3 ms·

From what I can see the TAGSAM head did use stainless steel screws, but the majority of the structure is aluminium [1]. So its possible there is a galvanic corr

From what I can see the TAGSAM head did use stainless steel screws, but the majority of the structure is aluminium [1]. So its possible there is a galvanic corrosion issue that caused the screws to bind, but I would be a little surprised at that based on how the TAGSAM has been handled throughout its life. Still does feel like the most likely issue though. Regarding lubrication on screws in space, it is done quite regularly with a variety of lubricants (as well as thread lockers) [2]. I can imagine that none were used in a system that is meant to be kept as free of contaminants as the TAGSAM is though. Hard to know with any amount of confidence. From experience with spacecraft integration, when the article mentions that they didn't have a suitable tool for removal of two screws, my head immediately jumps to an access issue. Its amazing the number of times I have heard 'it fits in the CAD' from the designers, when you have no access at all for getting a screwdriver to the screw, let alone a torque wrench. So it could be as simple as that. [1] - https://link.springer.com/article/10.1007/s11214-018-0521-6 https://link.springer.com/article/10.1007/s11214-018-0521-6 [2] - https://ecss.nl/hbstms/ecss-e-hb-32-23a-threaded-fasteners-handbook/ https://ecss.nl/hbstms/ecss-e-hb-32-23a-threaded-fasteners-h...

