Republic of China: Ace Pilot

Chapter 642 Selection of Rocket Guidance Technology, Active Radar Seeker
Fang Wen was very interested in the details about the heavy-duty bicycle.

He asked Shen Weitao to explain in more detail.

The military and civilians in the base area would further modify the heavy-duty bicycles—strengthening the frame, adding wooden or iron racks (one in the front and one in the back, and some would also add hanging baskets on both sides of the wheels) to further improve the load-bearing capacity.

Such a military-grade heavy-duty bicycle can carry a load of about 300 kilograms.

A bicycle transport team has 20 bicycles and can transport 3 tons of goods in a single trip.

They were often used to transport daily necessities such as food, cloth, and medicine, as well as military supplies such as bullets, grenades, and explosives.

During counter-"mopping-up" operations, the militia would use heavy-duty bicycles to travel at night along mountain paths, transporting grain hidden in caves to various villages or delivering stored ammunition to the front-line troops.

Because bicycles are small and quiet, they can travel flexibly along field ridges and forest paths, and can even be carried across shallow rivers and over low hills, making them easier to avoid Japanese sentries and patrols than horse-drawn carriages or oxcarts.

On the battlefield, they were favored by combat squads: bicycle cavalry, rapid communications personnel, and flexible battlefield relocation.

That's why there was a 'large order' for 1200 vehicles.

He asked, "How long will it take to produce 1200 heavy-duty bicycles?"

Shen Weitao explained, "For a month and a half, we used scraps from our processing, mainly because we didn't have enough workers."

There aren't enough workers.

Although Fang Wen was not at the base during this time, he still knew about it.

Bicycle parts are not manufactured in fixed factories; instead, they are processed in the workshops of rocket factories and then sent to assembly plants in Yangon for assembly.

Therefore, to speed up production, the workers at the rocket factory had to suspend their original production projects and switch to this one.

Fang Wen made the decision: "Temporarily transfer a group of machinists from each factory to produce heavy-duty bicycles. We must prioritize the needs of the front lines. In addition, we need to consider their feedback and make those add-on parts as well. Shen Weitao, you are in charge of this."

At his request, Shen Weitao met with the heads of various departments in the conference room to discuss the matter.

Fang Wenze and Lu Zexuan went to the Taishan Research Institute.

The three arrived at the research institute, where Fang Wen showed his identification to the guard and passed the inspection.

Upon entering the research institute, Fang Wen went directly to the computing center.

The computing center is bustling with activity these days.

People from different research groups are queuing here, waiting to submit their project group's computing requests.

Those who submit a computation request will perform computation operations together with the computation operator at a fixed time.

Transistor computers perform very complex operations; the input process alone can take a long time.

These calculations cannot yield results in one go; they need to be broken down into multiple formulas and performed one by one.

Compared to future computers, it is still very rudimentary, but it can already meet the computational needs of scientific research.

After learning about the situation at the computing center, Fang Wen returned to his office at the research institute.

In his office, Fang Wen recalled the battle in Guinan.

He then pondered how to enable the Taishan air-to-ground rockets to achieve guidance functionality.

His first thought was: With the current level of technology, is it possible to achieve guidance functionality?

The answer is yes.

Five years later, Germany's V2 rocket will use inertial guidance.

Although the detailed structure is unknown, Fang Wen's current mechanical knowledge allows him to make a rough deduction.

It should be a system consisting of a gyroscope, an accelerometer, and a mechanical computer. Once a heading deviation affects the gyroscope, the flight attitude can be corrected by adjusting the gas injection angle through a mechanical device.

Can this technology be used in Taishan's rockets?
Fang Wen shook his head in denial.

That's too primitive.

Even with inertial guidance, the V2 rocket's range of several hundred kilometers can only ensure that the direction is not too far off, but the actual deviation from the target may be several to ten kilometers.

This is for long-range rocket guidance; if used for short-range rockets, the effect would be even worse.

Another method combines manually operated radio remote control guidance technology.

The operator visually observes the tracer tube to correct the flight path. Once a deviation is detected, the operator activates the rocket booster via radio to adjust the rocket's trajectory mid-flight.

However, this operation requires highly skilled personnel.

After rejecting both proposals, Fang Wen continued to think.

In fact, an active radar seeker is the optimal solution.

However, this technology is also the most difficult to implement.

An active radar seeker is a missile that carries its own radar transmitter and achieves autonomous guidance by actively emitting electromagnetic waves and receiving the reflected echoes from the target.

