We are just about 24 hours away from the scheduled undocking of Boeing’s Starliner spacecraft. For weeks now teams have been busy adjusting the mission plan and flight profile knowing the vehicle will now return without a crew.
In just the last few days cargo has been loaded onto the spacecraft in addition to thorough inspections inside the vehicle. With these steps complete, today the hatch is set to be closed, and assuming everything goes as planned, won’t be opened until Starliner is back on Earth.
Closing The Hatch
If everything stays on schedule, the uncrewed Starliner is scheduled to undock from the Harmony Module’s forward port at 6:04 PM EDT on Friday the 6th, and land in New Mexico about six hours later. About 20 minutes before the undocking, NASA is expected to begin live-streaming the event. In the event it gets pushed back due to weather or any other reasons, they have backup dates on the 10th, 14th, 18th, and so on. They did mention a slight weather concern related to rain but the chances of an undock tomorrow are still high.
In terms of final prep, crews on the ISS have been busy. Yesterday, “NASA astronauts Butch Wilmore Suni Williams spent the day loading cargo inside the Boeing Starliner spacecraft for return to Earth.” NASA highlighted that, “The pair removed Starliner’s crew seats, which will later be reinstalled, for better access when storing the extra cargo, then photographed and inspected the spaceship’s cabin ahead of its hatch closure scheduled for Thursday.”
Yesterday, on the 4th, there also was another media teleconference this time focused on the undocking and return of the spacecraft. Here we learned that after undocking and before the reetnry burn, they are planning a number of thruster firings to continue trying to gather information and determine the issue. Since these thrusters are in the service module, soon before reentry the service module will disconnect from the capsule and end up burning up in the atmosphere. In other words, these test thruster firings will be the last opportunity to directly gather data from the module.
More specifically, Steve Stich, the commercial crew program manager said, “We’re gonna look at doing a couple of hotfires on the way with some of the thrusters. In fact, that’s going to the Starliner mission management team today and we’re going to talk about maybe hot firing after we undock, after we clear what we call the approach ellipsoid around the space station. We’ll go ahead and maybe hot fire a few of those thrusters, the forward thrusters, and maybe the aft thrusters. And the purpose of that is to continue to learn” he said.
In the past, they had mentioned that they were planning to perform a slightly different undocking that would position the vehicle away from the station quicker than normal. Recently they clarified that it was called a breakout burn and would involve a much faster departure from the station. The NASA space station flight director said in a quote, “Without the crew on board, able to take manual control if needed, there’s just a lot less variables that we need to account for when we do the breakout burn, and allows us to get the vehicle on a trajectory home that much sooner.”
Interestingly Steve Stich added, “It really puts less stress on the thrusters. In other words, there are a lot fewer thruster firings. Essentially about 30 seconds after undock well start this small series of burns, using primarily the forward thrusters, not putting the stress on the aft thrusters. It really just takes about 5 minutes or so to actually execute that whole sequence” he said. This makes it more clear that the goal is to both speed up the process but also avoid using certain thrusters due to the complications over the past couple of months.
Steve Stich also talked about the issue with the thrusters and said “Clearly, the way we fire the thrusters causes the thrusters to overheat. We need to understand what kinds of pulses in particular cause that swelling, the number of pulses.” He then went on say, “We know the thrusters are working well when we don’t command them in a manner that overheats them and gets the poppet to swell. We know that the thruster is a viable thruster,” he said.
These comments among others suggest that they are planning to possibly change how the thrusters are used in the future rather than change the hardware itself. In one final quote, he said, “The easiest thing to do is to figure out how do we lower the temperature the thruster is operating at and maybe not firing it in a manner that causes it having this overheating phenomenon.”
An Uncrewed Return
Without a crew, a lot of the mission milestones and general events after undocking needed to be altered. By now the agency has a detailed flight profile of exactly what we can expect when Starliner does begin its journey back to Earth.
