The return of Boeing's CST-100 Starliner to Earth has been postponed again: now it is planned that it will depart from the International Space Station only on June 26 and land in the area of the White Sands test site in the United States on the same day. NASA traditionally notes that the postponement will give the teams "a little more time" to evaluate the available information and make sure that the ship is ready to go home. However, the need to once again extend the stay of the Starliner in orbit raises concerns — after all, the unfortunate ship is already beginning to cause problems at the station itself.
Last week, on June 13, the 90th American spacewalk was supposed to take place, but NASA postponed it "due to a problem with discomfort in a spacesuit that arose from one of the astronauts." According to the plan, Tracey Dyson and Matthew Dominic were supposed to stay overboard for 6.5 hours, which was announced in advance. But the exit had to be postponed when a message about discomfort appeared.
The cancellation of the planned extravehicular activity (VCD) attracted public attention after an audio recording of an emergency medical training session on the ISS accidentally got on the air. Although NASA immediately confirmed the absence of an emergency situation at the station, questions about the true reasons for the cancellation of the exit arose with renewed vigor, especially due to the fact that the department did not provide any additional information, even answering direct questions…
It was then that the idea surfaced that the negative consequences of the arrival of the Starliner ship on the ISS were at the heart of the concern. The "butterfly effect" comes to mind, when a small accidental change in the initial operating conditions of a complex system can lead to significant consequences in the future. It is known that even before the launch, a helium leak was detected on the CST-100. This inert gas is used to displace fuel from tanks in propulsion systems for orientation and maneuvering. Experts believe that the permission to launch a ship with a leak, which was considered minimal and acceptable, was a mistake: the situation worsened in orbit, and one leak turned into five. About everything in order.
The tacit consent of NASA
Back on earth, after the first cancellation of the launch, experts discovered a leak in one of the engines of the reactive control system (RCS) of the service module. The ship's developer, Boeing, inflated the propulsion system to flight level and tried to monitor the helium leak in order to make a forecast. The press release stated that "pressure tests of the helium system conducted on May 15 showed that the leak in the flange is stable and does not pose a risk to flight performance."
Tests have also shown that the rest of the propulsion system is effectively sealed. Boeing has developed procedures to ensure that the system retains capabilities and reliability during flight. With the tacit consent of NASA, preparations for the launch continued.
Steve Stitch, manager of the NASA Commercial Crew Program, said before the flight that engineers believe that the flaw is caused by a flange and a seal — a rubber ring about 10 sheets of paper thick. According to him, air or a particle of debris got into the seal. "However, you can fly even if you had to completely remove the seal," said Mark Nappi, vice president of Boeing and manager of the commercial manned spacecraft program. "The rate of leakage will not exceed our ability to deal with it."
To duplicate and increase reliability, the CST-100 Starliner propulsion system has several parallelized circuits. If trouble arises in one, the contour can be blocked — the rest will cope with the tasks of orientation and correction. When officially announcing the discovery of several new leaks for the first time, NASA representatives mentioned that they had reported to Butch Wilmore and Sunita Williams about what to expect. It was assumed that experts would conduct an in-depth analysis of the situation and try to resolve all issues while the astronauts were resting.
Shortly after, during a NASA live broadcast, a Boeing engineer reported: "After launch, our team monitored a leak in the ship's propulsion system… When the specialists closed all the valves of the “current” circuit, two more small leaks were found. After making sure of their location, we tested all eight helium collectors and determined the leak location on the flange of one of the 28 DCS engines. The gas was leaking out through a seal the size of a shirt button. I would like to note that helium is not flammable and non-toxic. We will close some circuits overnight, leaving only those where there is no leakage. This will make it possible to control the orientation of the ship normally. The helium system is still safe, such cases [of leakage] are planned."
Despite the reassuring statements from representatives of Boeing and NASA, experts reported that the published materials of the review of measures to eliminate the leak actually show the structural vulnerability of the propulsion system: in rare circumstances, the Starliner will not be able to perform a descent from orbit if two adjacent engine blocks of the DCS and orbital maneuvering, called "doghouses" behind the eyes, fail. In this case, thrust asymmetry may occur when a braking pulse is issued, and the DCS engines may not be able to cope with the disturbance.
In order to solve this problem in a timely manner, engineers have worked out several modes of descent from orbit with a modified engine operation process. It is clear that such an outcome is unlikely, but just in case, experts want to hedge their bets. It was necessary to evaluate the performance of the system during maneuvering during rendezvous and docking with the station, including using manual control. The mode of termination of the docking and early termination of the flight was provided, but was not needed. Astronauts on board the spacecraft checked communications, manual and automatic navigation, assessed the operation of the life support system, and the station crew closely monitored the approach.
