Shenzhen-20 had some of the cracks in the window that went completely through. That fact, which was later revealed during televised interviews with the crew, reweighed what had initially been reported as small spots on a return capsule that had landed on the Tiangong space station in China.
The accident started as a standard, post-mission inspection checklist: one of the crew members checking the spacecraft that was to ferry 3 taikonauts home saw a peculiar shape in the viewport- this is one of the elements that astronauts use to ensure that they have visual checks and to know where they are. In the retelling broadcasted on state television and reflected in subsequent reporting, Shenzhou-20 chief Chen Dong recounted his initial wrong interpretation of the anomaly in a manner that emphasized the appearance of damage to the orbit. “My first thought was whether a small leaf had somehow stuck to the outside of the window,” he thought. However, suddenly I came to know that this was impossible since we were in space. There could not be a fallen leaf there, how could there be one?
What ensued was a systematic cabin inspection that transformed a disturbing hunch into an engineering issue. To view what could not be determined by the naked eye, the crew used a pen-shaped microscope attached to a tablet, which normally sealed surfaces on extravehicular suits. When using a microscope, Chen remembered, it was possible to see very clearly the small cracks. A few of them were rather long, and one of shorter length. We were able to observe that the cracks had broken through some of them as well.
The very words penetrated through are important because spacecraft windows are not transparent panels; they are multi-layered pressure constructions, which are also required to withstand heating loads and vibration during reentry. The stacked design of the viewport was indicated by fellow crew member Wang Jie, who is an aerospace technician who had previously become an astronaut: there was a protective outer layer, then two pressure-bearing layers. Well, I was not really nervous. The very top layer is a protective layer, and within it we have two layers that carry pressure, and we can rest easy provided that cabin pressure does not vary as it may cause the change in the cabin pressure to ruin everything, he said.
This reaction was then translated into the actual embodiment of what the term “crew safety” entails in a modern space program not just the hardware redundancy, but also schedule flexibility and launch readiness. Mission planners reassembled vehicles such that the crew would be able to come back on a different spacecraft but the damaged capsule would still be on-orbit. China also made delivery speedier on a repair tool, with the China National Space Administration hailing a porthole fix gadget on a push of emergency logistics. The agency subsequently mentioned that astronauts put it in the Shenzhou-20 capsule, which was in effect enhancing the thermal protection of the spaceship and its closing properties on reentry.
Eventually Shenzhou-20 landed without crew, transforming its landing into another type of test. No one was on the ground to use their hands to open the main parachute once the astronauts were on the ground, increasing the chances that the capsule would be torn around by the winds. Recovery forces immediately rushed to stabilize it and post-landing checks reported that the exterior was typically in good condition.
The longer arc however is above the capsule itself: orbital debris. An alleged strike of debris that causes a program level vehicle change is not as one time a jolt as it reminds that human spaceflight is irrevocably becoming an environment where it shares space with dense traffic and long lived debris. The Shenzhou-20 incident demonstrated the ability of layered windows and backup vehicles to keep the crews safe, but it also demonstrated how minor impacts can lead to complicated operation choices- especially when the damage is not only cosmetic, but structural.
With the increase in the density of low Earth orbit there is no longer an engineering problem of launch and reentry. It is constructing toward the silent, accruing danger of residing in a location where even a small fissure may prove to be yet another thing altogether.
