-
#640
by
RotoSequence
on 21 Jan, 2020 15:44
-
-
#641
by
whitelancer64
on 21 Jan, 2020 15:52
-
Article from Eric Berger: Starliner’s thruster performance receiving close scrutiny from NASA
8+ thrusters failed in flight, with one fuel manifold shut down for low system pressure. 
"In response to a question about thruster performance, Boeing provided the following statement to Ars: "After the anomaly, many of the elements of the propulsion system were overstressed, with some thrusters exceeding the planned number of burns for a service module mission. We took a few cautionary measures to make sure the propulsion system stayed healthy for the remainder of the mission, including re-pressurizing the manifold, recovering that manifold’s thrusters. Over the course of the mission we turned off 13 thrusters and turned all but one back on after verifying their health."
-
#642
by
Eric Hedman
on 21 Jan, 2020 15:55
-
-
#643
by
VulcanCafe
on 21 Jan, 2020 16:00
-
Overstressing the hardware because of overuse is one thing, but this is another: 'The NASA source said eight or more thrusters on the service module failed at one point and that one thruster never fired at all'
-
#644
by
rcoppola
on 21 Jan, 2020 16:02
-
How many burns did they expect? What were their design margins for additional burns? And how many actually happened beyond design limits causing the over-stress?
-
#645
by
FutureSpaceTourist
on 21 Jan, 2020 16:02
-
If I understand correctly it comes down to whether - as Boeing seem to be saying - the thrusters behaved to spec (but were stressed beyond expected limits due to the timing anomaly causing excessive propulsion adjustment), or the thrusters showed unexpected behaviour even within expected limits.
If it’s the latter then I certainly wouldn’t be putting a crew on the next Starliner flight.
If it’s all a consequence of the timing issue then just maybe crew on the next flight is justifiable.
-
#646
by
whitelancer64
on 21 Jan, 2020 16:14
-
It sounds to me like the clock issue that forced the thrusters to fire way too much is the main problem, not the thrusters.
"In response to a question about thruster performance, Boeing provided the following statement to Ars: "After the anomaly, many of the elements of the propulsion system were overstressed, with some thrusters exceeding the planned number of burns for a service module mission. We took a few cautionary measures to make sure the propulsion system stayed healthy for the remainder of the mission, including re-pressurizing the manifold, recovering that manifold’s thrusters. Over the course of the mission we turned off 13 thrusters and turned all but one back on after verifying their health."
However, as the article itself mentions - "Both Boeing and NASA officials said it would be premature to discuss the matter further until the investigations are complete."
-
#647
by
Coastal Ron
on 21 Jan, 2020 16:24
-
We have to remember that SpaceX was very reticent to comment after their Super Draco test accident, so dealing with a lack of information at this point is not unusual.
However this latest revelation shows, I think, that NASA and Boeing won't be able to quickly come to a conclusion, since this thruster issue is showing either a lack of design capability of a fault in the thruster system. A lack of design capability can be dealt with I think, but a fault in the thruster system would need to be investigated.
I would not be surprised if this thruster issue is what paces their return to flight...
-
#648
by
kevinof
on 21 Jan, 2020 16:28
-
It's hard to know if the Boeing statements are correct and accurate - as you say we will have to wait and likely or not will not hear anything for quite a while. However happening "after the anomaly" doesn't explain why one thruster failed to fire at all.
It sounds to me like the clock issue that forced the thrusters to fire way too much is the main problem, not the thrusters.
"In response to a question about thruster performance, Boeing provided the following statement to Ars: "After the anomaly, many of the elements of the propulsion system were overstressed, with some thrusters exceeding the planned number of burns for a service module mission. We took a few cautionary measures to make sure the propulsion system stayed healthy for the remainder of the mission, including re-pressurizing the manifold, recovering that manifold’s thrusters. Over the course of the mission we turned off 13 thrusters and turned all but one back on after verifying their health."
