" A friend said, he would never forget the sight of the alien looking TR-3B based at Papoose. The pitch black, triangular shaped TR-3B was rarely mentioned--and then, only in hushed whispers--at the Groom Lake facility where he worked. The craft had flown over the Groom Lake runway in complete silence and magically stopped above Area S-4. It hovered silently in the same position, for some 10 minutes, before gently settling vertically to the tarmac. At times a corona of silver blue light glowed around the circumference of the massive TR-3B. The operational model is 600 feet across. "
From YouTube video description
" The TR3B is Code Named Astra. The tactical reconnaissance TR-3B first operational flight was in the early 90s. The triangular shaped nuclear powered aerospace platform was developed under the TopSecret, Aurora Program with SDI and blackbudget monies. At least 3 of the billion dollar plus TR-3Bs were flying by 1994. The Aurora was the most classified aerospace development program in existence. The TR-3B is the most exotic vehicle created by the Aurora Program. It is funded and operationally tasked by the National Reconnaissance Office, the NSA, and the CIA. The TR-3B flying triangle is not fiction and was built with technology available in the mid 80s. Not every UFO spotted is one of theirs. The TR-3B vehicles outer coating is reactive to electrical Radar stimulation and can change reflectiveness, radar absorptiveness, and color. This polymer skin, when used in conjunction with the TR-3Bs Electronic Counter Measures and, ECCM, can make the vehicle look like a small aircraft, or a flying cylinder–or even trick radar receivers into falsely detecting a variety of aircraft, no aircraft, or several aircraft at various locations. A circular, plasma filled accelerator ring called the Magnetic Field Disrupter, surrounds the rotatable crew compartment and is far ahead of any imaginable technology. They have been spotted all over the USA as the military is not hiding them anymore. This craft wast most likely responsibe for the infamous PhoenixLights in March 1997. "
text above from 4biddenknowledge (where you can watch a related video)