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Shuttle Safety [was: Re...
On 24 Jun 2006 10:34:58 -0700, "columbiaaccidentinvestigation"
wrote: The probabilistic risk assessment for a foam shedding event causing a crit1 failure happening in future flights is not quantifiable, simply because the base sample for analysis has been ever changing, without revisions reflecting those changes. The data set for analyzing the dynamic loading events during the shuttles ascent is over 100, but the actual missions that are similar is very few, and therefore a true reliable base may not be achievable. [Much more of the same. Much, much more...] Translation: The shuttle program has maybe twenty billion dollars to spend before it gets cancelled five or six years from now. We want you to give us all that money, but instead of, you know, actually flying any space shuttles like we did in the last twenty-five years of shuttle ops, we're just going to prepare you a really bitchin' powerpoint presentation explaining just how dangerous it would have been to fly the space shuttle in 2006-2012 but how safe it would be to fly the space shuttle in the future, if you give us another twenty billion dollars. Either you know how to fly space shuttles with reasonable safety, or you don't. If you don't, you all can clean out your desks and start looking for jobs you do know how to do. -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * |
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Shuttle Safety [was: Re...
"columbiaaccidentinvestigation"'s argument seems to be that any changes
to the shuttle, even ones made with the objective of making it safer, put it into a flight regime that has not been tested. The only way to address this concern is to never change anything ever. Is this the way to do anything new in space? The point of the launch decision is that even in the case of foam shedding from the tank impacting the thermal protection system, the effect will be on re-entry-- the launch itself is safe up through the time the shuttle gets to orbit. As noted, if there is a foam impact event, the astronauts transfer to the space station, and shuttle is inspected on orbit to determine the nature and extent of damage. It's then either reparied, or the astronauts are returned by a different mission. Uncerrtainty about the foam is a question about a possible loss of the vehicle, and not loss of astronauts. Since "columbiaaccidentinvestigation" is arguing that any changes whatsoever put the shuttle into a regime where the only way to validate the change is by flying ("columbiaaccidentinvestigation" claims not to trust wind tunnel results), this seems the only sensible thing to do. -- Franklin Jefferson ***My blog: Jefferson's Democracy*** http://franklinjefferson.blogspot.com |
#3
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Shuttle Safety [was: Re...
The probabilistic risk assessment for a foam shedding event causing a
crit1 failure happening in future flights is not quantifiable, simply because the base sample for analysis has been ever changing, without revisions reflecting those changes. The data set for analyzing the dynamic loading events during the shuttles ascent is over 100, but the actual missions that are similar is very few, and therefore a true reliable base may not be achievable. ISS support missions such as sts-121 are much different from the early missions of the program standard weight tank SWT, and light weight tanks LWT, and therefore many of the previous missions even sts-107's ET#93 (LWT) must be eliminated from a data set. The original external tank design or standard weight et was modified primarily for weight reduction, with the light weight tanks starting flights on sts-6. But this weight reduction was achieved mainly by a reduction on the safety factors, from 1.4 to 1.25 for well defined loads based on flight data (thrust loads, internal pressure and inertia loads), and kept at 1.4 for all aerodynamic and dynamic loads. This means a 0.15 reduction for some of the orbiter stacks elements meant the sts-1 safety recommendations were converted from reduction in payloads, to a reduction of safety margins. The implementation of the performance enhancements (angle of attack, early q throttle up, 1st and 2nd stage gimbal change) for iss support has increased loading on the orbiter stack, and previous risk analysis must be updated to reflect the increased risks associated with such loading increases. Updating a quantitative risk assessment with flight data, in conjunction with the increased loading on the orbiter stack caused by performance enhancements may give a clearer picture as to the cause of foam shedding events, and the risk associated with sts-121. STS-51L Challenger The push by nasa to make the shuttle stack lift more payload weight was implemented with sts-8, by modifying the solid rocket boosters. A srb thrust modification was implemented to increase payload lift capability resulting from a stronger solid fuel propellant coupled with a lighter rocket casing. The rogers commission concluded the information demonstrating a pattern of "O ring" burn through was available, but this information was not correlated, and then eventually disregarded by nasa officials in launching sts-51L. STS-61a, sts-61b and specifically sts-61c the programs 24th flight srb post flight inspection completed on January 12, demonstrated a pattern of obvious problems with srb casing burn through and "o ring" failures (NSTS-22301). STS-61C flight landed January 18, 1986, just 10 days prior to the last flight of challenger, and the death of the sts-51L crew. The two records set that ill fated launch day of Jan 28, 1986, still stand today, the commonly known coldest launch temp of 36 f deg, and the lesser known fact that sts-51l utilized a lightweight srb casing and still was the heaviest shuttle stack to launch at 4,529,681 lbs. The rogers commission concluded the lightweight SRB casings aggravated the "joint rotation", a spacing in the O ring seal area that would allow the hot gases a path to the rocket casing if filler putty had suffered blow through, a common problem. The O ring failure occurred after nasa managers clearly