NASA F-15 835 (ex 71-0287) was a unique one-of-a-kind aircraft called the F-15 Flight Research Facility. It was instrumented and equipped with an Highly Integrated Digital Electronic flight Control system (HIDEC). It looks rather sad sitting in the desert with no more work to do. It has lost the NASA titles on the fin. The USAF serial is not visible here as it is carried in small script on the fuselage behind the wing.