Rocket sled launch
Encyclopedia
A rocket sled launch is a method of launching
space
vehicles. A rail or maglev track and a rocket or jet booster is used to accelerate a sled
holding a vehicle
up an eastward facing mountain slope. By starting 2000+ meters above sea level and accelerating to Mach 0.8 to Mach 3 or more, substantial fuel savings can be gained, allowing a single stage to orbit reusable vehicle.
For hypersonic research in general, tracks at Holloman Air force base have tested, as of 2011, small rocket sleds moving at up to Mach 8.5.
Effectively a 'sky ramp' would make the most expensive, first stage of a rocket fully reusable since the sled is returned to its starting position, to be refueled and may be reused in the order of hours after use. Present launch vehicles have performance-driven costs of thousands of dollars per kilogram of dry weight; sled launch would aim to reduce performance requirements and amortize hardware expenses over frequent, repeated launches. Designs for mountain based inclined rail 'rocket' sleds often use jet engines or rockets to accelerate the spacecraft mounted on it. Electromagnetic methods (such as Bantam, Maglifter, and StarTram
) are another technique investigated to accelerate a rocket before launch, potentially scalable to greater rocket masses and velocities than air launch
.
Maglifter study estimated that 270 m/s (Mach 0.8) launch of an ELV
rocket from a 3000 meter altitude mountain peak could increase payload to LEO
by 80% compared to the same rocket from a conventional launch pad
. Mountains of such height are available within the mainland U.S.
for the easiest logistics, or nearer to the Equator for a little more gain from Earth's rotation. Among other possibilities, a larger SSTO could be reduced in liftoff mass by 35% with such launch assist, dropping to 4 instead of 6 engines in one case considered.
At an anticipated efficiency close to 90%, electrical energy consumed per launch of a 500-ton rocket would be around 30 GJ, 8000 kilowatt hours (each kilowatt-hour costing a few cents at the current cost of electricity), aside from any additional losses in energy storage, a system with low marginal costs dominated by initial capital costs. Although a fixed site, such is estimated to provide substantial net payload increase for a high portion of the varying launch azimuths needed by different satellites, with rocket maneuvering during the early stage of post-launch ascent (an alternative to adding electric propulsion for later orbital inclination change
). Maglev guideway costs were estimated as $10 - $20 million per mile in the 1994 study, which had anticipated annual maglev maintenance costs on the order of 1% of capital costs.
(the cost of lifting fuel in a gravity well). The thinner air will reduce air resistance and allow more efficient engine geometries. Rocket nozzles have different shapes (expansion ratios) to maximize thrust at different air pressures. (Though NASA's aerospike engine
for the Lockheed Martin X-33
was designed to change geometry to remain efficient at a variety of different pressures, the aerospike engine had added weight and complexity; X-33
funding was canceled in 2001; and other benefits from launch assist would remain even if aerospike engines reached flight testing).
For example, the air is 39% thinner at 2500 meters. The more efficient rocket plume geometry and the reduced air friction allows the engine to be 5% more efficient per amount of fuel burned.
Another advantage to high altitude launches is that it eliminates the need to throttle back the engine when the "Max Q
" limit is attained. Rockets launched in thick atmosphere can go so fast that air resistance may cause structural damage. Engines are throttled back when Max Q is reached, until the rocket is high enough that they can resume full power. The Atlas V
551 gives an example of this. It reaches its Max Q at 30,000 feet. Its engine is throttled back to 60% thrust for 30 seconds. This reduced acceleration adds to the gravity drag the rocket must overcome. Additionally, space craft engines concerned with Max Q are more complex as they must be throttled during launch.
A launch from high altitude need not throttle back at Max Q as it starts above the thickest portion of the Earth's atmosphere.
Debora A. Grant and James L. Rand in: "The Balloon Assisted Launch System - A Heavy Lift Balloon" wrote: "It was established some time ago that a ground launched rocket capable of reaching 20 km would be able to reach an altitude of almost 100km if it was launched from 20km." They suggest that small rockets are lifted above the majority of the atmosphere by balloon in order to avoid the problems discussed above.
