A yo-yo de-spin mechanism is a device used to reduce the spin of satellites, typically soon 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 A yo-yo (also spelled yoyo) is a toy consisting of an axle connected to two disks, and a string looped around the axle, similar to a spool. It is an ancient toy with proof of existence since 500 BCE. The yo-yo was also called a bandalore in ...

. When the weights are released, the spin of the rocket flings them away from the

spin axis Rotation around a fixed axis is a special case of rotational motion. The fixed-axis hypothesis excludes the possibility of an axis changing its orientation and cannot describe such phenomena as wobbling or precession. According to Euler's rota ...

. This transfers enough

angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...

to the weights to reduce the spin of the satellite to the desired value. Subsequently, the weights are often released. De-spin is needed since some final stages are spin-stabilized, and require fairly rapid rotation (now typically 30-60 rpm; some early missions, such as Pioneer, rotated at over 600 rpm) to remain stable during firing. (See, for example, the

Star 48 The Star 48 is the largest of a family of solid rocket motors used by many space propulsion and launch vehicle stages. It is used almost exclusively as an upper stage. It was developed primarily by Thiokol Propulsion and is now, after several ...

, a solid fuel rocket motor.) After firing, the satellite cannot be simply released, since such a spin rate is beyond the capability of the satellite's attitude control. Therefore, after rocket firing but before satellite release, the yo-yo weights are used to reduce the spin rates to something the satellite can cope with in normal operation (often 2-5 RPM). Yo-yo de-spin systems are commonly used on NASA sub-orbital sounding rocket flights, as the vehicles are spin stabilized through ascent and have minimal flight time for roll cancellation using the payload's attitude control system. As an example of yo-yo de-spin, on the ''Dawn'' spacecraft, roughly of weights, and cables, reduced the initial spin rate of the spacecraft from 46 RPM to 3 RPM in the opposite direction. The relatively small weights have a large effect since they are far from the spin axis, and their effect increases as the square of the length of the cables. Yo-yo de-spin was invented, built, and tested at

Caltech The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, La Cañada Flintridge, California ...

. Yo-yo hardware can contribute to the

space debris Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacec ...

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 A solid-propellant rocket or solid rocket is a rocket with a rocket engine that uses solid propellants ( fuel/ oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used in warfare by the Arabs, Chinese, ...

, the stage may continue to thrust slightly even after spacecraft release. This is from residual fuel and insulation in the motor casing

outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...

, 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 accumulating 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 leftover yo-weight caused a scare when it came too close to the

International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...

References

{{Reflist Spacecraft propulsion Spacecraft components Articles containing video clips Spacecraft design

Yo-weight

See also

Further reading

References