The Mk 77 Guided Missile Fire Control System (GMFCS) controlled the flight of the missile after launching. It was composed of the AN/SPG-49 target tracking radars, the AN/SPW-2 missile guidance radars, the Fire Control System computer, and a PDP-11 surface trajectory computer. In addition information was provided from the ship's air search radars to initiate target acquisition and intercept. The ship's AN/SPS-10 surface search radar or the Mk 37 gunfire director could supply target information for surface targets.
SPS-43 Air search and SPS-30 tracking/altitude radars
These radars were not specifically parts of the Talos system, but were necessary for initial target identification. The AN/SPS-43 was a "bedspring" style long range air search radar. It provided bearing and range, but no altitude information. It normally operated in a circular sweep mode to search airspace above the horizon out to several hundred miles.
The AN/SPS-30 was a height finder radar that provided altitude information for objects of interest. It could be operated in circular sweep mode, or it could be aimed directly at a specific contact to provide continuous altitude and tracking information. It had a large circular parabolic reflector with a side-mounted feed horn. Effective range was 150 miles or more.
SPG-49 target tracking radar
Each missile battery had two AN/SPG-49 long range automatic tracking C-band radars. These were very high power monsters (about 3 megawatts) capable of tracking the moon 240,000 miles away. In fact, the moon was used to calibrate the range of the radars. The megawatt radar beam was hot enough to cause flesh burns on anyone unfortunate enough to be in the beam, and it could damage electronic devices. During the Apollo missions to the moon Talos ships were issued orders to avoid tracking the spacecraft, or even transmitting signals into space while a spacecraft was overhead.
Each radar was assigned to a single target and aimed directly at it. The 49s operated in two modes. The monopulse transmitter generated 3 megawatt pulsed mode signals in a wide vertically polarized beam during target acquisition and switched to a narrow pulsed horizontally polarized beam for tracking to get target range and bearing information. When the missile approached the target the transmitter switched to 50 kilowatt vertically polarized continuous wave mode to illuminate the target for the missile's homing system. The continuous wave signal was frequency modulated to provide target doppler information for the missile.
SPW-2 guidance system
The AN/SPW-2 was a data link between the ship's Fire Control System computer and the missile. It's C-band transmitter generated the guidance beam that led the missile to the target. The SPW-2 provided missile range data during cruise to target and missile to target range data during the homing phase.
Mk 111 Fire Control System computer
The Mk 111 guidance computer was an automobile sized collection of cabinets full of tubes, servo motors and gears, a follow on from World War II era mechanical gunfire target solution calculators. Prior to launch it calculated the booster splashdown area to allow the launcher to be aimed so the spent booster wouldn't strike friendly ships. During the guidance phase the computer received target tracking information from the SPG-49 tracking radar and missile range information from the SPW-2 radar set and calculated guidance beam control commands to direct the missile to the intercept point. It also determined when the 49s should switch from pulsed to continuous wave mode for the intercept. During anti-radiation shots the computer guided the missile to the target area and told it when to start looking for the target radar.
PDP-8 surface trajectory computer
A Digital Equipment Corporation PDP-8 minicomputer in Weapons Control was used to determine missile flight trajectory to over the horizon surface targets. This was a state of the art minicomputer in the 1960s. It was mounted in a rack about half the size of a refrigerator. The computer itself was several times the size of a modern (2009) desktop computer but actually had far less computing power than a modern calculator. The program was stored on punched paper tape and loaded into the computer through an ASR-33 Teletype terminal that had a tape reader and punch, a keyboard and a printer. This procedure took about half an hour. The ship's and the target's geographic coordinates were typed into the computer and the program calculated the flight profile. An early satellite navigation system provided the ship's geographic location (longitude and latitude).