. Angled at 55 degrees to vertical, a track on a tall mountain could allow a single stage to orbit reusable vehicle with no new technology.
Non-rocket spacelaunch
Non-rocket space launch is a launch into space where some or all needed speed and altitude is provided by non-rocket means, rather than simply using conventional chemical rockets from the ground. A number of alternatives to rockets have been proposed...
space
Space
Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...
vehicles. A rail or maglev track and a rocket or jet booster is used to accelerate a sled
Sled
A sled, sledge, or sleigh is a land vehicle with a smooth underside or possessing a separate body supported by two or more smooth, relatively narrow, longitudinal runners that travels by sliding across a surface. Most sleds are used on surfaces with low friction, such as snow or ice. In some cases,...
holding a vehicle
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
up an eastward facing mountain slope. By starting 2000+ meters above sea level and accelerating to Mach 0.8 to Mach 3 or more, substantial fuel savings can be gained, allowing a single stage to orbit reusable vehicle.
For hypersonic research in general, tracks at Holloman Air force base have tested, as of 2011, small rocket sleds moving at up to Mach 8.5.
Effectively a 'sky ramp' would make the most expensive, first stage of a rocket fully reusable since the sled is returned to its starting position, to be refueled and may be reused in the order of hours after use. Present launch vehicles have performance-driven costs of thousands of dollars per kilogram of dry weight; sled launch would aim to reduce performance requirements and amortize hardware expenses over frequent, repeated launches. Designs for mountain based inclined rail 'rocket' sleds often use jet engines or rockets to accelerate the spacecraft mounted on it. Electromagnetic methods (such as Bantam, Maglifter, and StarTram
StarTram
StarTram is a proposal for a maglev space launch system. The initial Generation 1 facility would be cargo only, launching from a mountain peak at 3 km to 7 km altitude with an evacuated tube staying at local surface level, raising ≈150,000 tons to orbit annually...
) are another technique investigated to accelerate a rocket before launch, potentially scalable to greater rocket masses and velocities than air launch
Air launch
Air launching is the practice of dropping a parasite aircraft, rocket, or missile from a mothership. The parasite aircraft or missile is usually tucked under the wing of the larger mothership and then "dropped" from underneath the wing while in flight...
.
Overview of the problem
NASA studies have shown that the Space Shuttle uses more than a third of its fuel just to reach 1000 mph (Mach 1.3). If a rocket was already moving Mach 1.3 or faster at launch, with corresponding reduced propellant needs, a greater fraction of liftoff mass could be payload and hardware.An example
Due to factors including the exponential nature of the rocket equation and higher propulsive efficiency than if a rocket takes off stationary, a NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Maglifter study estimated that 270 m/s (Mach 0.8) launch of an ELV
Expendable launch system
An expendable launch system is a launch system that uses an expendable launch vehicle to carry a payload into space. The vehicles used in expendable launch systems are designed to be used only once , and their components are not recovered for re-use after launch...
rocket from a 3000 meter altitude mountain peak could increase payload to LEO
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...
by 80% compared to the same rocket from a conventional launch pad
Launch pad
A launch pad is the area and facilities where rockets or spacecraft lift off. A spaceport can contain one or many launch pads. A typical launch pad consists of the service and umbilical structures. The service structure provides an access platform to inspect the launch vehicle prior to launch....
. Mountains of such height are available within the mainland U.S.
Mountain peaks of the United States
This article comprises three sortable tables of the major mountain peaks of the United States of America.Topographic elevation is the vertical distance above the reference geoid, a precise mathematical model of the Earth's sea level as an equipotential gravitational surface...
for the easiest logistics, or nearer to the Equator for a little more gain from Earth's rotation. Among other possibilities, a larger SSTO could be reduced in liftoff mass by 35% with such launch assist, dropping to 4 instead of 6 engines in one case considered.
