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Source: Privy Council No. 10

After struggling for a long time, NASA finally dealt a heavy blow to Boeing: two American astronauts stranded on the International Space Station will be sent back to Earth by the manned "Dragon" spacecraft of the Space Exploration Technologies Corporation (SpaceX) in February next year, while Boeing's faulty "Starliner" spacecraft will return on its own in unmanned mode in September this year.

It should be said that the outside world had actually anticipated this outcome. After all, NASA gave Boeing enough time, but it still failed to completely resolve the malfunction of the "Starliner" spacecraft, which means that the problem may not be solved in a short time.

Two astronauts sent to the International Space Station by the "Starliner" have not yet returned to Earth

Simply put, the main known problems of the Starliner spacecraft were exposed on the way to the International Space Station - including helium leaks and the failure of five of the 28 attitude control thrusters. Mark Nappi, Boeing's vice president and manager of the commercial manned space program, revealed that the engineering team is dealing with "more than 30 measures" related to thruster problems and helium leaks, but has not come up with a convincing conclusion for NASA. The Boeing engineering team believes that the reason for the failure of the attitude control thrusters is that the design defects of the spacecraft caused the attitude control thrusters to be concentrated in four doghouse-shaped thruster compartments around the spacecraft service module. The heat released when the thrusters are started cannot be discharged immediately, which causes the thrusters to automatically shut down due to overheating. However, Boeing later admitted that it failed to fully reproduce the problems of the attitude control thrusters of the Starliner spacecraft in space during ground tests at the White Sands Proving Ground in New Mexico, so NASA is skeptical about the actual effectiveness of these improvement measures.

Therefore, as NASA Administrator Bill Nelson said, the decision to return the Boeing spacecraft to Earth empty was "out of a commitment to safety." This will allow the collection of relevant test data to continue during the return of the spacecraft, while not allowing the astronauts to "take risks beyond the scope of necessity."

But even if the Starliner is no longer usable, isn't there another manned Dragon spacecraft currently docked at the International Space Station? Why did NASA leave the existing spacecraft unused and force the two American astronauts to wait another six months for the next manned Dragon spacecraft?

This requires explaining a few concepts. First, the "Starliner" spacecraft must leave quickly to vacate the docking port of the International Space Station so that a new batch of astronauts (Crew-9) can board the "Freedom" manned "Dragon" spacecraft to enter the International Space Station. At present, the astronaut handover of the International Space Station adopts the method of on-orbit rotation, that is, the previous batch of astronauts will leave only after the new batch of astronauts arrive at the International Space Station to complete the work handover, which means that the International Space Station will dock two manned spacecraft at the same time. The two docking ports of the International Space Station that can dock American standard manned spacecraft are respectively docked with the "Endeavour" manned "Dragon" spacecraft and the "Starliner" spacecraft carrying the previous batch of astronauts (Crew-8). This also means that the "Starliner" must first leave the International Space Station to vacate the docking port before the new manned "Dragon" spacecraft can be launched.

In fact, it was because the Starliner spacecraft occupied a docking port that caused the astronauts of the Crew-8 mission group to be deployed beyond their deadline...

Secondly, according to NASA's plan, the two astronauts, Wilmore and Williams, were forced to stay in space for an extra six months, which was also a helpless choice - the Endeavour manned Dragon spacecraft currently docked with the International Space Station is fully occupied. When SpaceX first developed the manned Dragon spacecraft, the design indicator was that it could carry seven astronauts at the same time, but after evaluation, NASA believed that there was a problem with the tilt angle of its internal seats, which might cause serious impact to the astronauts when the spacecraft landed. After improvements, the tilt angle of the seats of the manned Dragon spacecraft was flattened, but this also reduced the number of people on board to four. In addition, according to the relevant regulations of NASA and SpaceX, astronauts must wear matching cabin spacesuits when boarding the manned Dragon spacecraft. At present, there are no extra SpaceX cabin spacesuits on the International Space Station, and they need to wait for the Freedom manned Dragon spacecraft to arrive at the International Space Station to bring their spacesuits up together before they can switch to the manned Dragon spacecraft to return. For this reason, the Freedom Dragon spacecraft can only carry two astronauts into space to ensure that Wilmore and Williams can return to Earth on the spacecraft.

The manned Dragon spacecraft was designed to accommodate seven people in its early stages (above), but ultimately could only carry four astronauts at a time (below)

Therefore, the earlier optimistic prediction by the outside world that the two astronauts could return home on the Endeavour manned Dragon spacecraft with the four astronauts of the Crew-8 mission group was not actually feasible.

Of course, in addition to waiting for the manned Dragon spacecraft, there are other solutions for the two American astronauts to return to Earth. In this regard, SpaceX CEO Musk said on social media: "Russia is the only option." Because the International Space Station currently has multiple Russian-standard docking ports that can dock with the Russian Soyuz manned spacecraft.

But it is very obvious that given the current nearly frozen US-Russia relations, the United States is unlikely to ask Russia for help on this issue unless it is absolutely necessary...