disregarded the Morton Thiokol engineer Roger Boijoly's recommendation to not launch, demonstrating humans erred in the decision making process a failure mode not demonstrated in the stated risk analysis. But another the fact is the lightweight srb casings utilized for challengers ascent jan 28, 1986 launching the heaviest shuttle stack ever used in flight history were concluded to being "aggravating" to the O ring failure which resulted in the death of the sts-51L crew (Rogers commission report chapter VII Casing Joint Design) STS-107 was the 5th heaviest shuttle stack to launch in flight history at 4,526,034 lbs (Caib report vol V page 105). STS-121 will be the 7th heaviest orbiter stack in the programs lifetime at 4,523,850 lbs (sts-121 press kit). But Given the fact STS-121's SLWT #119 has had the (-Y) protuberance air load ramp removed, and this ramps original purpose was to redirect undesirable aerodynamic flow, and where flow problems can cause greater loading, the removal of the ramp may cause more greater loading on the orbiter/ET interface than previous missions, therefore this mission may be at a greater risk for failure than other missions. But even after concluding sts-121 is performing a test flight to assess the risk associated what the caib determined was the cause for the death of the sts-107 crew and loss of Columbia, nasa is still performing an operational mission in iss support. Objectively performing the flight test with sts-121 to determine true risk associated with a foam loss, with the 7th heaviest launch in program history, could be seen as pushing the envelope the 2nd flight after a death of crew and loss of vehicle. A true objective test would not have a necessity to perform an operational task such as iss support, where weight and launch window are driving the test parameters, and therefore biasing the test data in a risk analysis. Establishing a mission is safe based on the fact the total remaining missions in the programs lifetime is less than the projected failure rate is not based on sound principles, as the mission failure can occur in bin #1 or bin#100 and therefore does not provide a clear picture of the true risk to the sts-121 crew or discovery. The sts-51l, and sts-107 tragedies both demonstrate areas were safety was compromised for performance, increasing the risk of death of crew and loss of vehicle to occur at a higher frequency than risk analysis predicted. Understanding what safety compromises in the space shuttle program have been made to bring back preprogram expectations, demonstrates the probability of failures increased due to human subjectivity pushing the system, instead of objectively working with the systems limitation for better or worse. Ethical engineering, science, maintenance practices/standards in designing and operating space vehicles and their programs should not allow for acceptance of astronaut deaths, or should anyone provide an illogical, circular excuse such as "it's a dangerous profession" when tragedies happen. Every life is precious, and risks associated with the loss of life whether it is your own or somebody else's should not be trivialized. As we are all members of the "space interested community" it is important for all of us to understand why the previous tragedies happened, because we cannot allow them to be repeated. Tom Tom wrote: "columbiaaccidentinvestigation"'s argument seems to be that any changes to the shuttle, even ones made with the objective of making it safer, put it into a flight regime that has not been tested. The only way to address this concern is to never change anything ever. Is this the way to do anything new in space? The point of the launch decision is that even in the case of foam shedding from the tank impacting the thermal protection system, the effect will be on re-entry-- the launch itself is safe up through the time the shuttle gets to orbit. As noted, if there is a foam impact event, the astronauts transfer to the space station, and shuttle is inspected on orbit to determine the nature and extent of damage. It's then either reparied, or the astronauts are returned by a different mission. Uncerrtainty about the foam is a question about a possible loss of the vehicle, and not loss of astronauts. Since "columbiaaccidentinvestigation" is arguing that any changes whatsoever put the shuttle into a regime where the only way to validate the change is by flying ("columbiaaccidentinvestigation" claims not to trust wind tunnel results), this seems the only sensible thing to do. -- Franklin Jefferson ***My blog: Jefferson's Democracy*** http://franklinjefferson.blogspot.com |
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Shuttle Safety [was: Re...
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#5
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Shuttle Safety [was: Re...
On 24 Jun 2006 11:54:44 -0700, in a place far, far away,
" made the phosphor on my monitor glow in such a way as to indicate that: wrote: The point of the launch decision is that even in the case of foam shedding from the tank impacting the thermal protection system, the effect will be on re-entry-- the launch itself is safe up through the time the shuttle gets to orbit. Assuming it gets to orbit. The odds of a major foam strike followed by two SSMEs shutting down are not high, but they're not insignficant either. They are, actually. That's a joint probability that's very low. |
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Shuttle Safety [was: Re...
Rand Simberg wrote: On 24 Jun 2006 11:54:44 -0700, in a place far, far away, " made the phosphor on my monitor glow in such a way as to indicate that: wrote: The point of the launch decision is that even in the case of foam shedding from the tank impacting the thermal protection system, the effect will be on re-entry-- the launch itself is safe up through the time the shuttle gets to orbit. Assuming it gets to orbit. The odds of a major foam strike followed by two SSMEs shutting down are not high, but they're not insignficant either. They are, actually. That's a joint probability that's very low. |
#7
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Shuttle Safety [was: Re...