At an anticipated efficiency close to 90%, electrical energy consumed per launch of a 500-ton rocket would be around 30 GJ, 8000 kilowatt hours (each kilowatt-hour costing a few cents at the current cost of electricity), aside from any additional losses in energy storage, a system with low marginal costs dominated by initial capital costs. Although a fixed site, such is estimated to provide substantial net payload increase for a high portion of the varying launch azimuths needed by different satellites, with rocket maneuvering during the early stage of post-launch ascent (an alternative to adding electric propulsion for later orbital inclination change
Orbital inclination change
Orbital inclination change is an orbital maneuver aimed at changing the inclination of an orbiting body's orbit. This maneuver is also known as an orbital plane change as the plane of the orbit is tipped. This maneuver requires a change in the orbital velocity vector at the orbital nodes Orbital...
). Maglev guideway costs were estimated as $10 - $20 million per mile in the 1994 study, which had anticipated annual maglev maintenance costs on the order of 1% of capital costs.
Benefits of high altitude launches
Rocket sled launch helps a vehicle gain altitude, and proposals commonly involve the track curving up a mountain. Advantages to any launch system that starts from high altitudes include reduce gravity dragGravity drag
In astrodynamics and rocketry, gravity drag is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field...
(the cost of lifting fuel in a gravity well). The thinner air will reduce air resistance and allow more efficient engine geometries. Rocket nozzles have different shapes (expansion ratios) to maximize thrust at different air pressures. (Though NASA's aerospike engine
Aerospike engine
The aerospike engine is a type of rocket engine that maintains its aerodynamic efficiency across a wide range of altitudes through the use of an aerospike nozzle. It is a member of the class of altitude compensating nozzle engines. A vehicle with an aerospike engine uses 25–30% less fuel at low...
for the Lockheed Martin X-33
Lockheed Martin X-33
The Lockheed Martin X-33 was an unmanned, sub-scale technology demonstrator suborbital spaceplane developed in the 1990s under the U.S. government-funded Space Launch Initiative program. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was planned to be a...
was designed to change geometry to remain efficient at a variety of different pressures, the aerospike engine had added weight and complexity; X-33
Lockheed Martin X-33
The Lockheed Martin X-33 was an unmanned, sub-scale technology demonstrator suborbital spaceplane developed in the 1990s under the U.S. government-funded Space Launch Initiative program. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was planned to be a...
funding was canceled in 2001; and other benefits from launch assist would remain even if aerospike engines reached flight testing).
For example, the air is 39% thinner at 2500 meters. The more efficient rocket plume geometry and the reduced air friction allows the engine to be 5% more efficient per amount of fuel burned.
Another advantage to high altitude launches is that it eliminates the need to throttle back the engine when the "Max Q
Max Q
In aerospace engineering, the maximum dynamic pressure, often referred to as maximum Q or max Q, is the point at which aerodynamic stress on a vehicle in atmospheric flight is maximized...
" limit is attained. Rockets launched in thick atmosphere can go so fast that air resistance may cause structural damage. Engines are throttled back when Max Q is reached, until the rocket is high enough that they can resume full power. The Atlas V
Atlas V
Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...
551 gives an example of this. It reaches its Max Q at 30,000 feet. Its engine is throttled back to 60% thrust for 30 seconds. This reduced acceleration adds to the gravity drag the rocket must overcome. Additionally, space craft engines concerned with Max Q are more complex as they must be throttled during launch.
A launch from high altitude need not throttle back at Max Q as it starts above the thickest portion of the Earth's atmosphere.
Debora A. Grant and James L. Rand in: "The Balloon Assisted Launch System - A Heavy Lift Balloon" wrote: "It was established some time ago that a ground launched rocket capable of reaching 20 km would be able to reach an altitude of almost 100km if it was launched from 20km." They suggest that small rockets are lifted above the majority of the atmosphere by balloon in order to avoid the problems discussed above.
Compatibility with reusable launch vehicles
Rocket sleds at China Lake testing ground have reached Mach 4 while carrying 60,000 kg masses. A sled track that gave a Mach 2 or greater launch assist could reduce the fuel to orbit by 40% or more, while helping counter the weight penalty when aiming to make a fully reusable launch vehicleReusable launch system
A reusable launch system is a launch system which is capable of launching a launch vehicle into space more than once. This contrasts with expendable launch systems, where each launch vehicle is launched once and then discarded.No true orbital reusable launch system is currently in use. The...
. Angled at 55 degrees to vertical, a track on a tall mountain could allow a single stage to orbit reusable vehicle with no new technology.