MilStdJunkie 3y ago
There's a lot of push in the defense world to get to so-called "Digital Twin", where cabling, conduit, maintainability and other late-stage product work is done purely in CAD and in simulation. I'm very open to the idea . . however . . when I get a pile of geometry with no fastener material data, no soft bodies of any kind (tape, string, wire, cloth, rope, etc), broke fillets . . and then someone tells me "there you go, you can figure out the maintenance breakdown now. DIGITAL TWIN!" . . I'm not filled with confidence. Someone, somewhere, needs to spec out the minimum required for each stage of this kind of work . . they might find that doing things like wire channels in new product isn't fantastically easier than doing it in a prototype. You can do it in CAD< but you still have to get the design right. Tool clearance doesn't magically appear in the right place by screaming DIGITAL TWIN. This is all aerospace. In another industry, with less demanding performance requirements, the easy solution to all problems is always "increase the tolerances". Then you can jam anything in there. Another problem: logistics systems want to know the sparing level for what's being supported, not what's being designed. This, incredibly, isn't addressed so far as I can see; adopters are just sort of pretending that bleeding edge is the same as the as-built, supported configuration. When I bring it up, the general response is that LSA can be batch-create from the design, totally ignoring the fact that a lot of changes come the other way, from field modifications. The solution for this - for NGAD and Raider - is to just not do logistics as it's been practiced for the last forty years. Spoiler: this is the correct answer. 30 year sustainment programs are hilarious fictions that do nothing but generate high margin work for primes.
- exmadscientist 3y ago
  "DIGITAL TWIN!!" would be a lot less of a punchline if I understood the prototype on my desk well enough to predict its behavior. And I can look straight at that one. The idea that we can understand real hardware in unusual conditions well enough to make a simulation/Digital Twin the One True Reference is simply hilarious. Though as you point out, it sure does generate a lot of high margin work and great ad copy.
  - MilStdJunkie 3y ago
    I'll concede that when you write off maintainability down to the nuts-and-bolts-level, that does make things a whole lot easier. But I don't think that's digital twin; that's just tighter tolerance, and aaalllll the things that ride along with that. But doing something like scheduled maintenance just from the Twin?! Ehhhhhh sheesh, I dunno. I'm not one of the smart guys, but you would need to combine the solid-model FM sort of simulation with the more fluxy CFD models, and then have them interact. I realize computers are super powerful these days, but that is a HELL of a lot to ask from a simulation running on commodity equipment with commodity software. I've seen single-assembly CFD choke when it had to extend to just a single fuel system's materials data - and that was nothing compared to doing that for an entire airframe. Or even a reasonable chunk of an airframe. I'm at peace leaving this stuff to the guys who know what they're doing, but I don't see a lot of those people actually doing the decision making. It's finbros all the way down. I'm afraid what I'll be ending up with, at the end of the day, is the Reification Fallacy made flesh: a box of parts that's supposedly a flyable airframe. "Just write a preflight checklist for it!" they might say. "Copy and paste something or whatever." Why knows, they're RIFing more or less everyone with technical knowledge this week, so it probably won't be my problem for long.
adolph 3y ago
The Springer link is to the original TAGSAM paper--very interesting. I found it while doing a screw count of the below sampler head--there are 21 phillips-like head and 6 with allen head. The NASA press release [1] says "two of the 35 fasteners on the TAGSAM head could not be removed with the current tools approved for use." That doesn't match, which lead me to the Bierhaus et al. at Springer [2] which shows how they put the sampler head screws down into the dirt. The diagrams from Bierhaus and Walsh et al. [3] are both interesting. 0. https://www.nasa.gov/wp-content/uploads/2023/10/nelson-tagsam-shot-b.jpg https://www.nasa.gov/wp-content/uploads/2023/10/nelson-tagsa... 1. https://blogs.nasa.gov/osiris-rex/2023/10/20/nasas-osiris-rex-achieves-sample-mass-milestone/ https://blogs.nasa.gov/osiris-rex/2023/10/20/nasas-osiris-re... 2. https://link.springer.com/article/10.1007/s11214-018-0521-6 https://link.springer.com/article/10.1007/s11214-018-0521-6 3. https://link.springer.com/article/10.1007/s11214-022-00887-2 https://link.springer.com/article/10.1007/s11214-022-00887-2
johnwalkr 3y ago
Generally in aluminum parts in aerospace, locking stainless steel threads inserts (“helicoils”) are added for pullout strength, repairability, reducing risk of damage when fastening multiple times and to meet the requirement (which almost always exists) for secondary back-off prevention (primary is usually controlled preload). The locking feature is 1-2 threads in the insert that are deformed to provide a decent amount of friction even if preload is lost. But for a special case like this it’s possible a unique design was used; I would be interested to read about it. From the images, it’s not clear which fasteners are removed but if the issue is not access it could be a stuck fastener for whatever reason and maybe a rounded head. I wouldn’t be surprised if nothing is damaged but the procedure was stopped due to higher than expected torque, and they are taking it slow to decide how to proceed.
- cuSetanta 3y ago
  I hadbt consudered a stuck locking helicoil in fairness. And seeing the pictures of the fasteners it does seem unlikely to be an access issue, so you are probably right about the torque.
- HeyLaughingBoy 3y ago
  > procedure was stopped due to higher than expected torque I should have done this. Just broke a brand new 10-32 tap!

MilStdJunkie 3y ago

There's a lot of push in the defense world to get to so-called "Digital Twin", where cabling, conduit, maintainability and other late-stage product work is done purely in CAD and in simulation. I'm very open to the idea . . however . . when I get a pile of geometry with no fastener material data, no soft bodies of any kind (tape, string, wire, cloth, rope, etc), broke fillets . . and then someone tells me "there you go, you can figure out the maintenance breakdown now. DIGITAL TWIN!" . . I'm not filled with confidence. Someone, somewhere, needs to spec out the minimum required for each stage of this kind of work . . they might find that doing things like wire channels in new product isn't fantastically easier than doing it in a prototype. You can do it in CAD< but you still have to get the design right. Tool clearance doesn't magically appear in the right place by screaming DIGITAL TWIN. This is all aerospace. In another industry, with less demanding performance requirements, the easy solution to all problems is always "increase the tolerances". Then you can jam anything in there. Another problem: logistics systems want to know the sparing level for what's being supported, not what's being designed. This, incredibly, isn't addressed so far as I can see; adopters are just sort of pretending that bleeding edge is the same as the as-built, supported configuration. When I bring it up, the general response is that LSA can be batch-create from the design, totally ignoring the fact that a lot of changes come the other way, from field modifications. The solution for this - for NGAD and Raider - is to just not do logistics as it's been practiced for the last forty years. Spoiler: this is the correct answer. 30 year sustainment programs are hilarious fictions that do nothing but generate high margin work for primes.

