Soft x-ray imaging telescopes for remote observation of the magnetosphere

X-ray astronomers have used orbital X-ray telescopes since the 1970s to observe some of the hottest and most violent regions of the universe: galactic halos, and clusters of galaxies, supernova and their remnants, the accretion disks in black hole binaries or the supper-massive black holes powering active galactic nuclei. X-ray emission from these objects is highly diagnostic yielding information on the temperature, composition, velocity structure of the emitting plasma, and to measure the state of the intervening matter. In the 1990s, it was discovered that the earth's exosphere also glows strongly in soft X-rays (< 1 keV) where it interacts with the highly ionized solar wind. This allows time-resolved remote imaging of the entire magnetosphere. Multiple missions are currently in development (CuPID, LEXI, SMILE) or proposed (STORM) to use soft X-ray emission to trace the dynamics of solar wind plasma in the dayside magnetosheath. Traditional X-ray telescopes are very large, massive, and expensive, having narrow fields of view and are thus ill-suited for large scale magnetospheric imaging. In this presentation, we discuss the technology underlying current and future wide field of view X-ray telescopes for magnetospheric imaging and the scaling rules that govern optimizing the technology for a typical multi-instrument heliophysics spacecraft.