Rocket sled launches in fiction
- Robert A. HeinleinRobert A. HeinleinRobert Anson Heinlein was an American science fiction writer. Often called the "dean of science fiction writers", he was one of the most influential and controversial authors of the genre. He set a standard for science and engineering plausibility and helped to raise the genre's standards of...
used a lunar maglev launcher in The Moon is a Harsh MistressThe Moon Is a Harsh MistressThe Moon Is a Harsh Mistress is a 1966 science fiction novel by American writer Robert A. Heinlein, about a lunar colony's revolt against rule from Earth....
. One on Earth was built by the novel's end. - Dean IngDean IngDean Ing is an American author, who usually writes in the science fiction and techno-thriller genres.Dean Charles Ing was formerly a member of the United States Air Force, an aerospace engineer, and a university professor who holds a doctorate in communications theory. He has been a professional...
used a similar system in his 1988 novel "The Big Lifters". - Fireball XL5Fireball XL5Fireball XL5 is a science fiction-themed children's television show following the missions of spaceship Fireball XL5, commanded by Colonel Steve Zodiac of the World Space Patrol...
was launched on a sled from sea level. - When Worlds Collide (film)When Worlds Collide (film)When Worlds Collide is a 1951 science fiction film based on the 1933 novel co-written by Philip Gordon Wylie and Edwin Balmer. The film was shot in Technicolor, directed by Rudolph Maté and was the winner of the 1951 Academy Award for special effects....
used a rocket sled to launch the Ark, but the book did not.
See also
- Laser propulsionLaser propulsionLaser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass...
- Non-rocket spacelaunchNon-rocket spacelaunchNon-rocket space launch is a launch into space where some or all needed speed and altitude is provided by non-rocket means, rather than simply using conventional chemical rockets from the ground. A number of alternatives to rockets have been proposed...
- Skyhook (structure)Skyhook (structure)Skyhooks are a theoretical class of cable based techniques intended to lift payloads to high altitudes and speeds. The name skyhook is a reference to an imaginary hook that hangs from the sky....
- Silbervogel
- SpaceplaneSpaceplaneA spaceplane is a vehicle that operates as an aircraft in Earth's atmosphere, as well as a spacecraft when it is in space. It combines features of an aircraft and a spacecraft, which can be thought of as an aircraft that can endure and maneuver in the vacuum of space or likewise a spacecraft that...
- StarTramStarTramStarTram is a proposal for a maglev space launch system. The initial Generation 1 facility would be cargo only, launching from a mountain peak at 3 km to 7 km altitude with an evacuated tube staying at local surface level, raising ≈150,000 tons to orbit annually...
- InductrackInductrackInductrack is a passive, fail-safe electrodynamic magnetic levitation system, using only unpowered loops of wire in the track and permanent magnets on the vehicle to achieve magnetic levitation. The track can be in one of two configurations, a "ladder track" and a "laminated track"...
- Hopper (spacecraft)Hopper (spacecraft)Hopper was a proposed European Space Agency orbital and reusable launch vehicle. The shuttle prototype spaceplane was one of several proposals for a European reusable launch vehicle planned to cheaply ferry satellites into orbit by 2015...
External links
- A website discussing "Skyramps": http://www.g2mil.com/skyramp.htm
- "A Light Gas Gun Approach To Achieving 'First Stage Acceleration' for the Highly Reusable Space Transportation System" 1997 M. Frank Rose, R .M. Jenkins, M. R. Brown, Space Power Institute, Auburn University, AL, 36849
- Link to Lockheed Proposal for a sled based reusable launch vehicle. http://www.astronautix.com/lvs/recstics.htm
- Europe's Phoenix: Test Craft Sets Stage For Reusable Rocketry http://www.space.com/missionlaunches/europe_phoenix_020621.html
- Holloman Air Force Base: http://www.holloman.af.mil/photos/index.asp?galleryID=2718
- NASA Studies pneumatic rocket boosts: http://www.techbriefs.com/content/view/2257/32/
- Describes rocket efficiency at various air pressures & aerospike engine: http://www.aerospaceweb.org/design/aerospike/compensation.shtml