The AXAF mission is built around a high resolution mirror for imaging and dispersive grating spectroscopy at x-ray wavelengths. With a "regular" telescope like a ground-based radio or optical telescope, the light comes in perpendicular to the mirror. However, X-rays hitting a mirror straight-on are absorbed rather than reflected. For focusing X-rays, the AXAF telescope utilizes grazing-incidence reflection. X-rays come in at very shallow or grazing angles nearly parallel to the mirror surface, almost like stones skipping across the surface of a pond. Under these conditions, the X-rays are reflected and focused to a sharp image.
For a given opening at the front of the spacecraft, we get more collecting area by
nesting the mirrors, putting successively smaller cylindrical shells inside
one another. AXAF will have four nested pairs, or eight pieces of glass overall.
(Figure and text courtesy of Hughes Danbury Optical Systems(HDOS). HDOS produced all twelve optical components of the HRMA)
HDOS inspectors perform a visual inspection of the P1(Paraboloid 1) optic. Paired with H1(hyperboloid 1), this set will form the outermost, and largest, of the four concentric grazing incidence mirror pairs. P1 measures 1.2 meters in diameter by one meter in length and weighs 520 pounds. The wall of the optic is only nine tenths of an inch thick. (Figure courtesy of Hughes Danbury Optical Systems(HDOS)