BASIC LAYOUT

All MOD I’s consisted of two radar systems: a monopulse TRACK for position and a Doppler RATE for velocity. The physical configuration was in a cross, called a cruciform with the Track and main Rate antennas located at the center of the cross. The legs of the cross were 1 mile long with doppler antennae at the ends of each, connected to the center with waveguide. Waveguide was pressurized with nitrogen to provide dry air for operation.

Both these systems required the installation of a transponder on the payload. Both Track and Rate would transmit their signals to the payload/transponder and process the return signals. For simulation, SIM would activate transponders on the boresight tower, about 1/2 mile from the center of the cruciform.

Aircraft tests would be periodically performed. The aircraft, a Convair 340 with a transponder installed, would fly a course for us to track. A strobe light on the aircraft was used to optically track the aircraft position against the night stars. Photographs were taken and analyzed to determine the absolute accuracy of our system.

Most of the sensitive system components, like the antennae were transported to SanSal by C119 and C124 aircraft.

TRACK

The early MOD I Track antennas were single sail configuration. These were designated as MOD I, systems 1 &2. This was also the antenna that was first installed on SanSal in 1957. I believe this was designated MOD I, System 3. The reflector that fed the two “pillboxes” or feedhorns was reminiscent of a square-rigger sail.

MOD I, System 4, at SanSal was upgraded with a “transition” antenna. It was a new configuration with two sails, shaped like banana peels on each side of a “snout” that held the two pillboxes.

All the MOD I antennas were gear-driven from DC servo motors that were powered by a servo motor-generator (M-G). The M-G field coils were controlled from tube-type servo amplifiers. The position information was collected by capacitive-type Norden encoders.

MOD III antennas were similar in appearance to the MOD I, System 4 on SanSal, however appearances are deceiving. The drive system eliminated the gears so the azimuth and elevation were driven by 1 revolution per minute DC motors. The encoders were optical-type built by Baldwin. There is not a single picture of this unique antenna other than the one shown here, during installation at the Cape. In this picture, the two sails are flat on their backs with the snout pointing straight up. This assembly is about to be connected to the azimuth drive.

MOD IIIs were also upgraded with a track receiver that was built onto the rear of the antenna. This was a much improved version of the older MOD I’s with the receiver in the trailer, or in an electronics bay fed directly with waveguide. The new receivers processed all of the azimuth and elevation information and only demodulated signals were sent to the servos for antenna control. The AGC system was also much improved. The result was a receiver that was free of the false locks (we called them side-lobes) and AGC overload that was inherent in the MOD I systems. This much-improved system was a “feet-on-the-desk” system that did not require the constant tweaking and strain of the MOD Is.

All MOD IIIs were housed in a radome to reduce sun loading that would cause mechanical distortion of the sails and resultant error.

The team that operated System 4 on SanSal performed outstanding maintenance and operation. During our time there, the Cape remarked that they had never seen data from the MOD I as we consistently delivered. This, I believe was due to the the outstanding training provided by Darrel Hartung, the solid support of Jim Peeples and the best crew: Dick Maplesden, Bob Hankal, Arleigh Black...and of course our Sanborn Hotshot: Lowell Busching.

L: MOD III sail and snout installation. Sails are in prone position, snout pointing up /
R: MOD III in radome at the Cape (Chuck Flower with binoculars)

Azimuth and elevation tracking was accomplished by processing the two X-band pulses reflected off the sails into the feedhorns. Azimuth was decoded by comparing the phase of the microwaves between the two feedhorns; elevation was detected by the difference in amplitude. The Local Oscillator was a tunable Klystron labeled “SECRET”. The servos that controlled the antenna were type 1, meaning that they were zero error in position with constant error in velocity. The velocity pointing error was compensated with servo motors on the encoders that turned in proportion to the amount of error.

Range was determined by counting a reference oscillator from time of transmission of the pulse of microwaves until they were received. At that time, the vacuum tubes could only count to 1.3 MHz, or about 250 yards, so a unique and classified circuit, the vernier oscillator acted like a mechanical vernier works on a caliper to increase the resolution to 2.5 yards.

On MOD III at Vandenberg, the servo was redesigned to a type 2 with accelerometers on the antenna. The pointing error was so small that the RATE system was not needed; with the accurate track information, the Harris Computer used Kalman Filtering to extract angle, range and rate data. The ultimate range resolution was in the order of 2 feet.

Considering that all of this gear was designed in the late 1950’s, 100% vacuum tube, it is a tribute to the designers at Electronics Park in Syracuse, NY.

Now for the kicker: The MOD III at Vandenberg operated (with upgrades) in just about the same vacuum tube configuration until it was deactivated in 1995! That system guided and tracked every single ICBM from Vandenberg, a total of over 500 missiles without a single failure!

AMAZING!

RATE

Three critical parameters required to predict the impact of the missile were Yaw, Pitch and Slant RATE. These three velocity parameters were delivered by the RATE system. Most apparent of a MOD I site was the “cruciform” configuration, the cross of waveguide legs that were the microwave communication from the Rate processing system to the four outlying Doppler antennae. There were 5 Rate antennae in total, the four at the ends of the cross and the central, main antenna. Central would transmit a continuous microwave beam to the transponder, and it turn, it would transmit back, to be received by Central and the four others. From the shift in frequency, the three parameters would be computed in the Rate processing equipment.

The rate receiver was unique. It was a “phase-lock” loop receiver, highly advanced in those days; today it is the main type receiver used in consumer radios. The phase lock enabled precise determination of the frequency deviation due to the motion of the missile to an accuracy of about 50 feet per second from a missile traveling at 12,000 miles per hour:
17,600 feet per second!

