Northrop is currently working in secret on a third embodiment of the T-38 aircraft, equipped with three rocket engines in the tail. This aircraft is called the Northrop "Space Trainer" and was specifically designed to train future space pilots, such as the pilots of the X-15 rocket plane.
The three rockets have enough fuel to work for about 90 minutes. In those 90 minutes, however, they will take the plane to a dizzying height. The Space Trainer would take off almost vertically from a rail system. According to the Los Angeles Times, which reported about the existence of the Space Trainer for the first time, the Pentagon needs 30-40 examples of this Space Trainer in the near future to train U.S. space pilots.
Whether this device will really be built is not known.