View source for Wake Shield Facility

{{Short description|American scientific satellite}}
{{Use American English|date=February 2022}}
{{Use dmy dates|date=February 2022}}

[[File:Wake shield facility.jpg|thumb|upright=1.0|right|Deployment of the WSF using the Space Shuttle robotic arm, [[Canadarm]]]]

'''Wake Shield Facility''' ('''WSF''') was a [[NASA]] experimental science platform that was placed in [[low Earth orbit]] by the [[Space Shuttle]]. It was a {{cvt|3.7|m}} diameter, free-flying [[stainless steel]] disk.

The WSF was deployed using the Space Shuttle's [[Canadarm]].<ref name="NewScientist-mg14719892">{{cite news |url=https://www.newscientist.com/article/mg14719892-700-making-semiconductors-out-of-thin-air/ |title=Making semiconductors out of thin air |publisher=New Scientist |last=Kiernan |first=Vincent |date=5 August 1995}}</ref> The WSF then used [[nitrogen]] gas thrusters to position itself about {{cvt|55|km}} behind the Space Shuttle, which was at an orbital altitude of over {{cvt|300|km}}, within the [[thermosphere]], where the atmosphere is exceedingly tenuous.<ref name="NewScientist-mg14719892"/> The WSF's [[orbital speed]] was at least three to four times faster than the speed of thermospheric gas molecules in the area, which resulted in a cone behind the WSF that was entirely free of gas molecules.<ref name="scfh-2012"/> The WSF thus created an ultrahigh vacuum in its wake.<ref name="scfh-2012"/> The resulting vacuum was used to study [[epitaxial]] [[Thin-film deposition|film growth]]. The WSF operated at a distance from the Space Shuttle to avoid contamination from the Shuttle's rocket thrusters and water dumped overboard from the Shuttle's [[Space toilet|Waste Collection System]] (space toilet).<ref name="NewScientist-mg14719892"/> After two days, the Space Shuttle would rendezvous with the WSF and again use its robotic arm to collect the WSF and to store it in the Shuttle's payload bay for return to [[Earth]].<ref name="NewScientist-mg14719892"/>

The WSF was flown into space three times, aboard Shuttle flights [[STS-60]] (WSF-1), [[STS-69]] (WSF-2) and [[STS-80]] (WSF-3). During STS-60, some hardware issues were experienced, and, as a result, the WSF-1 was only deployed at the end of the Shuttle's Canadarm. During the later missions, the WSF was deployed as a free-flying platform in the wake of the Shuttle.

These flights proved the vacuum wake concept and realized the space [[epitaxy]] concept by growing the first-ever crystalline semiconductor [[thin film]]s in the vacuum of space.<ref>{{cite journal |title=Advanced thin-film materials processing in the ultra-vacuum of space |journal=Acta Astronautica |first=Alex |last=Ignatiev |volume=48 |issue=2–3 |pages=115–120 |date=January 2001 |doi=10.1016/S0094-5765(00)00148-X |bibcode=2001AcAau..48..115I}}</ref> These included [[gallium arsenide]] (GaAs) and [[aluminum gallium arsenide]] (AlGaAs) depositions. These experiments have been used to develop better [[Photodetector|photocells]] and thin films.<ref>{{cite journal |title=Photoluminescence of GaAs grown by metallorganic molecular beam epitaxy in space ultra-vacuum |journal=Journal of Crystal Growth |first1=A. |last1=Freundlich |first2=C. |last2=Horton |first3=M.&nbsp;F. |last3=Vilela |first4=M. |last4=Sterling |first5=A. |last5=Ignatiev |first6=G. |last6=Neu |first7=M. |last7=Teisseire |volume=209 |issue=2–3 |pages=435–439 |date=February 2000 |doi=10.1016/S0022-0248(99)00586-2 |bibcode=2000JCrGr.209..435F}}</ref> Among the potential resulting applications are artificial [[retina]]s made from tiny [[ceramic]] detectors.

Pre-flight calculations suggested that the pressure on the wake side could be decreased by about 6 orders of magnitude over the [[ambient pressure]] in low Earth orbit (from {{10^|-8}} to {{10^|-14}}&nbsp;[[Torr]]). Analysis of the pressure and temperature data gathered from the two flights concluded that the decrease was about 2 orders of magnitude (4 orders of magnitude less than expected).<ref>{{cite journal |title=Wake vacuum measurement and analysis for the wake shield facility free flying platform |journal=Vacuum |first1=J.&nbsp;A. |last1=Strozier |first2=M. |last2=Sterling |first3=J.&nbsp;A. |last3=Schultz |first4=A. |last4=Ignatiev |volume=64 |issue=2 |pages=119–144 |date=November 2001 |doi=10.1016/S0042-207X(01)00383-9 |bibcode=2001Vacuu..64..119S}}</ref>

The WSF was sponsored by the Space Processing Division in NASA's Office of Life and Microgravity Sciences and Applications. It was designed, built and operated by the [[Center for Advanced Materials, University of Houston|Space Vacuum Epitaxy Center]], since renamed the Center for Advanced Materials, at the [[University of Houston]], a NASA Commercial Space Center in conjunction with its industrial partner, [[Space Industries Incorporated|Space Industries, Inc.]], also in [[Houston]], [[Texas]].

{{As of|2012}}, the Wake Shield Facility spacecraft is being preserved at the Center for Advanced Materials.<ref name="scfh-2012">{{cite journal |url=https://scfh.ru/en/papers/vacuum-in-the-wake/ |title=Vacuum in the Wake |journal=Science First Hand |volume=31 |date=10 April 2012}}</ref>

== See also ==
{{Portal|Spaceflight}}
* [[Space manufacturing]]

== References ==
{{Reflist|30em}}

== External links ==
* [http://www.cam.uh.edu/projects/space-materials Space Materials Science] by the Center for Advanced Materials
* [https://web.archive.org/web/20120220121603/http://www.cam.uh.edu/WSF.php Wake Shield Facility program] by the Center for Advanced Materials (archive)
* [https://web.archive.org/web/20191017172744/http://www.svec.uh.edu/wsfp.html Wake Shield Facility program] by the Space Vacuum Epitaxy Center (archive)

{{commons category}}
{{Space Shuttle}}
{{Orbital launches in 1994}}
{{Orbital launches in 1995}}
{{Orbital launches in 1996}}

[[Category:NASA programs]]
[[Category:Space science experiments]]
[[Category:Space manufacturing]]
[[Category:Thin film deposition]]
[[Category:Spacecraft launched in 1994]]
[[Category:Spacecraft launched in 1995]]
[[Category:Spacecraft launched in 1996]]
[[Category:Spacecraft launched by the Space Shuttle]]
[[Category:Space hardware returned to Earth intact]]