Detectability Analysis of Low Earth Orbital Infrared Detectors for Near Space Hypersonic Targets

Using the infrared detector of the STSS LEO demo satellite as an example, the detectability of aerial hypersonic targets such as AGM-183A was analyzed. To visually compare the detectability of the targets under different conditions, the number of pixels on the focal plane with output signal-to-noise ratio (SNR) higher than a specified threshold was quantified. First, the aerodynamic temperature and spectral radiant energy of the hypersonic target were calculated. The infrared detector model was used to predict the peak value of the SNR and the number of responding pixels in the focal plane for specified detection distances and angles. The analysis results indicate that in the sub-satellite point detection mode, the SNR of the focal plane reaches the highest value (335), and the number of responding pixels with SNR higher than the threshold (6) reaches its maximum(54×54), representing the maximum detectability of the LEO detector for AGM-183A targets. In the edge detection mode, the variation in target detectability with detection angle and target temperature was calculated. The results show that, when the target temperature approaches 800 K and the detection azimuth angle ψ is less than 10° (or greater than 170°), the number of responding pixels on the focal plane reaches the lowest value of 4×4, indicating that the AGM-183A target detectability approaches the theoretical limit of the LEO detector (3×3). By comparison, changes in the target temperature have a more substantial impact on target detectability. In edge detection mode, the escape probability of the target is relatively high when the target uses active cooling to reduce its surface aerodynamic temperature to less than 800 K. From the perspective of improving early warning capability, the SNR threshold value of LEO detector focal plane should be increased for targets with surface temperatures approaching 800 K at the most unfavorable angles of ψ (less than 10° or greater than 170°, with the minimum number of responding pixels in the focal plane no fewer than 8×8).