Hexagon system was the last satellite employing film reentry vehicles.[167] Hexagon was declassified in 2011.[168]
Space Transportation System/Space Shuttle (1972–2011)
The Space Shuttle program was NASA's fourth human spaceflight program and was comprised of the first reusable spacecraft to carry humans into Earth's orbit.[169] The space shuttle fleet—Columbia, Challenger, Discovery, Atlantis, and Endeavour—flew 135 missions, serviced the Hubble space telescope, and helped construct the International Space Station.[170] The first shuttle launch, Columbia, was conducted on April 12, 1981.[171]
HAVE Blue/F-117A Nighthawk/TACIT Blue (1975)
The Defense Advanced Research Project Agency (DARPA) oversaw the development of HAVE Blue in the mid-1970s, which was the first practical, combat-stealth aircraft. HAVE Blue completed its first test flight in 1977, and the success of this program led the USAF to later produce the F-117A Nighthawk, as well as the TACIT Blue aircraft. The HAVE Blue, F-117A Nighthawk, and TACIT Blue programs laid the foundations for the later development of the B-2 stealth bomber.[172]
Advanced Technology Bomber/B-2 Spirit (1980)
The B-2 is a USAF low-observable stealth bomber capable of delivering conventional and nuclear payloads. It uses a combination of reduced infrared, acoustic, and electromagnetic signatures. It was first publicly displayed on November 22, 1988 in Palmdale, California and conducted its first flight on July 17, 1989. The first aircraft was delivered on December 17, 1993.[173]
Strategic Defense Initiative (March 1983)
At the initiative of President Ronald Reagan, the Strategic Defense Initiative Organization was established in 1984 to explore a multi-layered strategic defense against ballistic missiles; this program involved research into space-based and ground-based systems including laser and interceptor missiles. This intensive research effort involved national laboratories and academia. Some of the technologies researched were determined to be years from development, and funding was reduced. The program ended in 1993 and was replaced by the Ballistic Missile Defense Organization.[174]
Advent of Unmanned Aerial Vehicles 1980s–Present
The research and development, flight testing, evaluation, deployment, and the operation of drones—Unmanned Aerial Systems (UAS), Unmanned Aerial Vehicles (UAV), Remotely Piloted Aircraft (RPA), and Remotely Piloted Aircraft Systems (RPAS)—almost certainly resulted in reported sightings of UAP. Some of these systems had a "saucer" or triangle-shaped appearance and were capable of loitering aloft.
The USG acquired and operated a number of systems for a range of missions including intelligence, surveillance, reconnaissance, and strike, among others. The below systems
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