Tending to « Misty Rain » This is the front end of line-of-sight pipe, 875 feet from the Zero Room. The Misty Rain test explosion took place inside this pipe on April 6, 1985. Once the proper equipment was in place, the large, round steel door was welded shut and the line-of-sight pipe was made into a vacuum simulating conditions 300,000 feet above the surface of the earth. Data from the test were used to evaluate the hardness of MX reentry vehicles and the vulnerability of satellities. X-ray laser lethality testing was also conducted.