In October 2007, NASA's Curiosity rover tests parachutes in the world's largest wind tunnel. The unfolded area is 280 square meters and bears a load of 36,000 kilograms. Isn't it just an oversized parachute, what's the difficulty? When we're talking about a spacecraft landing on another planet, it's actually more like hitting the planet at a speed. If left unchecked, the spacecraft can be damaged on impact, especially with humans inside, making soft landings all the more important. The more massive the spacecraft, the more difficult it is to achieve a soft landing. If there is no reverse thrust, the current technology is difficult to achieve, but if it is not manned, it is not impossible to rely on high-mass parachutes alone. However, the opening area will be quite large. In order to colonize Mars, more massive objects must be landed. In this regard, Mars is much better than the Moon, at least having an atmosphere. Although the density of the atmosphere is less than one percent of the Earth's atmosphere, and the atmospheric environment is also very different from that of the Earth, it is better than nothing. NASA established the Low Density Supersonic Speed Reducer ( LDSD ) project to test various Mars parachute designs. LDSD developed the largest parachute in human history to help slow the lander. One of the difficulties in testing a parachute of this size is that it is so large that most wind tunnels cannot fit it, so NASA built a wind tunnel room the size of a football field for this purpose. The main difficulties in research and development are as follows:
1. Flying too long Flying from Shanghai to New York will take more than ten hours to sit in the flight center, and to reach Mars by parachute, it will take more than ten months to hide in the spacecraft. In such a long deep space flight, the environment that the parachute deceleration system faces will be extreme environments such as long-term vacuum and high-temperature storage. Not only that, long-term high-density packaging will have a certain impact on the mechanical properties of the parachute's special-woven material. The performance of the Umbrella Barrel Potion may also change. 2. Too fast The difficulty of opening a parachute is much more difficult than that of the earth: if opening a parachute on earth is compared to the difficulty of writing a composition in the middle school entrance examination, then opening a parachute on Mars is like writing a graduate thesis in one week (or the kind that cannot be copied). Compared with the subsonic parachute opening on the earth, opening the parachute under supersonic conditions will lead to a complex shock wave flow field , the aerodynamic interference between the spacecraft and the parachute is also more complicated, and the probability of the rope sail phenomenon  will increase ( It can be understood that the rope is pulled out of line, please ignore the term directly), during supersonic flight, the parachute will also appear a series of desperate phenomena such as "breathing" and high-frequency flutter, which can make the stitched part of the parachute. torn apart, causing damage to the canopy. In order to reduce the probability of the rope sail phenomenon and let the parachute quickly pass through the supersonic wake region of the spacecraft, it is necessary to develop a parachute tube with high ejection speed. When necessary, it is still necessary to rely on reverse thrust to slow down. 3. The density is too low The density of the Martian atmosphere is only 1% that of Earth, and the atmospheric pressure is only 0.6% to 0.75%. Such a low-density atmospheric environment is a fatal blow to the parachute. why? Because the free travel of molecules in the low-density atmosphere is very large, the effective air permeability of the parachute canopy material decreases sharply compared with the earth, and the decrease in air permeability will make the stability of the parachute worse; and because of the low density of the atmosphere , the deceleration efficiency of the parachute will also decrease. In order to achieve the required steady descent speed under the condition of poor stability , a larger area of the parachute is required; and a larger area will significantly increase the quality of the parachute, correspondingly The ground will also increase the ejection mass and volume of the umbrella barrel; several factors add up to cause the umbrella to become larger and heavier. The low density also leads to low dynamic pressure, which makes it difficult to establish the pressure difference between the inside and outside of the canopy, making it more difficult to open the umbrella; due to insufficient aerodynamic damping, the canopy will also experience enhanced swinging and "breathing" during the opening process. "And so on, recovery has also become more difficult.
