An Overview of the BAE Systems R1 Mission to Develop and Demonstrate Hyperspectral RF Radiometer Technology

An Overview of the BAE Systems R1 Mission to Develop and Demonstrate Hyperspectral RF Radiometer Technology

David Newell,

BAE Systems, Boulder, Colorado, USA

1. Introduction

BAE Systems is conducting a mission, known as R1, on the International Space Station (ISS) which includes a hyperspectral radiometer named the Full Atmosphere Sounding Radiometer (FASTER). The R1 mission is demonstrating key next-generation radiometer technologies including hyperspectral sampling at the oxygen absorption lines from 55 to 58 GHz. This frequency range was selected because this hyperspectral data provides significant improvements in the Atmospheric Vertical Temperature Profile (AVTP) Environmental Data Records (EDRs) when compared to heritage discrete channel instruments like ATMS and SSMIS [1]. This paper gives an overview of the R1 mission and the FASTER instrument. On-orbit performance is also summarized with direct comparisons to heritage instruments.

BAE Systems has multiple space microwave radiometers currently in operation including GMI [2] and is continuing to develop next-generation radiometers to support upcoming mission. One of the key technologies identified for these next-generation missions is hyperspectral radiometry. The R1 mission is an internally funded activity to develop and demonstrate a CubeSat-compatible hyperspectral radiometer and advance the technology readiness level (TRL) of this hardware through space operation.

The R1 mission was executed through the BAE Systems Agile-Space organization. The Agile-Space organization leverages standard BAE components, commercial space products along with optimized processes to allow faster and lower cost developments of high-quality space hardware. Using these processes the FASTER radiometer was designed, built and tested, RF-in to digital-counts-out, in 12 months. This included comprehensive FASTER-level performance and environmental testing. The entire R1 payload was shipped to Airbus 23 months after program start.

2. R1 Mission Overview

The R1 mission is hosted on the Airbus Bartolomeo platform, attached to the European Columbus Module of the International Space Station (ISS). The R1 hardware was integrated at BAE Systems and underwent comprehensive environmental testing and instrument calibration. The R1 payload was then provided to Airbus. After end-to-end testing at Airbus the payload was launched onboard the CRS-30 Cargo mission to the ISS in March of 2024. Final installation on the Bartolomeo platform and the start of operational measurements is scheduled for August of 2024. The instrument is scheduled for one year of operation.

3. FASTER Instrument Overview

The R1 mission is demonstrating a hyperspectral radiometer with the FASTER instrument. The FASTER instrument is a hyperspectral radiometer sampling the oxygen absorption line from 55 to 58 GHz. The FASTER instrument is made up of an antenna, receiver, and the digital receiver. The antenna is a fixed lensed feed providing 60 km sampling from the ISS orbit. The fixed lensed feed was chosen to meet the delivery schedule and cost constraints of the R1 mission.

The RF front end is provided by L3Harris, a longtime teammate of BAE Systems on multiple flight missions including GMI. The RF front end covers the frequency range from 51 to 59 GHz. The incoming RF signal is amplified and down converted to an Intermediate frequency (IF) with multiple IF output channels provided. For the R1 mission only one IF channel was fully populated providing the frequency band from 55-58 GHz to the digital receiver.

The digital receiver is a commercial-space Advanced Data Converter Module (ADCM) from Trident. The Trident ADCM is made up of two cards: a Xilinx ZU19EG Multi-Processor System on Chip (MPSoC) based Ultra Digital Radar Transceiver (UDRT) base card and a high-speed RF receiver mezzanine board. The mezzanine board performs RF-sampling using a high-speed Analog-to-Digital Converter (ADC). The ADCM is available with 2 ADCs but due to the delivery schedule the R1 mezzanine only has one high speed ADC. The ADC operates at 6.4 Giga samples per second providing 3.2 GHz of bandwidth.

The raw data from the ADC is ingested into the FPGA on the MPSoC. The data is converted to spectral bins, integrated and aggregated. An FFT provides 1024 output channels each with 3.125 MHz bandwidth across the entire 3.2 GHz of sampled bandwidth. In parallel, three additional FFTs are used to process higher resolution spectrums with a resolution of 97 kHz over a 100 MHz bandwidth. These finer resolution spectrums are used to sample the absorption lines near the top of the frequency range which provide response functions in the upper atmosphere.

The output of the FPGA data streams is passed to the processors on the MPSOC for further processing and formatting. FASTER outputs the data in internet protocol file sharing format compatible with the latest commercial busses.

The FASTER instrument also demonstrates advanced Radio Frequency Interference (RFI) detection and mitigation. A selectable 20 MHz bandwidth is digitally down-converted providing raw I and Q samples to the processor. This data stream is used to perform at-the-edge RFI detection and mitigation including the use of AI algorithms. The frequency range for this sampling is selectable allowing the entire input frequency range to be scanned for RFI.

4. EDR Processing and results

BAE Systems has partnered with AER to provide the EDR processing algorithms that turn the calibrated sounding measurements into AVTP EDR products. This work leverages the ongoing operational experience AER has in providing atmospheric retrieval algorithms for government customers. AER developed and tuned an algorithm to optimize the use of the FASTER hyperspectral data.

This algorithm has been used to process on-orbit data from FASTER. The ISS orbit provides roughly 10 daily intersections with polar orbiters like ATMS and SSMIS allowing for direct comparison between coincident measurements. The performance of the on-orbit data is presented along with the results of the direct comparisons to ATMS, SSMIS, NWP and other truth data. Results from the RFI detection is also presented.

5. References

[1] C. D. Kummerow et al., "Hyperspectral microwave sensors—Advantages and limitations", IEEE J. Sel. Topics Appl. Earth Observ. Remote Sens., vol. 15, pp. 764-775, Dec. 2022.

[2] Newell, D, et. al., “GPM microwave imager key performance and calibration results,” Proceedings IGARSS 2014, pp 3754 – 3757, 2014