Microgravity science and space life science

If hot air is lighter than cold air, it must float upwards; The flame of a fire always goes up instead of down. In addition, the emergence of life on Earth cannot rule out the influence of gravity. These problems can be solved by microgravity experiments in orbit to discover the essential laws of phenomena between matter and life.

How do you simulate microgravity

1. Microgravity falling tower

Microgravity towers are structures that are tens or even hundreds of meters high, usually in the form of circular towers, with space in the middle for free-falling objects. Since air resistance will change the speed of the object's free fall, a vacuum vertical pipe should be built in the middle of the tower for experiments requiring higher microgravity level, so that the experimental device can fall without air resistance. Due to the height limitations of artificial structures, such towers typically only gain a few seconds of microgravity. More complex designs include a combination of falling Wells and towers to extend microgravity time. There is also the addition of up throwing mechanism, the experimental device is accelerated from the bottom of the tower up to throw, after the acceleration stops, the device will enter the microgravity state, and continue to move upward for a period of time to reach the peak of the tower and then fall, so that the microgravity time obtained only by falling can be doubled. However, due to the high accuracy of the up-throwing mechanism, it is necessary to ensure the verticality of the experimental device in the vacuum tube, so as not to touch the tube wall. In addition, the acceleration during the upthrow is very high, and the overload may destroy the test sample before the device enters the microgravity time. The only tower in the world that can actually drop up and down is the microgravity laboratory in Bremen, Germany

2. Microgravity aircraft

Microgravity aircraft refers to an aircraft in flight, the pilot simulates the parabola of free fall to fly, as shown in the picture, during the fall, all the devices inside the aircraft into microgravity. The aircraft reaches its lowest point and then pulls up, and when it reaches its peak, it falls again in a parabola, once again entering a microgravity environment. Such flights can be made multiple times in a single mission. However, due to the high gravity environment when the aircraft is pulled up, there is a certain degree of disturbance to the experimental samples. Since the aircraft flies at a maximum altitude of only about 10,000 meters, only about 30 seconds of microgravity can be achieved in a parabolic flight. It also requires a high level of flying skills.

Microgravity balloons and microgravity rockets

In both simulations, an experimental device is carried to an altitude of tens of kilometers (a high-altitude balloon) to hundreds of kilometers (a sounding rocket), and then dropped to free fall. However, the experiment could only be completed before reaching the 30km altitude as the atmospheric density gradually increased and the resistance caused by the drop destroyed the microgravity environment. Since the highest altitude of high-altitude balloons is only 40-50km, the microgravity time obtained by high-altitude balloons is not much improved. Using sounding rockets to carry out microgravity experiments, high quality microgravity time can be obtained from several minutes to ten minutes. But sounding rockets are expensive. Both ESA and NASA conduct microgravity and life science experiments using sounding rockets in the one - to double-digit range each year. Both microgravity and life science experiments using sounding rockets require sample recovery, so sample recovery technology should be considered at the same time. Most of the world's sounding rocket launch sites are on land in no man's land, retrieving samples by parachute. After landing, accurate positioning information can be obtained by helicopter or OFF-road vehicle as soon as possible. Very few sounding rocket test sites, such as Norway's, use sea recovery.

4. Recoverable microgravity experimental satellite

If the centrifugal force of an artificial satellite moving in a circle is equal to the gravitational force of the earth, the satellite will keep moving in the orbit without falling off. In the gravitational field of the Earth, such orbital velocity is called the "first cosmic velocity." Depending on the altitude of the orbit, the speed is 7.6 to 7.8km/s. When a satellite reaches these orbital speeds, a simulated microgravity environment occurs on an artificial satellite as the centrifugal force counteracts the earth's gravity. While not a true microgravity environment, the simulation lasts as long as the orbital life of a satellite, measured in weeks, months and years. Therefore, satellites are the best experimental platform for conducting long-term microgravity and life science experiments. At the same time, it should be pointed out that sample recovery will bring additional technical problems, such as the aerodynamic heat protection of the recovery capsule after entry into the atmosphere, the problem of opening the parachute before landing, the problem of uncertain landing point after opening, as well as the problem of finding and obtaining samples as soon as possible after landing. Retrievable experimental microgravity satellites are more expensive than sounding rockets and satellites that do not require recovery.

5. Manned space laboratory and space station

Different from microgravity recoverable satellites, microgravity and life science experiments in manned missions add human factors, which can greatly improve the efficiency of microgravity and life science experiments and deal with random experimental phenomena. Therefore, more advanced and more complex experiments can be done, but their costs are also greatly increased. Therefore, demonstrating suitable and scientifically significant experimental missions for the manned space laboratory and space station is an important challenge for the microgravity and life science teams.

