Skylight Compartment

Several of the proposed experiments needed to expose telescopes or other devices to the atmosphere at high altitudes. To accommodate this, North American devised the "skylight" modification, which consisted of a hatch that opened at high altitude to give a portion of the instrument compartment free access to the outside environment. This required the installation of pressure bulkheads around a portion of the instrument elevator to allow the lower portion of the instrument compartment that held the data recorders to remain pressurized. The proposed hatch was 18 by 12 inches, with the 18-inch dimension lengthwise of the aircraft, and a pair of 6-inch­wide doors split along the centerline to open. Several of the experiments also required a stabilized platform inside the compartment. Since the University of Wisconsin had the first experiment that needed such a platform, NASA awarded the university a contract to develop a star-tracking, gyro – stabilized platform that would replace the upper portion of the instrumentation elevator. The university estimated that this platform could be available about six months after it received the go-ahead.[62]

Several of the proposed experiments needed to expose telescopes or other devices to the atmosphere at high altitudes. To accommodate this, North American devised the "Skylight" modification that consisted of a hatch that opened at high altitude to give a portion of the instrument compartment free access to the outside environment. A skylight compartment was installed during the rebuilding of X-15A-2 and, somewhat later, on X-15-1. This is the Ultraviolet Stellar Photography Experiment (#1) on X-15A-2. (NASA)

North American anticipated that it would take about two months to perform the modification to X-15-2, with most of that time required for rerouting wiring in the instrument compartment and building the pressure bulkheads. A change order was prepared for the modification and was awaiting approval when Jack McKay’s landing accident damaged X-15-2 and put the entire effort on hold. The Air Force decided to press ahead with the skylight modification as part of rebuilding X-15-2 into the advanced configuration, but for some reason the actual implementation changed somewhat. The hatch became slightly larger, with two upward-opening doors that were 20 inches long by 8.5 inches wide. Otherwise, the changes were mostly the same as originally conceived.[63]

North American also installed a similar but slightly smaller compartment on X-15-1 in early 1966 to carry the "Western Test Range (WTR) launch-monitoring" experiment (#20). Only the WTR and MIT experiments used this X-15-1 capability.-64