Problems with shuttle risk assessment
The death of 2 crews and the loss of two vehicles clearly demonstrate a revision to the current orbiter criticality ratings and consequent failure probabilities are not accurate, therefore quoting and haphazardly stating failure rates or scenarios for the shuttle system is not realistic. Understanding what risk associated with modifications to the space shuttle/orbiter stack, and specifically with the upcoming sts-121 mission requires an objective assessment of the space shuttle programs history. The original safety and criticality ratings for the shuttle resulted from the failure mode and effects analysis (fmea), a method used for the expandable vehicles in the space progam, but the shuttle is a reusable vehicle and therefore required expanding the database for element failures and criticality ratings based on flight experience. A study by Pate-Cornell in 2000, demonstrated the weaknesses with the fmea original critical item list for the orbiters, and the benefits of a qra in analyzing the orbiters true risks. There were a tremendous of unknowns associated with the failure modes for the shuttle/et/srb's, therefore ranking of the system elements in a critical items list (CIL) was based on historical and subjective analysis, as the The shuttle independent assessment team of 2000, refers to something known as "MEDA". MEDA is a philosophy of many things contributing to a failure ranging from maintenance to administration, therefore no one crit1 component needs to fail for loss of crew and vehicle, but instead a series of crit2 or less, such as managerial decisions can lead to a systems failure. The concept of were the failures initiating events have interdependencies, may not be clearly represented in the existing criticality ratings, but can be a causal event is exactly what happened to Columbia's launch on jan 16, 2003. True criticality ratings must be set and based from safety, reliability, maintainability, as well as chain event sequences involving less critical items, and contributions from human errors. Early in the program the space shuttle technical conference produced some safety assessments resulting in modifications and recommendations based on flight experiences. Post challenger flight safety assessment recommendations resulted in more modifications and changes to the program, only some of which were implemented by nasa, a pattern repeated throughout the programs history. After challenger as the shuttle program matured nasa failed to compile, and correlate the data associated with anomalies and subsequent corrective actions, in a comprehensive review effort to update the failure modes and effects of all shuttle systems and therefore current risk assessments do not reflect real failure probabilities. tom Rand Simberg wrote: On 24 Jun 2006 11:54:44 -0700, in a place far, far away, " made the phosphor on my monitor glow in such a way as to indicate that: wrote: The point of the launch decision is that even in the case of foam shedding from the tank impacting the thermal protection system, the effect will be on re-entry-- the launch itself is safe up through the time the shuttle gets to orbit. Assuming it gets to orbit. The odds of a major foam strike followed by two SSMEs shutting down are not high, but they're not insignficant either. They are, actually. That's a joint probability that's very low. |
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Shuttle Safety [was: Re...
A SENIOR NASA engineer and astronaut has been removed from his position
after writing a congratulatory email to engineers who voiced concerns over the safety of the next shuttle launch. source: http://www.smh.com.au/news/world/ema...174269564.html |
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Shuttle Safety [was: Re...
Ethical engineering, science, maintenance practices/standards in
designing and operating space vehicles and their programs should not allow for acceptance of astronaut deaths, or should anyone provide an illogical, circular excuse such as "it's a dangerous profession" or "Columbus would never have sailed with such an attitude". This circular logic DOES NOT make the 2nd flight after the death of the sts-107 crew, and loss of Columbia ANY safer but instead betrays the honesty/integrity that it takes to make the best and safest vehicles for those who are willing to risk their lives as explorers. Both vessel types the noa and caravel used by Columbus in his voyage across the Atlantic had already proven to be seaworthy or "safe" years before departing for the americas in 1492, and yes it would have been unethical and stupid to set out on such a voyage with first understanding the vessel was seaworthy. Participating in the space program, is not for the faint of heart, for it takes a culmination of intelligence, bravery, ethics, and professionalism to be in the business of space flight. This means having the qualities to be in the space program also requires the utilizing all of our gifts and skills to overcome our desires to-launch, and arrive to a conclusion we do not desire, to not-launch for safety concerns. Ensuring a program is safe or a launch is not safe, requires utilizing all of our human abilities to ensure the utmost safety for a shuttle crew is the highest priority, which means demanding NO other factors should be allowed to bias the decisions for a mission's launch or a programs priorities. tom George Evans wrote: in article , columbiaaccidentinvestigation at wrote on 6/24/06 10:34 AM: snip ...Ethical engineering, science, maintenance practices/standards in designing and operating space vehicles and their programs should not allow for acceptance of astronaut deaths, or should anyone provide an illogical, circular excuse such as "it's a dangerous profession" when tragedies happen. Every life is precious, and risks associated with the loss of life whether it is your own or somebody else's should not be trivialized. As we are all members of the "space interested community" it is important for all of us to understand why the previous tragedies happened, because we cannot allow them to be repeated. This section which is tack on to the end of the section is, pardon my bluntness, a bunch of BS put in to placate congress. Certainly every life is precious, which makes the price some are willing to pay, to advance the cause, awe inspiring. How arrogant for the author to try and place himself shoulder to shoulder with such brave men and women as members of the "space interested community?" There would be no space if these daring individuals were not willing to risk for us. Can you imagine such drivel coming from Colombus' mouth when one of his ships went down? We cannot "allow" these tragedies to be repeated? We can stand by quietly with heads bowed in appreciation, is what we can do. George Evans |
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