Yo-yo de-spin
Encyclopedia
A yo-yo de-spin mechanism is a device used to reduce the spin of satellite, typically right after launch. It consists of two lengths of cable with weights on the ends. The cables are wrapped around the final stage and/or satellite, in the manner of a double yo-yo
. When the weights are released, the spin of the rocket flings them away from the spin axis. This transfers enough angular momentum
to the weights to reduce the spin of the satellite to the desired value. The weights are often released.
De-spin is needed since some final stages are spin-stabilized
, and require fairly rapid rotation (perhaps 50 rpm) to keep stable during firing (See, for example, the Star 48
, a solid fuel rocket motor.) After the firing, the satellite cannot be simply released, since such a spin rate is beyond the capability of the satellite's attitude control. Therefore after the rocket firing but before satellite release, the yo-yo weights are used to reduce the spin rates to something the satellite can handle (often 2-5 RPM).
As an example of yo-yo de-spin, on the Dawn Mission
, roughly 3 kg of weights, and 12 meter cables, reduce the initial spin rate of the 1420 kg spacecraft from 36 RPM down to 3 RPM in the opposite direction. The relatively small weights can have such a large effect since they are far from the axis of the spin, and their effect grows as the square of the length of the cables.
Yo-yo de-spin was originally invented, built, and tested at Caltech's Jet Propulsion Laboratory
.
Yo-yo hardware can contribute to the space debris
problem on orbital missions, but this is not a problem when used on the upper stages of earth escape missions such as Dawn as the cables and weights are also on an escape trajectory.
even without significant combustion. In a few cases, the spent stage has rammed the payload. By using one weight without a matching counterpart, the stage eventually tumbles. The tumbling motion prevents residual thrust from integrating in a single direction; instead, the stage's exhaust averages out to a much lower value over a wide range of directions.
In March 2009, a left-over yo weight caused a scare when it came too close to the International Space Station
.
Yo-yo
The yo-yo in its simplest form is an object consisting of an axle connected to two disks, and a length of twine looped around the axle, similar to a slender spool...
. When the weights are released, the spin of the rocket flings them away from the spin axis. This transfers enough angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
to the weights to reduce the spin of the satellite to the desired value. The weights are often released.
De-spin is needed since some final stages are spin-stabilized
Spin-stabilized satellite
A spin-stabilized satellite is a satellite which has the motion of one axis held fixed by spinning the satellite around that axis, using the gyroscopic effect.The attitude of a satellite or any rigid body is its orientation in space...
, and require fairly rapid rotation (perhaps 50 rpm) to keep stable during firing (See, for example, the Star 48
Star 48
The Star 48 is a type of solid rocket motor used by many space propulsion and launch vehicle stages, including the Space Shuttle and the New Horizons probe. It is used almost exclusively as an upper stage...
, a solid fuel rocket motor.) After the firing, the satellite cannot be simply released, since such a spin rate is beyond the capability of the satellite's attitude control. Therefore after the rocket firing but before satellite release, the yo-yo weights are used to reduce the spin rates to something the satellite can handle (often 2-5 RPM).
As an example of yo-yo de-spin, on the Dawn Mission
Dawn Mission
Dawn is a NASA spacecraft tasked with the exploration and study of the two largest members of the asteroid belt – Vesta and the dwarf planet Ceres. The spacecraft was constructed with some European cooperation, with partners in Germany, Italy, and the Netherlands providing Dawns framing...
, roughly 3 kg of weights, and 12 meter cables, reduce the initial spin rate of the 1420 kg spacecraft from 36 RPM down to 3 RPM in the opposite direction. The relatively small weights can have such a large effect since they are far from the axis of the spin, and their effect grows as the square of the length of the cables.
Yo-yo de-spin was originally invented, built, and tested at Caltech's Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
.
Yo-yo hardware can contribute to the space debris
Space debris
Space debris, also known as orbital debris, space junk, and space waste, is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellites to erosion, explosion...
problem on orbital missions, but this is not a problem when used on the upper stages of earth escape missions such as Dawn as the cables and weights are also on an escape trajectory.
"Yo-weight"
Sometimes, only a single weight and cable is used. Such an arrangement is colloquially named a "yo-weight." When the final stage is a solid rocket, the stage may continue to thrust slightly even after spacecraft release. This is from residual fuel and insulation in the motor casing, outgassingOutgassing
Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in some material. As an example, research has shown how the concentration of carbon dioxide in the Earth's atmosphere has sometimes been linked to ocean outgassing...
even without significant combustion. In a few cases, the spent stage has rammed the payload. By using one weight without a matching counterpart, the stage eventually tumbles. The tumbling motion prevents residual thrust from integrating in a single direction; instead, the stage's exhaust averages out to a much lower value over a wide range of directions.
In March 2009, a left-over yo weight caused a scare when it came too close to the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
.