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#660
by
whitelancer64
on 21 Jan, 2020 21:53
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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.
That's why NASA and Boeing are reviewing everything, yes.
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#661
by
clongton
on 21 Jan, 2020 22:36
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It's demonstrably sure that NASA wants Boeing to look good. That has been obvious for many, many years. Also sure is that Boeing, when reporting on an anomaly in <whatever> system it is building, won't hide the negative observation but will bury a negative observation in a mountain of nominal or good observations. Most likely hoping that it is overlooked to the casual observer. That has also been obvious for many, many years. So when NASA's assessment of the anomaly is worse than Boeing's, that is telling. Remember, 1 of those thrusters never fired at all, ever. It was not over stressed - it just plain didn't work. THAT is a red flag, especially in a system that is supposedly ready for the big demonstration.
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#662
by
clongton
on 21 Jan, 2020 22:40
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They didn't get the correct delta V for the "back away maneuver" because the thrusters were over stressed.
That is an assumption on your part. All that was reported is that the delta-v was subnominal. That could have been caused by any one of dozens of potential causes.
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#663
by
Lar
on 21 Jan, 2020 23:00
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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.
Assumes facts not in evidence.
It's demonstrably sure that NASA wants Boeing to look good.
Assumes facts not in evidence.
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#664
by
whitelancer64
on 21 Jan, 2020 23:13
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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.
Assumes facts not in evidence.
It's demonstrably sure that NASA wants Boeing to look good.
Assumes facts not in evidence.
Well it's been said by Boeing. In any event, based on watching the orbital flight video, you can SEE the Snoopy being thrown around from the thruster firings. Anyone strapped in a seat would notice the capsule moving around. With training, they'd know that wasn't supposed to be happening at that point in the flight. The controllers on the ground certainly knew it wasn't supposed to be happening.
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#665
by
SteveU
on 22 Jan, 2020 00:23
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They didn't get the correct delta V for the "back away maneuver" because the thrusters were over stressed.
That is an assumption on your part. All that was reported is that the delta-v was subnominal. That could have been caused by any one of dozens of potential causes.
From Eric Berger’s article
"In testing the system the spacecraft executed all the commands, but we did observe a lower than expected delta V during the backing away phase," Boeing said in a statement. "Current evidence indicates the lower delta V was due to the earlier cautionary thruster measures, but we are carefully reviewing data to determine whether this demonstration should be repeated in the subsequent mission."
That sure reads to me that they believe the delta V issue was related to the thruster issues.
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#666
by
TorenAltair
on 22 Jan, 2020 01:21
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I wonder about the Starliner architecture‘s robustness. There shouldn‘t be single points of failure in spacecrafts. We always got hammered in university about robustness of systems. Things can fail, programs do have bugs, but there always should be stoppers implemented. In this case I would have expected some kind of safe mode. „Hey, I‘m firing thrusters for much, much longer than in any planned situation, this is strange, I better switch to safe mode“
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#667
by
WindnWar
on 22 Jan, 2020 02:58
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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.
I am still failing to understand why a capsule and service module as light as Starliner is, needs 30,000 pounds of thrust via twenty 1,500 pound thrusters when the Shuttle was able to get to orbit with only 12,000 pounds of thrust from the two 6,000 pounds thrust OMS pods? Is it simply just to control the abort phase, which seems to imply the abort motors can't use differential thrust to to guide the trajectory, or is it to impart enough delta v to get to orbit, even though that seems unlikely given the small amount of delta v needed to make it to orbit. It just seems wildly excessive. Counting every single thruster on Starliner including abort motors you get 64 of them. Dragon has 28 including abort motors, the Shuttle and 44 RCS thrusters, 38 with 807 pounds thrust each and 6 with 24 pounds thrust each and the OMS with 6,000 pounds each for a total of 46 for a total output of about 43,000 pounds from all of them while its max weight was 10 times the Starliner stack. Not including the abort motors, Starliner has almost 34,000 pounds of thrust across all its thrusters. Dragon total is 1800 pounds of thrust not including the Super Dracos.
That just seems crazy in the difference between the two. What am I missing?
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#668
by
TheRadicalModerate
on 22 Jan, 2020 05:39
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They didn't get the correct delta V for the "back away maneuver" because the thrusters were over stressed.
That is an assumption on your part. All that was reported is that the delta-v was subnominal. That could have been caused by any one of dozens of potential causes.
From Eric Berger’s article
"In testing the system the spacecraft executed all the commands, but we did observe a lower than expected delta V during the backing away phase," Boeing said in a statement. "Current evidence indicates the lower delta V was due to the earlier cautionary thruster measures, but we are carefully reviewing data to determine whether this demonstration should be repeated in the subsequent mission."