This technology enables missiles to have "fire-and-forget" capability, which can significantly improve operational flexibility and hit rate.

Although he had the knowledge, he had no idea how to implement it.

Therefore, Fang Wen got up and opened the door, saying to Gong Xiuneng outside the door, "Go and invite Jiang Wenjin over. I have something to talk to him about."

"Yes." Gong Xiuneng went downstairs.

Ten minutes later, Jiang Wenjin arrived at Fang Wen's office.

"General Manager, what can I do for you? My project is at a critical juncture and can't be delayed for too long."

Jiang Wenjin, who was engrossed in scientific research, spoke very directly. Fang Wen didn't mind and smiled, "Sit down. The reason I'm here today is to solve the guidance problem of rockets. We used 1800 air-to-ground rockets in the air battle in Guinan, and many of them were wasted. For Taishan Military Industry, we can't afford such a large consumption. We need to develop guidance technology that can achieve single-shot hits."

Jiang Wenjin frowned slightly: "You want to equip rockets with 'eyes'? That's very difficult."

"Yes, I know. At first, I considered two options: either using an inertial gyroscope or relying on radio remote control. However, the former has poor accuracy, and the latter is too dependent on the operator, so neither is practical. Now I have thought of a new method: an active radar seeker."

Fang Wen offered his idea, and seeing Jiang Wenjin's eyes widen in surprise, he added, "It's about having rockets carry their own radar, emit electromagnetic waves to find targets, and then operate automatically based on signal feedback, achieving 'fire and forget'."

Upon hearing Fang Wen's words, Jiang Wenjin immediately became interested.

"That's a good research direction, but the technical difficulty must be enormous. General Manager, you can't just have this one concept, can you?"

“I do have some ideas. It all starts with an animal.”

"What animal?"

"bat."

Fang Wen drew a picture of a bat on the paper: "Bats are very strange creatures. They hide in the dark during the day, but at night they can accurately catch flying insects. They won't crash into walls even with their eyes closed. They don't rely on their eyesight, but on the ultrasonic waves emitted from their mouths."

Following his train of thought, Jiang Wenjin's brows gradually relaxed, as if she had grasped the key point: "You mean... the ultrasonic positioning of bats works on the same principle as active radar seekers?"

“Exactly.” Fang Wen pulled up a chair and sat down next to Jiang Wenjin. He picked up a pencil from the table and drew a simple diagram on a piece of paper. “Bats can emit dozens of high-frequency sound waves per second. When these sound waves hit flying insects or obstacles, they are reflected back. After their ears receive the echoes, their brains can quickly calculate the distance, direction, and speed of the target. Our active radar seeker is actually imitating this process—the radar transmitter is like the bat’s mouth, the antenna is like its ears, and the signal processor is its ‘brain’.”

Jiang Wenjin stared at the blueprints, his finger lightly tapping on the label "radar transmitter": "But bats' ultrasonic waves are mechanical waves, while radar uses electromagnetic waves. Their propagation speeds and reflection characteristics are completely different. Moreover, bats' brains can process echoes in real time. How can we implement the 'brain' of the rocket?"

“That’s why I came to you—we don’t need to do it all at once.” Fang Wen wrote a few words on the blueprint: ‘Simplified computing module.’ “We don’t need to create a complex brain to think about problems. Instead, we just need to deal with the radar feedback, which makes things much easier. Without pursuing full autonomy, the radar is only responsible for measuring distance and direction, transmitting the data to a mechanical module with pre-set parameters, and the module controls the tail fin to adjust its attitude, just like a bat uses its instincts to avoid obstacles.”

He paused, then took out a palm-sized component from the drawer. It was a magnetron made for the miniaturization of radar. "Our radar magnetron can generate electromagnetic waves with a wavelength of 10 centimeters. If we make it even smaller, it can be installed in the head of a rocket. It does not require a lot of energy and only starts within 3 seconds after launch. It first locks onto the general direction of the target, and then relies on inertia and simple echo correction."

Jiang Wenjin took the magnetron and examined it carefully against the light, his eyes growing brighter: "You mean, we should first make a transitional version of 'semi-active-active combined'? During launch, the gunship's radar 'illuminates' the target first, and then the rocket's radar adjusts autonomously after receiving the reflected signal?"

“That’s right.” Fang Wen nodded with a smile. “This way, we only need to do two things: radar lock-on and launch correction. It’s much simpler to implement.”