exmadscientist 3y ago
"DIGITAL TWIN!!" would be a lot less of a punchline if I understood the prototype on my desk well enough to predict its behavior. And I can look straight at that one. The idea that we can understand real hardware in unusual conditions well enough to make a simulation/Digital Twin the One True Reference is simply hilarious. Though as you point out, it sure does generate a lot of high margin work and great ad copy.
- MilStdJunkie 3y ago
  I'll concede that when you write off maintainability down to the nuts-and-bolts-level, that does make things a whole lot easier. But I don't think that's digital twin; that's just tighter tolerance, and aaalllll the things that ride along with that. But doing something like scheduled maintenance just from the Twin?! Ehhhhhh sheesh, I dunno. I'm not one of the smart guys, but you would need to combine the solid-model FM sort of simulation with the more fluxy CFD models, and then have them interact. I realize computers are super powerful these days, but that is a HELL of a lot to ask from a simulation running on commodity equipment with commodity software. I've seen single-assembly CFD choke when it had to extend to just a single fuel system's materials data - and that was nothing compared to doing that for an entire airframe. Or even a reasonable chunk of an airframe. I'm at peace leaving this stuff to the guys who know what they're doing, but I don't see a lot of those people actually doing the decision making. It's finbros all the way down. I'm afraid what I'll be ending up with, at the end of the day, is the Reification Fallacy made flesh: a box of parts that's supposedly a flyable airframe. "Just write a preflight checklist for it!" they might say. "Copy and paste something or whatever." Why knows, they're RIFing more or less everyone with technical knowledge this week, so it probably won't be my problem for long.

adolph 3y ago

The Springer link is to the original TAGSAM paper--very interesting. I found it while doing a screw count of the below sampler head--there are 21 phillips-like head and 6 with allen head. The NASA press release [1] says "two of the 35 fasteners on the TAGSAM head could not be removed with the current tools approved for use." That doesn't match, which lead me to the Bierhaus et al. at Springer [2] which shows how they put the sampler head screws down into the dirt. The diagrams from Bierhaus and Walsh et al. [3] are both interesting. 0. https://www.nasa.gov/wp-content/uploads/2023/10/nelson-tagsam-shot-b.jpg https://www.nasa.gov/wp-content/uploads/2023/10/nelson-tagsa... 1. https://blogs.nasa.gov/osiris-rex/2023/10/20/nasas-osiris-rex-achieves-sample-mass-milestone/ https://blogs.nasa.gov/osiris-rex/2023/10/20/nasas-osiris-re... 2. https://link.springer.com/article/10.1007/s11214-018-0521-6 https://link.springer.com/article/10.1007/s11214-018-0521-6 3. https://link.springer.com/article/10.1007/s11214-022-00887-2 https://link.springer.com/article/10.1007/s11214-022-00887-2

johnwalkr 3y ago

Generally in aluminum parts in aerospace, locking stainless steel threads inserts (“helicoils”) are added for pullout strength, repairability, reducing risk of damage when fastening multiple times and to meet the requirement (which almost always exists) for secondary back-off prevention (primary is usually controlled preload). The locking feature is 1-2 threads in the insert that are deformed to provide a decent amount of friction even if preload is lost. But for a special case like this it’s possible a unique design was used; I would be interested to read about it. From the images, it’s not clear which fasteners are removed but if the issue is not access it could be a stuck fastener for whatever reason and maybe a rounded head. I wouldn’t be surprised if nothing is damaged but the procedure was stopped due to higher than expected torque, and they are taking it slow to decide how to proceed.

cuSetanta 3y ago
I hadbt consudered a stuck locking helicoil in fairness. And seeing the pictures of the fasteners it does seem unlikely to be an access issue, so you are probably right about the torque.
HeyLaughingBoy 3y ago
> procedure was stopped due to higher than expected torque I should have done this. Just broke a brand new 10-32 tap!