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 MK 111 Fire Control System computer, and a PDP-8 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 monopulse radars that could track targets at a range of 150 nautical miles. These were very high power monsters (about 3 megawatts) that were 19 feet high, 17 feet wide, and weighed 22 tons. The megawatt radar beam was hot enough to cause flesh burns on anyone close by that was 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 a 5 kilowatt vertically polarized continuous wave (CW) transmitter was turned on to illuminate the target for the missile's homing system. The CW signal was frequency modulated to provide target doppler information for the missile. The missile homed on the CW signal reflected off the target.

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 operated independently from the SPG-49 tracking radar, allowing the missile to be guided to an intercept point ahead of the target being tracked.

The signal from the SPW-2 was detected and decoded by the missile. Then the missile transmitted a tracking signal that was detected by the SPW-2 and sent to the MK 111 Fire Control Computer to provide missile range data during cruise to target and missile to target range data during the homing phase. The missile maneuvered to stay near the center of the guidance beam. The MK 111 computer steered the beam to guide the missile to intercept the target. When the missile neared the target commands in the SPW-2 guidance beam switched the missile to homing mode to intercept the target.

Mk 111 Fire Control System computer

The Mk 111 guidance computer was a 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 transmit continuous wave mode for the intercept and when the missile should switch to homing mode. 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 (2011) desktop computer but actually had far less computing power than a modern pocket 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).