Jiang Wenjin's eyes lit up. "Let the aircraft carry an illumination radar to 'mark' the target, and the rocket will only be responsible for receiving the reflected signal to correct its direction. This way, we can save the transmitter, and reduce the size and power consumption—the transistor computer in the computing center can calculate the correction parameters for different distances in advance and install them in the rocket's mechanical controller."

Fang Wen nodded, got up and took out a rocket model from the cabinet, unscrewing the stabilizing fin at the tail: "I have an idea for the mechanical part. Referencing the gas-jet rudder of German rockets, but not that complicated—add four adjustable iron plates to the tail nozzle, control the angle with electromagnetic coils, and directly adjust the thrust direction after receiving signals. Use leftover aluminum alloy scraps from the rocket factory, which is both lightweight and durable."

"General Manager, your plan is excellent, I agree."

"So, how quickly do you think we can produce the first batch of prototype missiles?"

Jiang Wenjin analyzed: "It takes 10 days for the electronics group to modify the radar receiving module, 15 days for the mechanical group to make the gas turbine and electromagnetic rudder, and 5 days for the computing center to calculate the ballistic parameters. If we transfer lathes from the rocket factory and prioritize the processing of parts, we can put together 3 prototype missiles in a month. However, these prototype missiles may not be successful on the first try, and we may face a process of repeated trial and error."

“We have to take the risks.” Fang Wen put the model back on the table, his tone firm. “As for processing the parts, since we’re going to start processing parts for 1200 heavy-duty bicycles, we can’t delay their production. Therefore, I’ll be in charge of processing the parts needed for the prototype missile. You’ll lead the establishment of a guidance team, and the research institute will fully cooperate with your work. We’ll be working on the second floor of the research institute. If you have any problems, just come to me.”

Jiang Wenjin tucked the notebook into his pocket, stood up and saluted: "Don't worry, I'll hold a coordination meeting tonight."

After he finished speaking, he hurriedly left.

The guidance project team was established the next day.

Fang Wen also joined the research and development team for this project.

He and Jiang Wenjin designed the entire guidance system together.

The first step is the physical construction of the signal link.

Airborne radar target targeting employs magnetron technology, where the airborne radar emits a continuous wave signal at a specific frequency and locks onto the target by forming a narrow beam through a parabolic antenna.

The radar operator observes the target echo through the echo display and manually adjusts the antenna pointing to keep the beam center aligned with the target.

At this time, the radar not only undertakes the detection task, but also needs to continuously emit a stable "illumination beam", whose signal characteristics (such as pulse repetition frequency and phase coding) are pre-coded into the rocket's receiver.

Then there's the signal acquisition of the rocket.

The rocket's nose cone is equipped with a miniaturized radar receiver, which is composed of a superheterodyne circuit made of transistors.

The receiver retains only the distance tracking function, calculating the target's relative position by measuring the time delay of the echo signal.

The third structure is the generation and transmission of guidance commands.
Analog signal processing mechanisms are used here.

The intermediate frequency signal output by the receiver is used to extract the amplitude information of the target echo through the envelope detector, and then input into the mechanical integrator.

The integrator consists of a gear train driven by a spring, which generates a DC voltage proportional to the target's azimuth deviation based on changes in signal strength.

This voltage is transmitted through a slip ring to the rudder control unit at the tail of the rocket, driving the gas rudder or air rudder to deflect and correct the trajectory.

The fourth structure is the implementation of frequency synchronization.

To ensure that the rocket receiver and the carrier aircraft radar are on the same frequency, a "pre-programmed + phase-locked loop" technology is used.

Before launch, technicians adjusted the taps of the receiver's local oscillator coil to match its center frequency with the carrier aircraft's radar. During flight, the receiver's built-in LC tuning circuit tracks minute frequency drifts in the radar signal via a phase-locked loop, a process implemented by a phase detector composed of transistors and a voltage-controlled oscillator.

Of course, the entire system includes more than just these.

Precise linkage and power supply are also important in mechanical control systems.

As the actuator for ballistic correction, its tail-mounted electric control surface is driven by a small DC motor.

The motor's control signal comes from the analog voltage output by the receiver: when the target is on the left side of the beam, the left control surface deflects +5°; when it is on the right side, the right control surface deflects -5°, forming proportional guidance.

The power source is a small turbine generator installed on the side of the missile body. It uses the exhaust gas from the rocket engine to drive the turbine and generate 50Hz AC power for the receiver.

These structures make air-to-ground rockets much more complex.

To achieve this, a more compact internal structure is required, along with high-precision components.

To this end, Fang Wen personally went into the field to process various parts for the guidance device.

(End of this chapter)