Earth to orbit
Encyclopedia
Earth to Orbit describes the process or means of placing a payload into an orbit
around the Earth
. Traditionally this has used rockets, however ETO can also include much more exotic forms of transportation such as railgun
s and hypersonic cannon
s and Space elevator
s.
s are used in order to accelerate a payload to orbital velocities.
This is the only method of placing a payload into an earth orbit which has been successfully used. It involves constructing a series of
rockets which are usually stacked on one another, imparting their change in momentum to the payload before dropping away.
Although a series of suborbital rockets are usually used. Other schemes involving SSTO or Single Stage To Orbit
vehicles have been proposed. However they all suffer from a low Mass fraction
, reducing their effectiveness for transporting payloads into orbit.
by using the Earth to react against. Examples of this may be a railgun
, coil guns, or a hypervelocity gun. Because the payload is accelerated to velocities greater than required for orbital velocity
by the time the payload has left the device, either very high accelerations are required, or very large structures (thousands of kilometres long) are needed.
, already in earth orbit to impart part of the required momentum to accelerate the payload to orbital velocities. The most accepted candidates used various configurations of a Tether
. The most promising is the Skyhook elevator which uses momentum exchange to boost the payload from a suborbital trajectory to an orbital trajectory . As momentum is transferred from the momentum exchange tether to the payload it loses orbital energy, decreasing in altitude.
The loss in altitude of the tether must be recovered, otherwise the tether itself may reenter the Earth's Atmosphere. Although this can be done in many ways. One way is to use a conductive tether and pass electricity through it, forming an Electrodynamic tether
to generate a force to accelerate the tether after a loss of momentum.
The end of the skyhook tether dips in the atmosphere. However because it has zero relative velocity
to the Earth's surface. It is not effected by atmospheric heating that would otherwise destroy an object entering earth's atmosphere without a Heat shield
.
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...
around the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Traditionally this has used rockets, however ETO can also include much more exotic forms of transportation such as railgun
Railgun
A railgun is an entirely electrical gun that accelerates a conductive projectile along a pair of metal rails using the same principles as the homopolar motor. Railguns use two sliding or rolling contacts that permit a large electric current to pass through the projectile. This current interacts...
s and hypersonic cannon
Cannon
A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellents to launch a projectile. Cannon vary in caliber, range, mobility, rate of fire, angle of fire, and firepower; different forms of cannon combine and balance these attributes in varying degrees,...
s and Space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
s.
Methods
Earth to orbit transportation can be roughly broken up into four groups, these are:- Rocket transportation
- Ballistic methods
- Orbital transportation
- Relay transportation
Rocket Based Transportation
A series of suborbital rocketRocket
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...
s are used in order to accelerate a payload to orbital velocities.
This is the only method of placing a payload into an earth orbit which has been successfully used. It involves constructing a series of
rockets which are usually stacked on one another, imparting their change in momentum to the payload before dropping away.
Although a series of suborbital rockets are usually used. Other schemes involving SSTO or Single Stage To Orbit
vehicles have been proposed. However they all suffer from a low Mass fraction
Mass fraction
In aerospace engineering, the propellant mass fraction is a measure of a vehicle's performance, determined as the portion of the vehicle's mass which does not reach the destination...
, reducing their effectiveness for transporting payloads into orbit.
Ballistic methods
A stationary platform at least partly in Earth's atmosphere that delivers the required momentumMomentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
by using the Earth to react against. Examples of this may be a railgun
Railgun
A railgun is an entirely electrical gun that accelerates a conductive projectile along a pair of metal rails using the same principles as the homopolar motor. Railguns use two sliding or rolling contacts that permit a large electric current to pass through the projectile. This current interacts...
, coil guns, or a hypervelocity gun. Because the payload is accelerated to velocities greater than required for orbital velocity
Orbital velocity
Orbital velocity can refer to the following:* The orbital speed of a body in a gravitational field.* The velocity of particles due to wave motion, in particular in wind waves....
by the time the payload has left the device, either very high accelerations are required, or very large structures (thousands of kilometres long) are needed.
Orbital Transportation
This method uses a satelliteSatellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
, already in earth orbit to impart part of the required momentum to accelerate the payload to orbital velocities. The most accepted candidates used various configurations of a Tether
Tether
A tether is a cord, fixture, or signal that anchors something movable to a reference point which may be fixed or moving. There are a number of applications for tethers: balloons, kites, tethered wind-energy conversion systems, anchors, tethered water-flow energy conversion systems, towing, animal...
. The most promising is the Skyhook elevator which uses momentum exchange to boost the payload from a suborbital trajectory to an orbital trajectory . As momentum is transferred from the momentum exchange tether to the payload it loses orbital energy, decreasing in altitude.
The loss in altitude of the tether must be recovered, otherwise the tether itself may reenter the Earth's Atmosphere. Although this can be done in many ways. One way is to use a conductive tether and pass electricity through it, forming an Electrodynamic tether
Electrodynamic tether
Electrodynamic tethers are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy...
to generate a force to accelerate the tether after a loss of momentum.
The end of the skyhook tether dips in the atmosphere. However because it has zero relative velocity
Relative velocity
In non-relativistic kinematics, relative velocity is the vector difference between the velocities of two objects, as evaluated in terms of a single coordinate system....
to the Earth's surface. It is not effected by atmospheric heating that would otherwise destroy an object entering earth's atmosphere without a Heat shield
Heat shield
A heat shield is designed to shield a substance from absorbing excessive heat from an outside source by either dissipating, reflecting or simply absorbing the heat...
.
Relay Transportation
This method uses a combination of the above methods over to cover the various parts of the journey into orbit.See also
- Orbital spaceflightOrbital spaceflightAn orbital spaceflight is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee above...
- Spacecraft propulsionSpacecraft propulsionSpacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
- Space elevatorSpace elevatorA space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
- Space fountainSpace fountainA space fountain is a proposed form of space elevator that does not require the structure to be in geostationary orbit, and does not rely on tensile strength for support. In contrast to the original space elevator design , a space fountain is a tremendously tall tower extending up from the ground...
- Tether propulsion
- SkyhookSkyhook (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....