"Achieving the Dream of Becoming a 7th Space Power"... A Preview of the Nuriho Launch Site [Reading Science]

[Asia Economy Reporter Kim Bong-su] On the 21st of next month at 4 p.m., the Korean-made space launch vehicle Nuriho, carrying the dream of the Korean people to become one of the world's top seven space powers, will attempt its first flight. Let's take a look in advance from the day before the launch preparations to the final confirmation of success on the day.

◇ The day before launch: 'Be careful even of the blowing wind'

The Korea Aerospace Research Institute (KARI) recently released a video titled "A Preview of the Nuriho Launch." According to it, Nuriho completed its final checks (WDR), including propellant loading and unloading, at the end of last month, then separated its stages and is currently being reassembled. After assembly, Nuriho is transported to the second launch pad at Naro Space Center on the morning of the day before launch and erected vertically. Measuring 47.2 meters in length, Nuriho is transported in a horizontal position without propellant, loaded on a long transporter, and moved 1.8 km from the hangar to the launch pad. For safety, it moves slowly at 1.5 km/h, much slower than walking speed, and is vertically mounted on the launch pad.

Afterward, the lower part of Nuriho is firmly fixed to prevent it from toppling over due to wind. Since it is light without propellant and oxidizer, it could be blown down by strong winds. At this time, the ground holding device (VHD) plays an important role by firmly supporting and fixing the lower part of Nuriho with four rings. The VHD especially holds Nuriho tightly as the engine ignites and thrust gradually increases, releasing the launch vehicle only when maximum thrust (300 tons) is reached, playing a very critical role.

In the afternoon, the "umbilical cords" are connected to Nuriho. These umbilicals supply propellant, oxidizer, and electricity to Nuriho. There are six in total, with two connected to each of the first, second, and third stages. If even a slight leak or blockage occurs in the umbilicals, the launch is immediately postponed or halted, so a leak test is conducted as soon as they are connected. While the umbilicals are connected, the launch pad system is also prepared. Inspections of underground tanks supplying fuel and oxidizer, water tank pressure tests under the launch pad, and fire suppression system checks are conducted.

◇ On launch day: Propellant and oxidizer loading

Weather conditions are checked in the morning. The instantaneous maximum wind speed must be below 21 m/s (strong wind warning), and cloud conditions must be such that there is no risk of lightning discharge along the flight path. Temperature, humidity, and pressure are also checked. In particular, the possibility of collision with space debris is examined. Tracking stations at Naro Space Center, Jeju Island, and Palau Island turn on communication antennas and enter launch control mode.

Launch preparations begin by checking various electronic devices, computers, and sensors on Nuriho. Before loading propellant and oxidizer, helium gas is injected first. Ambient temperature helium gas is used to open and close hundreds of valves inside Nuriho to purge foreign substances. Cryogenic helium gas is also injected to maintain pressure in the propellant tanks.

Then, propellant (kerosene) and oxidizer (cryogenic liquid oxygen) are loaded. Especially, cryogenic liquid oxygen is extremely cold at minus 183 degrees Celsius, making loading difficult. Pipes and tanks are pre-cooled before charging, but evaporation begins immediately after loading. Therefore, charging continues until just before launch. The white smoke seen rising before a rocket launch is the vaporization of the oxidizer.

◇ At the moment of launch

Once the propellant and oxidizer are fully loaded and the erector that held Nuriho vertically is detached, the launch procedure begins. This is 30 minutes before launch. The inertial navigation guidance system alignment is performed. From 10 minutes before launch, the countdown starts, and launch automatic operation (PLO) is initiated by computer control rather than humans. All decisions are entrusted to the computer, which checks all conditions such as pressure, temperature, humidity, and communication status, and if any abnormality is detected, it stops the launch automatically. If all conditions are normal, the countdown ends, the first-stage engine automatically ignites, and Nuriho heads skyward. The automatically ignited first-stage engine reaches maximum thrust within seconds. Propellant and oxidizer equivalent to five drums (1,000 kg) explode per second, generating thrust. When maximum thrust of 300 tons is reached, a release command for the VHD is issued, and the umbilicals are automatically detached simultaneously with liftoff.

What is the huge smoke coming from under the launch pad during this process? It is steam generated by water sprayed underground to prevent Nuriho from melting due to the backflow of ultra-high temperature flames exceeding 3,300 degrees Celsius. Also, ice falling off the body immediately after liftoff is frost formed on the tank due to the cryogenic liquid oxygen.

◇ After launch: The 16-minute challenge

The visible time of Nuriho after launch is not long. The first-stage burn time is about 127 seconds, burning for about 2 minutes to exit the atmosphere and reach the thin air of the stratosphere. At this time, the first stage separates, with a retro motor pulling the first stage backward to avoid collision and a ullage motor pulling the second stage upward, while the second-stage rocket ignites simultaneously. Having already reached the stratosphere, Nuriho sheds more than half its weight after first-stage separation, doubling its speed and altitude. Since there is almost no air friction, fairing separation also occurs at this time. After racing at a speed of 4.3 km/s for about 147 seconds, the second stage also separates.

The remaining third stage burns for 521 seconds, flying the farthest, fastest, and highest. Flight speed reaches 7.5 km/s, and at an altitude of 700 km, the third-stage engine shuts down, followed by payload separation after the final orbital flight. This occurs 16 minutes after liftoff. However, this launch uses a 1.5-ton dummy satellite. Thirty minutes after launch, KARI confirms the final success of the launch through analysis of launch data. The success of the first Korean-made space launch vehicle, developed and manufactured over more than 10 years since 2010 with a budget of about 2 trillion won and cooperation with over 300 companies producing 300,000 parts, is determined at this time.