Rocket launches fail for different reasons

In 2022, there were 186 orbital launches worldwide, of which 178 were completely successful, 1 was partially successful, and 7 failed, with a complete success rate of 95.7%. There were 6 types of failed rockets, namely the US Astra 3.3 rocket (twice), the European Space Agency's Vega-C, Japan's Epsilon Enhanced, India's SSLV, and my country's private commercial aerospace company's Hyperbola 1 and Suzaku 2. So what are the reasons for the failure of these rocket launches? What lessons can aerospace practitioners learn from them?

The heart is complex and prone to accidents

The engine provides power for the rocket and can be called the "heart" of the rocket. Once a failure occurs, it is very easy to cause a launch failure. The problem is that the engine has a complex structure, many parts, and a harsh working environment, which makes it relatively easy to fail. According to statistics, the proportion of rocket launch failures caused by engine failures is close to 50%. Among the 7 launch failures in 2022, except for the first failure of the Astra 3.3 rocket and the failure of the Indian SSLV rocket, the remaining 5 failures were directly caused by engine failures, accounting for as high as 71%.

The US Astra 3.3 rocket has been decommissioned after a series of launch failures

Specifically, in the five engine failures, three were caused by the main engine. The main engine failure is equivalent to the atrium and ventricle of a person's heart. If there is a problem with it, it will inevitably lead to serious consequences.

The failed launch of the US Astra 3.3 rocket on June 13 was caused by the rapid consumption of fuel in the second-stage liquid engine, which caused it to shut down prematurely. On December 21, the European Space Agency's Vega-C failed due to negative pressure in the second-stage solid engine.

ESA's Vega-C rocket fails on first commercial launch

In addition to the main engine, the rocket also has an attitude control engine that provides auxiliary power for attitude control. Once there is a problem with it, the rocket's flight attitude will easily deviate significantly, leading to mission failure.

The attitude control engine of the third stage of the Hyperbola-1 launched by my country on May 13 leaked fuel and ran out of fuel in advance, and lost its attitude control capability in the later stages of the flight. The enhanced attitude control engine of the third stage of the Epsilon launched by Japan on October 12 could not work properly due to low pressure in the propellant supply pipeline, and the mission ultimately failed. The liquid oxygen-methane swimming rocket engine used for attitude control and terminal velocity correction of the second stage of my country's Suzaku-2 launched on December 14 malfunctioned, causing the rocket's attitude to deviate.

Rocket engines are prone to failure, and the fundamental reason is determined by the characteristics of the rocket. Under the premise of strictly controlling its own weight, the rocket needs to rely on the engine to accelerate to the first cosmic speed in about 10 minutes. Therefore, the engine is required to have high thrust, high specific impulse, high thrust-to-weight ratio, low cost and other indicators, which are high and contradictory. This determines the working characteristics of the engine: operating with extreme parameters that exhaust the material's extreme performance, achieving high-level energy release and conversion in a small structural space, that is, the engine must convert the chemical energy of the fuel into flight kinetic energy in a very short time, and the power and power density are very large.

For example, when the Long March 5 rocket takes off, the total engine power can reach 16 million kilowatts, which is equivalent to the power generation of 0.7 Three Gorges Hydropower Stations. Another example is the energy density of the main engine of the space shuttle can reach 1,400 kilowatts per kilogram, which is more than 1,600 times that of a common automobile engine.

It is precisely this series of stringent requirements that lead to the challenges in the development and application of rocket engines, such as complex and harsh load environments, prominent structural strength and fatigue problems, and high difficulties in manufacturing and use and maintenance. It is not surprising that failures occur.

There are many basic quality issues

A specific analysis of these launch failure cases in 2022 shows that some of them were caused by technical quality problems, while others exposed basic quality problems such as defects in the performance of conventional products and operational errors.

On February 11, the Astra 3.3 rocket failed to launch for the first time this year. The direct cause was a fairing separation failure and a software failure. At that time, the fairing failed to separate correctly before the second-stage engine ignited. The accident investigation found that the cable layout design of the separation system was wrong, resulting in the separation timing being inconsistent with expectations, causing the fairing separation to fail. In addition, the rocket's software had data packet loss, which prevented its second-stage engine from using the thrust vector control system for attitude control. Although the manufacturer believes that the two problems with the rocket are "independent" and not a chain reaction, it also shows that the root cause of the launch failure was defects in product design, insufficient technology, and inadequate quality control.

