Flight 15P of SpaceShipOne (X0) was the first privately funded human spaceflight. It took place on June 21, 2004. It was the fourth powered test flight of the Tier One program, with the previous three test flights reaching much lower altitudes. The flight carried only its pilot, Mike Melvill, who thus became the first non-governmental astronaut.

The first launch of the Delta IV Heavy on 21 December 2004 carried a boilerplate payload and was a partial failure. Cavitation in the liquid-oxygen propellant lines caused shutdown of both boosters eight seconds early, and the core engine nine seconds early; this resulted in a lower staging velocity for which the second stage was unable to compensate. The payload was left in a lower than intended orbit.^[1]