Air launch to orbit
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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 A low Earth orbit (LEO) is an geocentric orbit, orbit around Earth with a orbital period, period of 128 minutes or less (making at least 11.25 orbits per day) and an orbital eccentricity, eccentricity less than 0.25. Most of the artificial object ...
. It is a follow-on development of air launches of
experimental aircraft An experimental aircraft is an aircraft intended for testing new aerospace technologies and design concepts. The term ''research aircraft'' or '' testbed aircraft'', by contrast, generally denotes aircraft modified to perform scientific studies, ...
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, cost of the rocket, geographical factors, and natural disasters. Air launching has also been developed for sub-orbital
spaceflight Spaceflight (or space flight) is an application of astronautics to fly objects, usually spacecraft, into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such ...
. In 2004 the Ansari X Prize $10 Million purse was won by a team led by Burt Rutan's
Scaled Composites Scaled Composites (often called simply Scaled) is an American aerospace company founded by Burt Rutan and currently owned by Northrop Grumman. It is located at the Mojave Air and Space Port in Mojave, California, United States. Founded to d ...
, launching the
SpaceShipOne SpaceShipOne is an experimental air launch, air-launched rocket-powered aircraft with sub-orbital spaceflight capability at speeds of up to / using a hybrid rocket motor. The design features a unique "Feathering (reentry), feathering" atmosph ...
from the purpose-built White Knight carrier aircraft. The first air-launch-to-orbit was a test launch of the
ASM-135 ASAT The ASM-135 ASAT is an air-launched anti-satellite multistage missile that was developed by Ling-Temco-Vought's LTV Aerospace division. The ASM-135 was carried exclusively by United States Air Force (USAF) F-15 Eagle fighter aircraft. The pro ...
antisatellite rocket, the first commercial air-launch-to-orbit took place on 5 April 1990 with a Northrop Grumman Pegasus.


Advantages

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 amount of extra work to overcome. Higher densities at lower altitudes result in larger drag forces acting on the vehicle. In addition, thrust is lost due to over-expansion of the exhaust at high ambient pressure and under-expansion at low ambient pressure; a fixed nozzle geometry cannot provide optimal exhaust expansion over the full range of ambient pressure, and represents a compromise solution. Rockets launched from high altitude can be optimized for lower ambient pressure, thus achieving greater thrust over the entire operating regime. Propellant is conserved because the air-breathing carrier aircraft lifts the rocket to altitude much more efficiently. Airplane engines do not require on-board storage of an oxidizer, and they can use the surrounding air to produce thrust, such as with a
turbofan A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a combination of references to the preceding generation engine technology of the turbojet and the add ...
. 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. 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-to-orbit also works well as part of a combination launch system such as a reusable air-launched single-stage-to-skyhook launch vehicle powered by a rocket or jet engine. An additional benefit of air-launch-to-orbit is a reduced delta V needed to achieve orbit. This results in a greater payload to fuel ratio which reduces the cost per kilogram to orbit. To further leverage the delta V advantage, supersonic air-launch-to-orbit has been proposed. 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).


Disadvantages

According to '' Aviation Week and Space Technology'', air-launch-to-orbit is limited by aircraft size. Additionally, airplanes may generate large lateral forces which could damage payloads.


Air launch systems

Operational: *
Northrop Grumman Innovation Systems Orbital ATK Inc. was an American aerospace manufacturer and defense industry company. It was formed in February 9, 2015 from the merger of Orbital Sciences Corporation and parts of Alliant Techsystems (ATK). Orbital ATK designed, built, and deli ...
(originally Orbital Sciences, then Orbital ATK, since 2018 Northrop) Pegasus Retired: *
ASM-135 ASAT The ASM-135 ASAT is an air-launched anti-satellite multistage missile that was developed by Ling-Temco-Vought's LTV Aerospace division. The ASM-135 was carried exclusively by United States Air Force (USAF) F-15 Eagle fighter aircraft. The pro ...
(anti-satellite system) * NOTS-EV-1 Pilot * Virgin Orbit LauncherOne Under development: *
Stratolaunch Stratolaunch LLC is a private American aerospace company providing high-speed flight test services. It was founded in 2011 to develop a new air-launched space transportation system, with its corporate headquarters in Seattle. The company and ...
* CubeCab *
ARCASPACE Romanian Cosmonautics and Aeronautics Association (), also known as ARCAspace, is an aerospace company based in Râmnicu Vâlcea, Romania. It builds rockets, high-altitude balloons, and UAV, unmanned aerial vehicles. It was founded in 1999 as a ...
ARCA Space
Haas Orbital Rocket Launcher
fact sheet, Dec. 2, 2008 (accessed 22 Sept 2014)
* Generation Orbit Launch Services - contracted for NASA NEXT * NASA Armstrong Flight Research Center Towed Glider Air-Launch System * CDTI,
CNES CNES () is the French national space agency. Headquartered in central Paris, the agency is overseen by the ministries of the Armed Forces, Economy and Finance and Higher Education, Research and Innovation. It operates from the Toulouse Spac ...
, DLR Aldebaran (rocket) * Antonov, Aerospace Industry Corporation of China Antonov An-225 Mriya *Orbit Boy microsatellite air-launch system Proposed: * Vulcan Aerospace 75-percent-scaled Dream Chaser crew-carrying spaceplane with rocket by Orbital Sciences * (proposed by
Ukraine Ukraine is a country in Eastern Europe. It is the List of European countries by area, second-largest country in Europe after Russia, which Russia–Ukraine border, borders it to the east and northeast. Ukraine also borders Belarus to the nor ...
) * (proposed by
Ukraine Ukraine is a country in Eastern Europe. It is the List of European countries by area, second-largest country in Europe after Russia, which Russia–Ukraine border, borders it to the east and northeast. Ukraine also borders Belarus to the nor ...
) Abandoned projects: *
DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adva ...
ALASA * AirLaunch LLC * MAKS * IshimRussia, Kazakhstan to develop unique space system
: "Ukrainian experts moved to develop the Svityaz system based on the
An-225 The Antonov An-225 Mriya (; NATO reporting name: Cossack) was a large strategic airlift cargo aircraft designed and produced by the Antonov, Antonov Design Bureau in the Soviet Union. It was originally developed during the 1980s as an enlarged ...
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."
* * Orbital Sciences Pegasus II – contracted design/build for Stratolaunch Systems * Swiss Space Systems SOAR * XCOR Aerospace Lynx Mark III * Falcon 9 Air Developed 2011-2012, In partnership between
SpaceX Space Exploration Technologies Corp., commonly referred to as SpaceX, is an America, American space technology company headquartered at the SpaceX Starbase, Starbase development site in Starbase, Texas. Since its founding in 2002, the compa ...
and Stratolaunch systems


See also

* NOTS-EV-1 Pilot * NOTS-EV-2 Caleb * Buoyant space port * Rockoon * Launch vehicle types by launch platform * Black Horse (rocket) * Rocketplane XS


References


External links

{{commons category-inline
A Study of Air Launch Methods for RLVs
(AIAA 2001-4619)
Low Cost Launch of Payloads to Low Earth Orbit Illini Space Jet
Rocketry Space access