Chapter 20

I've added a paper theater story titled "Hayabusa's Errand."

It's unrelated to the main story, and I would be grateful if you could read it.

"Okay, this is the Kingdom of Rastel. Has everyone seen it before?"

"It's a map, right?"

"Yes, it's a map. So, where is the Kingdom of Rastel?"

"On the continent of Astelia—!"

"Where is the continent of Astelia?"

"Earth!"

"It's Earth!"

"Right, Earth. This land is actually a round sphere."

"But the priest said that's a lie."

"He said the world is flat?"

"A bit outdated. Now, we have the heliocentric theory, which says the Earth is round and orbits the Sun. Observing stars, the Sun, the Moon, and planets helped us understand this. Earth is one of the stars in the solar system, a member of the Sun's family. Earth, along with Mercury, Venus, Mars, Jupiter, and Saturn, orbits the Sun in this universe. Earth is in the solar system."

"The solar system?"

"Right, the solar system formed and Earth was born long before humans appeared. It's a distant, ancient memory. Today, we'll explore that memory. What do you see when you look up at the night sky?"

"The Moon!"

"Stars!"

"The Milky Way!"

"The Moon, stars, and the Milky Way are all stars. They appear large or small depending on their distance. There are countless stars in the universe. However, we on Earth can't travel to space yet because it's so high up, even birds can't fly that high. We don't know how our home, Earth, and the solar system it's part of, were formed or when. But if we want to know, we must one day leave Earth and collect and study fragments of asteroids that existed before the solar system was formed."

"Wow."

"Hmm... Are they as high as the stars?"

"Right. 300 million kilometers from Earth. The asteroid belt between Mars and Jupiter. That's where we go to collect asteroid fragments. That's the mission of—"

"Wow—"

"It's Hayabusa's job. This mission, impossible for humans, was entrusted to the asteroid explorer MUSES-C, 'Hayabusa.'"

"Isn't Hayabusa a bird?"

"Hayabusa is a machine. It's a highly precise, state-of-the-art machine built within budget. But Hayabusa is a bit different from ordinary machines."

"Different how?"

"Hayabusa has a heart. It can think, make decisions, and act autonomously, not just follow commands. That's what makes it different!"

"Like a human?"

"Right. This is the story of Hayabusa's great adventure in a distant future, centuries from now. Let's begin—"

"Wow—applause—"

"First, the rocket launch! There's no air in space, so you can't fly by flapping wings like a bird. The only way to travel in space is by rocket!"

"Rocket?"

"Right, the only thing that can fly in the vast emptiness of space is a rocket. It propels itself by ejecting hot gases at high speed, using the reaction to move! Hayabusa will ride this to space! On May 9, 2003, the countdown for the M-V5 solid-fuel rocket launch began at the Uchinoura Space Center! The launch angle is 80 degrees, the diameter is 2.5 meters, the length is 30.8 meters, the weight is 140 tons, and the maximum thrust is 3 million horsepower! The payload capacity is 1.8 tons!"

"Wow, it's huge..."

"5, 4, 3, 2, 1, ignition!"

"Wow—"

"The M-V5 rocket pierces the blue sky and ascends rapidly! Good attitude, good acceleration! Good direction! Breaking through the atmosphere! First stage separation! Hayabusa, now in space, ignites the second stage! This all happens in just 75 seconds!"

"Amazing—"

"By separating the first stage, Hayabusa, now lighter, accelerates further. The second stage separates, and the nose fairing opens! The third stage ignites, and orbit insertion control begins! After breaking free from Earth's gravity, the third stage separates! All of this happens in just six minutes!"

"Wow, that's fast!"

"Finally, the fourth stage kick motor ignites and separates! Hayabusa, now heading for the asteroid Itokawa, extends its solar panels and embarks on its space journey!"

"Applause—"

"Having left Earth, Hayabusa must now fly on its own. The asteroid Itokawa is 300 million kilometers away, beyond Mars' orbit. Even the capable Hayabusa doesn't have the power to fly straight there. So, Hayabusa's first goal was to enter the same orbit as Itokawa and gradually catch up. The distance is 6 billion kilometers round trip... The return is planned for four years later. To travel this distance, Hayabusa was equipped with an ion engine!"

"Ion...?"

"This ion engine is the world's first electric propulsion system for planetary exploration, using electrical energy."

"Electricity?"

"Like when lightning strikes and makes a loud boom—"

"Oh—"

"That's electricity. Hayabusa uses this power. It ejects xenon gas from its tanks, ionizes it, and accelerates it with microwaves to propel itself. Hayabusa's 'food' is sunlight, which it converts into energy using solar panels."

"Lightning seems really powerful."

