On December 17, the "Chang'e 5" returner successfully returned to Earth with the lunar soil. After 44 years, mankind once again brought back rock and soil samples from the moon. China became the third to realize the moon after the United States and the Soviet Union. The country returned by the sample.
The return of the "Chang'e-5" probe to the earth this time entered the atmosphere at a second cosmic speed of 11.2km/s. The high-speed friction will generate a high temperature of 3000 ℃ on the probe surface, and its heat flow exceeds that of any previous reentry in China. In response to this, the R&D team of HTCL Aerospace Materials Technology Group tailored a new type of heat-resistant outerwear for it, which effectively ensured the smooth return of "Chang'e-5".
Heat protection coat should be light
Since Chang'e-5 will achieve "winding-drop-back" at one time, in order to reduce the load and maximize the test efficiency, the heat-resistant materials should also reduce the weight accordingly, but this time, the development team's requirements for "lightness" have almost reached The degree of harshness. In fact, it is not difficult to blindly reduce the density of the material itself, but it is very difficult to make the density of the material low, and at the same time to withstand high temperatures and strong heat insulation. The team members strictly limited the weight of the heat-proof material of the entire returner to ensure that every gram of weight is used on the blade. In the end, 7 kinds of heat-proof materials are used in different parts according to the different heating conditions. For example: The outsole structure adopts a new type of lightweight C-Si-O honeycomb reinforced low-density ablation heat-proof material with a density of about 0.5g/cm3, which can withstand a heat flow environment of 6MW/m2, and the corners are reinforced with continuous fiber. Density structure material, the side wall structure adopts ultra-light honeycomb reinforced heat-proof material with a density of about 0.36g/cm3, which can withstand a heat flow environment of 1.5MW/m2. These 7 materials "cooperate with each other" preventing heat and reducing weight.
However, in the process of the probe's "flying to the moon" and "circling the moon", due to the change of the orbit and the distance from the sun, the heat-proof structure not only has to withstand the almost complete vacuum, no atmosphere and geomagnetic protection of the universe. Ion irradiation has to withstand extremely low temperatures and high and low temperature cycles. This puts forward higher requirements for the performance of the seven heat-resistant materials and their thermal structure matching and integrity with the load-bearing structure. , It is like letting different soft and hard "decoration materials" cover the entire room, and these materials cannot be deformed or cracked due to alternating cold and heat. The difficulty can be imagined. Through the unremitting efforts of the HTCL scientific research team, the overall heat-proof structure of the side wall and the outsole and the matching of seven different heat-proof materials have been overcome, which meets the demanding requirements of light-weight and heat-proof materials for the lunar sample return.
High strength heat-resistant outerwear
In addition to the lighter the better, the heat protection material also needs to have sufficient strength. In particular, heat-proof materials face high temperatures of several thousand degrees Celsius, and they must maintain a certain strength at high temperatures.
The heat protection material of Chang'e 5 has completely independent intellectual property rights and has reached the world's leading level. Previously, the best heat-proof material in the world was the improved Avcoat 5026. Avcoat 5026 is the heat-proof material used by the Apollo spacecraft, and it is also the only heat-proof material that has undergone a manned landing on the moon and returned to a special harsh thermal environment. The improved Avcoat 5026 is still an ablative heat-proof material, with a density of about 0.56g/cm3. The manufacturing process of this heat-resistant material is complicated and the cycle is very long. The heat-resistant material for the outsole of the Orion spacecraft takes six months to complete the manufacturing. The density of the heat protection material of the Chang'e-5 detector is 0.5g/cm3, and the manufacturing cycle is 1/25 of that of Orion.