ASC-15 - ASC-15 For Titan II

ASC-15 For Titan II

The first inertial guidance system for the Titan II was built by AC Spark Plug, and included an inertial measurement unit based in designs from Draper Labs at MIT and the ASC-15 computer designed and built by IBM in Owego, NY. The first Titan II missile carrying this system was launched 16 March 1962. Acquiring spares for this system became difficult, and the Air Force decided to replace it with a new system. The AC Spark Plug system, including the ASC-15, was replaced by the Delco Electronics Universal Space Guidance System (USGS) on operational Titan II missiles starting in January 1978. The guidance computer in the USGS was the Magic 352, made by Delco.

The ASC-15 was built on an aluminum frame about 1.5x1.5x1 feet. The sides, top and bottom were covered by pieces of laminated plastic, covered with gold-plated aluminum foil. These covers were slightly convex and ribbed for stiffness. Inside the covers were fifty-two logic sticks, each containing four welded encapsulated modules. These surrounded a bell frame housing a drum memory. See Figure 2.

The drum was a thin-walled stainless steel cylinder 3 inches long and 4.5 inches in diameter covered with a magnetic nickel-cobalt alloy. It was driven by a synchronous motor at 6,000 rpm. The drum had 70 tracks, of which 58 were used and 12 were spare. These tracks were used as follows:

The capacity of a track was 1,728 bits. Instruction words were 9-bits long, and data was stored in 27-bit words.

Coincident with 58 tracks were 67 read heads and 13 write heads. While the drum was spinning at 6,000 rpm, the heads floated above the surface of the drum on a thin layer of air. When the drum was spinning up or slowing down, the heads were raised off the drum by camshafts rotated by a chain that was driven by a motor on top of the drum housing, to avoid scoring the magnetic surface. See Figure 3.