According to the China Manned Space Engineering Office, Shenzhou 18 is aimed at being launched at 20:59 on April 25, and the astronaut crew of the Shenzhou 18 manned mission is composed of three astronauts, Ye Guangfu, Li Cong, and Li Guangsu, with Ye Guangfu as the commander. The crew includes 1 second batch of astronauts and 2 third batch of astronauts, all of whom are "post-80s".
This is Shenzhou-18 astronauts Ye Guangfu (middle), Li Cong (right), and Li Guangsu. Xinhua News Agency
As the first of the latest batch of Shenzhou manned spacecraft, Shenzhou 18 has a number of technical upgrades, especially the comprehensive upgrade of the spacecraft's power supply system, which has improved the performance and safety of the spacecraft. In addition, at the press conference of the Shenzhou 18 manned mission, it was also mentioned that the astronauts will raise fish in space for the first time.
This time, we invited Professor Zhou Binghong from the National Space Science Center of the Chinese Academy of Sciences and Professor Zhang Wei from the Space Application Engineering and Technology Center of the Chinese Academy of Sciences to tell us about Shenzhou-18.
The Shenzhou-18 battery system has undergone these upgrades and improvements
In the Shenzhou 5, 6, and 7 manned missions, the astronauts had to eat cold meals due to insufficient power supply. For manned spaceflight, the power system is as important as the heart and blood of the human body, and it needs to be continuously supplied with electricity.
So, what are the parts of the power supply system of the mainland Shenzhou spacecraft? What are the different uses? What important improvements have been made to the power supply system of manned spaceflight, and why should it be continuously improved? The following is an interview with Zhou Binghong, a teacher from the National Space Science Center of the Chinese Academy of Sciences.
1. The power system composition of the Shenzhou spacecraft
First of all, the power supply system of the Shenzhou spacecraft consists of four parts: main power supply, emergency power supply, return and landing power supply and pyrotechnics power supply.
As the name suggests, the emergency power supply and the return landing power supply are relatively easy to understand. For example, the emergency power supply has an important "life-saving" role, and in case of an unexpected situation, the emergency battery will be activated. The emergency battery uses a high-performance silver-zinc battery, which acts like a UPS uninterruptible power supply. In the event of an emergency, it takes 4 hours for the spacecraft to return to the ground, and the emergency battery ensures the spacecraft's power consumption.
The main power supply is divided into three parts: solar cell wings, regulation controllers, and batteries. The spacecraft orbits the Earth for approximately 90 minutes, passing through the Light Zone and the Shadow Zone. In the light zone, solar cell wings convert solar energy into electricity while charging and storing energy for the battery. In the shadow of the earth, where the sun cannot shine, the battery is responsible for powering the entire ship.
2. Upgrade and improvement of power supply system
With the development of the continental manned space project, what upgrades and improvements have the power supply system undergone?
The power consumption of the spacecraft is about 2 kilowatts, which is equivalent to the power consumption of an ordinary household air conditioner or a microwave oven with high power, so that the Shenzhou spacecraft consumes more than 40 kilowatts of electricity a day.
In the first phase of the manned space project, due to the limited power supply capacity, the astronauts ate cold rice. In the power supply system used in the second phase of the manned space project, the material of the solar panel sail is gallium arsenide, which replaces the polysilicon used in the first phase, and the power generation capacity is doubled, which can ensure that the astronauts have a hot meal.
The spacecraft before Shenzhou-18 had always used nickel-cadmium batteries with a working voltage of 28 volts. In the process of the development of manned spaceflight, two other batteries have also been developed, namely a 100-volt high-voltage nickel-hydrogen battery for the Tiangong laboratory, and a lithium-ion battery for the Tianzhou cargo spacecraft, and the Shenzhou 18 has also been upgraded to a lithium-ion battery.
3. Upgrade to lithium-ion battery
Why upgrade to lithium-ion batteries?
This is due to the change in the environment and length of use of spacecraft in the space station era. After the era of the space station, the dwell time in orbit was usually 6 months.
In this way, it faces two very serious problems: one is the occlusion problem of the space station module, the connection length of the module is tens of meters, and there are huge flexible solar wings, which form a relatively serious light blocking for the solar wings of the Shenzhou manned spacecraft, resulting in insufficient independent power generation capacity. Another is that the Shenzhou spacecraft needs to receive power supply from the space station during docking, which produces an unstable situation of constant switching of charging and discharging states, resulting in irregular charging and discharging.
From Shenzhou-1 to Shenzhou-17, the spacecraft is equipped with a "cadmium-nickel battery", which has the advantages of high safety, high reliability, overcharge resistance, overdischarge resistance, etc., and can meet the mission requirements of the Shenzhou spacecraft for high safety operation. But it also has a drawback, which is the "memory effect". The "memory effect" is generated when the battery is constantly charged and discharged under the condition of long-term small load, and once the power consumption increases and returns to the full load state, the problem of insufficient power supply capacity of the battery may occur.
In view of the safety of long-life large-capacity lithium-ion batteries, they have been widely verified in Tianzhou cargo spacecraft. In order to make the Shenzhou spacecraft more powerful, starting from Shenzhou 18, it has been replaced with lithium-ion batteries.
