NASA learnt to give the Space Shuttle a hull inspection before it docked to the ISS. Will the Commercial Crew vehicles be required to undergo a similar inspection?We may be able to patch a hole at the ISS. We can certainly launch a replacement vehicle.
Good choice! Interesting article on an important topic - I didn't realize MMOD was such a large factor in the estimated risk.Is it possible to add captions or tooltips to the images? I don't always know what I'm looking at or the context to the article. Is the mouse-cursor-hand in image #6 (STS EVA) pointing out anything? Looks inadvertent, but I'm not sure.
Even Shuttle didn't receive a fatal strike to its enormous heat shield from MMOD.
Does anyone think they may move up the time frame for the commercial crews due to recent events with the Russian failures?
... the Shuttle showed that even though it had fatal flaws, like no realistic way to survive an inflight failure ...
Quote from: Coastal Ron on 05/31/2015 10:10 PM... the Shuttle showed that even though it had fatal flaws, like no realistic way to survive an inflight failure ... Only a catastrophic failure of an SRB during the first two minutes of flight presented this hazard. Everything else to my knowledge had an abort mode or modes to provide a means of crew survival. One orbiter actually did an abort-to-orbit when it lost an SSME.But yes, those first two minutes were hard to watch, every time. And let's not forget that CST-100 will also be lifted by two powerful solid motors during the first 90 seconds of flight, which have some of the same failure modes present in SRBs. - Ed Kyle
Quote from: A_M_Swallow on 05/31/2015 03:14 AMNASA learnt to give the Space Shuttle a hull inspection before it docked to the ISS. Will the Commercial Crew vehicles be required to undergo a similar inspection?We may be able to patch a hole at the ISS. We can certainly launch a replacement vehicle.Commercial Crew TPS isn't exposed during launch like STS was. Shuttle vs. capsule.
...And let's not forget that CST-100 will also be lifted by two powerful solid motors during the first 90 seconds of flight, which have some of the same failure modes present in SRBs.
Quote from: Coastal Ron on 05/31/2015 10:10 PM... the Shuttle showed that even though it had fatal flaws, like no realistic way to survive an inflight failure ... Only a catastrophic failure of an SRB during the first two minutes of flight presented this hazard. Everything else to my knowledge had an abort mode or modes to provide a means of crew survival. One orbiter actually did an abort-to-orbit when it lost an SSME.
Quote from: edkyle99 on 05/31/2015 11:39 PMQuote from: Coastal Ron on 05/31/2015 10:10 PM... the Shuttle showed that even though it had fatal flaws, like no realistic way to survive an inflight failure ... Only a catastrophic failure of an SRB during the first two minutes of flight presented this hazard. Everything else to my knowledge had an abort mode or modes to provide a means of crew survival. One orbiter actually did an abort-to-orbit when it lost an SSME.Well, some of those abort modes had asterisks to footnotes with something like "* requires a metric ton of good luck and some acts of god". Also before Challenger any abort mode that did not land on a runway was... umm... unlikely to result in a happy ending. Those scenarios did get better once pressure suits and bailout procedures were added.
Quote from: edkyle99 on 05/31/2015 11:39 PM...And let's not forget that CST-100 will also be lifted by two powerful solid motors during the first 90 seconds of flight, which have some of the same failure modes present in SRBs.My assumption is that no transportation system will be perfect, and certainly the far more mature mass transit systems we have today are not perfect either.Which is why I suggested that each new system should be compared to the last, not some made up number. And if they are more safe then that's good. CST-100 on Atlas V sure looks more inherently safe than the Shuttle.
So what I would propose is a system that simply determines if a new system is potentially more safe than the previous system, and then make sure to quantify what the dangers still are (both known and and potential) such as MMOD.For instance, what if the crew is in the vehicle on the launch pad and something goes wrong, is there a system that can get them to safety? ... And going forward as more transportation systems get added the free market forces will guide what levels of safety are acceptable.
NASA learnt to give the Space Shuttle a hull inspection before it docked to the ISS. Will the Commercial Crew vehicles be required to undergo a similar inspection?
To me, the obvious first step is to have at least one level of failure tolerance allowing ATES (Abort to Earth Surface) for all critical systems where this is practical. For example, there has yet to be a spacecraft designed with a redundant re-entry TPS. However, some kind of lamination of view-ports to increase their resistance to MMOD and redundant flight controls are an obvious step.Both the CCP finalists are heavily-automated with touch-screen controls. I was glad to see that SpaceX had installed alternate physical controls (including, hopefully, at least one redundant control data path) in Dragon v.2. This is the sort of thinking that shows the contractors are taking potential faults and maximising crew survivability seriously.
Quote from: Hog on 05/31/2015 06:11 AMQuote from: A_M_Swallow on 05/31/2015 03:14 AMNASA learnt to give the Space Shuttle a hull inspection before it docked to the ISS. Will the Commercial Crew vehicles be required to undergo a similar inspection?We may be able to patch a hole at the ISS. We can certainly launch a replacement vehicle.Commercial Crew TPS isn't exposed during launch like STS was. Shuttle vs. capsule.Good.The primary TPS across the underneath of the capsules is covered but the side walls, top and windows are exposed permitting MMOD.
