The Up and Down of Space – LVLH Attitude
「I wonder how the view looks from outside…」
「Kou. We are in the middle of interstellar navigation. Do you need me to explain the risks of doing something stupid while moving at these speeds?」
「I know, I know. I’d rather not get scolded.」
Kou nodded at Blue’s warning. Interstellar navigation carried immense risks.
「Our current speed is fifty kilometers per second, right? I wonder how battles were fought during the Interplanetary War era.」
「They only fought in certain locations. Designating regions like the Asteroid Belt allowed for the generation of artificial gravity. Combat wouldn’t be feasible at interplanetary navigation speeds. Just like how fighter jets on Earth could fly at Mach 2.5 but typically engaged in combat at around Mach 1, space battles are recommended to take place at speeds below fifty kilometers per second.」
「One wrong move and I’d end up lost in space, all alone.」
「Precisely. If you want to test it, now would be the time.」
Their arrival at planet Libya was imminent. To enter the planet’s gravitational sphere, they needed to decelerate beforehand.
Kou wanted to take advantage of this deceleration timing to attempt a silhouette spacewalk.
「So all three vessels will be decelerating simultaneously?」
Kou prepared to attempt a spacewalk using a Silhouette—a form of interstellar navigation utilizing a Silhouette.
Upon entering the deceleration zone, Kou proposed the idea to the other two ships, and to his surprise, every crew was highly enthusiastic about it.
「All spacecraft can generate a certain degree of artificial gravity around their hulls. Otherwise, they would have a hard time using their onboard units. However, equipping a safety tether is mandatory.」
「Of course.」
Kou’s Unit 5 began preparations for extravehicular activity.
「Kou, we’re ready on our end too.」
「I’ll be in the rear seat.」
It seemed Kurose and Kinukawa were also eager to try spacewalking. It wasn’t surprising—they wouldn’t want to miss such an opportunity.
「This is an invaluable experience. I sincerely appreciate this, Kou-kun. I will never forget this debt.」
「You’re exaggerating.」
「Exaggerating? Not at all. I’ve spent my whole life looking up at space, and now, here I am—standing in it.」
Kinukawa’s excitement was impossible to hide, making both Kurose and Kou smile.
「To all Silhouette pilots: In space, Fennel OS will operate at maximum capacity to assist your sensory perception. Your speed will be approximately eleven kilometers per second—around Mach 30—but you won’t feel that velocity.」
Astraea, unusually, issued a shipwide announcement to all crew members before their deployment into space.
「Without atmospheric resistance, your speed can exceed fifty kilometers per second—equivalent to Mach 150 or more—depending on thruster performance. However, do not be intimidated. The Fennel OS will compensate for your perceived velocity to some extent, but this does not mean that hatch doors or personnel inside the ship will move any faster. Be particularly careful with delicate operations.」
As they became accustomed to the adjusted perception of speed, shipboard activities might begin to feel sluggish in comparison.
「Lastly, as you all know, the Fennel OS assists with your five senses in battle. In space, it also adjusts for sound, light, and color perception. For instance, if an explosion occurs, the Fennel OS will reproduce the sound of the blast.」
In the vacuum of space, there is no sound. Without an atmosphere, neither heat nor noise can travel. Missiles, for example, require oxidizers to trigger explosions, and waste heat dissipation is far more difficult than in an atmosphere. The Silhouettes were designed with built-in heat radiation systems to counteract this issue.
「Kinukawa’s space equipment pack design is flawless. I guarantee it. Now, let’s gradually get accustomed to it.」
Trireme’s Space Fleet already had deep trust in Kinukawa’s expertise. But with Astraea’s seal of approval, that confidence was now absolute.
Libya let out an impressed sigh.
「A-Rank Development Engineers truly are remarkable… For Astraea to guarantee perfection is no small feat.」
「In matters of space, Kinukawa-san is in a league of his own. In Kou’s homeland, he’s considered one of the founding figures of space development.」
Aki replied to Libya’s admiration.
「Kou looks like he’s having fun.」
Aimer watched Unit 5 closely on the monitor, following its movements with her eyes.
「Incoming object detected at high velocity. — Confirmed friendly signal. The incoming friendly appears to be engaged in combat.」
「What?」
「It is heading toward our fleet. Estimated engagement time in approximately twenty-five minutes. Contact with the hostile target will occur fifteen minutes after that.」
Without hesitation, Aimer issued an immediate recall order to all Silhouettes currently outside the ships.
「Unidentified combatants are approaching. One of them is transmitting a friendly signal.」
Kou froze for a moment at those words, then immediately opened a communication channel to Kinukawa.
Kinukawa seemed to have reached the same conclusion. The two locked eyes and nodded.
「Kinukawa-san… shall we?」
「Of course. Our first battle in space, huh?」
Kurose, unable to grasp the situation, shouted in frustration.