Initially, approximately 24 hours before undocking, NASA will analyze weather predictions for the various landing sites. Winds at the selected landing site must be 6 mph (approximately 6 knots) or less when flying with crew, and approximately 13 mph (12 knots) or less when uncrewed. Ground temperatures must be warmer than 15 degrees Fahrenheit, and the cloud ceiling must be at least 1,000 feet. One nautical mile of visibility is required, and the area must be clear of precipitation, thunderstorms, and lightning within approximately a 22-mile (35-kilometer) radius.
When teams proceed with undocking, Starliner will complete a series of departure burns, allowing it to reach its landing site in as little as six hours. A final weather check also occurs before the spacecraft’s deorbit burn. Winds must be at or below 10 mph (9 knots). If winds exceed these limits, teams will waive the deorbit burn, and Starliner will target another landing attempt between 24 and 31 hours later.
After it’s left the station and made its way from the ISS, it will then begin the reentry process. NASA highlights that “Once clear to proceed, Starliner executes its deorbit burn, which lasts approximately 60 seconds, slowing it down enough to re-enter Earth’s atmosphere and committing the spacecraft to its targeted site. Immediately after the deorbit burn, Starliner repositions for service module disposal, which will burn up during re-entry over the southern Pacific Ocean.
Following service module separation, the command module maneuvers into re-entry position. During re-entry, the capsule experiences plasma buildup – reaching temperatures up to 3,000 degrees Fahrenheit – that may interrupt communications with the spacecraft for approximately four minutes. Once Starliner re-enters Earth’s atmosphere, the forward heatshield – located on the top of the spacecraft – is jettisoned at 30,000 feet, exposing the two drogue and three main parachutes for deployment. The parachutes will continue to slow the spacecraft down as the base heatshield is jettisoned at 3,000 feet, allowing the six landing bags to inflate. At touchdown, the spacecraft is traveling at approximately 4 mph.”
“The NASA and Boeing landing and recovery team is stationed at a holding zone near Starliner’s intended landing site. After landing, a series of five teams move in toward the spacecraft in a sequential order. The first team to approach the spacecraft is the gold team, using equipment that “sniffs” the capsule for any hypergolic fuels that didn’t fully burn off before re-entry. They also cover the spacecraft’s thrusters. Once given the all-clear, the silver team moves in. This team electrically grounds and stabilizes Starliner before the green team approaches, supplying power and cooling to the crew module since the spacecraft is powered down.
The blue team follows, documenting the recovery for public dissemination and future process review. The red team, which includes Boeing fire rescue, emergency medical technicians, and human factors engineers, then proceed to Starliner, opening the hatch. Finally, the landing and recovery team begins unloading time-critical cargo from Starliner. The spacecraft is then transferred to Boeing facilities at NASA’s Kennedy Space Center in Florida for refurbishment ahead of its next flight.”
One of the pros of an uncrewed return rather than crewed is the less strict weather conditions necessary for the undocking to go ahead. At the same time, we have already seen two uncrewed Starliners return in the past with OFT-1 and OFT-2. This will now make the third uncrewed Starliner return.
The main concern for the return has to do with the reentry burn itself. Yesterday Stich said, “Really the thrusters on the service module, the next big job they have is to hold the attitude, while the big OMACS fire, like Anthony said it’s about a 60-second deorbit burn, and that’s the critical thing that’s needs to happen to get the crew module on a safe trajectory to enter into the atmosphere and then land at White Sands. There’s good redundancy in those thrusters, we’ve got 4 thrusters in each direction so we expect that to go well” he said.
Once it returns the start of even more work will begin. Stich said, “After we get the vehicle back, we’ll go through a couple of months of post-flight analysis of the trajectory and how the thrusters performed during the final phase of flight. We also are already working hand in hand with Boeing to look at modifications to the system. Are there ways that we can fly the vehicle differently, do we need to do some more thruster testing at White Sands, to fill in some of the gaps that we had perhaps in qualification. So all that is gonna start taking place and there are teams starting to look at what we do to get the vehicle fully certified in the future” he said.
Conclusion
In just about one day Starliner is set to undock and perform a number of important milestones in an attempt to successfully reenter the atmosphere and land. While there’s no crew aboard, its still important that the spacecraft comes back in one piece.