Wake Shield Facility (WSF) was a NASA experimental science platform that was placed in low Earth orbit by the Space Shuttle. It was a 3.7 m (12 ft) diameter, free-flying stainless steel disk. The WSF was deployed using the Space Shuttle's Canadarm. The WSF then used nitrogen gas thrusters to position itself about 55 km (34 mi) behind the Space Shuttle, which was at an orbital altitude of over 300 km (190 mi), within the thermosphere, where the atmosphere is exceedingly tenuous. 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. The WSF thus created an ultrahigh vacuum in its wake. The resulting vacuum was used to study epitaxial film growt