Impact of Space radiation on Ultra-Sensitive In-Orbit IR Telescopes

This paper evaluates possible design considerations in reducing disruptions of scientific data in ultra-sensitive Infrared (IR) spaced-based telescopes by charged particles in space radiation. The particles modeled are protons, alphas, and heaver ions with an atomic number as high as that of iron. Performance results of proposed designs are based on a model developed at Boeing. The components modeled are the energy spectra of the ion species in cosmic rays and solar flares, the transport of the primary ions and any secondary particles produced including neutrons, the generation electron hole pairs (EHPs) by the particles passing through the focal point array (FPA), and the spread of the charge through neighboring pixels. The results show noise levels between 100 and 10000 electrons per pixel in stressing environments. IR telescopes now have a noise level as low as 100 electrons per pixel making the analysis results significant. The analysis results indicate secondary ionization alone can exceed the noise threshold of 100 e/pixel. Measures that reduced the number of electrons per pixel below the threshold given are discussed. The model can be used in selecting or de-selecting designs that potentially reduce radiation induced charging of focal point arrays before implementation.