Quote from: A_M_Swallow on 08/30/2016 12:53 amQuote from: SWGlassPit on 08/29/2016 06:32 pmIf that even works (signal-to-noise ratio issues abound here), what would that accomplish? You look at it and go, "yep, that's a strike." Then what?If pieced into the main room duck tape a patch across the hole to stop the air escaping. Pipes can be sealed with a plaster. Broken windows can be covered.Damage to outside parts of the spacecraft may have to be repaired by a robot or EVA. Such a repair was performed to the ISS solar panels on January 30, 2007. There may be a way to glue or weld heat shield material across a hole the size of Columbia's.More likely IMO send a replacement vehicle up and use the damaged one only in the very unlikely case of a ISS evacuation. BTW if the pressure hull is compromised it is not only quite easy to fix but will inevitably be detected.
Quote from: SWGlassPit on 08/29/2016 06:32 pmIf that even works (signal-to-noise ratio issues abound here), what would that accomplish? You look at it and go, "yep, that's a strike." Then what?If pieced into the main room duck tape a patch across the hole to stop the air escaping. Pipes can be sealed with a plaster. Broken windows can be covered.Damage to outside parts of the spacecraft may have to be repaired by a robot or EVA. Such a repair was performed to the ISS solar panels on January 30, 2007. There may be a way to glue or weld heat shield material across a hole the size of Columbia's.
If that even works (signal-to-noise ratio issues abound here), what would that accomplish? You look at it and go, "yep, that's a strike." Then what?
Nothing is "quite easy to fix" in space. If the pressure shell is compromised that means there exists a hole in the back shell that would also need to be fixed. And these fixes would have to withstand reentry.
Quote from: srtreadgold on 08/30/2016 09:23 amNothing is "quite easy to fix" in space. If the pressure shell is compromised that means there exists a hole in the back shell that would also need to be fixed. And these fixes would have to withstand reentry. How do you get this idea? The backshell is very well protected by the trunk and protective coating. Anything penetrating the pressure hull will come from the side. A patch is easily applied from the inside.
The back shell is the side. You're thinking of the heat shield, which is mostly protected by the service module. The back shell also protects the vehicle from reentry gasses/temperatures.
Quote from: A_M_Swallow on 08/30/2016 12:53 amQuote from: SWGlassPit on 08/29/2016 06:32 pmIf that even works (signal-to-noise ratio issues abound here), what would that accomplish? You look at it and go, "yep, that's a strike." Then what?If pieced into the main room duck tape a patch across the hole to stop the air escaping. Pipes can be sealed with a plaster. Broken windows can be covered.Damage to outside parts of the spacecraft may have to be repaired by a robot or EVA. Such a repair was performed to the ISS solar panels on January 30, 2007. There may be a way to glue or weld heat shield material across a hole the size of Columbia's.Duct tape / plaster is not exactly what you want keeping reentry gasses/temperatures from breaching your delicate spacecraft.
A couple of thoughts--Using accelerometers to detect impacts might work above some threshold. But how to remove the non-impact twitches? (E.g., collant flowing, astronauts shifting in seats, etc.). You can't have the master alarm going off every 10 seconds.-Triangulating sounds would probably be a nasty business of modeling, because the microphones are (presumably) attached to metal, and the sound waves would be propagating through the metal structures of the spacecraft. You'd need to have some sort of acoustical model (edit: which could well be very different than the one used to analyze launch noise) and pinpointing a hit for detailed inspection might not be possible. I could easily imagine saying, "Oh, we took a hit on the aft," but saying, "It's at PICA chunk 387" or whatever sounds like too much to ask.-There was a good point made above, that just because the analysis says MMOD is the risk driving the LOCV stats doesn't mean it's that much worse than any number of others. If MMOD is 1/1500, say, there may be a whole bunch at 1/1510. We will almost surely not be told thedetailed numbers for proprietary reasons. I doubt Contractor A wants Contractor B to know their numbers and be able to snipe at them in reports and future proposals.-The two losses with which I'm most familiar, the shuttles, were from what I think of as known-knowns that turned out to be what I might describe as unknown-knowns (to coin a Rumsfeldian variant). That is, both failure modes were recognized, but inaccurately characterized to the extent that they were judged as low risks, even though that did not turn out to be the case. It seems to me that mischaracterized risk is different than a known-unknown. Does that make sense?
