liquid sprayed into the shock layer, or passed through channels in the heat shield. Advantages included the possibility of more all-metal designs which would be cheaper to develop, be more rugged, and eliminate the need for classified and unknown technology. The disadvantages are increased weight and complexity, and lower reliability. The concept has never been flown, but a similar technology (the plug nozzle) did undergo extensive ground testing. Propulsive entry Fuel permitting, nothing prevents a vehicle from entering the atmosphere with a retrograde engine burn, which has the double effect of slowing the vehicle down much faster than atmospheric drag alone would, and forcing the compressed hot air away from the vehicle's body. During reentry, the first stage of the SpaceX Falcon 9 performs an entry burn to rapidly decelerate from its initial hypersonic speed. Feathered entry In 2004, aircraft designer Burt Rutan demonstrated the feasibility of a shape-changing airfoil for reentry with the sub-orbital SpaceShipOne. The wings on this craft rotate upward into the feathered configuration that provides a shuttlecock effect. Thus SpaceShipOne achieves much more aerodynamic drag on reentry while not experiencing significant thermal loads. The configuration increases drag, as the craft is now less streamlined and results in more atmospheric gas particles hitting the spacecraft at higher altitudes than otherwise. The aircraft thus slows down more in higher atmospheric layers which is the key to efficient reentry. Secondly, the aircraft will automatically orient itself in this state to a high drag attitude. However, the velocity attained by SpaceShipOne prior to reentry is much lower than that of an orbital spacecraft, and engineers, including Rutan, recognize that a feathered reentry technique is not suitable for return from orbit. On 4 May 2011, the first test on the SpaceShipTwo of the feathering mechanism was made during a glideflight after release from the White Knight Two. Premature deployment of the feathering system was responsible for the 2014 VSS Enterprise crash, in which the aircraft disintegrated, killing the co-pilot. The feathered reentry was first described by Dean Chapman of NACA in 1958. In the section of his report on Composite Entry, Chapman described a solution to the problem using a high-drag device: Inflatable heat shield entry Deceleration for atmospheric reentry, especially for higher-speed Mars-return missions, benefits from maximizing "the drag area of the entry system. The larger the diameter of the aeroshell, the bigger the payload can be." An inflatable aeroshell