Earth to orbit
Earth to Orbit (ETO) 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 other forms of transportation such as; Orbiting skyhooks, railguns, hypersonic cannons, and Space elevators.
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 rockets 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.
A stationary platform at least partly in Earth's atmosphere that delivers the required momentum 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.
This method uses a satellite, 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 affected by atmospheric heating that would otherwise destroy an object entering earth's atmosphere without a Heat shield.
This method uses a combination of the above methods over to cover the various parts of the journey into orbit.
- Orbital spaceflight
- Spacecraft propulsion
- Space elevator
- Space fountain
- Tether propulsion
- Orbiting skyhooks
Nowicki, Andrew. "Earth-to-Orbit Transportation Bibliography". Retrieved 2005-02-18.
- NASA documents
- Highly Resuable Space Transportation: Approaches for Reducing ETO Launch Costs to $100-$200 per Pound of Payload