiments. We conclude with a description of the 500-kW system and the future Next Generation Very Large Array (ngVLA) as the receiver.
Date of Conference: September 27-20, 2022
Track: SSA/SDA