The next morning, the fifth space vibration occurred.
"It reportedly lasted for about a thousandth of a second this time. The origin was in the orbit of Ars, approximately seventy degrees ahead."
The report arrived from Jack at the Moon (Uni), providing a precise bearing.
"Hmm, it really does seem to be getting closer bit by bit..."
Jin reaffirmed his belief that their current countermeasures were indispensable.
The duration of the vibrations was increasing. That likely meant the window in which the two worlds overlapped was growing longer.
If Ars were to enter that overlapping space... He didn't even want to consider the possibility, but Jin intended to do everything in his power to ensure it never happened.
"Laojun, let’s begin mass production of ethenol."
"Understood. We shall utilize the Free Ether Cloud for the free ether, I assume?"
"Exactly."
"In that case, we can move there in a short time by utilizing the intermediate base. We should use the construction ship Vulcan."
"Right, I'll leave that to you."
The remaining problem was how to generate a Space Isolation Barrier on a scale large enough to cover both Ars and the Moon (Uni).
Generating the Space Isolation Barrier itself was no longer an issue. However, because the scale was so astronomically large, it was difficult to determine the most efficient approach.
"Jin-nii, are you going to deploy the barriers for the Moon and Ars separately?"
"Eh?"
At Elsa’s sudden question, Jin seemed unable to process the words for a moment. However, he quickly grasped her intent and a smile broke across his face.
"I see, you're right!"
He felt a wave of relief.
"No matter how I look at it, trying to cover everything out to the Moon's orbit would be way too massive."
A barrier with a radius of 400,000 kilometers was terrifying just to imagine—mainly in terms of energy consumption, Jin thought.
"If we only cover Ars, a radius of 40,000 kilometers—one-tenth of the distance—will be enough."
Since the surface area would be one-hundredth of the larger sphere, the consumed free ether would also be reduced by a factor of a hundred.
This value included the Watcher satellites in stationary orbit. If they ignored the Watchers, they could make the radius even smaller.
"And for the Moon, a radius of 1,000 kilometers should be plenty."
Thinking about it that way made him feel a bit more at ease.
"One generator should be enough for the Moon, but for Ars, one won't cut it, will it?"
After all, the radius was 40,000 kilometers. The surface area was approximately 2 x 10^10 square meters.
If a barrier covering a person had a radius of 1.5 meters, its surface area was about 28.3 square meters. This planetary project would consume over 700 million times more free ether.
"700 million times, huh..."
To put that number into perspective using time, 100 million seconds was approximately 1,157 days. It was a value that undoubtedly exceeded the bounds of ordinary imagination.
One of the largest barriers Jin had ever created was the guard barrier for the spaceship Adriana. Its radius was approximately 200 meters, with a surface area of roughly 500,000 square meters.
Compared to that, this planetary barrier was 40,000 times larger.
"When I think about it that way, I can visualize the scale a bit better."
"Jin-nii, can you explain?"
Since Elsa was tilting her head beside him, Jin decided to explain it in simpler terms.
"You can think of the size of the magi-machine used to generate the Adriana’s guard barrier as a sphere about ten centimeters in diameter."
"Mm."
"To put it simply, we'd need a magi-machine forty thousand times that size. Well, considering efficiency and mana transmission, we could probably make it a bit smaller, but we'd still need it to be about ten thousand times larger."
"Um... are you talking about volume?"
"Yes. In other words, the diameter would be the cube root of ten thousand times larger... Laojun, how much would that be?"
"Since the factor is roughly 21.5, the diameter would be just under 2.2 meters, My Lord."
While that wasn't an impossibly vast size, magi-crystals of that magnitude did not exist in nature.
Of course, since they would use multi-layered magic circles for the Space Isolation Barrier, a direct comparison wasn't entirely accurate, but there wouldn't be a significant difference in the required volume of magi-crystals or the consumed free ether.
"...I understand now. It sounds very difficult."
"We can make them if we synthesize them, though..."
"Yes, My Lord. Hourai Island’s warehouse has a stock of magi-crystals about ten times that amount, so synthesis is possible. Furthermore, if we include the magi-crystals recovered from the fragments of the long-period planet Modenu last year, we have more than enough."
In other words, the project required a hundred years' worth of magi-crystals. Even with their existing stockpile, it was still an extraordinary amount.
"But we shouldn't be stingy at a time like this," Jin declared firmly.
Elsa didn't object. She understood all too well that this was a dire emergency.
"Besides, it's not like they'll be consumed and disappear."
The biggest reason for the device becoming so large was the supply of free ether required by the multi-layered magic circles. Since it would likely consume a massive amount of free ether in a micro-duration of time, Jin wanted to give the magi-circuits plenty of leeway.
"It might not end with just a single activation, after all."
There was no guarantee that the crisis would be averted after one event. Space vibrations might occur several, or even dozens of times.
"Should we install it near the summit of Hourai Island?"
"Considering maintenance, that would be ideal, but..."
Laojun suggested that given the process of detecting the space vibration and then activating the barrier, it would be preferable to mount the generators on satellites and install them in outer space.
Jin agreed.
"True..."
Jin began considering the method of deployment, including the shape of the barrier.
"Should we install them above the North and South Poles and have each deploy a hemispherical barrier?"
"Indeed, My Lord. If the two hemispheres align perfectly, I believe that would be the best approach."
"Alright."
With Laojun's agreement, Jin decided to finalize his thoughts in that direction.
"First, let's equip it to a spaceship."
Jin thought that if they projected a hemispherical barrier in the direction of travel, the ship would be safe regardless of what kind of object it collided with.
"Jin-nii, just for example... what would happen if you collided with something larger than the spaceship?"
"Eh..."
He understood the intent behind Elsa's question.
I hadn't thought about that, Jin realized, pondering the problem for a moment.
"Hmm... Now I'm not so sure..."
"I... I'm sorry."
Seeing Jin agonizing over the logic, Elsa apologized.
"It is quite alright, Elsa-sama. My Lord has simply mistaken the application."
"What do you mean, Laojun?"
"The original purpose was intended to be 'space isolation,' after all."
"...That's true."
Jin reflected on his error. He had strayed by starting to think of its function as a conventional physical barrier.
"Sorry, Elsa. Or rather, thank you. My thoughts had wandered down a side path."
Jin honestly admitted his mistake, apologizing and thanking Elsa at the same time.
"No, if I was able to be helpful unexpectedly, I'm happy."
Elsa shook her head. She was a bit bewildered to hear that a comment she hadn't intended as a critique had been so useful.
"At any rate, I think there's merit in making a ship-based version. It means the vessel will no longer be affected by spatial distortions or gravitational anomalies."
"That is correct."
"Alright, as a prototype test, let's equip it to the Vulcan before sending it out."
It would be disastrous if the ship encountered a space vibration on the way to the Free Ether Cloud without protection.
"Understood. I shall make the arrangements immediately."
Hourai Island finally began to move toward implementing its countermeasures.