「What are you two talking about?!」
「It’s a friendly force in combat, Kurose-san.」
「Human factions are prohibited from engaging in warfare in space. That means… it must be Mythology Weapons.」
「We’ve already taken down Murders in space before. Combat against unmanned machines isn’t prohibited. If the friendly unit is a Mythology Weapon from Kryptos, then their enemy must also be a Mythology Weapon… most likely from Teras.」
「If they are an ally, we have to help them. — Let’s move out. All unarmed personnel, return to the ship immediately. If anyone feels uneasy, return as well.」
◆ ◆ ◆ ◆ ◆
「We will provide support for the allied unit. All ships, decelerate to combat speed. Prepare for space combat.」
Confirming Kou’s resolve, Aimer swiftly took command.
「This is the Pericles, Matt speaking. Roger that.」
「This is the Izumo, understood.」
The captain of Izumo was Eri, who had been newly and unexpectedly assigned to the role.
「Trireme’s Space Fleet synchronization initiated. Establishing local virtual coordinate field. Transitioning to combat mode.」
Astraea took control of all three ships simultaneously.
「Local tangent plane coordinates established. Virtual 3D coordinates set. The Trireme Space Fleet and all affiliated Silhouettes will orient themselves using the LVLH attitude (Local Vertical, Local Horizontal). The red dwarf Nemesis has been locked as a reference point. The target celestial body is designated ahead—Nemesis will serve as the Z-axis, allowing us to operate within an XYZ coordinate system based on it.」
「Axis?」
「It’s how coordinates are set in space. The LVLH attitude—Local Vertical, Local Horizontal frame—was used in Earth’s space stations as well. Using the NED coordinate system, Earth is positioned downward as the negative Z-axis. North is defined as the X-axis, and East as the Y-axis. The direction of travel is considered forward.」
「In this deep-space sector, the red dwarf Nemesis serves as the central reference point for our coordinate system, with the direction toward Planet Libya set as forward. The Trireme Space Fleet will operate within this virtual coordinate axis.」
By establishing and synchronizing these parameters, the fleet could maintain stable attitude control. Likewise, the Silhouettes, serving as the fleet’s mobile units, moved in formation, navigating space in an orderly fashion.
「So even in space, there are rules for up and down.」
「These are the spatial rules for the Nemesis system. Until reaching deep space, a fleet’s home planet serves as the reference point. Once beyond the home planet, the red dwarf Nemesis becomes the Z-axis reference, allowing for localized coordinate adjustments and uniform fleet attitude control. The enemy force is likely adhering to the same system.」
「So Nemesis is our landmark.」
「A star makes a reliable reference in deep space. Based on Earth’s standard, anything beyond two million kilometers is already considered deep space. Even at its closest, Venus is still about 42 million kilometers away.」
「Kinukawa is correct.」
「It makes more sense than having both sides fight with contradictory notions of up and down. If every mobile unit were floating in zero gravity without a shared frame of reference, there’d be no way to coordinate directions.」
Kou recalled games where humanoid mechs and fighter jets adhered to a common up and down orientation. There were also space-themed games that ignored these conventions, but that didn’t necessarily make them more engaging.
「Kurose-san, take Kinukawa-san back inside the ship.」
「This old man refuses to go!」
「What are you saying? This will be the first and last time I get to participate in space combat. I don’t care if I die.」
Kou didn’t like the situation, but he understood Kinukawa’s feelings. He was mainly an academic and an important Development Engineer, he would likely never have another chance to fight in a space battle.
「I understand. We don’t know what’s coming. Stay as far back as possible. I expect you to observe the battlefield from a distance, serve as a strategist, and provide tactical analysis.」
「You can count on me.」
No one knew what kind of enemy they were about to face.
「That being said, I’m only putting on a brave face. I am anxious. But it’s not about dying in an enemy attack. What scares me is the thought that the space combat equipment I developed might fail… and cost someone their life.」
「Kinukawa-san…」
「Kurose is highly skilled. If I’m behind him, I can accept whatever happens. But if someone were to die because of a flaw in the equipment, that would be unbearable. After all, this is the first Silhouette space battle in over a thousand years in the Nemesis System. Completely unprecedented.」
「Talk about piling on the pressure, Kinukawa-san.」
Kurose chuckled wryly. Kou, however, understood Kinukawa’s fears as if they were his own. Kou was fortunate—he had Astraea as his mentor. Kinukawa, however, was different. He had spent his life predicting the unpredictable when it came to Silhouette operations in space. Driven by both wonder and fear of the unknown, he had designed space combat systems that no other Development Engineer had ever dared to attempt—entirely on his own.
「Rest assured, Kinukawa. There are no defects in the additional space armor you designed.」
Astraea gave a reassuring smile, a rare sign of respect for one of the greatest Development Engineer in human history.
「Thank you, Astraea.」
There were no defects. That simple statement gave Kinukawa the courage he needed.
「We have the seal of approval from the Goddess of Justice herself! Let’s go, Kou!」
「Yes!」
Kou switched the weapons on Unit 5.
「D-Rifles are useless in space. This will have to do.」
At minus 270 degrees Celsius, the extreme cold was advantageous for maintaining metallic hydrogen, but with no atmosphere, projectile shape dynamics worked differently compared to ground combat.
Unit 5 armed its space-combat railgun, entering battle mode.
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