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→Deployment Mechanisms
''This page has been inspired from [http://www.princeton.edu/~stengel/MAE342Lecture19.pdf here]''
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== Trigger Mechanisms ==
=== Pyrotechnic Cables and Bolt Cutters ===
This mechanism employs a small controlled expansion to propel a bolt towards a cable placed on an anvil. The bolt strikes the cable and cuts it, thus releasing the deployable that the cable was securing. An animation for the same can be found [http://spot4.cnes.fr/spot4_gb/images/pyro/pan.gif here].
==== Advantages ====
They are quick, small and simple in use
====Disadvantages ====
The explosion may generate a lot of internal force and create hazards for the satellite<br \> <br \>----A very good animation can be found [[Filehttp:Pyro1//spot4.cnes.fr/spot4_gb/images/pyro/pan.jpg|frame|center]gif here].----
=== Burn Wire Mechanism ===
The release mechanism utilizes a compressed spring system to ensure permanent contact with the cable that is securing a deployable. When heated the burn wire would cut through the cable due to pre-compressed spring. After a successful cut the spring extends to its natural length. Usually the burn wire is made of Nichrome, which is heated to high temperature and the cable is made of Vectran (A high strength, high thermal stability and low creep fiber)
====Disadvantages ====
May fail to cut through the wire in one shot i.e. unreliable (To tackle this, usually redundant setups are used to ensure that the mechanism works well)
----For more information and graphics on burn wire mechanism, click [[Filehttps:Burn1//www.techbriefs.jpg|frame|center]com/component/content/article/tb/techbriefs/mechanics-and-machinery/24810 here]. ----
=== Shape Memory Alloy (SMA) ===
[[File:SMA1LinearActuator2.jpggif|thumbright|frame|Conceptual design of a basic traveling-nut linear actuator. Note that in this example the lead screw (gray) rotates while the lead nut (yellow) and tube (red) do not. Attribution: Public Domain, https://en.wikipedia.org/w/index.php?curid=12285672]]
A SMA is an alloy that “remembers” its original shape when it was formed and returns to it from its deformed state when heated. There are multiple actuators already in use as well as several under development that exploit use of SMAs for release of the deployable. <br \>
Some of the mechanisms that use SMAs are listed:
====Disadvantages====
They are not yet tested extensively in space and are in development, some parts are too small and difficult to manufacture hence are expensive currently. Also they may be susceptible to external rise in temperature and cause untimely deployment
----More information about Shape Memory Alloys and their space heritage can be found [[Filehttp:SMA2//www.esa-tec.jpg|frame|center]eu/space-technologies/from-space/new-shape-memory-alloy-for-high-transformation-temperature/ here].----
=== Paraffin release mechanism ===
This mechanism uses the property of paraffin wax to expand greatly on heating it. This causes it to compress a cylindrical casing which holds a pin initially. As the casing (made of polymer) gets squeezed it releases the pin, slowly triggering the deployment
==== Advantages ====
==== Disadvantages ====
Slow deployment, spontaneous trigger at elevated temperature
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More information can be found [http://www.vernatherm.com/thermal_actuators.html here].
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==Deployment Mechanisms ==
Here are some commonly used mechanisms:
* '''Coilable Mast:''' This an important mechanism for deployment of structures such as antennas. The mast is flexible in nature and coiled on a reel to reduce the dimension during launch. A good image can be found [https://www.jpl.nasa.gov/nmp/st8/tech/sailmast_tech3.html here].
* '''Lazy Tongs:''' The actual definition for this being scissor-like extendable structure used to reach things at a distance. These type of structures are employed when space constraints are imposed on one dimension of structures.
[[File:LazyTongs2.png|frame|center|A representative image for lazy tongs. Image reproduced from [https://www.flickr.com/photos/internetarchivebookimages/14742323506 here]]]
* '''Telescopic:''' This mechanism uses compression of a long structure into smaller structure by sliding one part into another.
[[File:Telescopic2.png|thumb|center|400px|Telescopic]]* '''Foldable Mast:''' The structure of the mast is broken into smaller parts of the shape of a triangle and connected with the help of plastic flexible hinges to stiffen the folded structure once deployed.[Good images can be found [Filehttp:FoldableMast//mechanismsrobotics.png|frame|center|Foldable Mast|200px]asmedigitalcollection.asme.org/article.aspx?articleid=2474215 here][[File:LazyTongs.png|frame|left|Lazy Tongs]][[File:Telescopic.png|frame|left|Telescopic]]
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If you are done reading this page, you can go back to [[Mechanical Subsystem]]