I believe the system operated in “C” band, just right for cooking steaks. Microwave ovens had not yet come to market, but there are many stories about radar systems in this band being used to heat coffee and snacks. The transmitter operated in the Kilowatt range, so it was lethal. Once, when one of the techs was doing some maintenance in the Main Radome, Gil or some other malevolent operator decided to have some fun. During some procedure, the RATE operator began to slew the antenna in a direction towards the tech (he couldn’t see him, but guessed where he might be). The result was a panic message to the operator (which was ignored) as the antenna was slewed to “trap” the unlucky tech in the radome, away from the door. The tech ended up panicked and yelling for help while the guys in the RATE trailer laughed their silly heads off. Of course, there was nothing transmitted at the time, but the terror of being cooked alive might have caused other problems. We all had a big laugh about that one.

The 4 miles of waveguide was a headache. It was pressurized with dry nitrogen to keep it working and to prevent arcing. There were sliding expansion joints along the way to allow for considerable movement with change in temperature. Howard Hupe’s SYSTEMS team was responsible for maintaining that part of the system; they were never really appreciated for the work they had to do to keep that stuff working.

MOD III, Vandenberg, was highly advanced over MOD I. The Track system was upgraded significantly so the tracking error was nil. Angle information was sent directly to the Harris Computer. Only the transmit pulse and return pulses were sent to the Computer, where Range, and three velocity parameters were computed with a Kalman Filter. The accuracy of RATE and RANGE was increased by over 10x.

Rare Rate Pictures: Cameras were not allowed on site, how did these get taken? Hmmmm?

LtoR: looking towards central from east Rate pad (look real close and you can see the boresight tower...to the right of the tower, a very small light blob is the Track Antenna; looking towards Cockburn Town from east Rate pad / East Rate pad / Rate radome

DATA/RECORD/EXCERCISE (SIMULATOR)

Data from the TRACK and RATE trailers was sent to DATA/RECORD, where it was stored, recorded on tape and sent to the Burroughs Computer and FLIGHT DATA. Art Rackow was the Engineering lead for this system but stayed mostly in his trailer. Ken O’Keefe was mostly in the SIMULATOR trailer.

Well, Art didn’t like wearing headphones for operations, so he decided to put up speakers in his trailer. He designed an audio amplifier (transistors) to provide the power necessary to do the job. His design experience must have been in RF, since he used a common base amplifier configuration, good to provide low impedance, 50 ohm input impedance for coaxial cable, but really unsuitable for audio work. When an operation began, and we all logged on, Art would turn on his amplifier and essentially short out the entire PA system so that Hupe’s people would then have to turn up the gain...the result was a nasty, distorted, noisy audio that was a mystery for a LONG time, until the site was being deactivated. Someone found the clandestine amp and the mystery was solved, a year or so after the problem began!

SIMULATOR was connected to transponders on the Boresight Tower, about 1/2 mile from the TRACK antenna. TRACK would slew to the boresight tower, ask for a SIM, and they would then become the payload transponder. There were 4 antennas on the Boresight tower:

1. Main Track
2. Elevation Track response test
3. Azimuth Track response test
4. Rate Beacon

The Main Track and Rate Beacon were used to verify basic operation of the two systems, and verify “lock” for both of them. The response test in Azimuth and Elevation was used to test the response of the Error Compensation Servo (ECS) in TRACK with a step change in position.

MOD III Vandenberg installed equipment that could simulate an entire mission, with microwave feed directly to the pillboxes. This system was operated by the TRACK system and would effectively exercise every operating condition of a real mission and provide a training opportunity for operators. Nice system!

FLIGHT DATA

In the blockhouse, a large room was filled with recording equipment. Primary were digital tape recorders that recorded all of the flight data.

Secondary was 8 or so 8-channel Sanborn recorders that recorded all of the analog data from the RATE and TRACK systems. This included Automatic Gain Control voltages, Automatic Frequency Control, Phase Lock Loop Control, Error Correction Servo, and many, many more. These recorders melted wax-like plastic coated paper imprinted with red grids on 8 channels of data, side-by-side, about 2 inches wide for each channel. After a shot, we would go to the Blockhouse with “Sanborns” from our own trailers and we would unroll the shot anatomy on the hallway floor to examine the post-mortem. We learned a lot, believe me.

Third level, or digital backup was on Teledeltos Recorders that burned digital data into zinc oxide coated paper. I can still smell the smoke from those recorders and see the techs brushing away the residue resulting from the sparking wires on the paper with small “acid brushes”.

BURROUGHS COMPUTER

The following are excerpts from a book I am writing about SanSal:

To the left is a door that is labeled “BURROUGHS”. We open the door and are met with a blast of cold, dry air and the sound of a jet winding up for takeoff. This is a large room about the size of the FLIGHT DATA Room that is home to a digital computer. This computer is housed in a number of 7 foot racks, very nicely designed with elegant art-deco ribbing on the front of the panels and artfully decorated with diffused, subtle lighting. The computer is all vacuum tube, hence the sound resulting from the whistle of cooling air moving through the cabinets. This is just out of science fiction. What machines! What sounds! There is a console with a keyboard and a teletype attached to it. There are a number of switches and lights. In the center is a “table” about 5’x 5’ that is a large plotter. I have been taken here to impress me with the purpose of the mission of GE on this Site.

The plotter table’s surface is a 4’ x 4’ piece of paper on which is printed a map of all of the area from Cape Canaveral to past San Sal. There are thick red lines outside of which are crosshatched areas in red. These are all of the land areas in the Bahamas and the east end of Cuba. If the plotter walks past one of these red lines, a signal will be sent to the Cape and the Range Safety Officer (RSO) will push a button and destroy the missile. It is hoped that the smaller pieces of debris will do less damage than a 100 ton missile filled with kerosene and liquid oxygen.