"Hayabusa, a small satellite weighing about 500 kg, can only generate enough thrust to lift a sheet of paper, but it can run continuously for long periods, making it perfect for long-distance interplanetary travel."

"Wow... I don't understand everything, but it sounds amazing."

"However, one of the four engines, the A engine, malfunctioned, and Hayabusa had to operate with only three. This was Hayabusa's first malfunction. It continued to face equipment failures. Worse, six months after leaving Earth, a record-breaking solar flare occurred, exposing Hayabusa to intense cosmic radiation. A solar flare is an explosion on the Sun. While Earth is protected by the Van Allen belts and the atmosphere, being hit by such radiation in space can be fatal. Although the damage to Hayabusa's body was minimal, the efficiency of the solar panels, which convert sunlight into energy, decreased, reducing engine output. The arrival at Itokawa was delayed by three months."

"Wow, that's tough..."

"Actually, Hayabusa didn't head straight for Itokawa. It orbited Earth once, was overtaken by Earth, and then caught up with it again. To catch up with Itokawa, which orbits faster than Earth, Hayabusa needed to increase its speed. That's where the Earth swing-by comes in!"

"Earth swing-by...?"

"A technique to increase speed and change direction by using Earth's gravity. Earth orbits the Sun at a speed of 110,000 km/h. By using Earth's gravity, Hayabusa gets a boost, like a gravitational slingshot."

"Sounds amazing."

"However, this requires extremely precise calculations. Even a slight deviation means missing Itokawa, 300 million kilometers away. Hayabusa doesn't have the engine power to correct such a deviation. The allowed altitude error is within 1 km, and the speed error is less than 1 cm/s. It's a one-shot deal, with no second chances! Here comes Earth!"

"Swallow—"

"One year after leaving Earth, on May 19, 2004, Hayabusa entered Earth's gravitational sphere. The closest approach to Earth was 3,700 km! Accelerating to 36 km/s! That's a speed that would cross the Kingdom of Rastel in just 15 seconds!"

"Fifteen seconds?"

"Even at such speeds, space is so vast that it feels incredibly slow. After being launched from Earth with unprecedented accuracy, it took Hayabusa another year to capture the image of Itokawa. After flying alone in space for a long time, on July 29, 2005, Hayabusa captured Itokawa with its star tracker! Two years and four months after launch, on September 12, 2005, Hayabusa finally arrived 20 km above the asteroid Itokawa!"

"Wow—applause—"

"Hayabusa immediately began surveying Itokawa. This took two months. Here's the image of Itokawa it sent back. It's 535 meters long and 209 meters wide. It's squat, elongated, and curved..."

"It looks like a soybean."

"A sleeping cat?"

"A raccoon?"

"We usually call it a sea otter."

"A sea otter?"

"An animal that floats in water, dives to collect shells, and breaks them open on a stone on its belly..."

"Ha ha ha! That's just a sleeping cat!"

"Never mind that! The actual Itokawa was very different from expectations. Its gravity distribution is light, like a cluster of rocks. However, its composition is almost identical to meteorites that fall to Earth. This was the first proof that meteorites and asteroids are the same. One of Hayabusa's achievements."

"Meteorites are pieces of asteroids that fall to Earth."

"Exactly. But the surface is covered with large rocks, and there's hardly any fine, sandy ground suitable for sample collection. The only place where landing seemed possible was this indented area, the 'belly.' It's a very narrow area. Hayabusa decided to land here."

"Is that difficult?"

"It's difficult, but it's okay! Hayabusa has been preparing for this. However, one of the three reaction wheels on board had already failed."

"Reaction... wheel?"

"Everyone, if you were floating in the air, how would you change direction?"

"In the air?"

"Yes, there's no gravity in space. There's no up or down, and everything floats. What would you do?"

"Um, maybe wave my arms around?"

"Right, the reaction wheel does just that. It controls the spacecraft's orientation without using fuel in zero gravity. It controls pitch, roll, and yaw. All three need to work together for precise control."

"That's impossible."

"But, just in case!"

"Really!?"

"This malfunction was anticipated, so the program was modified to use the remaining two reaction wheels and the hydrazine chemical thrusters. Operations continued."

"Phew—"

"However, just as Hayabusa was about to land, on October 2, 2005, the second of the three reaction wheels also failed! It was a critical situation! It seemed impossible! There was nothing to be done—"

"Hayabusa has too many malfunctions..."

"It's hopeless..."

"But, just in case!"

"Again?"

"Everyone thought it was impossible. Two failures were beyond expectations. Repeated test landings were conducted, and the program was modified to use the remaining single reaction wheel and thruster-based attitude control. It was unreliable, but it was the only option. On the 926th day since launch, on November 19, 2005, the touchdown for sample collection began!"

