Editing Micrometeoroid (section)

== Effect on spacecraft operations ==
{{see also|Space debris}}
[[File:SMM panel hole.jpg|thumb|Electron micrograph image of an orbital debris hole made in the panel of the [[Solar Maximum Mission|Solar Max]] satellite]]
Micrometeoroids pose a significant threat to [[space exploration]]. The average velocity of micrometeoroids relative to a [[spacecraft]] in orbit is 10 kilometers per second (22,500&nbsp;mph). Resistance to micrometeoroid impact is a significant design challenge for spacecraft and [[space suit]] designers (''See [[Thermal Micrometeoroid Garment]]''). While the tiny sizes of most micrometeoroids limits the damage incurred, the high velocity impacts will constantly degrade the outer casing of spacecraft in a manner analogous to [[sandblasting]]. Long term exposure can threaten the functionality of spacecraft systems.<ref name=":0">{{Cite web|url=https://www.nasa.gov/centers/wstf/laboratories/hypervelocity/mmod.html|archive-url=https://web.archive.org/web/20091028100716/http://www.nasa.gov/centers/wstf/laboratories/hypervelocity/mmod.html|url-status=dead|archive-date=October 28, 2009|title=Micrometeoroids and Orbital Debris (MMOD)|last=Rodriguez|first=Karen|date=April 26, 2010|website=www.nasa.gov|access-date=2018-06-18}}</ref>

Impacts by small objects with extremely high velocity (10 kilometers per second) are a current area of research in [[terminal ballistics]] (although accelerating objects up to such velocities is difficult; current techniques include [[linear motor]]s and [[shaped charge]]s). The risk is especially high for objects in space for long periods of time, such as [[satellite]]s.<ref name=":0" /> They also pose major engineering challenges in theoretical low-cost lift systems such as [[Momentum exchange tether#Rotovator|rotovators]], [[space elevator]]s, and orbital airships.<ref>{{Cite book |last=Swan |first=Peter A. |title=Space Elevators: An Assessment of the Technological Feasibility and the Way Forward |last2=Raitt |first2=David I. |last3=Swan |first3=Cathy W. |last4=Penny |first4=Robert E. |last5=Knapman |first5=John M. |publisher=International Academy of Astronautics |year=2013 |isbn=9782917761311 |location=Virginia, USA |pages=10–11, 207–208}}</ref><ref>Swan, P., Penny, R. Swan, C. Space Elevator Survivability, Space Debris Mitigation, Lulu.com Publishers, 2011</ref>

=== Spacecraft micrometeoroid shielding ===
[[File:Hypervelocity Impact Demonstration.jpg|thumb|The "energy flash" of a [[hypervelocity]] impact during a simulation of what happens when a piece of orbital debris hits a spacecraft in orbit]]

Whipple's work pre-dated the [[Space Race]] and it proved useful when space exploration started only a few years later. His studies had demonstrated that the chance of being hit by a meteoroid large enough to destroy a spacecraft was extremely remote. However, a spacecraft would be almost constantly struck by micrometeorites, about the size of dust grains.<ref name=whipple1951 />

Whipple had already developed a solution to this problem in 1946. Originally known as a "meteor bumper" and now termed the [[Whipple shield]], this consists of a thin foil film held a short distance away from the spacecraft's body. When a micrometeoroid strikes the foil, it vaporizes into a plasma that quickly spreads. By the time this plasma crosses the gap between the shield and the spacecraft, it is so diffused that it is unable to penetrate the structural material below.<ref name=Marsden>Brian Marsden, [https://www.independent.co.uk/news/obituaries/professor-fred-whipple-533019.html "Professor Fred Whipple: Astronomer who developed the idea that comets are 'dirty snowballs'."] {{Webarchive|url=https://web.archive.org/web/20180211080325/http://www.independent.co.uk/news/obituaries/professor-fred-whipple-533019.html |date=11 February 2018 }} ''The Independent'', 13 November 2004.</ref> The shield allows a spacecraft body to be built to just the thickness needed for structural integrity, while the foil adds little additional weight. Such a spacecraft is lighter than one with panels designed to stop the meteoroids directly.

For spacecraft that spend the majority of their time in orbit, some variety of the Whipple shield has been almost universal for decades.<ref>Fred Whipple, [http://www.sciencemag.org/cgi/content/full/289/5480/728 "Of Comets and Meteors"] {{Webarchive|url=https://web.archive.org/web/20080629032626/http://www.sciencemag.org/cgi/content/full/289/5480/728 |date=29 June 2008 }} ''Science'', Volume 289 Number 5480 (4 August 2000), p. 728.</ref><ref>Judith Reustle (curator), [http://ares.jsc.nasa.gov/ares/hvit/basic.cfm "Shield Development: Basic Concepts"] {{webarchive|url=https://web.archive.org/web/20110927133616/http://ares.jsc.nasa.gov/ares/hvit/basic.cfm |date=27 September 2011 }}, NASA HVIT. Retrieved 20 July 2011.</ref> Later research showed that [[Ceramic engineering|ceramic fibre]] woven shields offer better protection to hypervelocity (~7&nbsp;km/s) particles than [[aluminium]] shields of equal weight.<ref>[http://www.3m.com/market/industrial/ceramics/pdfs/CeramicFabric.pdf Ceramic Fabric Offers Space Age Protection] {{Webarchive|url=https://web.archive.org/web/20120309094614/http://www.3m.com/market/industrial/ceramics/pdfs/CeramicFabric.pdf |date=9 March 2012 }}, 1994 Hypervelocity Impact Symposium</ref><!-- This summary source from 3M is not an ideal WP source but it provides a very good summary of a number of extensive NASA-funded studies on hypervelocity projectile impacts and several references in the technical literature for further research. --> Another modern design uses [[Transhab#Multi-Layer Inflatable Shell|multi-layer flexible fabric]], as in [[NASA]]'s design for its never-flown [[TransHab]] expandable space habitation module,<ref name="nasa20030627">Kim Dismukes (curator), [http://spaceflight.nasa.gov/history/station/transhab/ "TransHab Concept"] {{Webarchive|url=https://web.archive.org/web/20070601021217/http://spaceflight.nasa.gov/history/station/transhab/ |date=1 June 2007 }}, NASA, 27 June 2003. Retrieved 10 June 2007.</ref> and the [[Bigelow Expandable Activity Module]], which was launched in April 2016 and attached to the [[International Space Station|ISS]] for two years of orbital testing.<ref name=sdc20141006>{{cite news |last1=Howell |first1=Elizabeth |title=Private Inflatable Room Launching to Space Station Next Year |url=http://www.space.com/27356-bigelow-inflatable-room-space-station.html |access-date=2014-12-06 |work=Space.com |date=2014-10-06 |archive-url=https://web.archive.org/web/20141204004125/http://www.space.com/27356-bigelow-inflatable-room-space-station.html |archive-date=4 December 2014 |url-status=live }}</ref><ref>{{Cite web |url=https://www.nasaspaceflight.com/2016/04/iss-crs-8-dragon-arrival-flawless-launch/ |title=ISS welcomes CRS-8 Dragon after flawless launch |date=9 April 2016 |access-date=14 May 2016 |archive-url=https://web.archive.org/web/20160423015518/https://www.nasaspaceflight.com/2016/04/iss-crs-8-dragon-arrival-flawless-launch/ |archive-date=23 April 2016 |url-status=live }}</ref>

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