Skyhook (structure)
Encyclopedia
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.
Plausible near-term proposals for skyhooks include designs that employ tethers spinning at hypersonic speeds for catching payloads from very high speed, high altitude aircraft and placing them in orbit.
There are also hypothetical skyhooks that are intended to be used for non-rocket spacelaunch
into orbit
, for example, a space elevator
.
Another concept is orbital ring
s with geostationary 'spokes'.
See tether propulsion for more details on various types of skyhooks.
.
Note that the skyhook acts as a momentum bank. If it is used to lift many payloads into orbit its own orbit will degrade. However, if it catches fast moving 'junk rocks' on the high end of the skyhook, their kinetic energy
will help lift the sky hook into higher orbits. Thus if a sky hook has been created, it can effectively convert waste asteroid or lunar material thrown to it, into high grade rocket fuel (that is by replacing the fuel spent to maintain its own orbit), by virtue of their kinetic energy. Another way around the energy loss would be to use electrodynamic tether technology to reboost the skyhook once it has lost some momentum (see tether propulsion).
The rotation rate of these kinds of skyhooks depends on the altitude that the center is maintained at, and is lower at higher altitudes. When the center of mass is placed in geostationary orbit
then the cable rotates once per day with the Earth, and is usually referred to as a space elevator
. Current materials technology does not permit these kinds of 'space elevator' structures to be practical, although advanced carbon nanotubes could in principle have the specific strength
necessary to permit this.
This is probably possible with current technology as it doesn't need such high strength materials for the cable.
novel Deepsix.
In the anime Bubblegum Crisis: Tokyo 2040, the three main protagonists arrive at the series' climactic battle with Galatea in Earth orbit by commandeering a skyhook transit system.
Turn-A Gundam, anime series, depicts an ancient hypersonic skyhook which has been maintained operationally by nanomachines over thousands of years. An ancient mass driver is also used for transporting space-vessels from earth's surface to the skyhook.
In the Star Wars expanded universe
, skyhooks are common above Coruscant
. They are frequently private retreats owned by corporations or wealthy individuals.
In the LucasArts
video game Star Wars: The Force Unleashed
a skyhook is being constructed on the planet Kashyyyk
.
The planet of Tara K. Harper
's Grey Ones series features a number of skyhook stations. The tethers are apparently no longer functioning, but large terminal structures still exist. They are used as a plot device, as ferrous weapons are impossible to use near the structures due to their intense magnetic fields.
A skyhook figures prominently in Arthur C. Clarke
's posthumous novel The Last Theorem
, which he co-wrote with Frederik Pohl
. The novel describes the skyhook as a means of interplanetary travel rather than simply a means to reach orbit. It is used as a means of transport by athletes and delegates to the "first-ever lunar Olympics".
The construction of skyhooks, including a space elevator
and several other orbital devices for launching craft into orbit and interplanetary travel, as well as decelerating and capturing craft on arrival, is a central theme in the science fiction novel The Barsoom Project, the second book in the Dream Park
series, by Larry Niven
and Steven Barnes
. The destructive potential of a falling skyhook is also explored, and the potential for this to be exploited by terrorists.
In the sequel by Roald Dahl
Charlie and the Great Glass Elevator
, Willy Wonka
mentions in passing that the titular elevator flies by skyhooks.
Plausible near-term proposals for skyhooks include designs that employ tethers spinning at hypersonic speeds for catching payloads from very high speed, high altitude aircraft and placing them in orbit.
There are also hypothetical skyhooks that are intended to be used for non-rocket spacelaunch
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...
into 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...
, for example, a space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
.
Another concept is orbital ring
Orbital ring
An Orbital Ring is a concept for a space elevator that consists of a ring in low earth orbit that rotates at above orbital speed, that has fixed tethers hanging down to the ground.The structure is intended to be used for space launch....
s with geostationary 'spokes'.
See tether propulsion for more details on various types of skyhooks.
