|The Orbiter Enterprise, OV-101, is eligible for listing on the National Register of Historic Places in the context of the U.S. Space Shuttle Program (1969-2011) under Criterion A in the areas of Space Exploration and Transportation and under Criterion C in the area of Engineering. As Enterprise has achieved exceptional significance within the past 50 years, Criteria Consideration G applies. Under Criterion A, Enterprise is exceptionally significant because of its role in major events of the Space Shuttle Program. Enterprise, the first and only full-scale prototype of the orbiter fleet, was first used during the Approach and Landing Tests, one of the earliest missions of the Space Shuttle Program. Additional tests involving Enterprise prepared Cape Canaveral for the first of 135 space shuttle launches. As part of the Approach and Landing Tests program Enterprise was the first orbiter to fly in Earth's atmosphere, doing so thirteen times, five of which saw it separate from the Shuttle Carrier Aircraft in order to fly and land unaided. Additionally, Enterprise was used in the investigations and procedural revisions following the Challenger and Columbia accidents. Following the Challenger accident in 1986, Enterprise aided in crew escape tests. Following the Columbia accident in 2003, one of Enterprise's wing edges and a landing gear door were borrowed for tests related to foam chunks striking an orbiter during launch. Although the loss of two space shuttle orbiters was devastating to NASA and the United States, Enterprise helped the program return to flight and continue its mission. Enterprise significantly advanced the United States' ability to explore outer space, and allowed the other five orbiters to make significant advancements in a range of scientific and technological fields. Under Criterion C, Enterprise is exceptionally significant for its .role in the practical application and testing of orbiter designs and features. Enterprise was of paramount importance in testing the feasibility of the Shuttle Carrier Aircraft- a modified 747 that transported the orbiters. Enterprise was indispensable in proving the flightworthiness of the space shuttle orbiter and the continued testing and modification of the orbiter fleet throughout the space shuttle program. The information gathered during the Approach and Landing Tests led to alterations in materials used for certain components (such as titanium instead of aluminum) and modifications in orbiter design. Leroy Chiao, NASA astronaut on STS-65 (1994), STS-72 (1996), and STS-92 (2000), as well as commander and science officer on International Space Station Expedition 10 (2004-2005), stated that [The] shuttle, to me, represents a triumph and remains to this day a technological marvel. We learned so much from the program, not only in the advancement of science and international relations, but also from what works and what doesn't on a reusable vehicle. The lessons learned from shuttle will make future US spacecraft more reliable, safer, and cost effective.