Air launch

Air launching is the practice of releasing a rocket, missile, parasite aircraft or other aircraft payload from a mother ship or launch aircraft. The payload craft or missile is often tucked under the wing of the larger mother ship and then "dropped" while in flight. It may also be stored within a bomb bay, beneath the main fuselage or even on the back of the carrier aircraft, as in the case of the D-21 drone. Air launching provides several advantages over ground launching, giving the smaller craft an altitude and range boost, while saving it the weight of the fuel and equipment needed to take off on its own.

History
One of the earliest uses of air launching used an airship as a carrier and docking station for biplane parasite fighters. These planes would connect to their mothership through a trapeze-like rig, mounted to the top of the upper wing, that attached to a hook dangling from the bottom of the dirigible above. Fighters could be both launched and retrieved this way, giving the airship the speed and striking power of fixed-wing craft, while giving the fighters the range and lingering time of an airship. With advances in airplane technology, especially in range, the value of a dirigible mothership was reduced and the concept became obsolete. Nevertheless, the idea of lighter-than-air motherships for fleets of smaller aircraft remains romanticized in fiction today, in games such as Crimson Skies and Final Fantasy.

The parasite fighter concept was later revived several times, in an attempt to solve the problem of how to protect bombers from fighter attack. The Convair B-36 was used to air launch several prototype fighters for defense, but none offered performance that could match ground-launched fighters &mdash; even the largest bomber ever mass-produced was too small a mothership for the jet age &mdash; and docking presented its own problems.

Air launch is mainly used for rocket-powered craft, allowing them to conserve their fuel until lifted to altitude by a larger aircraft. The B-52 Stratofortress and B-29 Superfortress have both served in the carrier role, most famously for the X-15 and Bell X-1 respectively.

The SR-71 program attempted to launch a Lockheed D-21/M-21 drone at Mach 3.2. This is potentially far more problematic and difficult due to the shock wave pattern around an aircraft at supersonic speeds. After three reasonably successful tests, the fourth attempt to do this caused the drone to crash into the mother ship and the accident led to the drowning of a crew member. The project was abandoned.

Recently, the air launch method has gained popularity in the fledgling civilian rocket world. The Ansari X-Prize $10 Million purse was won by a team led by Burt Rutan's Scaled Composites, launching the SpaceShipOne from the purpose-built White Knight carrier aircraft. Another company, AirLaunch LLC is developing the QuickReach small satellite launch system, which will deploy a rocket in-flight from the cargo bay of an unmodified C-17 aircraft.

Most recently, the B-52 was used to launch the X-43 hypersonic testbed aircraft. The Pegasus rocket is an air-launched orbital spacecraft, flown from a Lockheed L-1011.