[..]And let's not forget that CST-100 will also be lifted by two powerful solid motors during the first 90 seconds of flight, which have some of the same failure modes present in SRBs.
The MMOD thing for CC is very odd. Surely this must be an overly conservative estimate or ISS, Mir, Skylab, or the various Salyuts would've no doubt been punctured in their pressurized sections by now (considering they've been nearly permanently in orbit since the early 1970s). Even Shuttle didn't receive a fatal strike to its enormous heat shield from MMOD.
Quote from: spacenut on 05/31/2015 01:43 PMDoes anyone think they may move up the time frame for the commercial crews due to recent events with the Russian failures? Very desirable but won't happen. While 2 companies is great for redundancy it slows things down (spreads the money out and ties up the NASA resources), the money does not appear to be coming as needed for this (and as predicted), the companies are scrambling as hard as they can and they will be very hard pressed to make 2017 as it is. Not going to be able to reduce the time unless a LOT more $$$$ comes now.
Discovery suffered a MMOD strike on STS-128 which would have led to Loss of Mission (land within 24 hours) if not for modifications and hardening in the late 1990s:http://research.jsc.nasa.gov/BiennialResearchReport/2011/265-2011-Biennial.pdf
After STS-50, new flight rules were implemented that required the shuttle to fly with the payload bay to the Earth and the tail toward the velocity vector "unless payload or orbiter requirements dictate otherwise."
Well, Senate Launch System can still be a fine (if expensive) heavy lift vehicle. Just ditch the LAS (more room for cargo!) and deliver the crew to on-orbit Orion using a safe and cheap commercial crew vehicle.Doubt it will happen, but...
The discussion about safety has me wondering. Will commercial crew have some kind of flip maneuver or other visual inspection to see if the heatshield of the capsule is fit for reentry (i.e. that there hasn't been any micrometeorite damage to its heatshield during its stay at the ISS)?
Quote from: yg1968 on 09/10/2015 02:10 PMThe discussion about safety has me wondering. Will commercial crew have some kind of flip maneuver or other visual inspection to see if the heatshield of the capsule is fit for reentry (i.e. that there hasn't been any micrometeorite damage to its heatshield during its stay at the ISS)?The heat shields won't be visible, they're protected by the trunk/ SM so MMOD damage/ damage on ascent isn't a concern like it was for the orbiters who had an exposed TPS
Quote from: Robotbeat on 05/31/2015 01:33 PMThe MMOD thing for CC is very odd. Surely this must be an overly conservative estimate or ISS, Mir, Skylab, or the various Salyuts would've no doubt been punctured in their pressurized sections by now (considering they've been nearly permanently in orbit since the early 1970s). Even Shuttle didn't receive a fatal strike to its enormous heat shield from MMOD.models have been updated based on more data and a lot, LOT more debris. Recall ISS is now flying lower to mitigate risk of MMOD. Yes, the capsule heat shields are protected but they are going to be up there for 6 months with their butts into the debris wind so to speak for Node 2 forward. A lot can happen.
At the risk of going off topic, the ISS originally orbited around 390 km, dropped back as low as ~330 km, and then went up to ~440 km when the Shuttle retired. It has now sunk to just over 400 km. Is it trying to keep a constant drag/density to balance the MMOD risk with reboost fuel usage?
CST-100 looks OK with the SM protecting until reentry. Dragon could have cameras in the trunk to perform checks. Or a shield if no unpressurized cargo.
I will also note that the Russians, and before as the Soviets, have been keeping Soyuz on-station in LEO for up to six months at a time for, well, more than 30 years, going back to Salyut 6. They haven't lost any of them, not one of the dozens upon dozens, to TPS damage. And they have nothing more or less than Starliner or Dragon will have, a module covering the main TPS.None have ever been holed by MMOD to the extent they lost pressure or critical systems, either.
Shuttle was different because its TPS was always fully exposed to MMOD, and it had a far more fragile TPS than Dragon or Starliner will. The Shuttle-style TPS inspections will not be needful for the new commercial crew vehicles.
Quote from: the_other_Doug on 09/20/2015 03:31 AMI will also note that the Russians, and before as the Soviets, have been keeping Soyuz on-station in LEO for up to six months at a time for, well, more than 30 years, going back to Salyut 6. They haven't lost any of them, not one of the dozens upon dozens, to TPS damage. And they have nothing more or less than Starliner or Dragon will have, a module covering the main TPS.None have ever been holed by MMOD to the extent they lost pressure or critical systems, either.My thougts as well. It is a concern of NASA but I don't understand where that concern comes from.
If I remember correctly the TPS inspections were introduced because of possible damage on start, not because of possible MMOD. It would cover MMOD as well though. While the SpaceShuttle heat shield would be exposed for a much shorter time it is much shorter and probably more sensitive.