Thread by @heatloss1986

The RIM-8J was the last of the Talos missiles, and by far the best. With a range of up to 130nmi and a 465 pound warhead, the last model of Unified Talos could claim to be amongst the most lethal surface-to-air missiles of the Cold War, thanks in part to its Fire control System🧵

This thread will skip over the development side and skip straight to the juicy technical bits of the last Talos variant and shipborne radars. For a highly recommended overview including other variants, check out @VLS_Appreciator 's thread on the topic.

Engaging a target with Talos began long before the missile left the ship. It first began with detecting a target with the ship's air search radars.

An operator in the Combat Information Center would then designate a target for attack if it failed IFF and was deemed hostile.

This information would be sent to the Weapons Control Room to be displayed on the main Designation Indicator Monitors.
An officer at the Designator Console would select the highest priority target, which would transfer information to the Target Engagement Console.

The Target Engagement Console operator would then designate an SPG-49 operator team to track the target.
These radars were responsible for generating a track solution on the target, as no precise information on the target had yet been gathered.

The SPG-49 Fire Control Radar actually consisted of two main feed systems with an illuminator.
The first radar feed provided the Acquisition Console Operator with a 3-dimensional view of the target zone(acquisition field) through his dual displays.

This allowed him to identify the correct target as he slewed the radar through the target area.

The Tracking Console Operator would then identify the target based on the bearing shown on his search radar display and the exact target range along the radar beam on his tracking display. Once the target was selected, automatic track would through the second radar feed.

So how did SPG-49 work?
To begin, we should start with the acquisition scan. To provide enough rapidly updating, hyper-accurate data to allow target discrimination at over 150nmi, an unusual radar design was required. This began at the Foster scanner.

Foster scanners should be considered black magic, but they work by simple physics. A very narrow parabolic slot reflector is the source of the radiation. If a differential fold in the path is added, the time spent traversing the longer path changes the direction of the beam.

The parabolic reflector is set at a fixed angle with regards to the rest of the system. A cone with a constantly spinning rotor inside of it changes the path length constantly, but it does so at different rates for each end of the cone, since one end is larger than the other.

The end result of this is that the direction of the emitted beam changes constantly from one side to the other at an extremely high rate, and once it finishes one scan, it snaps back to the beginning of its pattern. The output of the foster scanner was horizontally polarized.

But this only took care of one dimension of scan. The other was taken care of by the vertically polarized reflector, seen in the middle of this diagram. This provided another extremely rapid method of scanning, meaning that the acquisition displays updated nearly continuously.

Once the target was selected and identified by the Tracking Console, the pulse transmitter feed would be switched from the foster scanner to the tracking horn, a vertically polarized monopulse tracker capable of 0.25 milliradian(0.014 degrees!) accuracy.

Since monopulse is relevant for both the tracker and RIM-8J, this is worth covering now. A monopulse radar is an angular tracking method that works by having four main receiver quadrants, A, B, C, and D. In the case of SPG-49, this works by phase comparison.

The outputs of A+B and C+D are combined, with one flipped 180 degrees out of phase. The same is done for A+D and B+C. This means that, if the target is in the exact center of the four quadrants, the output of all of these equations is zero. Thus, the error is zero.

However, if a target is slightly off of the center, there is a slight difference in the phase of the return signals. When run through the signal comparisons explained above, this generates an error. The chart below explains how error signals are interpreted.

These error signals were automatically processed by the fire control computer to change the physical direction of the antenna to constantly point directly at the target.

The final output of this tracking system is the sum of A+B+C+D. The delay between the transmitted pulse and the reception of the output of this sum is directly proportional to the range to the target. To increase range accuracy, a method called pulse compression was utilized.

Pulse compression, in this case, was done by frequency modulation. By constantly varying the frequency of the transmitted pulse in a linear fashion, a much longer pulse containing multiple returns can be split into much smaller returns in the time domain.

This gave SPG-49 a staggering range accuracy of 300 feet in both acquisition and track modes!

Once a target track was achieved, the range, bearing and elevation were transmitted to the fire control computer. The first thing this computer would do is determine the necessary flight trajectory to intercept the target.

While the computer was determining the correct solution, the Talos missiles which had been loaded onto the launchers began spooling up their internal gyroscopes and batteries in preparation for flight.

Once they were ready, the missile could be launched!

Once the missile was in the air, the first part of guidance could begin. This was controlled by a separate radar, the SPW-2. The purpose of this radar was to provide beam-riding guidance commands for the Talos during boost and cruise phases and track the missile's position.

