On July 23, China’s Long March 5 Yaosi carrier rocket was successfully launched, and the highly anticipated Mars rover "Tianwen-1" was sent into a predetermined orbit.
This is China's first Mars exploration mission. It will realize the three missions of Mars orbit, landing and patrol at one time in a completely unfamiliar Martian environment, carry out global and comprehensive circumnavigation exploration of Mars, and conduct regional inspections on the surface of Mars. , This is also the first case in the history of world aerospace.
Tianwen No.1 uses a landing and patrol combination to complete the two tasks of landing and patrolling. The landing patrol assembly includes two parts: the entry module and the rover. The entry module is responsible for landing and the rover is responsible for scientific exploration.
In the process of rushing to Mars, the biggest difficulty lies in reducing the probe's speed from more than 20,000 kilometers per hour to zero during reentry, descent and landing. How to do a good job in thermal protection of the probe is related to whether the rover can safely reach the surface of Mars to carry out related work, and it is related to the success or failure of the "Tianwen-1" exploration mission.
In order to safely escort the "Tianwen No. 1" to successfully land, ZGHT Thermal Insulation Material Technology Group has developed three kinds of materials, namely super Lightweight honeycomb reinforced low-density ablation heat-resistant materials, continuous fiber reinforced medium-density heat-resistant materials, and ultra-lightweight large-area heat-resistant coating materials.
These three materials work together. When the probe lands, the surface of the material frictions with the Martian atmosphere and a complex physical and chemical reaction occurs, and a large amount of heat is taken away. At the same time, the inside of the material also has good thermal insulation performance, although the surface "The heat waves are rolling", but the inside is still "cool and pleasant", which effectively protects the detector from burnout.
What are the advantages of new protective materials
Mars is far from the earth. In order to push the launch vehicle farther, the weight of the Tianwen-1 probe cannot be too large. Therefore, the weight requirements for the probe’s heat-resistant structure have reached a very strict level. To complete the mission of heat protection, it is necessary to adopt the most optimized design to "squeeze" the heat protection performance and efficiency of heat protection materials as much as possible.
During the landing of the "Tianwen No. 1" probe, the most severely heated outsole was made of ultra-lightweight honeycomb reinforced low-density ablation and heat-resistant materials. This material can be said to be a "veteran" member of spacecraft for heat protection. The "Shenzhou" manned spacecraft, the moon and the ground are loaded and returned to the aircraft at high speed, and the honeycomb-enhanced low-density ablation and heat-resistant materials all play a key role in thermal protection.
The new ultra-lightweight honeycomb reinforced low-density ablation and heat-proof material with optimized formula is used on the Mars rover. Compared with its "predecessors", this material has higher strength and lower density, and the honeycomb grid can be optimized with variable thickness according to the aerodynamic load distribution, ensuring that the corners of the detector can withstand more severe In the case of aerodynamic load, the material weight of the entire structure is lighter.
The diameter of the outsole structure of the detector reaches about 3.4m, with a total of about 70,000 honeycomb lattices. The team adopts an integral molding process to ensure that the materials are poured in place in so many honeycomb lattices at one time, whether it is molding efficiency, molding quality or reliable molding. Sex has reached the international leading level. The outsole structure of the entire probe has a very good integrity, ensuring its structural stability to withstand the alternating high and low temperature during the process of running to Mars.
The large area of the outsole of the detector uses ultra-light honeycomb to enhance low-density ablation and heat-proof materials
In addition to large-area low-density ablation heat-proof materials, other parts of the detector also need some heat-resistant materials with higher load-bearing capacity. For this reason, the team also developed continuous fiber reinforced medium-density heat-proof materials, which can meet Structural requirements and lightweight characteristics. This material is mainly used as the hatch cover, edge sealing ring, embedded parts, screw plug and other parts of the heat-proof structure of the detector outsole and back cover. Compared with lower density materials, it has higher strength and takes into account the ablation resistance and bearing capacity. .
On the back cover structure, which receives relatively low heat flow, the team uses an ultra-light ablative heat-resistant coating material. The basic thermal and physical properties of the material have reached the international advanced level, not only has excellent heat insulation performance, but also plays an important role in the weight reduction of the lander. At the same time, the environmental impact of the launch site and the total vacuum mass loss requirements are also fully considered, and the materials are continuously optimized so that the salt spray resistance, humidity and heat resistance have passed the test, and the total vacuum mass loss and condensable volatile content meet the design requirements.
Ultra-lightweight heat-resistant coating material
Three materials work together
In the structure, formulation and process design of these three materials, an important factor that needs to be considered is the structural thermal matching between them. It takes a long time for the probe to fly to Mars. Due to the change of orbit and the distance from the sun, the heat shielding materials have to withstand extremely low temperatures and the cyclical alternation of high and low temperatures during the flight. "Ice and fire" can easily lead to Catastrophic problems such as cracking and falling off of the material.
Under such severe conditions, the three heat-proof materials and structures need to maintain good structural thermal matching and integrity with the internal structure of the lander. The team used engineering calculations, numerical simulations, and necessary ground tests to design and simulate the structural changes and ablation compatibility of the three materials in an alternating space environment with extremely low temperatures and high and low temperatures, and then optimized the design based on the experimental results. To ensure the matching and integrity of these three materials, so that they can "cooperate" in the vast space, and escort the detectors to arrive safely and land smoothly.