Tail-Cone Box

Several experiments needed to view the sky behind the X-15, so NASA decided to build a "tail­cone box" behind the upper vertical stabilizer. In September 1961, NASA asked North American to investigate whether the installation would have an adverse effect on the aerodynamic stability of the airplane, and after a brief analysis the company concluded that none was expected. North American began detailed engineering for the box on 10 August 1962, with fabrication expected to take about two months. The program often referred to these as "boat-tail" boxes.[60]

Tail-Cone Box

Several experiments needed to view the sky behind the X-15 so NASA decided to build a "tail­cone box" behind the upper vertical stabilizer. This is the Phase II MIT Apollo Horizon Experiment (#17) on X-15-1. NASA procured two different types of boxes and installed them on the airplanes as needed to support the specific experiment manifested for a particular flight. The first style of box was equipped with a stabilized platform that allowed precise aiming of the experiment. The second style was a "lightweight" box used for experiments that did not require the stabilized platform. Both X-15-1 and X-15-3 ultimately included the capability to carry the tail-cone box. The rebuilt X-15A-2 sported a very similar protuberance, but in this case, the box housed a spherical helium tank that provided additional pressurization gas for the propellant system.

(NASA)

The box, which was located immediately behind the upper speed brakes, was the same width as the vertical stabilizer, as high as the speed brakes, and protruded aft to the extreme rear of the fuselage. It was closed on the sides and top, but open on the back to allow the instruments to view behind the airplane. The Inconel X structure provided no environmental control (temperature or pressurization) for the experiments it housed. NASA procured two different types of boxes and installed them on the airplanes as needed to support the specific experiment manifested for a particular flight. The first style of box was equipped with a stabilized platform that allowed precise aiming of the experiment. This box could also be equipped with a removable panel that covered the rear opening during the exit phase to prevent exhaust efflux from contaminating the experiment. The second style was a "lightweight" box used for experiments that did not require the stabilized platform. Both X-15-1 and X-15-3 ultimately included the capability to carry the tail-cone box. The rebuilt X-15A-2 sported a very similar protuberance, but in this case the box housed a spherical helium tank that provided additional pressurization gas for the propellant system.^