The SPW-2 emitted 3 coded pulses at a varying interval. These pulses were coded to identify the SPW-2, preventing the Talos from receiving guidance from the wrong radar. These pulses were sent out at a varying rate as the beam rotated in a cone around an axis.

The scan rate of 30 hz was processed by the missile's electronics to produce a reference frequency. If the missile was centered, the signal amplitude would be constant. If it was not, the amplitude modulated signal would be shifted in phase away from the reference signal.

The phase shift would indicate the direction of the error, and the amplitude would indicate the magnitude of the error. The SPW-2 would guide the Talos through its flight path until it came time to activate the onboard seeker.

So what about that flight? The RIM-8J achieved its impressive 130nmi range through the use of a ramjet, which necessitated the booster for launch. After it got up to speed, it ignited the ramjet which blew the booster away.

One of the changes in RIM-8J was the move to a more energetic fuel that increased the missile's range. This was called "Dimer fuel." JP-5 was used in older models, but Dimer significantly increased the effective range of Talos.

During this flight, the Fire Control Computer began measuring the difference in speed between the launching ship and the target. This version of Talos used semi-active radar guidance in the terminal phase, and it guided on the relative doppler shift of the target.

The advantage of this method of guidance is that the target speed would almost always be separated from ground clutter, and therefore the missile could track a target flying very low against the ocean.

Now, remember the part of the SPG-49 diagram that said "CW illuminator"? That's where this comes in. The CW illuminator was fed through the Foster scanner locked in the boresight position, meaning it aligned perfectly with the pulsed emissions of the monopulse tracking horn.

The estimated target doppler sent from the ship was called the GAA signal, and when fed into the rear reference receiver, would provide a narrow window of frequencies that could be processed by the front receiver.

This made doppler-based jamming extremely difficult.

So how did the homing system work without a radar dish? Interferometers. The four spikes around the front of the Talos missile were each a radar receiver. These were paired together diagonally to detect differences in signal phase for elevation and azimuth. (Homing Antenna)

These differences, when measured, would give an azimuth/elevation error signal. When Az/El were combined, a two-dimensional effective scan angle could be measured.

In older versions of Talos, the azimuth and elevation angles were measured sequentially, but this was vulnerable to angle-jamming and had to be changed. In RIM-8J, the original CW seeker was replaced with a new Monopulse CW seeker.

The new monopulse seeker processed each antenna output simultaneously and combined them to create a phase shift signal after some basic signal processing, further reducing the possibility of effective jamming.

ωₛ was the phase difference signal for each pair of antennae.

This guidance method, combined with a Home on Jam mode was, in practice, unjammable. In fact, the HOJ mode INCREASED the accuracy of RIM-8J, as it provided a very clear point-source rather than the complicated radar return of an Aircraft's aluminum skin.

At the same time as the seeker was activated, 15 seconds before impact, the fuze was too. This was connected, of course, to the warhead, the final part of Talos we're going to cover today.

This was as a colossal 465-pound Continuous Rod warhead, containing 225 pounds of 25/75 Cyclotol, a 25% RDX and 75% TNT mixture. The expanding ring had a maximum expansion diameter of 90 feet and an initial velocity of 4,600 feet per second.

Continuous Rod warheads have their downsides, but they can also provide immense amounts of damage to a target if accurate fuzing is provided.

In the case of Talos, this accuracy was provided by an active fuzing system.
This used a pulse radar with a "sea tracking gate", which constantly monitored returns from the sea if the missile had to intercept at low altitude to prevent returns from the sea activating the warhead.

Although I cannot find any photos or videos of a test with a live conventional warhead, I think one can assume the outcome.

Unfortunately, the service life of RIM-8J would be short. Though it was only introduced in 1971, it was removed from service in 1979.
Standard Missile-ER (SM-2) would replace it as the fleet's long-range SAM. Although effective, it didn't have quite the "cool factor" of Talos.

As requested @Lantirn40K @actualjib @TomcatJunkie @SpockNC @NotLuca81087036 @Thatdude2531 @m43day @ond144 @VLO225 @taiwaneseprick @RokkerBoyy @peck_oh @steeljawscribe @KiranPfitzner @whatismoo @VLS_Appreciator @Doha104p3 @BaA43A3aHY @StrokeNdistance @EricWelch42 @coldfoot666

special thanks goes out to the crew at Okieboat. There are a few diagrams and systems explanations that only they have on their website, and were crucial in the making of this thread.okieboat.com