This vehicle was used to test the parachute NASA planned to use to "soft land" the Viking on Mars. To simulate the thin Martian atmosphere the
parachute needed to be used at an altitude more than 160,000 feet above the earth. A balloon launched from Roswell, N.M. was used to initially lift
the aeroshell. The balloon drifted west to the missile range where the vehicle was dropped and the engines beneath the vehicle boosted it to the
required altitude where the parachute was deployed. The tests were conducted in the summer of 1966. NASA. There is one left, at White Sands Missile
Range, New Mexico.
Awhile back the USAF was trying to say that the aeroshell in question was the crashed disc of Roswell, 1947, fame. They argued that people saw the
thing getting lugged around at Roswell and, years later, mistook it for an alien craft.
When this theory was torn-apart by UFOlogists, the USAF went back to the Mogul balloon explanation.