In the early 1970s Lockheed's L-300 demonstrator was converted into NASA's Kuiper Airborne Observatory, and fitted with a 36-inch infrared telescope between the cockpit and wing. A cover retracted when in use. It was able to get above most of the atmospheric water vapour that affected terrestrial optical telescopes. Ex Lockheed demonstrator N4141A, N714NA retired in 1995 and has been preserved at Moffett Field. It was replaced by a Boeing 747SP.