That sure reads to me that they believe the delta V issue was related to the thruster issues.
I read this as an admission that no set of thrusters was available to expend more propellant to get to the "back away" delta-v. That implies that virtually all of them had reached the point where they couldn't provide any more impulse. With 60 of them on the vehicle, that's pretty sobering.
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#669
by
Joseph Peterson
on 22 Jan, 2020 05:56
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How far off-nominal but still-within-propellant-margins can a launch be before it has to be aborted due to loss of thrusters?
The only answer I have right now is, "There is not enough public information for an educated guess at this time."
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#670
by
Lar
on 22 Jan, 2020 06:11
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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.
Assumes facts not in evidence.
It's demonstrably sure that NASA wants Boeing to look good.
Assumes facts not in evidence.
Well it's been said by Boeing. In any event, based on watching the orbital flight video, you can SEE the Snoopy being thrown around from the thruster firings. Anyone strapped in a seat would notice the capsule moving around. With training, they'd know that wasn't supposed to be happening at that point in the flight. The controllers on the ground certainly knew it wasn't supposed to be happening.
I can come up with all kinds of scenarios in which poorly written software puts things in a state where astronauts cannot recover easily or quickly enough to save the mission. We've already established that this software was poorly written. We just don't know how poorly just yet. (and probably never will)
So yes, "So the overstressed thruster situation wouldn't have happened." does indeed assume facts not in evidence. We can't be 100% sure of that (crew can save the mission), and I'm not myself even 90% sure. YMMV.
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#671
by
woods170
on 22 Jan, 2020 10:43
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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.
I am still failing to understand why a capsule and service module as light as Starliner is, needs 30,000 pounds of thrust via twenty 1,500 pound thrusters when the Shuttle was able to get to orbit with only 12,000 pounds of thrust from the two 6,000 pounds thrust OMS pods? Is it simply just to control the abort phase, which seems to imply the abort motors can't use differential thrust to to guide the trajectory, or is it to impart enough delta v to get to orbit, even though that seems unlikely given the small amount of delta v needed to make it to orbit. It just seems wildly excessive. Counting every single thruster on Starliner including abort motors you get 64 of them. Dragon has 28 including abort motors, the Shuttle and 44 RCS thrusters, 38 with 807 pounds thrust each and 6 with 24 pounds thrust each and the OMS with 6,000 pounds each for a total of 46 for a total output of about 43,000 pounds from all of them while its max weight was 10 times the Starliner stack. Not including the abort motors, Starliner has almost 34,000 pounds of thrust across all its thrusters. Dragon total is 1800 pounds of thrust not including the Super Dracos.
That just seems crazy in the difference between the two. What am I missing?
Emphasis mine.
Only 12 of those 1,500 pound thrusters are aimed in the same (downward) direction. They provide additional thrust during low-altitude aborts and are the main abort thrusters for high-altitude aborts. Those 12 (18,000 pounds of thrust combined) are also the primary thrusters for getting Starliner into orbit after Atlas V has released Starliner into its suborbital trajectory.
Another four 1,500 pound thrusters are aimed forward in two pairs and are - if I recall correctly - the primary thrusters for emergency abort (rapid retreat) during ISS approach phase.
The remaining four are paired in roll-control configuration (firing sideways).
All 20 of the 1,500 pound thrusters provide attitude control during low-altitude aborts because the normal RCS thrusters are just not powerful enough for that purpose.
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#672
by
Johnnyhinbos
on 22 Jan, 2020 11:28
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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.
I am still failing to understand why a capsule and service module as light as Starliner is, needs 30,000 pounds of thrust via twenty 1,500 pound thrusters when the Shuttle was able to get to orbit with only 12,000 pounds of thrust from the two 6,000 pounds thrust OMS pods? Is it simply just to control the abort phase, which seems to imply the abort motors can't use differential thrust to to guide the trajectory, or is it to impart enough delta v to get to orbit, even though that seems unlikely given the small amount of delta v needed to make it to orbit. It just seems wildly excessive. Counting every single thruster on Starliner including abort motors you get 64 of them. Dragon has 28 including abort motors, the Shuttle and 44 RCS thrusters, 38 with 807 pounds thrust each and 6 with 24 pounds thrust each and the OMS with 6,000 pounds each for a total of 46 for a total output of about 43,000 pounds from all of them while its max weight was 10 times the Starliner stack. Not including the abort motors, Starliner has almost 34,000 pounds of thrust across all its thrusters. Dragon total is 1800 pounds of thrust not including the Super Dracos.
That just seems crazy in the difference between the two. What am I missing?
Emphasis mine.
