Boeing Needs More Time Before Undocking The Crewed Starliner
Earlier this morning NASA held a media teleconference and provided new information on Starliner’s condition and its departure from the ISS. What was originally intended to be around a week long stay was initially pushed back to the 22nd of this month and was just changed to the 26th at the earliest. This comes as teams continue to work on figuring out the exact source and significance of a few different issues.
Between 5 current helium leaks, 3 of which are larger than others, and a few thruster issues, NASA and Boeing are taking their time to make sure they learn as much as possible and bring Suni and Butch home safely. Here I will go more in-depth into the reentry date change, the current state of the vehicle, plans over the next week, and more.
Another Push-Back
Starliner launched earlier this month on the 5th with 1 known helium leak that was found last month in May. Upon reaching orbit, 4 more popped up bringing the total to 5. While not ideal, the agency and Boeing made it clear that there was plenty of margin and the leak rate was not nearly high enough to be a cause for concern. Later in the mission while approaching the station, issues with Starliner’s thrusters delayed an initial docking as teams worked to hot fire and test the system. Eventually, after a couple-hour delay, Starliner successfully docked to the station. This brings us to today as NASA and Boeing work to solve and prepare the spacecraft for undocking and reentry.
In this morning’s media teleconference, they gave some more information on the state of the vehicle and the reason for the change in departure date. Steve Stich, NASA Commerical Crew Program Manager said, “I would say overall Starliner is doing very well on orbit. This is a test flight and we are taking our time to understand the vehicle and also understand the service module. The Service Module is a component that we don’t get back, as you know after we execute the deorbit burn it burns up in the atmosphere. So we are taking our time to understand that service module and the things that we’ve had happened relative to the helium leaks and the thruster fail-offs at docking” he said.
As far as exactly why the date was pushed back again, Stich was quoted saying, “We are not targeting an undock and return no earlier than June 26th. We’ve moved off the 22nd, we want to give our teams a little bit more time to look at the data, do some analysis, and make sure we are really ready to come home” he said. With this in mind, and as highlighted later in the teleconference, NASA and Boeing are still trying to figure out what’s causing both issues with the helium leaks and thruster fail-offs. While they point out that they do have the margin to bring the astronauts home right now, they would prefer to take the time and check each aspect of the vehicle along with performing even more testing. Backup departure dates would be every 4 days meaning the next opportunity would be the 30th, and then the 4th, and so on.
Stich then went into more detail on the thrusters that failed. Here he said, “I told you about 5 reaction control system thrusters, these were all aft thrusters that failed during the final phase of the rendezvous after we had done the TPI burn in that final phase where there’s a lot of thruster firings we had 5 thrusters fail. Thruster B1A3 when we looked at that hot fire data we saw that it had 11% thrust on one of the firings and then 0% on another. These were the two firings that we did on the rendezvous day. That thruster we decided we are not going to hot fire that thruster anymore. We didn’t hot fire it on Saturday, we are just going to leave that thruster alone, because it shows a very strange signature where we’re getting almost no thrust out of that. So we are going to leave that thruster de-selected and are not going to use it for the rest of the flight” he said.
On the recent hot fire this Saturday, they did a short pulse on all 7 of the thrusters including 3 of the good thrusters that showed nominal behavior on rendevous day. Stich mentioned that during this test they saw very good chamber pressure when they fired. Specifically, they were around the 300 PSI mark, some were a little bit lower but for the most part they were good. He then said, “So coming out of that we feel very confident in the thrusters and the team is just making sure to look at the thrusters in detail and compare them to what happened on OFT-2. If you remember on OFT-2 during the rendezvous sequence, we had 2 thrusters fail. Both of those thrusters at the end of the flight and the team is looking at all that data and comparing it to OFT-2” he mentioned.
Three of the thrusters that had issues earlier in this mission are not back up to right around 100% thrust based on the recent static fire. Stich mentioned that the initial loss of thrust could have been due to the high demand for thruster use at the time the issues occurred around docking. In other words, they mostly recovered after that event. As partially mentioned before, these are issues within the Service module, which will burn up in Earth’s atmosphere and not land on the surface. For this reason, right now is practically the only time Boeing and NASA can gather data to figure out what is going wrong and make sure it doesn’t happen on the next flight.
Right now teams are running simulations to see what impact if any the current thruster and helium leaks would have on the milestones coming up. The major event includes the deorbit burn which requires the thrusters. Here, Stich pointed out, “So the path forward is really over the next week. We really need to be working this week to try and wrap things up by this Saturday the 22nd. Our teams are going to look through, and I listened to about a 6-hour review yesterday of all the thruster firing data. They’re going to look at that thruster firing data today and compare it to the simulations. So they are spending time doing that over the next week” he said.
In terms of the helium leaks, he confirmed that all the leak rates had gone down since they initially popped up. He also made a comment that they seem to be related to dynamic activity such as thruster use. For a solution, they are simply looking at the necessary margin and making sure there is enough. They are also doing some seal testing on the ground to get a better idea of the leak rates.
For the final issue, there was a valve that wasn’t properly closing in the service module. It’s used to isolate propellants in the port manifold. They have since used the other valve (B instead of A). They also clarified that this was different from the valves not functioning in OFT-2.
This sums up some of the main information provided during the teleconference which led to the question portion. One question asked what the minimum number of thrusters necessary for deorbit and reentry. Stich responded, “I think that’s a great question, and it’s really difficult to answer because each phase of flight requires certain thrusters.” He went on to highlight that rendezvous likely requires the most and then the next greatest would be departure and work around the deorbit burn. Eric Berger also asked about Starliner 1 and how these complications impact that mission. Stich replied, “We really haven’t looked that much at Starliner 1. I would say the whole team has been focused on understanding what’s happening with this vehicle for the crew flight test and our plan for return, so we haven’t looked ahead too much for Starliner 1. As Mark said we know we have to address the helium leaks. Were not going to go fly another mission like this with the helium leaks. We gotta go understand what the rendezvous profile is doing that is causing the thruster to have low thrust and then be de-selected by the flight control temps. So we got some of the work to do after this flight” he said.
When Starliner does eventually undock, the process requires each system including the service module to work well. A few days before the undocking they will power up the vehicle and load cargo onto the spacecraft. On undocking day they will do some leak checks and make sure they are ready to go. The vehicle will depart in mostly an automatic fashion. The crew has one command which is to tell Starlienr it is go to undock. After the undock Starliner is expected to depart much quicker than it rendezvous. It will first go up and above the station then do the departure initiation burn which will send it away from the station. There it will perform an automated hot fire test of the crew module propulsion system.
They will then phase down below the ISS around 3km, and do one last burn called the NSR which will set Starliner on the correct orbit. Finally, they will reach the deorbit burn which will take less than a minute. Soon after the service module is jettisoned and the module will take about 48 minutes from the deorbit burn to landing. Something we can hope to see by the end of this month.
Conclusion
Again the decision was made to push back Starliner’s launch date as teams work to get a better understanding of exactly what’s causing the spacecraft’s issues. The earliest departure opportunity is now the 26th with backup dates every 4 days later. They are confident that Starliner will be capable and just needs some time to get everything sorted before bringing the astronauts back. We will have to wait and see how it progresses and the impact it has on the space industry.
