SpaceWire-based Data Acquisition Network for the Solar Flare Sounding Rocket Experiment FOXSI-4 and FOXSI-5

TL;DR

This paper presents a SpaceWire-based data acquisition network for FOXSI-4 and FOXSI-5, addressing high-flux solar flare observations with a modular, multi-detector architecture. The authors implement FPGA-based readout boards (SPMU-001/002) and a central Formatter to standardize interconnects, enabling scalable integration of CdTe-DSDs, CMOS sensors, and Quad-Timepix3 detectors. Key results include validated high-rate throughput, real-time ground monitoring, and robust clock synchronization, with FOXSI-4 demonstrating successful solar flare imaging and FOXSI-5 extending the system for improved telemetry and startup diagnostics. The framework, along with open-source software and hardware documentation, provides a reusable template for future small-satellite and suborbital missions requiring heterogeneous detectors under resource constraints.

Abstract

We developed a SpaceWire-based data acquisition (DAQ) system for the FOXSI-4 and FOXSI-5 sounding rocket experiments, which aim to observe solar flares with high sensitivity and dynamic range using direct X-ray focusing optics. The FOXSI-4 mission, launched on April 17, 2024, achieved the first direct focusing observation of a GOES M1.6 class solar flare with imaging spectroscopy capabilities in the soft and hard X-ray energy ranges, using a suite of advanced detectors, including two CMOS sensors, four CdTe double-sided strip detectors (CdTe-DSDs), and a Quad-Timepix3 detector. To accommodate the high photon flux from a solar flare and these diverse detector types, a modular DAQ network architecture was implemented based on SpaceWire and the Remote Memory Access Protocol (RMAP). This modular architecture enabled fast, reliable, and scalable communication among various onboard components, including detectors, readout boards, onboard computers, and telemetry systems. In addition, by standardizing the communication interface and modularizing each detector unit and its associated electronics, the architecture also supported distributed development among collaborating institutions, simplifying integration and reducing overall complexity. To realize this architecture, we developed FPGA-based readout boards (SPMU-001 and SPMU-002) that support SpaceWire communication for high-speed data transfer and flexible instrument control. In addition, a real-time ground support system was developed to handle telemetry and command operations during flight, enabling live monitoring and adaptive configuration of onboard instruments in response to the properties of the observed solar flare. The same architecture is being adopted for the upcoming FOXSI-5 mission, scheduled for launch in 2026.

Figures (13)

• Figure 1: Block diagram of the SpaceWire data acquisition network and data flow in FOXSI-4 and FOXSI-5. Yellow, blue, and green boxes represent the detectors, readout FPGA boards, and CPU boards (Raspberry Pi 4B or 3B+), respectively. Arrows indicate the flow of data and commands: green dashed arrows represent the Ethernet interface, black double-headed arrows represent the UART interface, and blue arrows represent the SpaceWire interface.
• Figure 2: Pictures of the SpaceWire extension I/F board (SPMU-001-SpW), the SPMU-001 FPGA board, and the Raspberry Pi 4. All three boards can be stacked together, and the power can also be supplied directly from the SPMU-001 to Raspberry Pi 4 and SPMU-001-SpW.
• Figure 3: Formatter board stack.
• Figure 4: Header for all telemetry packets.
• Figure 5: Memory map of 128 MB SDRAM in the CdTe-DE SPMU-001