"Swallow—"

"Descent began from 7 km above, at a speed of 10 cm/s! The target marker was successfully deployed!"

"Target marker?"

"The target marker is a strobe reflector. Since Itokawa's surface is covered with sand and rocks, it's difficult to pinpoint the location using only laser altimeters. So, a target marker is dropped in advance, and the spacecraft descends using it as a guide. At this time, the distance from Earth was 300 million kilometers. It takes 34 minutes for a command to reach Hayabusa and for a response to return. It's impossible to give commands one by one. Hayabusa must judge the situation on-site, adjust its orientation, and complete the sample collection alone. The responsibility is immense."

"Uh—"

"Hayabusa descends closer to Itokawa. 2 meters remaining... 1 meter remaining..."

"Come on—"

"Go, Hayabusa!"

"At this moment!"

"Whoa!"

"Hayabusa detected an anomaly! There's an obstacle!"

"Is it a monster?"

"Is it a giant creature?"

"Abort descent! Abort descent! Reorient! Change vertical speed! Abort!"

"Ah—"

"On Earth, no one knew what was happening. Data showed that Hayabusa, which should have landed on Itokawa, was still descending, causing a commotion."

"What's Hayabusa doing?"

"At this time, Hayabusa's sensors detected an unexpected obstacle. What it was is still unknown. It might have been charged particles floating due to static electricity. After all, Itokawa's gravity is only one-sixty-thousandth of Earth's. Panicked, Hayabusa failed to perform an emergency altitude adjustment and bounced off the surface, losing orientation and making an emergency landing. It crashed."

"Ah—"

"Hayabusa was exposed to Itokawa's surface temperature, which exceeded 100°C, for over 30 minutes. That's hot enough to cook an egg. It took 17 minutes for a command to reach Hayabusa, and 34 minutes for a round trip. There was no time to waste! If nothing was done, Hayabusa would really burn up!"

"Ah—"

"Hayabusa received an emergency command from Earth to ascend. It managed to ascend, but the spacecraft suffered severe damage. This damage would later cause problems for Hayabusa..."

"Really, Hayabusa is such a troublemaker..."

"What do you do?"

"What do you mean?"

"Two years of travel, injured limbs, a damaged body, and no samples collected. Another attempt would be dangerous, and the time limit for returning to Earth is approaching. What would you do? Would you go home and say the errand failed?"

"Wow—"

"Go home? Just go home without doing anything?"

"No way..."

"Hayabusa—! Show some grit!"

"Try again!"

"Just one more time, just one more time, try again!"

"Right, Hayabusa remembered the errand it was asked to do. To collect samples from Itokawa. That's why it came here. Hayabusa mustered the courage to attempt another touchdown on Itokawa!"

"Wow—"

"On November 26, 2005, after modifying the sensor program, Hayabusa attempted the landing again. The target was the marker dropped in the Sea of Muses, the same location as before. For the second attempt, Hayabusa extended the sample horn and successfully touched down!"

"Yay—"

"I knew it!"

"Congratulations—"

"Great job—"

"At the moment of landing, a metal projectile was supposed to be fired to collect the sand that would be lifted into the sample container..."

"Supposed to?"

"Due to the impact of landing or the continuous use of the equipment, hydrazine fuel began to leak from Hayabusa's body. The gas caused it to spin uncontrollably, making attitude control impossible. The internal temperature dropped to -30°C due to the cooling effect. On December 4, 2005, Hayabusa became completely unable to function."

"Again..."

"Hayabusa lost all means of attitude control except for one reaction wheel... It was a situation beyond expectations. To control the uncontrolled spin and align the solar panels with the Sun, Hayabusa did something it was told never to do."

"Never to do..."

"It was to release xenon gas, which was saved for the return journey, from the ion engine. The xenon gas, which was supposed to be ionized and ejected from the ion engine, was directly released as neutral gas from the neutralizer to control the spin. This is usually not done. It worked because the neutralizer was accidentally positioned off-center from the center of mass."

"But, won't it prevent the return?"

"Will there be enough fuel?"

"Of course, if used recklessly, there wouldn't be enough fuel for the return. But Hayabusa had no other options. It's okay. The spacecraft was equipped with 66 kg of fuel, with 22 kg planned for the outbound journey and 12 kg for the return. There should be some extra. By using the safety margin, even if it's tight, the priority was to return to Earth as soon as possible. The time limit was that close."

"Hayabusa..."

"Using the last resort, Hayabusa finally managed to align the solar panels with the Sun and could 'eat' again. However, when full communication with Earth was restored, the news was disappointing."

"Disappointing?"

"The downloaded data did not show any record of the projectile being fired. The projectile, which was supposed to be fired at the moment of landing to collect sand, was not fired. There was only one projectile, and there