Vacuum cementing
Encyclopedia
Vacuum cementing or vacuum welding is the natural process of solidifying small objects in a hard vacuum
. The most notable example is dust on the surface of the Moon
.
This effect was reported to be a problem with the first American and Soviet satellites, as small moving parts would seize together.
However, in 2006, Henry Spencer
stated that the phenomenon of spontaneous cold welding
in outer space
is "basically a myth", pointing out that "there are no documented cases of it actually occurring in orbit, except in experiments deliberately designed to provoke it (with susceptible materials, great care to avoid contamination, and deliberate mechanical removal of oxide layers, etc.)."
Three years following this 2006 post the European Space Agency
published a peer review
ed paper detailing why cold welding is a significant issue that spacecraft
designers need to carefully consider. The conclusions of this appropriately titled study can be found on page 25 of "Assessment of Cold Welding between Separable Contact Surfaces due to Impact and Fretting under Vacuum". The paper also cites a documented example from 1991 with the Galileo spacecraft
high-gain antenna
(see page 2; the technical source document from NASA
regarding the Galileo spacecraft is also provided in a link here).
One source of difficulty is that vacuum (aka cold) welding does not exclude relative motion between the surfaces that are to be joined. This allows the broadly defined notions of galling
, fretting
, sticking, stiction
and adhesion
to overlap in some instances. For example, it is possible for a joint to be the result of both vacuum welding and galling (and/or fretting and/or impact). Galling and vacuum welding, therefore, are not mutually exclusive.
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
. The most notable example is dust on the surface of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
.
This effect was reported to be a problem with the first American and Soviet satellites, as small moving parts would seize together.
However, in 2006, Henry Spencer
Henry Spencer
Henry Spencer is a Canadian computer programmer and space enthusiast. He wrote "regex", a widely-used software library for regular expressions, and co-wrote C News, a Usenet server program. He also authored The Ten Commandments for C Programmers. He is coauthor, with David Lawrence, of the book...
stated that the phenomenon of spontaneous cold welding
Cold welding
Cold or contact welding is a solid-state welding process in which joining takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint....
in outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
is "basically a myth", pointing out that "there are no documented cases of it actually occurring in orbit, except in experiments deliberately designed to provoke it (with susceptible materials, great care to avoid contamination, and deliberate mechanical removal of oxide layers, etc.)."
Three years following this 2006 post the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
published a peer review
Peer review
Peer review is a process of self-regulation by a profession or a process of evaluation involving qualified individuals within the relevant field. Peer review methods are employed to maintain standards, improve performance and provide credibility...
ed paper detailing why cold welding is a significant issue that spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
designers need to carefully consider. The conclusions of this appropriately titled study can be found on page 25 of "Assessment of Cold Welding between Separable Contact Surfaces due to Impact and Fretting under Vacuum". The paper also cites a documented example from 1991 with the Galileo spacecraft
Galileo spacecraft
Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
high-gain antenna
High-gain antenna
A high-gain antenna is an antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signal - also known as a directional antenna...
(see page 2; the technical source document from NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
regarding the Galileo spacecraft is also provided in a link here).
One source of difficulty is that vacuum (aka cold) welding does not exclude relative motion between the surfaces that are to be joined. This allows the broadly defined notions of galling
Galling
Galling usually refers to the adhesive wear and transfer of material between metallic surfaces in relative converging contact during sheet metal forming and other industrial operations....
, fretting
Fretting
Fretting refers to wear and sometimes corrosion damage at the asperities of contact surfaces. This damage is induced under load and in the presence of repeated relative surface motion, as induced for example by vibration...
, sticking, stiction
Stiction
Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the term "static friction", perhaps also influenced by the verb "stick"....
and adhesion
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
to overlap in some instances. For example, it is possible for a joint to be the result of both vacuum welding and galling (and/or fretting and/or impact). Galling and vacuum welding, therefore, are not mutually exclusive.
See also
- Cold weldingCold weldingCold or contact welding is a solid-state welding process in which joining takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint....
- PassivationPassivationPassivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...
- Corrosion in spaceCorrosion in spaceCorrosion in space is the corrosion of materials occurring in outer space. Instead of moisture and oxygen acting as the primary corrosion causes, the materials exposed to outer space are subjected to vacuum, bombardment by ultraviolet light and x-rays, high-energy charged particles...