Only 12 of those 1,500 pound thrusters are aimed in the same (downward) direction. They provide additional thrust during low-altitude aborts and are the main abort thrusters for high-altitude aborts. Those 12 (18,000 pounds of thrust combined) are also the primary thrusters for getting Starliner into orbit after Atlas V has released Starliner into its suborbital trajectory.
Another four 1,500 pound thrusters are aimed forward in two pairs and are - if I recall correctly - the primary thrusters for emergency abort (rapid retreat) during ISS approach phase.
The remaining four are paired in roll-control configuration (firing sideways).
All 20 of the 1,500 pound thrusters provide attitude control during low-altitude aborts because the normal RCS thrusters are just not powerful enough for that purpose.
Bold emphasis in you quote mine.
So would it be correct to state this as, the 12 (18,000 lb thrust combined) thrusters are required to make up for a lack of delta v in the booster?
Also, from my experience as a mixed gas technical diver, where your life is completely dependent on the gear you wear and redundancy is absolutely critical, I have to say it really troubles me that the thrusters were unable to operate to fuel depletion. I understand it’s a common fuel system (meaning motors used for abort, oms, and rcs drink from the same well), but come on - you don’t have to look past the actual flight to envision a scenario where longer thruster burns might be required.
If I was assigned to this spacecraft I’d have some qualms.
(Of course, watching my spacecraft absolutely explode into a million pieces would give me pause as well - though at least with that one there were two very successful tests post incident before putting humans aboard)
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#673
by
edzieba
on 22 Jan, 2020 13:12
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As I understand, the issue was not so much total thruster operation time, but total high duty cycle operation. Operating in low-duty-cycle mode is sustainable, operating briefly in high duty-cycle (e.g. continuous burns for insertion or rapid-retreat burns) is sustainable, but operating in the mode they ended up stuck in (very rapid pulsing over a protracted time to try and overfit orientation to an erroneous value) was not sustainable.
As for a thruster not operating after the anomaly: there was explicit mention of an affected manifold: a valve jammed to due to overheating (e.g. though overtemp) could easily prevent operating of a thruster otherwise unaffected in and of itself. Not all the Starliner thrusters are active throughout the mission, so if this thruster had not been required before the anomoly it would have had no chance to demosntrate whether or not it was non-functioning from the start or whether it was a casualty of the overuse issue.
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#674
by
wardy89
on 22 Jan, 2020 14:14
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So would it be correct to state this as, the 12 (18,000 lb thrust combined) thrusters are required to make up for a lack of delta v in the booster?
Boing get the Starliner dropped on a suborbital trajectory by choice, this is very much like what NASA used to do with the shuttle, the initial orbit having a free return trajectory then the spacecraft making the final insertion burn. The Atlas V could put the capsule into orbit on its own no problem, it's not making up for a lack of delta V on the booster side, Just a slightly different approach.
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#675
by
envy887
on 22 Jan, 2020 14:51
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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.
I am still failing to understand why a capsule and service module as light as Starliner is, needs 30,000 pounds of thrust via twenty 1,500 pound thrusters when the Shuttle was able to get to orbit with only 12,000 pounds of thrust from the two 6,000 pounds thrust OMS pods? Is it simply just to control the abort phase, which seems to imply the abort motors can't use differential thrust to to guide the trajectory, or is it to impart enough delta v to get to orbit, even though that seems unlikely given the small amount of delta v needed to make it to orbit. It just seems wildly excessive. Counting every single thruster on Starliner including abort motors you get 64 of them. Dragon has 28 including abort motors, the Shuttle and 44 RCS thrusters, 38 with 807 pounds thrust each and 6 with 24 pounds thrust each and the OMS with 6,000 pounds each for a total of 46 for a total output of about 43,000 pounds from all of them while its max weight was 10 times the Starliner stack. Not including the abort motors, Starliner has almost 34,000 pounds of thrust across all its thrusters. Dragon total is 1800 pounds of thrust not including the Super Dracos.
That just seems crazy in the difference between the two. What am I missing?
With the large fins on the trunk, Dragon is aerodynamically stable in forward flight during the abort, even once the SuperDracos are shut down.
Even with the large OMAC thrusters, Starliner had stability concerns during aborts. See:
Abort System: Boeing is addressing a risk that its abort system, which it needs for human spaceflight certification, may not meet the program’s requirement to have sufficient control of the vehicle through an abort. In some abort scenarios, Boeing has found that the spacecraft may tumble, which could pose a threat to the crew’s safety. To validate the effectiveness of its abort system, Boeing has conducted extensive wind tunnel testing and plans to complete a pad abort test in July 2018.
https://www.gao.gov/assets/700/693035.pdf
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#676
by
mn
on 22 Jan, 2020 15:01
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...
