Current-generation solar observatories employ CCD image sensors to observe the Sun in the soft x-ray (SXR) and extreme ultraviolet (EUV) regimes. However, these observations are often compromised by pixel saturation and charge blooming in the CCD image sensors when observing large solar flares. To address these limitations, the Swift Solar Activity x-ray Imager Rocket (SSAXI-Rocket) program is developing CMOS image sensors (CIS) with low noise and high-speed readout (greater than 5Hz) for next-generation solar observatories. These CIS aim to enable the observation of large solar flares while significantly reducing the effects of pixel saturation and charge blooming. As a part of NASA’s 2024 solar flare sounding rocket campaign, the SSAXI-Rocket program demonstrated delta-doped CIS technology in a space environment by operating a novel camera as a sub-payload on board the High-Resolution Coronal Imager (Hi-C) sounding rocket. This paper describes the pre-launch laboratory tests performed with the SSAXI-Rocket CIS to characterize its linearity and soft x-ray spectral resolution.
The Swift Solar Activity X-Ray Imager (SSAXI-Rocket) sounding rocket experiment is a direct-imaging, soft Xray telescope optimized for the observation of large (GOES C class-X class) solar flares. SSAXI-Rocket has high temporal sampling cadence (> 5 Hz) enabled by a fast-readout CMOS detector. A single Wolter-1 optic focuses light onto the detector plane. The optic has a 15.8′′ half-power diameter (HPD) angular resolution on-axis and an effective area of 0.64 cm2 at 4.5 keV. The SSAXI-Rocket camera reads out a spectrally integrated signal, and the system spatial resolution is designed to be < 16′′ HPD over the instrument field of view (> 55′ × 55′). The detector is a back-illuminated delta doped CMOS (2048 × 2048 pixels) with 10 μm pitch pixels. This manuscript details our instrument design, and overviews the processes employed in telescope alignment, testing, delivery, and integration onto the Hi-C Sounding Rocket. We present the “as-built” projected flight performance of the delivered SSAXI-Rocket flight system, obtained by synthesizing the results of pre-flight subsystem testing and measurements performed during system integration and alignment.
The Swift Solar Activity X-ray Imager (SSAXI-Rocket) is a ride-along instrument to the High-Resolution Coronal Imager (Hi-C) Flare NASA sounding rocket launch campaign scheduled for the Spring 2024. In the short 5- minute rocket flight, SSAXI-Rocket will measure the soft X-ray near-peak emission phase of a large solar flare of GOES C-class or greater. The SSAXI-Rocket instrument has peak sensitivity to 10 MK solar plasma, similar to the current Hi-C flare extreme ultraviolet instruments, providing the exploration of the variability in heating and energy transport of solar flares. SSAXI-Rocket combines small X-ray focusing optic (Wolter-I) with onaxis imaging resolution of 9 arcseconds or better and high-speed readout CMOS detector, to image the flare soft X-rays at 5 hertz or faster, with minimized image saturation and pixel signal blooming. These high-time cadence measurements can help uncover the soft X-ray intensity variations which can provide constraints on the intermittent heating processes in the flare magnetic loops. SSAXI-Rocket is the testbed for technology that is planned for future heliophysics and astronomy SmallSat, CubeSat, and large satellite X-ray observatories.
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