However, as the article itself mentions - "Both Boeing and NASA officials said it would be premature to discuss the matter further until the investigations are complete."
-
#649
by
butters
on 21 Jan, 2020 16:30
-
Boeing's statement to Ars revealed that they observed a lower than nominal delta-V during the "retreat" part of the simulated ISS approach demo, presumably due to the overstressed propulsion system. Did they know before the approach demo that the condition of the propulsion system would degrade performance? How would they handle this with a live crew and a real ISS in the loop? Would they go ahead with an approach attempt after abnormal thruster utilization? Do they understand the temperature or duty cycle thresholds which, if exceeded, may jeopardize approach safety?
-
#650
by
whitelancer64
on 21 Jan, 2020 16:37
-
Boeing's statement to Ars revealed that they observed a lower than nominal delta-V during the "retreat" part of the simulated ISS approach demo, presumably due to the overstressed propulsion system. Did they know before the approach demo that the condition of the propulsion system would degrade performance? How would they handle this with a live crew and a real ISS in the loop? Would they go ahead with an approach attempt after abnormal thruster utilization? Do they understand the temperature or duty cycle thresholds which, if exceeded, may jeopardize approach safety?
A real crew would have noticed the thrusters were firing when they should not be, override them and shut them down. So the overstressed thruster situation wouldn't have happened.
-
#651
by
whitelancer64
on 21 Jan, 2020 16:45
-
It's hard to know if the Boeing statements are correct and accurate - as you say we will have to wait and likely or not will not hear anything for quite a while. However happening "after the anomaly" doesn't explain why one thruster failed to fire at all.
It sounds to me like the clock issue that forced the thrusters to fire way too much is the main problem, not the thrusters.
"In response to a question about thruster performance, Boeing provided the following statement to Ars: "After the anomaly, many of the elements of the propulsion system were overstressed, with some thrusters exceeding the planned number of burns for a service module mission. We took a few cautionary measures to make sure the propulsion system stayed healthy for the remainder of the mission, including re-pressurizing the manifold, recovering that manifold’s thrusters. Over the course of the mission we turned off 13 thrusters and turned all but one back on after verifying their health."
However, as the article itself mentions - "Both Boeing and NASA officials said it would be premature to discuss the matter further until the investigations are complete."
A cargo Dragon had a similar thruster issue on one flight, where IIRC the control valve didn't want to open. They had to cycle it a few thousand times to try to get it to open or something like that. That's an issue they'll have to resolve, but IMO quite a minor one. They have redundant thruster systems.
-
#652
by
meberbs
on 21 Jan, 2020 18:06
-
A cargo Dragon had a similar thruster issue on one flight, where IIRC the control valve didn't want to open. They had to cycle it a few thousand times to try to get it to open or something like that. That's an issue they'll have to resolve, but IMO quite a minor one. They have redundant thruster systems.
When you have a known failure, the redundancy argument is invalid. The single thruster that never fired is the most concerning statement in the article, and Boeing will need to address that somehow, but we don't have the information needed to even speculate about it. The rest of the article mostly just summarizes known things. For the low delta V on one test, I actually find Boeing's explanation reasonable, but it still may be one more thing that would be good to repeat, which is just one more reason to not put crew on the next flight.
-
#653
by
Lemurion
on 21 Jan, 2020 20:27
-
While I don't expect much news from anyone regarding the thruster issue I think it's fair to say Berger's source's characterization of the issue is significantly more serious than Boeing's statement implies.
According to Boeing's statement they shut down 13 thrusters and were able to restart 12. Given that they have already stated the thrusters were overstressed, this could be attributed to overuse. However, if the source in the article is correct, one of the thrusters never fired at all--indicating that it was completely non-functional. Given that Starliner apparently needs those thrusters for attitude control during a low-altitude abort this could be a much larger problem.
