Concept Development for Advanced Spaceborne Synthetic Aperture Radar

The P-band antenna array is built from rows and columns of antenna elements for the purpose of allowing beam steering up to the maximum desirable angle without incurring grating lobes in the radiation patterns. For flexible mission planning, a large array can be built from several of the small, panel-like elements. The elements are deployable from a folded or stacked stowed configuration during launch, arranged side by side during operation. Each antenna element is itself a fully functional small antenna array. The number of panels can be chosen as dictated by the mission objectives and budget. Three geometries were designed and tested. Geometry 1 features non-planar metal structures with minimal dielectric support, where the back cavity is closed. Geometry 2 features non-planar metal structures with minimal composite sheet dielectric support, but with an open cavity. Both geometries avoid large flat sheets, which are vulnerable to bending, thereby increasing the mechanical stiffness of the structure while using only thin sheet metal and maintaining an exceptionally low mass-to-size ratio. Geometry 3 features planar metal structures, with sandwich composite dielectric support and an open cavity. While it does not benefit from the mechanical stiffness utilized in non-planar designs, the planar sandwich structure increase robustness and reduces the cost of fabrication. All element geometries have wideband capabilities and are dual polarized. Although designed for space and planetary exploration, the P-band antenna is also valuable for various terrestrial use cases. The P-band antenna array is at technology readiness level (TRL) 5 (component and/or breadboard validation in relevant environment) and is available for patent licensing.

NASA Goddard Space Flight Center (GSFC) has developed a new approach that uses a single phased array antenna and a single pass configuration to generate interferograms, known as Digital Beamforming Interferometry. A digital beamforming radar system allows the implementation of non-conventional radar techniques, known as Digital Beamforming Synthetic Aperture Radar Multi-mode Operation (DBSAR). DBSAR is an L-Band airborne radar that combines advanced radar technology with the ability to implement multimode remote sensing techniques, including several variations of SAR, scatterometry over multiple beams, and an altimeter mode. The Multiple channel data acquired with a digital beamformer systems allows the synthesis of beams over separate areas of the antenna, effectively dividing the single antenna into two antennas. The InSAR technique is then achieved by generating interferograms from images collected with each of the antennas. Since the technique is performed on the data, it allows for synthesizing beams in different directions (or look angles) and performs interferometry over large areas. Digital Beamforming Interferometry has potential in many areas of radar applications. For example, NASA GSFC innovators developed the first P-Band Digital Beamforming Polarimetric Interferometric SAR Instrument to measure ecosystem structure, biomass, and surface water.

This NASA invention utilizes a simple waveguide-based measurement system to determine the complex dielectric permittivity and magnetic permeability of arbitrary-shaped planetary rock samples. The system operates at L-band frequencies (~1 GHz) and can be extended to P- and S-bands for broader applications. The approach involves placing an arbitrarily-shaped sample inside an open-ended waveguide excited by a coaxial probe, measuring the scattering parameters, and extracting dielectric and magnetic properties through computational modeling and optimization techniques. A key aspect of this system is its ability to handle non-uniform and irregularly shaped rock samples, enabling the measurement of real-world planetary materials without requiring extensive sample preparation. The methodology includes calibration in an anechoic chamber, computational modeling, and iterative refinement of measured vs. simulated scattering parameters to extract the material properties. Future advancements will involve expanding measurements to different frequency bands, refining computational models using artificial intelligence, and automatically rotating samples within the waveguide to obtain multiple directional measurements (enhancing precision while reducing test time). This NASA innovation has been successfully applied to two Martian meteorite samples, yielding values of dielectric permittivity and permeability relevant for Mars radar applications. The system will further be leveraged to build an expansive database of the dielectric properties of planetary soils and rocks to improve radar-based mapping (e.g., subsurface mapping) missions. The invention could also be applied for the non-destructive screening of a variety of samples using radio waves, including biological samples for medical purposes, additive manufacturing feedstock or finished parts, and mining-related rock samples to test for impurities or resources of interest. This NASA invention is at technology readiness level (TRL) 5 (component and/or breadboard validation in relevant environment) and is available for patent licensing.

NASA's SDR uses Field-Programmable Gate Array (FPGA) technology to enable flexible performance on orbit. A first-generation FM-modulated transceiver is capable of operating at up to 1 Mbps downlink and 50 kbps uplink, full duplex. An FPGA performs Reed-Solomon (255,223) encoding, decoding, and bit synchronization, providing Consultative Committee for Space Data Systems (CCSDS) and Near Earth Network (NEN) telemetry protocol compatibility. The transceiver accepts data from the onboard flight computer via a source synchronous RS422 interface. NASA's second-generation full duplex SDR, known as PULSAR (programmable ultra-lightweight system-adaptable radio, Figures 1 and 2 below) incorporates command receiver and telemetry transmitters, as well as updated processing and power capabilities. An S-band command receiver offers a max uplink data rate of 300 Kbps and built-in QPSK demodulation. X- and S-Band telemetry transmitters offer a max downlink data rate of 150 Mbps and flexible forward-error correction (FEC) using Reed-Solomon encoding (LDPC rate 7/8 and 1/2 convolution in development), and it uses QPSK modulation. The use of FEC adds an order of magnitude increase in telemetry throughput due to an improved coding gain. An onboard FPGA uses high-speed logic for uplink/downlink and encoding/decoding processes. Balloon flight testing has been conducted and is ongoing for PULSAR.

Langley has developed various technologies to enable the portable detection system, including: - 3-inch electret condenser microphone - unprecedented sensitivity of -45 dB/Hz - compact nonporous windscreen - suitable for replacing spatially demanding soaker hoses in current use - infrasonic calibrator for field use - piston phone with a test signal of 110 dB at 14Hz. - laboratory calibration apparatus - to very low frequencies - vacuum isolation vessel - sufficiently anechoic to permit measurement of background noise in microphones at frequencies down to a few Hz - mobile source for reference - a Helmholtz resonator that provides pure tone at 19 Hz The NASA system uses a three-element array in the field to locate sources of infrasound and their direction. This information has been correlated with PIREPs available in real time via the Internet, with 10 examples of good correlation.