Air launch to orbit
Encyclopedia
Air launch to orbit is the method of launching rocket launch vehicle
s at altitude from a horizontal-takeoff turbojet aircraft, either subsonic
or supersonic
. 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
.
The main advantage realized by the Pegasus air launch system, currently the only orbital air launch provider, is flexibility. 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. Other advantages include reduced national range scheduling constraints, minimum launch site requirements, and reduced range, safety concerns, and equatorial launch from the US
One advantage of air launching is the considerable amount of propellant
conserved. This is because the carrier aircraft
is able lift the rocket to altitude much more efficiently with use of turbojet engines, which 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 overall size. A larger fraction of the rocket mass can then include payload, thus 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 delta V required to reach orbit. Figure 1 below indicates that high speeds can reduce delta V requirements up to 15% over the vertical launch case.
Cost calculations show that a supersonic air launch system has the potential to reduce launch costs over conventional vertical takeoff vehicles by an order of magnitude
. Launch cost can be shown to be proportional to the peak power of the rocket engines, as given by the empirical relation:
Peak power at maximum thrust is expressed as:
where horizontal
is related to the initial launch acceleration, 
is the mass placed in low earth orbit, and
.
for the space shuttle
and Saturn V
Apollo moon rocket are 1.49 and 1.43 respectively. For an air launch with a climb angle of 30 degrees this number can be as low as 1.00. Figures 2 and 3 provide a comparison of launch costs versus thrust power for several launch vehicles.
4.0. Figure 4 shows the cost per kilogram in orbit versus system specific impulse and delta V. The figure indicates that launch cost to low Earth orbit
per kilogram is far more dependent on delta V requirements than on system specific impulse.
Air Launch to orbit is being explored on sub-scale turbojet-powered aircraft. Currently, a 1/10 scale subsonic model, with a 1/10 scale Falcon 1 rocket mounted on the upper side of the fuselage is being used to investigate the feasibility of an air launch to orbit system.
Ballon-based:
Launch vehicle
In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....
s at altitude from a horizontal-takeoff turbojet aircraft, either subsonic
Subsonic aircraft
A subsonic aircraft is an aircraft with a maximum speed less than the speed of sound ....
or supersonic
Supersonic aircraft
A supersonic aircraft is designed to exceed the speed of sound in at least some of its normal flight configurations.-Overview:The great majority of supersonic aircraft today are military or experimental aircraft...
. This method, when employed for orbital payload insertion, presents significant advantages over conventional vertical rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
launches, particularly because of the reduced mass, thrust and cost of the rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
.
The main advantage realized by the Pegasus air launch system, currently the only orbital air launch provider, is flexibility. Air launch to orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
offers the potential for aircraft-like operations such as launch on demand, and is also less subject to launch-constraining weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
. This allows the aircraft to fly around weather conditions as well as fly to better launch points. Other advantages include reduced national range scheduling constraints, minimum launch site requirements, and reduced range, safety concerns, and equatorial launch from the US
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
One advantage of air launching is the considerable amount of propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
conserved. This is because the carrier aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
is able lift the rocket to altitude much more efficiently with use of turbojet engines, which 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 overall size. A larger fraction of the rocket mass can then include payload, thus 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 delta V required to reach orbit. Figure 1 below indicates that high speeds can reduce delta V requirements up to 15% over the vertical launch case.
Cost calculations show that a supersonic air launch system has the potential to reduce launch costs over conventional vertical takeoff vehicles by an order of magnitude
Order of magnitude
An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
. Launch cost can be shown to be proportional to the peak power of the rocket engines, as given by the empirical relation:
Peak power at maximum thrust is expressed as:
where horizontal
is related to the initial launch acceleration, is the mass placed in low earth orbit, and. for the space shuttleSpace Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
and Saturn V
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...
Apollo moon rocket are 1.49 and 1.43 respectively. For an air launch with a climb angle of 30 degrees this number can be as low as 1.00. Figures 2 and 3 provide a comparison of launch costs versus thrust power for several launch vehicles.
Supersonic air launch
By providing an initial supersonic speed to the rocket, the delta V required to reach orbit can be significantly reduced over the subsonic case. Referring again to Figure 3 shows that for a horizontal air launch at 30 degrees inclination, the delta V reduction can be as much as 25% for an air launch at MachMach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
4.0. Figure 4 shows the cost per kilogram in orbit versus system specific impulse and delta V. The figure indicates that launch cost to low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
per kilogram is far more dependent on delta V requirements than on system specific impulse.
Air Launch to orbit is being explored on sub-scale turbojet-powered aircraft. Currently, a 1/10 scale subsonic model, with a 1/10 scale Falcon 1 rocket mounted on the upper side of the fuselage is being used to investigate the feasibility of an air launch to orbit system.
List of air-based launchers
Aircraft based:- Pegasus (rocket)
- AirLaunch LLCAirLaunch LLCAirLaunch LLC was an aerospace design and development company headquartered in Kirkland, Washington. They hope to provide launch services for launching payloads into orbits around the Earth. This is to be realized through a method called air launch where a rocket is carried within an aircraft and...
- SpaceShipTwo (suborbital, cannot reach orbit)
Ballon-based:
- ARCASPACEARCASPACEAsociația Română pentru Cosmonautică și Aeronautică or Romanian Cosmonautics and Aeronautics Association is a non-governmental organization that promotes aerospace projects as well as other space-related activities...
- RockoonRockoonA rockoon is a solid fuel sounding rocket that, rather than being immediately lit while on the ground, is first carried into the upper atmosphere by a gas-filled balloon, then separated from the balloon and automatically ignited...
, air launch from a high-altitude balloon
See also
- NOTS-EV-1 PilotNOTS-EV-1 PilotThe NOTS-EV-1 Pilot, also known as NOTSNIK was an expendable launch system and anti-satellite weapon developed by the United States Navy United States Naval Ordnance Test Station . Ten were launched during July and August 1958, all of which failed. It was the first air-launched rocket to be used...
- NOTS-EV-2 CalebNOTS-EV-2 CalebThe NOTS-EV-2 Caleb, also known as NOTS-500, Hi-Hoe and SIP was an expendable launch system, which was later used as a sounding rocket and prototype anti-satellite weapon. It was developed by the United States Navy Naval Ordinance Test Station as a follow-up to the NOTS-EV-1 Pilot, which had been...
- Buoyant space port
- Launch vehicle types by launch platform