Chapter 577 - 565: Violence

Although ARCA company has been established for quite some time, it can be said to have a peculiar style, belonging to the oddballs among many private aerospace companies.

Dr. Freeman was not wrong about their playful nature; this company never painted pie-in-the-sky promises to lure investor funds, nor has it developed commercial projects. Instead, they like to dabble in unorthodox stuff.

Besides the projects funded by NACA last century, they are probably the only ones who have also invested considerable effort to research the aerospike engine, and later they even came up with the heretical water engine.

As for why they were targeted by NACA and pushed Pratt & Whitney to acquire them, the reason goes back to the CZ-18.

Before it became official, NACA had already formally confirmed that XAP had truly initiated the project and made substantial progress, which then caught John’s utmost attention.

Whether it was the current director, Robert, or the former one, Claire, they both made it very clear to John that the practicality and investment of the CZ-18 were completely disproportionate. It could only be used for special missions like the Chapter 9, and NACA had hundreds of ways to achieve the same effects, so there was no need to forcefully compete.

But John didn’t understand aerospace, nor did the members of Congress, and they knew that many citizens didn’t understand it either. However, they understood that the criteria for judging the superiority of a rocket were to see who was bigger, heavier, and more impressive.

Even though technical experts kept explaining, once people compared the sizes of rockets, an indelible intuitive impression would form in their minds.

Therefore, a large number of senators strongly demanded the construction of an even more powerful rocket to surpass the CZ-18, and they turned over the "Sea Dragon", imposing immense pressure on NACA.

Robert also had to seriously consider the feasibility of the Sea Dragon rocket, but then he quickly dismissed it for the same reasons as the harried Aerospace Development Committee—launch support was too complicated, and even if it could be built, it would be very difficult to launch.

Keep in mind that the first stage of the Sea Dragon was a liquid oxygen kerosene engine, which alone needed to achieve a thrust of 30,000 tons, and it was quickly vetoed.

But clustering multiple engines was even more difficult. Even with the 680-ton thrust F1 engines, 44 would be needed to achieve the same thrust. The resonance at the base and the fuel lines alone were enough to cause a headache. The CZ-18’s 39 engines with 280-ton-class hydrogen-oxygen were basically the limit for multi-engine clustering; adding more would exponentially increase the difficulty of control, and the troubles of clustering F1 were much greater.

So, was there a rocket engine with extremely high thrust, low manufacturing difficulty, and most importantly, low cost?

That’s when ARCA company entered NACA’s field of vision. Their LAS 25DI engine achieved a thrust of 7,000 tons simply by heating water pressurized to 250 degrees Celsius through electric heat to supercritical state upon ejection, taking advantage of the heavy molecular weight of water. Moreover, this engine was quite compact; it was not much bigger than the F1 but boasted ten times the thrust.

Although the LAS 25DI had ridiculously low specific impulse and short operating time, it was indeed extremely cheap and had practical application value.

During a rocket’s journey to space, the phase that requires overcoming the greatest gravitational force is the acceleration from zero, particularly in the region below 10,000 meters in altitude.

During this phase, the most energy is consumed, and the air resistance faced is the highest. After this, the pressure on the rocket decreases substantially.

Take the Saturn V rocket, for example, with a launch mass of about 3,000 tons and an LEO payload capacity of 118 tons, the overall payload efficiency is 3.93%; but if you subtract the mass of the first stage, the remaining part is only 788 tons, and the payload efficiency of this part reaches an astonishing 16.4%.

The key indicator for the first stage of a rocket is the thrust-to-weight ratio, for the upper stages it’s the specific impulse, so it’s fine if the specific impulse of the first stage isn’t great, as long as the thrust-to-weight ratio is sufficient to carry the upper stages to the predetermined altitude and achieve a certain speed.

NACA then approached the ARCA company, requesting them to design an engine with a thrust exceeding 40,000 tons, and a specific impulse of at least 150 seconds using water.

According to NACA’s calculations, a water engine with a thrust exceeding 40,000 tons would require a fuel and rocket body mass of about 16,000 tons. The total weight of the upper stages would be 5,000 tons using hydrogen and oxygen for power, with only a 3,300-ton thrust needed. Ten existing RS68 engines would suffice, greatly reducing the design complexity.

And ARCA did not disappoint, proposing the even more aggressive LAS88N engine (88 million pounds of thrust, atomic power).

The LAS88 is composed of a very simple structure with only three parts: the combustion chamber, the reactor, and the water tank.

The water tank is still pre-filled with water heated to 250 degrees Celsius. Due to the ultra-high pressure inside the water tank itself, the LAS88 omits the turbopump mechanism and allows the superheated water to enter the reactor core directly.

Under the high pressure from the water tank and the high temperature in the reactor core, the superheated water instantly becomes supercritical steam at over 700K and a pressure exceeding 22Mpa, rapidly expanding and being ejected in the bell-shaped combustion chamber, thereby producing thrust.

The heating capability of a nuclear reactor is much more powerful than electrical heating, easily achieving a doubling of specific impulse and solving the issue of battery mass as well since the reactor can be lighter.

Because the New Sea Dragon Rocket has a thrust-to-weight ratio exceeding 1.9, it will inevitably create a massive water hammer effect at lift-off. The water in the tank will be forced downward more violently due to acceleration, resulting in higher pressure. This increased pressure will grow as the rocket continues to accelerate, maintaining the pressure flowing into the core despite diminishing water levels.

The LAS88N’s total operating time is only 52 seconds, but it can accelerate the rocket to 1,690 meters per second and a separation altitude of 40 kilometers. The remaining upper stages can at least carry a 600-ton payload into a 300-kilometer progress orbit.

One major advantage of the first stage of the New Sea Dragon Rocket is its low cost. Storing superheated water at 250 degrees is much easier than dealing with liquid hydrogen and oxygen fuels. Ordinary stainless steel (non-aerospace grade) can easily handle the pressure, and once used, there’s no burden to discard it.

The combustion chamber can also be discarded, and only the middle reactor needs to be modularized for ejection and separation, followed by parachute descent into the sea for recovery. In addition to the precious reactor, the rest of the first stage components might not even total up to 5 million US dollars.

As for the issue of water pollution through the combustion chamber? Since only high temperatures from the reactor are needed, NACA believes Dr. Freeman can make the expelled steam radiation levels meet atmospheric emission standards.

These water vapors will essentially become clouds in the rocket’s flight area. The level of radiation is far lower than that of a hydrogen bomb test, and since the Sea Dragon is launched on water, there are plenty of uninhabited areas in the vast oceans.

The LAS88N engine was eventually approved by NACA, and ARCA was thus "formally recruited" to serve NACA. Those researchers, whose work was once considered merely for entertainment, were also thrilled, believing that they had finally been "discovered" for their reclusive genius.

Upon understanding this, Freeman couldn’t help but be staggered by NACA’s extraordinary imagination, yet he found the LAS88N project unusually sensible. It truly embodied the concept of "achieving wonders with great effort." Other than the reactor, he couldn’t pick out any other unfair aspects of the design.

"All right, I’ll handle the reactor part, but please, for the love of all that’s good, don’t launch this thing on the East or West Coast, and the Gulf of Mexico is out of the question," he said.

Sterling replied, "If possible, it should still be launched in the South Pacific Ocean, near Tuvalu would be quite nice."