One of the outstanding advantages of lithium-ion batteries over nickel-cadmium batteries is that they have no memory effect and have a long service life. This enables the Shenzhou spacecraft to overcome the problem of irregular charging and discharging, obtain a longer time to dock the space station assembly, and at the same time be more safe and reliable.
Astronauts will conduct these experiments in space
Since the launch of the Shenzhou-1 spacecraft in 1999, the mainland manned space program has carried out various technical verification tests and carried out a large number of space science experiments, covering many fields such as space environment, space life science, space materials, space astronomy and physics.
What experiments will Shenzhou 18 carry out in space? Zhang Wei introduced that there are four main experiments: aquatic ecology experiment, organic molecule origin experiment, plant stem cell experiment, and lubricating material experiment.
1. Aquatic ecology experiments
The first is the aquatic ecology experiment of zebrafish and goldfish algae, which will be the first time we have brought zebrafish into space. The most obvious difference between raising fish in space and on the ground is that water and air are separated on the ground, and the fish tank does not need to be filled with water, while in space it is difficult to separate water and air, so the fish tank should be full. This experiment mainly studies the symbiotic coexistence of zebrafish and goldfish algae in the space environment.
Goldfish algae produce oxygen through photosynthesis for zebrafish to breathe, and carbon dioxide produced by zebrafish respiration is supplied to goldfish algae for photosynthesis. Through such a small aquatic ecosystem, it is possible to verify the aquatic ecological model in space.
After this research on small aquatic ecosystems, we will also carry out research on terrestrial ecosystems in the future, bringing mice into space. After solving the problem of odor emissions in mice, it was used for experiments to explore the long-term survival and adaptation of humans in space.
The stock copyright picture, reprinting and using may cause copyright disputes
2. Experiments on the origin of organic molecules
The second experiment is the molecular mechanism of the origin of life. Academician Zhao Yifeng, a Chinese scientist, proposed a mechanism for the co-origin of proteins and nucleic acids, through the reaction of nucleotides, amino acids and phosphorus to verify how inorganic molecules grow into organic molecules.
3. Plant stem cell experiments
The third experiment, plant stem cells. We need to look at how plant stem cells function under microgravity conditions, and how microgravity affects the regulation of plant stem cells, thereby affecting its growth and development.
4. Lubricating material experiment
The fourth experiment is the lubrication experiment, some lubrication experiments have been done before, we have an exposure device outside the cabin, which is dedicated to some of the exposure characteristics of the material under space conditions.
Lubricating materials should be a very simple thing, but in reality they are not the same in space. In space, the high temperature is more than 100 degrees above zero, and the low temperature is more than 100 degrees below zero, and under this temperature difference of 300 degrees, there is also the effect of radiation.
Our lubricating material has a very short lifespan, and many times it may volatilize at high temperatures. At low temperatures, it may be frozen. Therefore, we need to verify in space whether these solid-liquid mixed materials can last longer and play a better role under space conditions.
Of course, previous experiments are still continuing.
After our Shenzhou 18 crew entered space, we not only did the experiments brought by Shenzhou 18 this time, but also did a lot of experiments brought up before. For example, in life science, we also need to do the directional differentiation of human backbone cells, and study how the backbone cells differentiate under microgravity conditions, and how they can be regulated to make it grow better.
In the field of materials, we also have to carry out the preparation of a large number of materials. For example, iron-based superconducting materials, as well as aluminum-based materials, and even nanomaterials and some special materials, should be prepared in space with our solvent-free experimental cabinet and our high-temperature material experimental device. At the same time, its performance should also be tested in orbit, for example, its thermophysical properties, surface tension, viscosity and density should be measured without containers.
Very interesting is our combustion experiment. What we are bringing this time is the combustion experiment of the gas plug-in, and we will carry out the characteristics (experiment) of the propagation and extinguishing of the flame of the ignition flame of the gas small flame, and also reveal some of its essential laws.
The stock copyright picture, reprinting and using may cause copyright disputes
Because on the ground, we know that combustion is a buoyant convection-driven combustion, which is a teardrop-shaped flame and the temperature is relatively high. But in space, because the buoyant convection disappears, the combustion is a diffusion drive, so it is said to be a spherical flame, and the temperature of the flame is low. Therefore, we study these properties in space to reveal its essential laws, so as to guide us to develop cleaner fuels on the ground and improve combustion efficiency.
We also have some experiments that are fluid experiments, for example, in the microgravity conditions of space, because the buoyancy convection disappears, we want to do some fluid research. For example, evaporation and boiling, we are driven by buoyancy convection on the ground, and it has some boiling phenomena in space, and this boiling phenomenon changes.
For example, if we boil water with a lot of small bubbles, and then slowly there is a buoyant convection, and the whole water is boiling, and the small bubbles will get bigger and bigger in space until they burst. But the water on the top surface is very difficult to open, so we study the basic phenomena of evaporation and condensation, boiling and heat transfer in space.
At the same time, we may also have to study the management of propellants, for example, propellants are a very special form in space, so we need to combine these special convection phenomena in space, and conduct in-depth research on the management of the entire fluid and the transport of fluids.
I believe that in the future, we will definitely see more and more results brought by space experiments!
Planning and production
This article is a work of popular science China-Star Project
Editor-in-charge丨Wang Mengru
Reviewer丨Xu Lai Linlin