Translator: CKtalon Editor: CKtalon
At that instant, Tang Yue felt as though he had returned to a century ago in the era of Yuri Gagarin and Alan Shepard. The engineers had given their all to construct a launch pad weighing hundreds of tonnes and used the R-7 and Redstone rockets that weighed nearly thirty tonnes to send a payload of 70 kilograms.
That was extremely disproportionate in terms of mathematics and physics, with them spending massive amounts of resources to ultimately concentrate on such an individual.
A long period of time had passed, and during this time, humans gained the ability to build space stations, to land on the moon, and to head for Mars. However, they had forgotten that all of that once started from careful micro-steps. In the early days, liquid oxygen and ethanol engines that were sent to near-Earth orbit had a carrying capacity of fewer than three tonnes and the manned spacecraft was only two meters long.
However, those were the nascent steps of human aeronautical history.
When Tomcat firmly said “all we care about is that rounding error,” time seemed to rewind, returning back to the instant when the Voskhod 1’s Chief Designer, Korolev, decided on not wearing spacesuits. It had rewound to the moment when the Kennedy Space Center’s Wernher von Braun gave the order for the countdown. Back then, engineers used tons of scrap paper to calculate every single gram, just for that rounding error.
Human aeronautical success was obtained one step at a time through these tiny rounding errors.
“During the atmospheric entry, it’s not only the Eagle but also Orion. Is that right?” Tang Yue asked.
“Yes.” Tomcat nodded. “Orion is the lifeboat, the Aquarius lunar module on the Apollo 13.”
Orion II was a spacecraft that shuttled between Earth and Mars.
It was one of the biggest spacecraft created in human history. The reason it wasn’t the biggest was that Orion I was the same size. Compared to calling them spacecraft, they were more like mobile space stations. To provide sufficient living space for the six-member crew and provide them with enough survival resources, Orion’s structure was completely different from ordinary spacecraft.
Its main body was made of three trusses, making it reach a length of 88 meters.
At one end of the truss were the solar panels spanning sixty meters long. It was a module with eight panels that supplied electricity.
The middle truss was the central module which was the control center and living quarters. There were a total of eight cabins that were connected to one another in a circle.
The other end of the truss was the service module with the massive propellant reservoir tanks and the nine Raptor 10D liquid oxygen-methane high-pressure engine. The reservoir tanks could be refilled and the engine could be repeatedly used.
Design-wise, Orion was a rather weak structure. It was only a thin rod that seemed skewered together. It was unable to enter the gravisphere of both Earth and Mars. Once gravity acted upon it, the truss would undoubtedly fail to withstand the weight of the central module and engines, warping and snapping immediately.
The day it entered the atmosphere, was the day it was decommissioned.
Orion was born in space, but it would return to Earth.
“You want to let Orion enter the atmosphere with the Eagle?” Tang Yue asked. “Is… Is it possible?”
As someone who knew a bit about aerospace engineering, Tang Yue found the idea crazy. There were too many unresolved problems.
Without much thought, it was easily conceivable that the Orion spacecraft would disintegrate at high speeds, burning up and exploding as a result.
“At times…” Tomcat waved its paw. “The technique involved is the craziest.”
…
“Orion II is 88 meters long. This is the length of the truss.” Tomcat held the pen in its paw as it began explaining the plan to the duo. “If we…”
“Throw it down.” Mai Dong and Tang Yue knew what the cat was about to say.
“… Yes, if we throw it down, right into the atmosphere, it will definitely disintegrate and crash.” Tomcat held the pen and placed it horizontally across the table. “It cannot descend in this manner, but if we were to change the orientation…”
Tomcat held the pen in its paw vertically.
“By letting it descend this way, we can guarantee the structural integrity. This is determined by the truss’s materials and structure. When it’s vertical, it can withstand a force five to six times that of when it’s horizontal. When descending, it will be decelerating. The forces acting on the truss are compressive stress not tensile stress… As long as we ensure that it maintains a vertical orientation during the descent, it can go all the way down!”
“But how do we maintain its vertical orientation?” Tang Yue asked. He couldn’t imagine how an eighty-meter-long pole could maintain its vertical orientation at such high altitudes.
