Air-launch-to-orbit

Air-launch-to-orbit (ALTO) is the method of launching smaller rockets at altitude from a heavier conventional horizontal-takeoff aircraft, to carry satellites to low Earth orbit.

In 2004 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.

The principal advantage of a rocket being launched by a high-flying airplane is that it need not fly through the lower, denser atmosphere, whose drag requires a considerable[1] amount of extra work to overcome.

Rockets launched from high altitude can be optimized for lower ambient pressure, thus achieving greater thrust over the entire operating regime.

[2] Air-launch-to-orbit also serves as alternative if conditions do not allow launching a rocket vertically from ground to orbit due to certain reasons, such as natural disasters (earthquakes, tsunamis, floods and volcanic eruptions).