The Spacelab XRT, developed by the University of Birmingham, used a coded mask technique to make images. The instrument consisted of 2 co-aligned telescopes mounted together on an alt- azimuth system carried in the Space Shuttle payload bay. The main elements of each telescope were a gold coated coded mask in which the opaque elements occupied ∼50% of the mask area, supported about 3 m from a position sensitive proportional counter. The 2 masks had different sized holes, producing different angular resolutions of the sky. The higher resolution telescope was used to make detailed studies of the brighter sources and the other telescope was used to look at fainter regions of diffuse emission.