What changes in microgravity?

Liquids perform best in microgravity. Bubbles in the water will no longer float upwards, but move in all directions. Different liquids do not differentiate into distinct liquid layers because of their specific gravity. A drop of water will float in the air, and the most important force on it is surface tension, not gravity.

In microgravity, hot air does not move upwards, so the flame does not shoot upward all the time. It is rounded in still air.

In microgravity, plants will lose their sense of direction to grow upward, and since water in the soil won't sink, roots will lose their sense of direction and grow in all directions.

The cell itself is a liquid/living organism surrounded by cell walls, following the laws of liquid in a microgravity environment. The bones of advanced beings will soon become brittle. Astronauts will slow down the rate of bone loss to a certain extent after training in orbit.

In short, all the physics associated with gravity would disappear. Surface tension and interfacial adhesion are the main forces.

Bioradiation effect

For living things, after entering space, there is another special effect is the biological radiation effect. Deoxyribonucleic acid (DNA), the basic unit of biology, will break under the radiation of space particles, causing genetic variation. It should be noted, however, that the well-known extra-large space cucumber, or tomato, is not a universal phenomenon that passes through all seeds of space flight, but has been selected through several generations of large offspring.

If radiation can change the genes of biological seeds, can they be irradiated into accelerators on the ground and then planted? It was found that the effects of ground accelerators on seeds were not the same as those in space and could not replace the effects on seeds after space flight. However, the basic theories and principles of these phenomena have not been clearly studied.

Basic physics experiment

Some physical experiments that cannot be carried out on the ground or require high precision can also be carried out in space, such as the verification of the equivalence principle, the bose-Einstein condensation experiment, the high-precision cold atomic clock, and the long-distance distribution experiment of quantum entanglement. There's a lot of stuff going on, and some of it doesn't necessarily have to do with microgravity. For example, China's QUantum Experiments at Space Scale (QUESS) has carried out large-scale high-speed QUantum key distribution Experiments, QUantum entanglement distribution Experiments and QUantum teleportation Experiments in Space. These experiments have nothing to do with microgravity, but they fall under the category of basic physics experiments.

Important frontier issues

1. Convection, diffusion and transport of complex fluids

Under the influence of microgravity, the fluid changes its motion. When the composition and boundary conditions of a fluid become complicated, its motion in microgravity becomes the target of our research, such as stratification, diffusion and transport of multiphase liquids. These laws have a wide range of applications, such as the remaining fuel in the fuel tank of the rocket engine, the liquid flow in the heat pipe of the satellite, the motion of the lunar dust particles after landing on the lunar surface under 1/6g gravity, the motion of the liquid in living cells, etc.

2. Genetic variation of DNA after particle radiation

As mentioned above, any arm, or segment of the DNA double helix, breaks when exposed to particle radiation. Where and in what segment does it break, does it repair itself, does it pass on to future generations and affect them? These are important unknowns.

In addition, larger aspects, such as astronaut health problems, space breeding problems, are closely related to particle radiation.

3. Does Darwinian evolution still hold true beyond Earth?

It goes without saying that mathematics is universal in the universe. 1+1=2, should be the same wherever the language is written, although the expression may be different. The basic laws of physics that humans have so far understood (excluding those related to gravity) now seem to be universal in the universe. Einstein's general theory of relativity, for example, holds true for all cosmic observations so far, no matter how far away the galaxy being observed.

But the fundamental laws of life science, such as Darwinian evolution, have not been tested beyond Earth. That's mainly because, apart from Earth, we haven't found any signs of life in the solar system, let alone outside it. To this end, taking life from Earth into outer space, such as the space station or the moon, to carry out long-term research on the basic laws of life science is also the frontier of space life science.

4. How do you simulate microgravity on the ground?

As mentioned earlier, falling towers, microgravity aircraft, as well as microgravity balloons and sounding rockets are just a few of the ways humans can simulate microgravity environments. However, none of these methods can simulate microgravity for long. Many experiments have to be done in space, which makes the cost very high. Experiments on a manned space station also face many disturbances, such as the vibration of instruments, fans and even the rotation of the flywheel on the satellite, which can reduce the microgravity level. Currently, the microgravity level that can be achieved on microgravity satellites is 103g to 105g. In addition, there are also problems related to the smooth return of experimental samples, which increases the cost of the experiment.

At present, two incomplete ground simulation methods are being developed, one is magnetic levitation and the other is bio-gyroscope. However, neither method can fully simulate the real microgravity environment. Therefore, before the experiment, it is necessary to carefully analyze the purpose and requirements of the experiment, and consider whether magnetic levitation and biological gyroscope can be used to simulate the microgravity environment.