...If you read the ASAP report that drove this article, the total mention of MMOD amounts to less than a paragraph. This thread is getting wrapped around the axle on assumptions and incomplete/outdated information. That something is the "primary" threat does not mean the threat is "large." It just means that other identified and controlled threats are "smaller".
I have to agree with Robotbeat.This is just another example of NASA's long history of failing to adequately weight the "unknown unknowns" when doing risk assessment. The risk of some other failure mode being far more likely than expected in new vehicles dwarfs the risk of MMOD. For NASA to claim otherwise just makes them look foolish.
If damage detection doesn't work one could enclose the vehicles in some shielding after docking.
So how far off are Dragon and CST-100 from the requested 1 in 270 number?
Mr. Justin Kerr provided a briefing on MMOD and reviewed the current situation. The Agency has a requirement to achieve a Loss of Crew (LOC) risk of no worse than 1 in 270(1:270) for MMOD. To encourage risk mitigation, the Program has been looking at different ways to approach that. MMOD is the number one contributor to LOC risk and the primary means by which to close the gap between where the Program is and where it wants to be. The strategy that is being taken is to back off to 1:200 for the spacecraft themselves, but to require that the design and vehicle capability be the sole means to achieve that level. Any potential inspections or operational workarounds will be put aside and left for later consideration. That strategy appears to be working well. Both companies are now looking at potential changes to their vehicles to address the MMOD risks.
Regarding the MMOD issue, a decision was made to reallocate the protection for MMOD, which required the providers to focus on the vehicle. Currently, this means that operational procedures must make up the difference. The good news is that the Program has identified operational changes that can do that, but those changes are not “free.” NASA has estimated that those changes will cost the equivalent of $10 million per year until the end of ISS. That begs the question: Can we use other techniques to incentivize the contractors to go beyond the 1:200 requirement? The Program is hoping that the contractors would do that. Mr. Frost opined that he would look very carefully at trying to buy some more protection from the equipment.
At least impact events should be easily detectable through vibration sensors. Remember how much data they got from that second stage disintegration? Enough to pinpoint the source of the failure. Any detected impact with some level of energy can then trigger a closer inspection.
Quote from: guckyfan on 08/28/2016 05:40 amAt least impact events should be easily detectable through vibration sensors. Remember how much data they got from that second stage disintegration? Enough to pinpoint the source of the failure. Any detected impact with some level of energy can then trigger a closer inspection.No spacecraft to date uses this.
Dragon already contains strain gauges. Getting shot by a bullet should be detectable without 500lbs of wiring.
Quote from: SWGlassPit on 08/29/2016 02:20 pmNo spacecraft to date uses this. And we all know that SpaceX never deviates from what all others have done before them, right?Edit: sorry but I really, really dislike the argument it has never been done.
No spacecraft to date uses this.
Remember that it was said an inspection of the spacecraft for departure would reach the value of 1/270. It would mean they don't depart with that vehicle but wait for a replacement. In the unlikely event of a Space Station evacuation they could very likely still use that vehicle, just with reduced safety and redundancy.A few sensors could reduce that inspection to cases where the spacecraft has actually been hit, not just as a mandatory precaution. The inspection could be performed to find out potential damage at the time of the incident. No need to wait for the planned departure time. So a replacement vehicle could be sent early.
Are you aware that you are talking about the people who actually wrote the book on handling risk in scenarios of uncertainty?
Quote from: SWGlassPit on 08/29/2016 02:20 pmQuote from: guckyfan on 08/28/2016 05:40 amAt least impact events should be easily detectable through vibration sensors. Remember how much data they got from that second stage disintegration? Enough to pinpoint the source of the failure. Any detected impact with some level of energy can then trigger a closer inspection.No spacecraft to date uses this.Oh? What about http://research.jsc.nasa.gov/BiennialResearchReport/2009/RASS-4.pdf ?
Quote from: Robotbeat on 08/29/2016 03:28 pmDragon already contains strain gauges. Getting shot by a bullet should be detectable without 500lbs of wiring.Sure, if you hit really close to a strain gauge and do a lot of damage. Otherwise, they're useless for this....
Quote from: SWGlassPit on 08/29/2016 04:11 pmQuote from: Robotbeat on 08/29/2016 03:28 pmDragon already contains strain gauges. Getting shot by a bullet should be detectable without 500lbs of wiring.Sure, if you hit really close to a strain gauge and do a lot of damage. Otherwise, they're useless for this....If a huge MMOD hit Dragon, enough to fatally damage it, it would ring like a bell, like getting shot be a gun. You would hear it, and sound waves can be (and are) picked up by strain gauges. It may not be precise, but knowing that it happened would be useful info.
Did you read the minutes? NASA wants the requirement to be met without requiring inspection.