Air launch to orbit
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Air launch to orbit is the method of launching rockets at altitude from a conventional horizontal-takeoff aircraft, to carry satellites to low earth orbit. It is a follow-on development of air launches of experimental aircraft that began in the late 1940s. This method, when employed for orbital payload insertion, presents significant advantages over conventional vertical rocket launches, particularly because of the reduced mass, thrust and cost of the rocket.
Air launching is also being developed for sub-orbital spaceflight. 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 low, dense atmosphere, the drag of which requires a considerable amount of extra work and thus mass of propellant. Higher densities at lower altitudes result in larger drag forces acting on the vehicle, and higher pressures (back pressure at nozzle exit plane) reduce thrust and specific impulse overall. Propellant is conserved because the air-breathing carrier aircraft lifts the rocket to altitude much more efficiently with the use of engines that do not require onboard storage of an oxidizer. This allows the launch system to conserve a significant amount of mass that would otherwise be reserved for fuel, reducing the overall size. A larger fraction of the rocket mass can then include payload, reducing payload launch costs.
Launching at altitude also presents significant performance benefits to the rocket. The high horizontal speed provided by the aircraft gives the rocket a large initial velocity and reduces the amount of "effort" (delta-V) that is needed to reach orbit. If the carrier aircraft is capable of providing supersonic speed to the rocket, the delta-V required to reach orbit can be significantly reduced over the subsonic case. In addition, gravity (g) is slightly reduced at altitude versus the surface, further reducing delta-v, and the first stage nozzle can be optimized for low ambient pressure, improving specific impulse. It is also possible to make use of higher impulse fuels precluded from surface launches, such as those containing beryllium or fluorine, due to their toxicity.
Air launch to orbit offers the potential for aircraft-like operations such as launch on demand, and is also less subject to launch-constraining weather. This allows the aircraft to fly around weather conditions as well as fly to better launch points, and to launch a payload into any orbital inclination at any time. Insurance costs are reduced as well, because launches occur well away from land, and there is no need for a launch pad or blockhouse.
Air launch systems
- Under development
- Virgin Galactic LauncherOne
- XCOR Aerospace Lynx Mark III
- Orbital Sciences Pegasus II – contracted design/build for Stratolaunch Systems
- Virgin Galactic SpaceShipTwo (suborbital)
- Abandoned projects
- DARPA ALASA program
- NOTS-EV-1 Pilot
- NOTS-EV-2 Caleb
- Buoyant space port
- Launch vehicle types by launch platform
- Bergin, Chris (2013-05-25). "Stratolaunch and Orbital – The Height of Air Launch". NASA SpaceFlight. Retrieved 2013-05-24.
- "SpaceShipTwo.net". 2012. Retrieved 16 June 2013.
- "SpaceShipOne & White Knight". Retrieved 14 August 2013.
- Russia, Kazakhstan to develop unique space system: "Ukrainian experts moved to develop the Svityaz system based on the An-225 Mriya (Dream) Cossack jumbo transport plane and the Zenit-2 rocket", "The Ishim complex will include two MiG-31I aircraft, a three-stage launch vehicle on a streamlined store between engine nacelles, as well as an Ilyushin Il-76MD Midas surveillance plane."