We've already established that this software was poorly written.
...
In defense of the programmers (since I write bugs (aka software) for a living): (small time software, nothing mission critical or anywhere near that).
I'm not convinced that the software was poorly written.
Software does not need to contain extra code to handle things that are not possible.
There was certainly a major mistake in that the timer was wrong, but that is something that is supposed to be caught in development/testing, but once the testing was completed correctly, I fail to see how it's possible for the timer to be off - after being correct at least once.
To add logic to the software to handle things that are not possible just adds extra complexity and therefore extra opportunities for even more bugs.
The fact that things went haywire once the timer was off is not surprising but does not to me indicate 'poorly written'.
just my 2c
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#677
by
rcoppola
on 22 Jan, 2020 15:25
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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.
I am still failing to understand why a capsule and service module as light as Starliner is, needs 30,000 pounds of thrust via twenty 1,500 pound thrusters when the Shuttle was able to get to orbit with only 12,000 pounds of thrust from the two 6,000 pounds thrust OMS pods? Is it simply just to control the abort phase, which seems to imply the abort motors can't use differential thrust to to guide the trajectory, or is it to impart enough delta v to get to orbit, even though that seems unlikely given the small amount of delta v needed to make it to orbit. It just seems wildly excessive. Counting every single thruster on Starliner including abort motors you get 64 of them. Dragon has 28 including abort motors, the Shuttle and 44 RCS thrusters, 38 with 807 pounds thrust each and 6 with 24 pounds thrust each and the OMS with 6,000 pounds each for a total of 46 for a total output of about 43,000 pounds from all of them while its max weight was 10 times the Starliner stack. Not including the abort motors, Starliner has almost 34,000 pounds of thrust across all its thrusters. Dragon total is 1800 pounds of thrust not including the Super Dracos.
That just seems crazy in the difference between the two. What am I missing?
With the large fins on the trunk, Dragon is aerodynamically stable in forward flight during the abort, even once the SuperDracos are shut down.
Even with the large OMAC thrusters, Starliner had stability concerns during aborts. See:
Abort System: Boeing is addressing a risk that its abort system, which it needs for human spaceflight certification, may not meet the program’s requirement to have sufficient control of the vehicle through an abort. In some abort scenarios, Boeing has found that the spacecraft may tumble, which could pose a threat to the crew’s safety. To validate the effectiveness of its abort system, Boeing has conducted extensive wind tunnel testing and plans to complete a pad abort test in July 2018.
https://www.gao.gov/assets/700/693035.pdf
I completely forgot about that. Look, I'm just going to say it. The only reason Boeing didn't do an in-flight abort was to save money by not having to purchase another Atlas V and all associated costs with an IFA mission. That thruster system is complex, as is the software that runs it. We've found a corner case that brings the system to it's knees. Are there others? How would it actually handle the same abort conditions as Dragon just did? How good are their models? Obviously their testing protocols are not good enough to prevent what should be a robust hand-off procedure from booster to vehicle. Are we really to believe that the shareholder culture that has pervaded all of Boeing for years didn't find it's way into this program?
This system needs another un-crewed flight test.
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#678
by
Vettedrmr
on 22 Jan, 2020 15:27
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...
We've already established that this software was poorly written.
...
In defense of the programmers (since I write bugs (aka software) for a living): (small time software, nothing mission critical or anywhere near that).
I'm not convinced that the software was poorly written.
You trimmed Lar's comment one phrase too soon: What he said (using words I wouldn't have) was:
We've already established that this software was poorly written. We just don't know how poorly just yet. (and probably never will)
As one who spent a career doing safety-critical software, I can say that darn near every software "bug" that made it into flight testing was, at its root, a
system requirement that several software requirements were derived from. Was the software modified as a result of the system requirement error? You bet; it's a lot harder to change hardware than it is software. Is that a software error? Not in my book; the software faithfully implemented the requirements given to it.
What is the root cause in Starliner?
We don't know, and as Lars points out, we (the public) may not ever learn the details. Will the change be made in software? I sure hope so, because if there are hardware problems that have to be corrected, that's gonna be a hurt to Boeing, NASA, and space fans everywhere (but a WHOLE LOT LESS OF A HURT than losing a crew).
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#679
by
whitelancer64
on 22 Jan, 2020 15:45
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*snip*
Look, I'm just going to say it. The only reason Boeing didn't do an in-flight abort was to save money by not having to purchase another Atlas V and all associated costs with an IFA mission.
*snip*
You do not have to use the launch vehicle to do an in-flight abort test. All other in-flight abort tests prior to SpaceX's IFA test have used a much cheaper stand-in rocket booster for the in-flight abort test.