Leaks are out of control
The Starliner approached the station and autonomously docked with the front port of the Harmony module. Then Butch Wilmore and Sunita Williams opened the hatches and entered the station, checking the possibility of transferring rescue (emergency) equipment to the ISS (Starliner in the future should stay at the station for up to six months and serve as a "lifeboat" for the crew of the American segment) and, closing the hatches, demonstrated that the ship can serve as a safe haven in case of smoke stations or loss of atmosphere. After docking, the first main tasks of the Starliner launch were completed, and the last important milestone of the mission remained — re-entry into the atmosphere.
Unfortunately, a fourth leak was soon discovered, although it was much smaller than the others.
"In the next few days, we will have to look at the level of leaks and figure out what to do before the end of the mission," Stitch said at a briefing after the ship docked with the ISS.
NASA closed the helium collectors in the propulsion system to stop leaks, knowing that they would have to be opened after undocking to maneuver during descent from orbit. NASA said engineers estimate the Starliner has enough helium to provide 70 hours of autonomous flight, while it will take only six to seven hours to return to Earth. A fifth leak was discovered during the briefing…
"It is significantly smaller than the others," NASA spokesman Josh Finch said in an interview with SpaceNews. Thus, there were five places on the ship where helium was coming out, but officials still confirmed: "The crew is safe and the mission is currently continuing as planned. We will have to wait and see how the situation develops and what impact it will have on the entire space industry."
In addition to helium leaks, engineers are studying one DCS engine that shut down during the spacecraft's approach to the ISS. Four other engines were shut down at the command of the control system, but later turned on again. There was also a problem with closing the shut-off valve of the DCS oxidizer in the service module.
According to the plan prepared by NASA and Boeing, the Starliner, when docked with the station, turns on eight backward-facing engines for a second (four pulses of two engines, lasting less than a second each) to assess the performance of the DCS during future operational missions.
Initially, there was a hope to keep the leaks under control so that they would not cause any major problems or changes in the mission plan in the coming hours or days. However, then a series of events led to the fact that the arrival time of the ship as part of the ISS increased from a week to 20 days.
The Boeing Crew Flight Test mission is now scheduled to be completed no earlier than Wednesday, June 26.
There is still time
To summarize. Today, helium leaks on the CST-100 Starliner pose a serious problem. Apparently, it was a mistake to allow a ship to fly with an already discovered defect, since one leak turned into five in space, and now there are doubts about the possibility of returning from orbit. According to some experts, NASA representatives may underestimate the complexity of the problems.
Concerns are raised about the extension of the ship's stay on the ISS. Perhaps NASA and Boeing are trying to find a way out without calling for the use of other ships, such as Crew Dragon or Soyuz, to resolve the situation, which will be presented in an unfavorable light and will require explanations from the public.
"We have a commercial manned spacecraft program, the Boeing and ISS teams, all of them are closely integrated and work very well together to come up with a forward—looking plan that will help us get into the best position for undocking and re-entry into the atmosphere," said Dina Contella, NASA's deputy ISS program manager. She mentioned this on June 11 at a briefing on the upcoming VCD (which was canceled).
While there is still time. NASA originally planned to undock the Starliner on June 14, but on June 9 announced that it was postponing this operation no earlier than June 18. This delay was made in order to avoid conflict with the spacewalk scheduled for June 13.
"Two events one after the other — a spacewalk and subsequent undocking — is not very convenient," Contella said. Undocking, followed by re-entry into the atmosphere and landing, must be adjusted to such an orbit configuration so that the landing takes place in the southwestern United States, which does not happen every day.
But it all started with the fact that in early March, NASA announced that the first manned flight of the CST-100 was postponed from the end of April to the beginning of May due to conflicts in the ISS schedule, and not at all because of difficulties with the ship itself or its carrier. However, the launch attempt on May 7 was canceled two hours before launch due to a problem with the drain valve on the Atlas V rocket. Perhaps NASA and Boeing should take astronaut safety more seriously and be more responsible.
Experts point out that although the cancellation of the EVA and the detected problems with the ship may not be related, NASA's vague statement about the cancellation of the exit inadvertently indicates strange connections between both events. "It looks like the ISS is in trouble because of the Starliner ship."
Igor Afanasyev