The problem we have here is that we don't know which characterization is more accurate, so it's hard to come up with a clear understanding of what needs to happen going forward. Overstressed thrusters can be expected to exhibit less than perfect reliability--if it's a thruster that failed to fire they have to examine both the reason it failed to fire and how it got through QA testing.
I'm hoping the Boeing characterization is right, and fearing it isn't.
-
#654
by
SteveU
on 21 Jan, 2020 20:44
-
Okay - let me get this straight.
They didn't get the correct delta V for the "back away maneuver" because the thrusters were over stressed.
Over-stressing the thrusters was due to the timing anomaly and over-stressing would not have occurred during a nominal flight.
Just how many uses can the thrusters handle on the "reusable" craft?
ISTM that Starliner has some significant issues that need to be addressed.
-or- do we just tell the astronauts to go easy on the thrusters so we have enough life for future flights [/snark off]
-
#655
by
whitelancer64
on 21 Jan, 2020 20:54
-
While I don't expect much news from anyone regarding the thruster issue I think it's fair to say Berger's source's characterization of the issue is significantly more serious than Boeing's statement implies.
According to Boeing's statement they shut down 13 thrusters and were able to restart 12. Given that they have already stated the thrusters were overstressed, this could be attributed to overuse. However, if the source in the article is correct, one of the thrusters never fired at all--indicating that it was completely non-functional. Given that Starliner apparently needs those thrusters for attitude control during a low-altitude abort this could be a much larger problem.
The problem we have here is that we don't know which characterization is more accurate, so it's hard to come up with a clear understanding of what needs to happen going forward. Overstressed thrusters can be expected to exhibit less than perfect reliability--if it's a thruster that failed to fire they have to examine both the reason it failed to fire and how it got through QA testing.
I'm hoping the Boeing characterization is right, and fearing it isn't.
A single thruster out is never a mission failure. Like Dragon, Starliner has multiple redundant pairs of thrusters. The Starliner SM has 28 RCS thrusters and 20 more powerful orbital maneuvering thrusters, and the capsule has 12 RCS thrusters.
TL;DR,
Starliner has a total of 60 thrusters.
-
#656
by
jak Kennedy
on 21 Jan, 2020 21:14
-
We have to remember that SpaceX was very reticent to comment after their Super Draco test accident, so dealing with a lack of information at this point is not unusual.
However this latest revelation shows, I think, that NASA and Boeing won't be able to quickly come to a conclusion, since this thruster issue is showing either a lack of design capability of a fault in the thruster system. A lack of design capability can be dealt with I think, but a fault in the thruster system would need to be investigated.
I would not be surprised if this thruster issue is what paces their return to flight...
To be fair, SpaceX had little pieces to work with as well as any data recorded and didn’t it take them many days to even approach the site. Boeing’s problem might not be the thrusters or not even so much using an incorrect clock but that the software was not performing any checks before firing away willy nilly.
-
#657
by
rcoppola
on 21 Jan, 2020 21:37
-
I must admit to not having followed Starliner development as closely as Dragon's but why exactly do they have so many thrusters? Why does Starliner need (60?) thrusters?
-
#658
by
Vettedrmr
on 21 Jan, 2020 21:43
-
A single thruster out is never a mission failure. Like Dragon, Starliner has multiple redundant pairs of thrusters.
Absolutely correct. And, assuming space flight testing is similar to military flight testing that I was involved with, when that redundant device fails on its first flight, there's no more flying until the failure is understood, characterized, and corrective actions implemented.
-
#659
by
whitelancer64
on 21 Jan, 2020 21:52
-
I must admit to not having followed Starliner development as closely as Dragon's but why exactly do they have so many thrusters? Why does Starliner need (60?) thrusters?
There are 28 RCS thrusters on the CM. There are also 20 orbital maneuvering thrusters that are more powerful (they are also used to control pitch and yaw in the event of an abort). Starliner would be using those 20 to change orbits. Plus the 12 RCS thrusters on the capsule which provide orientation during EDL.