Distinguishing a MMOD from normal station sounds is the easiest thing ever. It will have a very short sharp attack to identify. A very simple filter will do that. Even a hammer blow will be much slower.They have devised materials to repair the Shuttle heat shield to some extent. Finding materials to mend a small hull breach will be many orders of magnitude easier. We are not talking about large ones as they will be exceedingly rare.Others have already commented on triangulation. That may be somewhat tricky but once an impact is identified as MMOD it is worth the effort.
Emphasis mine.One word: accessibility
Quote from: jgoldader on 08/30/2016 11:11 am-Triangulating sounds would probably be a nasty business of modeling, because the microphones are (presumably) attached to metal, and the sound waves would be propagating through the metal structures of the spacecraft. You'd need to have some sort of acoustical model (edit: which could well be very different than the one used to analyze launch noise) and pinpointing a hit for detailed inspection might not be possible. I could easily imagine saying, "Oh, we took a hit on the aft," but saying, "It's at PICA chunk 387" or whatever sounds like too much to ask.Triangulation.The speed of sound in aluminium is 6320 m/s.Triangulation can work by differences in volume and the delay between sensors hearing the bang. To detect down to 1 cm 0.01 m (0.39 inches) the surface would have to be sampled 2*6320/0.01 = 1,264,000 times a second.There are many off the shelf analoge-to-digital chips that will sample 8 bits a million times a second; for instance the Texas Instruments ADS7040, temperature range –40°C to 125°C, which costs less than a dollar.To detect MMOD an accuracy of 5 cm may be sufficient. Aluminium is also a (near) worst case problem since it is a very good conductor of sound. At about 355 m/s air is an order of magnitude slower.A practical system would have to handle several different types of material and filter out false alarms such as astronauts bouncing off the walls. I suspect that liquids going though pipes sounds different from the bang of something hitting the outside of a capsule.
-Triangulating sounds would probably be a nasty business of modeling, because the microphones are (presumably) attached to metal, and the sound waves would be propagating through the metal structures of the spacecraft. You'd need to have some sort of acoustical model (edit: which could well be very different than the one used to analyze launch noise) and pinpointing a hit for detailed inspection might not be possible. I could easily imagine saying, "Oh, we took a hit on the aft," but saying, "It's at PICA chunk 387" or whatever sounds like too much to ask.
Others have already commented on triangulation. That may be somewhat tricky but once an impact is identified as MMOD it is worth the effort.
And you need a system that can handle that in near-real-time.
Quote from: A_M_Swallow on 08/31/2016 04:46 amQuote from: jgoldader on 08/30/2016 11:11 am-Triangulating sounds would probably be a nasty business of modeling, because the microphones are (presumably) attached to metal, and the sound waves would be propagating through the metal structures of the spacecraft. You'd need to have some sort of acoustical model (edit: which could well be very different than the one used to analyze launch noise) and pinpointing a hit for detailed inspection might not be possible. I could easily imagine saying, "Oh, we took a hit on the aft," but saying, "It's at PICA chunk 387" or whatever sounds like too much to ask.Triangulation.The speed of sound in aluminium is 6320 m/s.Triangulation can work by differences in volume and the delay between sensors hearing the bang. To detect down to 1 cm 0.01 m (0.39 inches) the surface would have to be sampled 2*6320/0.01 = 1,264,000 times a second.There are many off the shelf analoge-to-digital chips that will sample 8 bits a million times a second; for instance the Texas Instruments ADS7040, temperature range –40°C to 125°C, which costs less than a dollar.To detect MMOD an accuracy of 5 cm may be sufficient. Aluminium is also a (near) worst case problem since it is a very good conductor of sound. At about 355 m/s air is an order of magnitude slower.A practical system would have to handle several different types of material and filter out false alarms such as astronauts bouncing off the walls. I suspect that liquids going though pipes sounds different from the bang of something hitting the outside of a capsule.I understand triangulation. But you'd probably end up with diffraction effects, reflections, etc., and the speed of sound depends on the tension in the metal, and... And you need a system that can handle that in near-real-time. Hence the spirit of my comment.
Quote from: woods170 on 08/31/2016 08:53 amEmphasis mine.One word: accessibilityA hull breach would be mended from the inside.
Major damage is rare. You don't even have to mend them. Just keep the door closed and take a different vehicle down. The issue you're trying to address here is otherwise-undetected significant damage leading to loss-of-crew.We're worried about LOC. LOM is more acceptable (provided it's still rare).
Keeping the door (hatch) closed is a mitigation for PNP (where damage to the visiting vehicle creates a hazard to ISS), not LOC/LOM.