There are many reasons for spacecraft leakage, and the emergency remediation method is wonderful

Recently, Russia's Progress MS-21 cargo spacecraft showed signs of leakage before leaving the International Space Station.

This accident is similar to the one that happened to the Russian Soyuz MS-22 manned spacecraft at the end of last year. The Russian side believes that both were probably caused by external impact.

In fact, there are many thrilling cases of accidental leakage of spacecraft. What are the reasons for this? How should researchers and astronauts take targeted remedial measures?

Russia's Soyuz MS-22 manned spacecraft coolant leak

Accidental leakage is dangerous

Spacecraft work in a harsh environment. They are affected by various factors such as the force of space, extreme temperature changes, noise, electromagnetic interference, vibration, meteoroid impact, etc. Some components are prone to failure, and it is difficult to ensure that there will be no problems during operation. Moreover, spacecraft are often composed of hundreds of thousands or even millions of components, and the system structure is very complex, so reliability is bound to face severe challenges.

With the rapid growth in the number of spacecraft launched by various countries in recent years, and the continuous trial of various new technologies and processes, the missions and structures of spacecraft have become increasingly complex, and more and more unexpected situations have been encountered. Spacecraft operating in space cannot return to the ground for repair. In the event of a failure, traditional manual intervention methods are limited. Among them, once a manned spacecraft fails, it may threaten the safety of astronauts and cause a disaster.

For example, in 1971, after the Soviet Soyuz 11 spacecraft completed the docking mission with the Salyut 1 space station, on its way back to Earth, when the orbital module and the return module separated, an explosive bolt malfunctioned, destroying the hatch sealing device, causing the air in the return module to leak rapidly, and three astronauts unfortunately died.

For example, in 2003, when the Columbia Space Shuttle was on its way to orbit, the insulating foam on the external fuel tank fell off and hit the left wing, causing the seal to fail and being ignored by the monitoring team. When the shuttle re-entered the atmosphere, hot gas entered the wing and triggered a series of failures, causing the shuttle to disintegrate and killing seven people.

The International Space Station is a place where astronauts can stay for a long time, and there have been many high-risk situations. In August 2018, a gas leak occurred in the International Space Station. After investigation, astronauts found that there was a 1.5 mm diameter hole on the wall of a Russian manned spacecraft. If it is not treated in time, the oxygen in the space station may be exhausted within 18 days, which may cause fatal consequences.

Recently, a series of leaks have occurred on Russian spacecraft docked at the International Space Station, causing concern from the outside world. In December last year, the Soyuz MS-22 manned spacecraft was hit by a micrometeoroid, and a small hole with a diameter of about 0.8 mm appeared near the solar wing. The coolant leaked out and the spacecraft lost its manned capacity. On February 11 this year, the Progress MS-21 cargo spacecraft was found to have a seal failure and a malfunction in the temperature control system.

The small hole that appeared after the Soyuz MS-22 manned spacecraft was hit by a micrometeoroid. Normally speaking, the probability of mature spacecraft having accidents in succession is very small, so the Russian space agency attaches great importance to this.

The investigation into the two spacecraft accidents has not yet been completed. Russian technicians will reproduce the faults on the ground to verify the analysis and formulate targeted response measures to improve the protection and reliability of the spacecraft. Next, the Soyuz MS-23 manned spacecraft will be launched empty to take the astronauts home, and there is no room for error.

There are many ways to remedy the situation on orbit

Once a manned spacecraft fails and leaks, it is extremely dangerous and must be discovered and dealt with quickly. The astronauts on the International Space Station should have the most experience in this area, and the handling methods vary greatly depending on the specific circumstances of the failure.

When encountering a dangerous air leak, astronauts on the International Space Station will close the doors one by one to reduce the scope of the fault. Once a hole appears at any position in the cabin, the air rushing out from the leak point will produce abnormal ultrasonic signal characteristics. Astronauts need to use handheld ultrasonic scanning equipment to quickly scan the outer wall of the cabin to determine the leak point. In 2004, astronauts found a leak on the porthole of the Destiny laboratory module and confirmed that the seal at the connection between the U-shaped tube for balancing air pressure and the porthole failed.

The analysis showed that the U-shaped tube was not marked with "Do not pull" and there was no handrail near the porthole, so astronauts often pulled the U-shaped tube when they were nearby, causing it to become deformed and loose, which over time led to air leakage. Later, the International Space Station replaced the U-shaped tube and added a special handrail near the porthole.

In 2018, astronauts discovered a leak on the cabin wall of the Russian Soyuz spacecraft and decided to take emergency sealing measures: first use tape for temporary sealing, and then use epoxy resin glue and gauze for permanent sealing.

