Energy Altitude Predictor

During the test flight, the TONU displayed a readout from the energy altitude predictor during the boost phase. Developed by aerodynamicist Jim Tighe, it worked by making calculations based on factors like SpaceShipOne"s speed and thrust. The pilot used this to decide when to turn off the rocket engine because SpaceShipOne was roughly half the distance to apogee after rocket-engine shutdown. For the second half, it coasted the rest of the way up.

The pilot needed a way to ensure he didn’t run the rocket engine too long or too short. The initial powered flights relied on a timer, but using the energy altitude predictor yielded much better results. By looking at the readout of the energy altitude predictor, the pilot had a very good idea of the altitude SpaceShipOne would reach if the rocket engine shut down at that exact moment.

For example, the energy altitude predictor may have read 200,000 feet (60,960 meters), but in actuality, SpaceShipOne may have only been at an altitude of 80,000 feet (24,380 meters). So, if

SpaceShipOne shut down the rocket engine at that precise moment, it would coast to an apogee of about 200,000 feet (60,960 meters). This would be 128,000 feet (39,010 meters) short of the Ansari X Prize requirement. Therefore, the pilot wouldn’t have shut down the rock­et engine at this point, but he would have waited until the energy alti­tude predictor read at least 328,000 feet (100,000 meters).