Charles Riggs and other members of USAF contractor Land-Air, Inc were preparing for an MX-776A Shrike air- to-ground missile test. The Askania theodolite crews saw, tracked, and filmed four high flying objects on a cinetheodolite at station P-10 and a theodolite at station M-7. Triangulation resulted in a calculation of 30 feet size and 150,000 foot altitude for the "high speed" objects located between Holloman AFB and Tularosa Peak.

Eight shiny balls, about 40 feet across, were observed by several witnesses near a missile for five minutes (Charles Riggs). No sound was heard.

Ruppelt's account:

The guided missile test range at White Sands is fully instrumented to track high, fast-moving objects--the guided missiles. Located over an area of many square miles there are camera stations equipped with cinetheodolite cameras and linked together by a telephone system.

On April 27, 1950, a guided missile had been fired, and as it roared up into the stratosphere and fell back to earth, the camera crews had recorded its flight. All the crews had started to unload their cameras when one of them spotted an object streaking across the sky. By April 1950 every person at White Sands was UFO-conscious, so one member of the camera crew grabbed a telephone headset, alerted the other crews, and told them to get pictures. Unfortunately only one camera had film in it, the rest had already been unloaded, and before they could reload, the UFO was gone. The photos from the one station showed only a smudgy dark object. About all the film proved was that something was in the air and whatever it was, it was moving.

Google map of this location.