Aircraft
The technique of hooking cargo on the ground or in the air with a capturing aircraft has been successfully used by the U.S. Air Force in the Fulton surface-to-air recovery systemFulton surface-to-air recovery system
The Fulton surface-to-air recovery system is a system used by the CIA, United States Air Force and United States Navy for retrieving persons on the ground from an MC-130E Combat Talon I aircraft. It involves using an overall-type harness and a self-inflating balloon which carries an attached lift...
.
'Conventional' orbital skyhooks
This is a type of cable that would be in orbit around the Earth, with a top speed equal to its orbital speed (around 7–8 km/s). The tip rotates down, and as it does so, it moves backwards, slows, enters the atmosphere at low speed and picks up a payload from the ground (or the atmosphere). It then carries it up into space.Note that the skyhook acts as a momentum bank. If it is used to lift many payloads into orbit its own orbit will degrade. However, if it catches fast moving 'junk rocks' on the high end of the skyhook, their kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
will help lift the sky hook into higher orbits. Thus if a sky hook has been created, it can effectively convert waste asteroid or lunar material thrown to it, into high grade rocket fuel (that is by replacing the fuel spent to maintain its own orbit), by virtue of their kinetic energy. Another way around the energy loss would be to use electrodynamic tether technology to reboost the skyhook once it has lost some momentum (see tether propulsion).
The rotation rate of these kinds of skyhooks depends on the altitude that the center is maintained at, and is lower at higher altitudes. When the center of mass is placed in geostationary orbit
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
then the cable rotates once per day with the Earth, and is usually referred to as a space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
. Current materials technology does not permit these kinds of 'space elevator' structures to be practical, although advanced carbon nanotubes could in principle have the specific strength
Specific strength
The specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength...
necessary to permit this.
Hypersonic orbital skyhooks
A variation of this technique that appears to be currently possible is to have the tip speed of the cable lower than the orbital speed and use hypersonic aircraft to catch the tip while it is in the upper atmosphere.This is probably possible with current technology as it doesn't need such high strength materials for the cable.
Orbital rings
Orbital rings are solid or quasisolid rings that would encircle the Earth and would spin at faster than orbital speed in low earth orbit. The ring would support geostationary skyhooks that hang down to the ground that could be used to carry payloads to high altitude.In fiction
A form of hard-structure subsonic skyhook was constructed during the events of Jack McDevitt'sJack McDevitt
Jack McDevitt is an American science fiction author whose novels frequently deal with attempts to make contact with alien races, and with archaeology or xenoarchaeology....
novel Deepsix.
In the anime Bubblegum Crisis: Tokyo 2040, the three main protagonists arrive at the series' climactic battle with Galatea in Earth orbit by commandeering a skyhook transit system.
Turn-A Gundam, anime series, depicts an ancient hypersonic skyhook which has been maintained operationally by nanomachines over thousands of years. An ancient mass driver is also used for transporting space-vessels from earth's surface to the skyhook.
In the Star Wars expanded universe
Star Wars Expanded Universe
The Star Wars Expanded Universe encompasses all of the officially licensed, fictional background of the Star Wars universe, outside of the six feature films produced by George Lucas. The expanded universe includes books, comic books, video games, spin-off films like Star Wars: The Clone Wars,...
, skyhooks are common above Coruscant
Coruscant
Coruscant is a planet in the fictional Star Wars universe. It first appeared onscreen in the 1997 Special Edition of Star Wars Episode VI: Return of the Jedi, but was first mentioned in Timothy Zahn's 1991 novel Heir to the Empire...
. They are frequently private retreats owned by corporations or wealthy individuals.
In the LucasArts
LucasArts
LucasArts Entertainment Company, LLC is an American video game developer and publisher. The company was once famous for its innovative line of graphic adventure games, the critical and commercial success of which peaked in the mid 1990s...
video game Star Wars: The Force Unleashed
Star Wars: The Force Unleashed
Star Wars: The Force Unleashed is a multimedia project developed by LucasArts along with Dark Horse Comics, Lego, Hasbro, and Del Rey Books...
a skyhook is being constructed on the planet Kashyyyk
Kashyyyk
Kashyyyk , also known as Wookiee Planet C, is a planet in the Star Wars universe. It is the tropical, forested home world of the Wookiees...