4. Time is too short It takes a minute or two from the parachute ejection to the separation of the Martian surface from the landing platform. The shortest is only 40 seconds, and the longest is only 114 seconds (in comparison, the "Shenzhou" spacecraft is about 800 seconds, and the "Chang'e 5" is about 500 seconds), in such a short time, it is necessary to complete the parachute, A series of key actions such as inflatable deployment, aerodynamic deceleration , throwing heat-proof outsole, landing bracket deployment, radar altimeter measurement, separation of parachute and landing platform, etc., must be realized with very accurate and reasonable strong timing design. If there is no aerodynamic deceleration link, the umbrella area will be much larger and the load must be quite strong. 5. Too little information We all know that the atmosphere on the surface of Mars will vary greatly with seasons and geographic locations (refer to the severe weather such as dust storms shown in "The Martian"). The amount of information in our country's hands is still too little and too rough to study the parachute deceleration system. Due to the blockade of information, the first-hand information on the Martian environment in China is still quite limited. We can only make inferences from limited data sources in other countries (such as the umbrella opening data of the Viking probe), and the atmospheric parameters as the main design basis are uncertain . The degree is very large, of course, it is not ruled out that the atmospheric parameters will change while developing. In 2014, the alternative umbrella type of the Mars parachute has been declassified. Is it possible to simulate the landing environment of the Martian atmosphere at high altitudes on Earth? Considering that the speed of sound in the Martian atmosphere is much different from the speed of sound on Earth, it is impossible to simulate supersonic speed, low dynamic pressure, and low density at the same time in the earth environment. Only two parameters, supersonic speed and low dynamic pressure, which have a greater impact on parachute opening, can be selected. To simulate, and this has to fly to an altitude of 35-50 kilometers on the earth, (NASA's JPL once conducted a high-altitude supersonic parachute inflatable research experiment (ASPIRE) in 2018, 38 kilometers at an altitude of 1.8 Mach parachute 37000 Kilogram load  ) is too difficult to operate in practice. Even under the constraints of so many unfavorable factors, my country's research institutes have achieved tremendous progress. One of the most representative tests is the high-altitude parachute opening test of the parachute.
In order to run fast and move steadily, the Beijing Institute of Space Mechatronics (the one that made the flag fabric for the National Day flag guard team), which is responsible for this research and development, first conducted a scale parachute high-altitude parachute opening test in 2016, using The Tianying sounding rocket developed by the Fourth Academy of Aerospace Science and Technology has been tested five times, which has verified the correctness of the design of the sub-system scheme. Then in 2018, four trials of high-altitude opening of a full-size parachute have been carried out, which has verified that China is also capable of doing so. A full-scale Mars parachute that meets combat standards. At present, China has basically mastered the key technology of the Mars parachute deceleration system , and is waiting for the good news of the landing of the Mars probe independently developed by China in 2021. You must know that this Mars exploration is China's first planetary exploration, while the success rate of other countries' Mars exploration is only about 40%. The probe's parachute can only succeed, never fail. Several people have been asking why it takes more than ten months to go to Mars. Isn't Tianwen- 1 launching in July and arriving in February? First of all, Tianwen-1 was only captured by Mars in February 2021, and it will not start deorbiting until at least around May. Secondly, we must take into account the special circumstances, and finally go once, and leave room for everything. When it comes to research and development, it is always impossible to say that it is too wasteful to develop one set quickly and develop another set slowly. On average, the time it takes for the probe to go to Mars is almost half a year. Let me take a moment to list: Mariner 4, the first spacecraft to go to Mars (flyby in 1965): 228 days Mariner 6 (1969 flyby): 155 days Mariner 7 (1969 flyby): 128 days Mariner 9, the first spacecraft to orbit Mars (1971): 168 days Viking 1, the first American spacecraft to land on Mars (1975): 304 days Viking 2 (1975): 333 days Mars Global Surveyor (1996): 308 days Mars Pathfinder (1996): 212 days Mars Odyssey (2001): 200 days Mars Express Orbiter (2003): 201 days Mars Reconnaissance Orbiter (2005): 210 days Curiosity (2011): 254 days The current success of the SLS rocket will provide a new possibility to go to Mars. In the future, it can also use light propulsion and directed energy propulsion (DEEP-IN) to send a 100-kilogram robotic spacecraft to Mars in three days (there is a research group at the University of California). In doing this), the Hohmann orbit and the 26-month window of Whatsminer will eventually be a thing of the past.