So this leak was in the Service Module’s port doghouse (one of four), and on helium manifold 2 in that doghouse. Each of the 28 Reaction Control System thrusters have a flange to supply them with...
Exemplary
So this leak was in the Service Module’s port doghouse (one of four), and on helium manifold 2 in that doghouse. Each of the 28 Reaction Control System thrusters have a flange to supply them with MMH (monomethyl hydrazine; fuel), NTO (nitrogen tetroxide; oxidiser), and helium. The helium is used to actuate valves on both the Reaction Control System thrusters and the Orbital Maneuvering and Attitude Control thrusters.
They can’t open up the flange to look at the helium seal while Starliner’s stacked, in the Vertical Integration Facility, because MMH and NTO are not exactly the most fun chemicals to be around; they’d have to de-stack Starliner to open up that system, which could delay the launch a month or more.
The service module is the section of Starliner that performs the deorbit burn before separating from the crew module for its reentry and burning up in the atmosphere. So there won’t be another chance to take a closer look at the seal unless they go for a de-stack, but this isn’t a big deal: they already have a good grasp on what’s happening. If Starliner is delayed again past the current batch of launch windows (June 1, 2, 5, and 6), I’d expect a de-stack and a closer look at this seal.
What surprised me was that this leak was 70 PSI per minute. This seems really high! But it turns out that the leak is from an area that has a volume of 15 cubic inches and a nominal pressure of 750 PSI. And from an informed guess, Starliner has about 12,000 cubic inches of helium storage at a nominal pressure of ~4,500 PSI. Assuming linear pressure → density, this leak alone would take almost a month to bring the main tanks down to 750 PSI. So the “70 PSI” part is, in my humble opinion, pretty misleading.
And if the leak does get worse, it can be isolated in flight by shutting down the manifold that the leak is from. I'm guessing that there aren’t any valves between the manifold and each thruster, but if there were the individual flange (along with its thruster) could also be isolated.
And the helium there only has to be pressurized when thrusters are needed, so it could probably be depressurized while Starliner’s docked to the ISS (International Space Station) which would mean the leaky section is only pressurized for 4-5 days. (The system is pressurized during the launch count, both because the thrusters would be necessary during a launch abort and to remove the possibility of a failure after launch. While it’s docked at the ISS, there isn’t any imminent danger if the thruster system can’t be started up.)
I dislike the headlines on these. Don't get me wrong, I wouldn't be shocked if current Nasa and Boeing shoved this project out the door when they shouldn't have and got people killed. Still, with...
I dislike the headlines on these. Don't get me wrong, I wouldn't be shocked if current Nasa and Boeing shoved this project out the door when they shouldn't have and got people killed.
Still, with the evidence we have, everything is supposedly within an acceptable risk tolerance, and that's pretty normal for literal rocket science.
So this leak was in the Service Module’s port doghouse (one of four), and on helium manifold 2 in that doghouse. Each of the 28 Reaction Control System thrusters have a flange to supply them with MMH (monomethyl hydrazine; fuel), NTO (nitrogen tetroxide; oxidiser), and helium. The helium is used to actuate valves on both the Reaction Control System thrusters and the Orbital Maneuvering and Attitude Control thrusters.
They can’t open up the flange to look at the helium seal while Starliner’s stacked, in the Vertical Integration Facility, because MMH and NTO are not exactly the most fun chemicals to be around; they’d have to de-stack Starliner to open up that system, which could delay the launch a month or more.
The service module is the section of Starliner that performs the deorbit burn before separating from the crew module for its reentry and burning up in the atmosphere. So there won’t be another chance to take a closer look at the seal unless they go for a de-stack, but this isn’t a big deal: they already have a good grasp on what’s happening. If Starliner is delayed again past the current batch of launch windows (June 1, 2, 5, and 6), I’d expect a de-stack and a closer look at this seal.
What surprised me was that this leak was 70 PSI per minute. This seems really high! But it turns out that the leak is from an area that has a volume of 15 cubic inches and a nominal pressure of 750 PSI. And from an informed guess, Starliner has about 12,000 cubic inches of helium storage at a nominal pressure of ~4,500 PSI. Assuming linear pressure → density, this leak alone would take almost a month to bring the main tanks down to 750 PSI. So the “70 PSI” part is, in my humble opinion, pretty misleading.
And if the leak does get worse, it can be isolated in flight by shutting down the manifold that the leak is from. I'm guessing that there aren’t any valves between the manifold and each thruster, but if there were the individual flange (along with its thruster) could also be isolated.
And the helium there only has to be pressurized when thrusters are needed, so it could probably be depressurized while Starliner’s docked to the ISS (International Space Station) which would mean the leaky section is only pressurized for 4-5 days. (The system is pressurized during the launch count, both because the thrusters would be necessary during a launch abort and to remove the possibility of a failure after launch. While it’s docked at the ISS, there isn’t any imminent danger if the thruster system can’t be started up.)
I dislike the headlines on these. Don't get me wrong, I wouldn't be shocked if current Nasa and Boeing shoved this project out the door when they shouldn't have and got people killed.
Still, with the evidence we have, everything is supposedly within an acceptable risk tolerance, and that's pretty normal for literal rocket science.