Question: Who owns the test unit operated by Aerospace Testing Alliance?
Context: The von Karman Gas Dynamics Facility at Arnold Engineering Development Complex, Arnold Air Force Base, Tennessee, provide aerothermal ground test simulations of hypersonic flight over a wide range of velocities and pressure altitudes.  The facility consists of three Hypersonic wind tunnels: Tunnel A, B, and C.  The wind tunnels can be run for several hours at a time thanks to a 92,500 horsepower air compressor plant system.  The test unit is owned by the United States Air Force and operated by Aerospace Testing Alliance. Aerospace Testing Alliance (ATA) is an aerospace engineering company in the United States of America.  It is the prime contractor of the US Air Force's Arnold Engineering Development Center (AEDC), in Tullahoma, Tennessee. AEDC Hypervelocity Wind Tunnel 9 is a hypersonic wind tunnel owned by the United States Air Force and operated by Aerospace Testing Alliance.  The facility can generate high Mach numbers and high Reynolds for hypersonic ground testing and the validation of computational simulations for the Air Force and Department of Defense. AEDC Range G is a two-stage light-gas gun owned by the United States Air Force and operated by Aerospace Testing Alliance. Arnold Engineering Development Complex (AEDC), Arnold Engineering Development Center before July 2012, located at Arnold Air Force Base, Tennessee is a ground-based flight test facility operated by the Air Force Test Center. The AEDC Sea Level Test Cells, located at Arnold Engineering Development Complex, is a collection of test cells used to economically perform durability testing on large augmented turbine engines at near sea level conditions.  All test units in the facility are owned by the United States Air Force and currently operated by Aerospace Testing Alliance. The Aero-propulsion Systems Test Facility, located at Arnold Engineering Development Complex is a unique national facility designed to test aircraft propulsion systems in true mission environments without leaving the ground.  The test unit is owned by the United States Air Force and operated by Aerospace Testing Alliance. The AEDC Space Chambers Test Facility, located at Arnold Engineering Development Complex, contains several test units used for simulating space conditions.  The facility has a variety test cells to accommodate various sized test articles.  Test articles range in size from the sensor level all the way up to full-scale space systems.  All test units in the facility are owned by the United States Air Force and currently operated by Aerospace Testing Alliance. AEDC Ballistic Range S-3 is a single stage air gun owned by the United States Air Force and operated by Aerospace Testing Alliance.  The gun is commonly used for bird strike testing and is often called a chicken gun. The Propulsion Wind Tunnel Facility, located at Arnold Engineering Development Complex, Arnold Air Force Base, Tennessee, holds three wind tunnels: the 16-foot transonic (16T), 16-foot supersonic (16S), and the aerodynamic 4-foot transonic (4T) tunnels.  The facility is devoted to aerodynamic and propulsion integration testing of large-scale aircraft models.  The tunnels are powered by a large compressor plant which allows the wind tunnels to run for extended periods of time.  The test unit is owned by the United States Air Force and operated by Aerospace Testing Alliance.
Answer: United States Air Force