“Korolev Cross!” Tomcat answered. “Or should I say, we mimic a Korolev Cross!”
Korolev Cross? Tang Yue frowned. He vaguely remembered that this term described a phenomenon when the booster rockets were detached from the rocket.
“We have nine Raptor 10D engines with nine gimbaled nozzles. Each engine has enough thrust,” Tomcat explained. “Keeping a pole vertical at high altitude isn’t as difficult as you imagine. Orion’s total mass is 409 tonnes. Out of that 329 tonnes are the propellant and engine. In order words, its center of mass is at the bottom because, during the descent, the engine is facing down.
“As long as four engines maintain their thrust in four directions, the pole will stand vertically in a stable manner.” Tomcat held the pen vertically in its paw tip. “With it being bottom-heavy and top light, this will maintain its stability. If it’s the other way round, that won’t work. Of course, it cannot withstand any horizontal forces during the process. This is also thanks to Mars not having much of an atmosphere. It’s impossible to do it on Earth because any strong gust of wind would doom this plan.”
“What… what about the heat?” Mai Dong asked.
“There’s no need to consider the heat, lady.” Tang Yue held his chin as he pondered for a few seconds. “This cat wants to descend with a reverse thrust the entire time; thus, controlling the speed of descent. However, is there enough propellant on Orion?”
“Bingo! That’s the crux of the matter.” Tomcat snapped its paws. “The propellant is key to the entire plan. We have a total of nine Raptor 10D engines. Orion’s propellant reservoir has a total of 300 tonnes of fuel. If there isn’t enough propellant, everything is pointless. Let’s do some accounting.”
Mai Dong and Tang Yue nodded.
All the hope was on the accounting.
“A Raptor 10D engine has a thrust of 900 kN in a vacuum, which is 90 tonnes. Nine engines will give a total thrust of more than 800 tonnes,” Tomcat said. “On average, a Raptor engine burns through the fuel at 60 gallons a second. In SI units, that’s 227 liters. A mix of 227 liters of liquid methane and liquid oxygen has a total mass of 202 kilograms.”
Tomcat pointed to the sky. “That is to say that the spacecraft’s engine, a Raptor 10D engine will burn through 202 kilograms of propellant a second. And we have a total of 300 tonnes of propellant to use. If all nine engines are used together, how long can the propellant last?”
“165 seconds.” Mai Dong immediately gave an answer. “Less than 3 minutes.”
Tang Yue was alarmed.
165 seconds was definitely insufficient.
To safely descend from an orbit of 125 kilometers, 165 seconds was definitely insufficient.
“This is clearly insufficient,” Tomcat said. “The spacecraft will expend all its fuel at an altitude of tens of thousands of meters. Then, it would crash.”
“What do we do?” Tang Yue asked. “You said that there’s hope.”
“We need to thank the designers of the Raptor 10D engines. An engine’s thrust is 90 tonnes. To support a 400-ton spacecraft’s descent, do we need all nine engines to be running?” Tomcat smiled.
Tang Yue immediately understood.
The spacecraft’s total weight was 409 tonnes.
An engine’s thrust was 90 tones. With just five engines, it could produce a total thrust of 450 tonnes.
“We can use a throttling process to control the engine’s thrust by only activating five engines. Then, do another count,” Tomcat said. “How long can the propellant last?”
“297 seconds.” Mai Dong’s voice trembled. “At least 297 seconds.”
“Yes, at least 297 seconds. In reality, the number will be bigger than that. This is because Mars’s gravity is only 40% of Earth’s. Therefore, Orion’s 400+ tonnes on Earth would only be about 160 tonnes.” Tomcat nodded. “Therefore, the engine’s expenditure of the propellant will be less than our calculations. In fact, Orion’s propellant can last a total of 12 minutes.
“In these 12 minutes and at a height of 125 kilometers, we need to have the spacecraft’s average speed of descent to be at 173 m/s. It’s not even at Mach 1.”
Tang Yue was stunned.
Mai Dong’s eyes reddened.
“You might be able to come down.” Tomcat turned its head and wriggled its ears at Mai Dong as it giggled. “Miss Mai Dong.”