Astra 3.3 rocket

On May 13, after my country's Hyperbola-1 Y4 carrier rocket was launched, it had an abnormal flight and failed to launch. An investigation found that the cause of the failure was that there was excess material in the rocket's 2000-Newton attitude control engine, which caused the main valve of the engine fuel path to be not closed tightly, causing fuel to leak and be exhausted prematurely, and the rocket lost its attitude control ability. After the attitude of the third-stage flight stage exceeded the tolerance, the rocket's active safety control conditions were triggered, and the rocket executed a self-destruction command. This is a production operation error, and excess material was left in the product, which is also a typical basic quality problem.

On August 7, after the Indian SSLV rocket was launched, the first three stages flew normally and separated, but the fourth stage (also known as the velocity correction module) was supposed to work and burn for 20 seconds, but it only burned for 0.1 seconds, making the rocket unable to reach the predetermined flight altitude and entering the wrong elliptical orbit. The accident investigation found that when the fourth stage of the rocket was flying, the acceleration sensor failed, causing the computer to switch to the wrong orbit according to the fault, resulting in the failure of the entire mission. This is a typical device-level product quality problem. A small acceleration sensor failure caused a major accident.

By analyzing the above three launch failure cases, it can be seen that rocket launch is a complex system engineering. Once there is a slight problem in any link such as design and production, it may lead to the failure of the launch mission.

First flight and winning streak are not easy

Among the six rockets that failed to launch in 2022, two were new rockets that failed during their maiden flights, including my country's Suzaku-2 and India's SSLV. In fact, the development of new rockets involves many challenges such as new technologies, new materials, new conditions, new environments, new positions, new personnel, and new equipment, and naturally faces greater risks.

For example, my country's "Zhuque-2" was the first in the world to use a liquid oxygen-methane engine for orbital launch. Although its "Tianque" 80-ton liquid oxygen-methane engine completed a number of ground tests, including the world's first pump-swinging high-thrust engine technology verification, no matter how thorough the simulation and ground tests are, they can never fully simulate the real flight environment.

It is precisely because the system solution and product reliability of the new rocket have not been assessed through flight tests that the probability of failure in the first flight is relatively high. The failure of the "Zhuque-2" to enter orbit is regrettable, but the first flight across the Karman line is of great significance, and the new launch site system, propellant, main power system, rocket body structure, test and launch system, etc. have all been tested in actual combat.

India's SSLV small solid-fuel carrier rocket was developed to meet the needs of the booming small satellite market. It is 34 meters long, weighs 120 tons at takeoff, has a low-Earth orbit carrying capacity of 500 kilograms, and has a launch cost of only 1/10 of the mature Indian PSLV rocket. The total assembly time is only 72 hours. Although the SSLV failed in its first launch, its rapid launch and low price make it very attractive to the market, which means that there will be more launch opportunities in the future.

India's SSLV fails in first launch

In fact, every rocket launch mission is not a simple repetition of previous missions. Any mistake in any link, any omission in any work, or any failure in any component may lead to the failure of the entire launch mission. Therefore, it is rare for a certain type of rocket to win consecutive battles.

Taking several rockets that failed to launch in 2022 as examples, Japan's Epsilon series is a relatively mature solid rocket that made its first flight in 2013 and had successfully completed five launch missions before 2022, but failed in its sixth launch due to new problems. The European Space Agency's Vega-C made its first successful flight on July 13, becoming the most powerful model of its kind, but its second launch, the first commercial launch in the same year, failed, and the model's future and market prospects are unclear.

In short, the rocket structure is complex and the technical requirements are high, which means that space launch is a high-risk system engineering. A simple analysis of the launch failures in 2022 shows that most of them were caused by some "small things" in terms of quality. It can be said that "failure is a little short of success."

No matter what, ensuring a successful launch is the eternal theme of rockets and the eternal pursuit of rocket developers. In the face of failure, global rocket developers will not be discouraged. By learning from failures, eliminating hidden dangers, making up for weak links, and continuously improving and iterating, I believe that space launches in 2023 will surely reach a higher level and create greater glory. (Author: Xu Zhenliang)