.
The planet of Tara K. Harper
Tara K. Harper
Tara K. Harper is an American science fiction author whose works include the Wolfwalker series.-Early life:Harper was raised in northwest Oregon. Her father had worked in a nuclear lab analyzing radioactive cloud samples from Russian atomic test blasts; her mother had been a uranium buyer. Her...
's Grey Ones series features a number of skyhook stations. The tethers are apparently no longer functioning, but large terminal structures still exist. They are used as a plot device, as ferrous weapons are impossible to use near the structures due to their intense magnetic fields.
A skyhook figures prominently in Arthur C. Clarke
Arthur C. Clarke
Sir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...
's posthumous novel The Last Theorem
The Last Theorem
The Last Theorem is a 2008 science fiction novel written by Arthur C. Clarke and Frederik Pohl. It was first published in the United Kingdom by HarperVoyager in July 2008, and in the United States by Del Rey Books in August 2008...
, which he co-wrote with Frederik Pohl
Frederik Pohl
Frederik George Pohl, Jr. is an American science fiction writer, editor and fan, with a career spanning over seventy years — from his first published work, "Elegy to a Dead Planet: Luna" , to his most recent novel, All the Lives He Led .He won the National Book Award in 1980 for his novel Jem...
. The novel describes the skyhook as a means of interplanetary travel rather than simply a means to reach orbit. It is used as a means of transport by athletes and delegates to the "first-ever lunar Olympics".
The construction of skyhooks, including a space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
and several other orbital devices for launching craft into orbit and interplanetary travel, as well as decelerating and capturing craft on arrival, is a central theme in the science fiction novel The Barsoom Project, the second book in the Dream Park
Dream Park
Dream Park was originally a novel set in a sort of futuristic amusement park of the same name.The books describe a futuristic form of live action role-playing games , although the term was not in use when the original novel was published. The novels inspired many LARP groups, notably the...
series, by Larry Niven
Larry Niven
Laurence van Cott Niven / ˈlæri ˈnɪvən/ is an American science fiction author. His best-known work is Ringworld , which received Hugo, Locus, Ditmar, and Nebula awards. His work is primarily hard science fiction, using big science concepts and theoretical physics...
and Steven Barnes
Steven Barnes
Steven Barnes is an African American science fiction writer, lecturer, creative consultant, and human performance technician....
. The destructive potential of a falling skyhook is also explored, and the potential for this to be exploited by terrorists.
In the sequel by Roald Dahl
Roald Dahl
Roald Dahl was a British novelist, short story writer, fighter pilot and screenwriter.Born in Wales to Norwegian parents, he served in the Royal Air Force during the Second World War, in which he became a flying ace and intelligence agent, rising to the rank of Wing Commander...
Charlie and the Great Glass Elevator
Charlie and the Great Glass Elevator
Charlie and the Great Glass Elevator is a children's book by British author Roald Dahl. It is the sequel to Charlie and the Chocolate Factory, continuing the story of young Charlie Bucket and eccentric candymaker Willy Wonka as they travel in the Great Glass Elevator.Charlie and the Great Glass...
, Willy Wonka
Willy Wonka
This article is about the fictional character. For the candy company, see, The Willy Wonka Candy Company.Willy Wonka is a fictional character in the 1964 Roald Dahl novel Charlie and the Chocolate Factory and the film adaptations that followed. The book and the 1971 film adaption both vividly...
mentions in passing that the titular elevator flies by skyhooks.
External link
- A paper by Hans MoravecHans MoravecHans Moravec is an adjunct faculty member at the Robotics Institute of Carnegie Mellon University. He is known for his work on robotics, artificial intelligence, and writings on the impact of technology. Moravec also is a futurist with many of his publications and predictions focusing on...
: http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/papers/scable.pox - A draft of an article by Hans Moravec that appeared in OmniOmni (magazine)OMNI was a science and science fiction magazine published in the US and the UK. It contained articles on science fact and short works of science fiction...
magazine