Space tether

Space tethers

Space tethers are long cables that can be used in space for many important jobs. They help give a spacecraft a push, change its direction, keep it steady, or even hold parts of a big satellite system in the right place. These cables can do many things that usually need special engines on a spacecraft.

Because of this, some people think that flying in space using tethers could cost much less than using regular rocket engines. This could make future space trips more affordable and help us explore space in new ways. Scientists and engineers are very interested in learning more about how tethers can be used to make space travel better and cheaper.

Main techniques

Tether satellites can be used for many purposes, such as learning about space movement and how space works. There are five main ways scientists are working on using space tethers:

Electrodynamic tethers
Main article: Electrodynamic tether

These tethers help move spacecraft by using electric currents and magnetic fields from planets.

Momentum exchange tethers
Main article: Momentum exchange tether

These tethers can catch a spacecraft and then let it go again, helping it change its path or speed.

Tethered formation flying
Main article: Tethered formation flying

This uses a special tether to keep several spacecraft at just the right distance from each other as they fly together.

Electric sail
Main article: Electric sail

This is like a sail for spacecraft, using electric tethers pushed by particles from the sun.

Universal Orbital Support System
Main article: Universal Orbital Support System

This idea uses a tether to hold an object steady while it orbits in space.

Scientists have thought of many uses for space tethers, like building tall towers in space or helping spacecraft move without using fuel.

History

Konstantin Tsiolkovsky (1857–1935) imagined a very tall tower reaching into space, held up by Earth rotating. But at that time, there was no way to build such a tower.

In 1960, Yuri Artsutanov described an idea for a strong cable stretching from a geosynchronous satellite down to Earth and up beyond. This was called the space elevator idea, but it was not practical with the materials available then.

Later, in the 1970s, Jerome Pearson thought about space elevators, especially for the Moon. Hans Moravec and Robert L. Forward studied rotating cables, called skyhooks, that could move objects to and from the Moon, Mars, and other planets.

In 1979, NASA started looking into these ideas more seriously. In 1990, Eagle Sarmont suggested a system where a cable could help move spacecraft between Earth and higher orbits. By 2000, NASA and Boeing explored a plan using a rotating cable to send payloads into orbit from high-speed aircraft.

Missions

A tether satellite is a satellite linked to another by a special cable in space. Several satellites have been launched to test these cable ideas, with different results.

Types

Main article: Momentum exchange tether

There are many kinds of space tethers, and some can be used for more than one purpose.

Main article: Skyhook (structure)

A skyhook is a special way to use tethers in space. It might help move things to very high places and speeds. Some ideas for skyhooks include spinning tethers fast to catch moving things and lift them into space.

Main article: Electrodynamic tether

Electrodynamic tethers are long wires that work in space. They can turn movement into electricity or use electricity to move. These tethers make electricity as they move through Earth's magnetic field. The metal for these tethers must be good at conducting electricity and not too heavy.

Main article: Tethered formation flying

Formation flying uses a tether to link several spacecraft together. In 2011, there was an idea to test this with a special experiment to learn more about space travel.

Main article: Universal Orbital Support System

The Universal Orbital Support System is a new idea for a type of tether. It would help support things high above a planet or moon, but not as high as the main spacecraft orbiting above.

Technical difficulties

Gravitational gradient stabilization

Main article: Gravity-gradient stabilization

Space tethers can stay straight because of tiny changes in gravity along their length. When two spacecraft at different heights are connected by a tether, they must move at the same speed. This makes the lower spacecraft slow down a little, and the higher one speed up. The forces change, helping the tether line up with gravity.

Atomic oxygen

Further information: Atomic oxygen

In low Earth orbit, tiny oxygen particles move very fast and can wear away at objects. This can damage space tethers over time.

Micrometeorites and space junk

Simple tethers can be harmed by tiny space rocks and bits of old satellites. Some ideas to make tethers stronger include special nets that spread the force if a piece breaks. Big pieces of space junk can still cut tethers, but we can track these with radar and move the tether out of the way when needed.

Radiation

Radiation, like ultraviolet light, can wear down tether materials. Tethers that pass through certain areas around Earth may not last as long because of this.

Construction

Space tethers are long cables used for moving spacecraft, keeping things steady, or holding parts of a big satellite in place. To save money and work better than rockets, these tethers are made from materials that are strong but also light.

Good materials for tethers include special plastics like ultra-high-molecular-weight polyethylene, aramid, carbon fiber, and maybe even carbon nanotubes in the future. These materials must be strong enough to handle pulling and light enough to not weigh too much. Designers also need to protect the tethers from space debris and tiny space particles.

For some jobs, the tether doesn’t need to be as strong, so different materials might be used depending on the mission. There are also equations that help designers choose the best materials and sizes for different kinds of tethers.

Control and modelling

Electrodynamic tethers can shake and wobble because of how they work with magnetic and gravity fields. Scientists think we could change the electric current in the tether to stop this shaking. This needs special tools, like tiny GPS on the tether, to measure the shaking.

Another idea is to spin the tether instead of letting it hang. This can help keep it steady without extra control.

Sometimes, tethers can get damaged by sudden electric jumps. This can break them or hurt the machines that handle them. Computer models show that tethers can also break from too much shaking. Special machines can help control this shaking by changing how they move along the tether.

Tethers are long and not like a small ball. This makes their balance points not in the same spot. Because of this, their paths around Earth can be hard to predict, especially if they spin in certain ways.