Space experiments are not afraid of being "exposed", how many tricks do you know?

Recently, the space radiation biology exposure experiment device on the Chinese space station was grabbed by a robotic arm, unloaded from the cargo airlock of the Mengtian laboratory cabin, and then installed on the exposure platform outside the cabin. It started working normally. Our common space experiments are generally carried out in the tightly protected spacecraft cabin. Why do some experiments need to be exposed to the space environment? What are the special features of these experiments? What unique value do they have?

Exposure experiments require a lot of attention

As the name implies, exposure experiments involve exposing experimental materials to a special environment to observe what special changes will occur in the experimental materials. Extravehicular exposure experiments involve exposing experimental materials to the space environment outside the spacecraft cabin, using complex and diverse space factors to observe subtle changes in experimental materials. During this process, astronauts and ground teams fully collect experimental data, analyze the mechanism of sample changes, and interpret the laws behind them.

The space radiation biology device is installed on the Mengtian cabin exposure platform

Spacecraft such as the space station float in the space environment, which has a very ideal microgravity environment for scientific experiments, and can complete many experiments that are difficult to complete on the ground. However, for some experimental goals, the microgravity environment is far from enough, and conditions closer to vacuum are required. In order to maintain the health of astronauts, the space station still maintains the atmospheric pressure level of the earth's sea level, and the air composition is also similar to the earth's atmosphere.

Similarly, it is impossible to maintain a radiation source that threatens the life and health of astronauts in the space station for a long time, and it cannot meet the radiation requirements of certain experiments. Therefore, researchers designed an extravehicular exposure platform for the space station to carry out special space experiments with more "extreme" requirements.

So what are the special requirements for these space experiments?

First, they need to use the external space environment that is basically impossible to simulate on the surface. Although space is often called a "vacuum," it is not empty. There are all kinds of complex substances in the low-Earth orbit where the space station is located, from micrometeoroids with a diameter of only a few microns, to atomic oxygen produced at the edge of the atmosphere, to inestimable harmful radiation, all of which provide the prerequisites for the changes in the characteristics of experimental materials.

Secondly, these experiments will not be overly dependent on astronauts. As the space environment is too harsh for the human body, astronauts must wear space suits with complex life-support functions before going out of the cabin, and the mission intervals and times are strictly limited, so it is impossible for them to go out of the cabin frequently to look after experimental equipment and materials.

Finally, the experimental equipment needs to ensure reliability and improve overall efficiency. As astronauts cannot frequently leave the cabin for care, and the operation of the robotic arm is inevitably limited, various unexpected factors must be considered in advance when designing the extravehicular exposure platform and experimental equipment, so as to carry out more space experiments in a longer period of time.

For example, my country's space radiation biology exposure experiment device is designed with 13 sample box units loaded with biological materials. It is planned to work for about five years and provide services for multiple scientific experimental projects.

Foreign practice has yielded fruitful results

In the foreign aerospace industry, extravehicular exposure experiments have been going on for decades and have yielded many meaningful experiences and results.

In 1970, NASA's Langley Research Center began designing a special scientific experiment satellite. After 14 years of demonstration and development, the satellite was intuitively named "Long-Term Exposure Facility". It was the size of a school bus and was carried into space on April 6, 1984 by the Challenger Space Shuttle, becoming the only satellite dedicated to extravehicular exposure experiments to date.

According to the plan, the satellite should be brought back to Earth after about a year and a half of orbital operation. However, due to the tragedy of the Challenger space shuttle in early 1986, its return time was repeatedly postponed until it was brought back from orbit by the Columbia space shuttle in early 1990. During its extended service, the satellite verified the reliability of materials and designs, and completed a total of 57 experiments using experimental materials from multiple countries (from tomato seeds to spacecraft coatings), with a variety of experimental results.

After all, the payload capacity of satellites is limited, and space stations are professional space laboratories. In the 1990s, on the Russian Mir space station, American aerospace experts developed a special extravehicular exposure platform called the "Mir Environmental Impact Payload", which was carried into space by the Atlantis space shuttle on March 27, 1996 and exposed outside the Mir space station for about a year.

Many experimental results have been produced on the above two platforms, making great contributions to the design and improvement of the International Space Station. At present, there are four professional extravehicular exposure platforms on the International Space Station, located on the European Space Agency's Columbus laboratory module, the Japanese Hope laboratory module, the Russian Zvezda core module and the frame structure.

However, the space exposure experiments conducted on these four platforms were carried out separately by research institutions in various countries. This has certainly improved flexibility and diversity, but it has also left regrets in the coordinated use of resources.

The Shenzhou 16 crew installed the payload on the payload transfer mechanism

From new materials to biology

What can be done in the extravehicular exposure experiment? Considering the characteristics of the space environment and relatively independent operation, it mainly includes two categories: material experiments and biological experiments.

Micrometeorites, atomic oxygen and various cosmic rays have extremely strong corrosive and degenerative effects on materials such as metals and plastics, causing the materials to undergo complex physical and chemical changes and lose their inherent properties.

Researchers can use this to their advantage by placing a batch of materials on an exposed platform outside the cabin to fully withstand the "wind and rain" of space, and then retrieve them for testing. By studying the final state of the materials, it will help researchers determine the corrosion resistance of the materials, develop them in a targeted and optimal manner, and synthesize new materials with stronger corrosion resistance.

Space is not necessarily a forbidden zone for life. Various important biological experiments can also be carried out on extravehicular exposure platforms.

For example, the ancient microorganism cyanobacteria is very important to the Earth's ecology. Can it play a similar role in space? After placing the cyanobacteria samples on the exposure platform for a period of time, the researchers compared their gene sequences with the control groups in the space station and on Earth to observe whether their "gene expression" and physiological morphology have undergone fundamental changes.

In the future, humans are expected to establish bases on the moon and Mars, which will inevitably require the construction of a self-sufficient extraterrestrial ecosystem. I believe that microorganisms such as cyanobacteria that can produce oxygen will play a huge role in this.

Load out of cabin screen

According to public information, my country's space radiation biology exposure experiment device can be used to conduct in-orbit experiments on plant seeds, microorganisms, small animals, etc. It will provide services for radiation damage to humans and organisms, genetic variation, preparation of radiation protection drugs, and radiation risk biology assessment. It is of great significance to the long-term survival of Chinese astronauts in orbit and manned lunar landing.

For example, if we want to develop our "vegetable talent" on the moon or even Mars in the future, we need to select the best and cultivate new varieties that are more adaptable to high radiation and microgravity environments. The International Space Station has completed many plant seed extravehicular exposure experiments. I believe that as my country's space station enters a new stage of application development, more novel and colorful biological extravehicular exposure experiments will surely increase.

Of course, the extravehicular exposure platform can do much more than these experiments. After being equipped with appropriate payloads, it can carry out space radiation medicine and protection experiments, space radiation resource development and testing, life origin and evolution and other cutting-edge research... These are the continuous contributions that the space station, a "space outpost", has made to mankind. (Author: Shi Xiaolong, review expert: Jiang Fan, deputy director of the Science and Technology Committee of China Aerospace Science and Technology Corporation)