These seemingly simple methods worked well, and no leakage problems occurred until the spacecraft separated from the International Space Station.

Compared with manned spacecraft, once an unmanned spacecraft fails, it will mainly cause economic losses, and whether these failures are worth repairing is a question. Not to mention deep space probes that are basically impossible to carry out subsequent repairs, for unmanned spacecraft in low-Earth orbit alone, whether it is sending astronauts or launching robots to repair, the cost may be higher than launching backups.

As multifunctional small satellites become more popular, the idea of ​​"repair is worse than building" is likely to become more common. Of course, if a special and valuable unmanned spacecraft encounters a malfunction, it is still necessary to send people into space for repair.

In the space shuttle era, every flight carried a repair mission. After all, it could carry seven astronauts and was equipped with a robotic arm and various repair equipment, making it an ideal "space clinic."

Over the past few decades, astronauts have saved many important spacecraft, the most famous of which is the Hubble Telescope, which has undergone five repairs to ensure that it has remained in good working condition for more than 30 years in orbit. Unfortunately, most unmanned spacecraft do not have such good "treatment" and mainly rely on component redundancy design and system reconstruction control mode to try to troubleshoot. When a simple fault occurs, ground engineers use remote control commands and uploaded data to switch backup components, switch system working modes, modify important control parameters, and strive to repair the unmanned spacecraft. If it encounters a complex fault, it is likely that it cannot be saved.

With the advancement of technology, abnormal leakage of unmanned spacecraft does not necessarily mean "death sentence". The end of the working life of a spacecraft is often due to the exhaustion of fuel, so some countries and commercial space forces have launched repair satellites and refueling satellites, which are essentially space robots that store fuel, carry parts and repair tools, and can provide on-orbit maintenance and refueling services.

Schematic diagram of satellite docking for on-orbit maintenance and replenishment work

In 2007, the United States launched the first unmanned space maintenance test spacecraft, Orbital Express. It consists of two satellites, one for repair and the other as a cargo hold carrying various tools. The two satellites are usually connected together. After receiving the mission, they enter the target orbit, separate, and the repair satellite performs the "operation". The cargo hold provides various parts or refuels to restore the faulty satellite to normal.

New technologies ensure safety

After years of development, the aerospace industry of various countries has accumulated a lot of experience and lessons, and the spacecraft development capabilities and technical levels have been continuously improved, and reliability and safety have been guaranteed. At the same time, with the application of new technologies and new materials, the ability of spacecraft to detect faults and self-repair is also constantly improving.

In terms of fault detection, the United States has developed a new leak detection technology for the International Space Station, which installs a complete set of sensor systems on the inner wall of the space station compartment to analyze the abnormal vibration signals of the compartment. If a leak occurs in the space station, the sensors capture and summarize the signals to quickly and accurately locate the leak point.

According to public information, my country's new generation manned spacecraft test ship was launched into orbit in 2020, and carried out a series of key technology tests and verifications such as high-speed re-entry, control, and recovery. One of the important contents was the leakage and collision detection system test.

The return capsule of my country's new generation manned spacecraft test ship

The collision and leakage detection system consists of a host and eight high-sensitivity acoustic emission sensors. Debris collisions and cabin gas leaks will generate sound waves. The system can calculate the location of the collision or leak based on the time difference between the sound waves reaching each sensor; and can determine the degree of collision and leakage based on the energy of the sound waves. By sensing small changes in the spacecraft structure in real time, the system can quickly troubleshoot hidden dangers and provide solutions to ensure the safety of astronauts.

In terms of self-repair, intelligent self-repairing materials have become a focus of aerospace research. This material draws on the principle of self-repair of organisms such as geckos, uses hollow fibers to simulate "blood vessel" channels, and makes two non-reactive liquids into "blood" and stores them in the material. Once the material is hit by external forces and cracks are generated, some "blood vessels" will rupture in time, and the two liquids will flow out and penetrate into the cracks, and then react chemically with the surrounding structures to achieve self-healing of the material, and ultimately achieve self-repair of spacecraft structural damage.

US researchers are studying another self-healing material for the outer layer of spacecraft, which uses a three-layer structure, with two outer layers of solid, hard polymers and a middle layer of liquid resin. When space debris penetrates the outer shell of a spacecraft, liquid resin will flow out from the inside of the material, and the gas leaking from the spacecraft will cause the resin to solidify quickly and seal the hole. The hardening process takes only a few milliseconds, which is expected to achieve emergency and immediate repair.

Looking into the future, with the continuous application of new materials and technologies, spacecraft will be safer and more reliable, helping humans fly to deeper space. (Author: Yang Shirui)