http://news.bbc.co.uk/1/hi/uk/5148758.stm
They lost some more foam, which was described as ..........."interesting".
Space shuttles up...............
Moderators: Guru's, The Ministry
-
andy
Space shuttles up...............
There's a video of the launch on the BBC news website....
http://news.bbc.co.uk/1/hi/uk/5148758.stm
They lost some more foam, which was described as ..........."interesting".
http://news.bbc.co.uk/1/hi/uk/5148758.stm
They lost some more foam, which was described as ..........."interesting".
-
DispatchDragon
- Battle of Britain
- Posts: 4925
- Joined: 23 Feb 2005, 01:18
- Location: On the corner of walk and dont walk somewhere on US1
- Contact:
-
Garry Russell
- The Ministry
- Posts: 27180
- Joined: 29 Jan 2005, 00:53
- Location: On the other side of the wall
-
Chris Trott
- Vintage Pair
- Posts: 2589
- Joined: 26 Jun 2004, 05:16
- Location: Wichita Falls, Texas, USA
- Contact:
Watched the replays on NASA TV (love having satellite). All I can say is that having watched the STS program with much interest for years is that the "foam" is probably not foam and if it is, it's too small to worry about anyway. The reason I say it's probably not foam is that the way it reflects makes me think it's more likely ice. They had a large chunk of ice come off during ET separation as well that caused some initial concern before NASA was able to analyze it and confirm it was ice and not part of Discovery.
One thing I've been wondering, maybe one of you engineering experts can put me right.
In the early days of the Shuttle program they used to paint the external tank; as this paint used to add something like 600 lb to the weight they stopped doing it to boost payload. Would this painting of the tank have prevented the foam from cracking?
AndyG
In the early days of the Shuttle program they used to paint the external tank; as this paint used to add something like 600 lb to the weight they stopped doing it to boost payload. Would this painting of the tank have prevented the foam from cracking?
AndyG
-
Chris Trott
- Vintage Pair
- Posts: 2589
- Joined: 26 Jun 2004, 05:16
- Location: Wichita Falls, Texas, USA
- Contact:
From my understanding, the paint was too thin to have any "adhesive" effect. Although, the chemistry of the applied paint would have been changed in the late 1980s/early 1990s when the foam application process was changed to be more "green". When this changeover occured, that is when they started loosing pieces of the ETs. That's right, it'd been happening for almost 10 years and nothing happened until Columbia. NASA had been trying to fix it, but because of their new EPA regulations, they couldn't use the foam that they wanted to. The foam that they were forced to use actually melts against the underlying skin of the ET once fuel is loaded and the whole mass begins to shift. Unless the Shuttle was launched immediately, there was a chance of large pieces leaving the ET on launch. This is what happened with Columbia, there were multiple delays and the Shuttle was left fueled for nearly a week. As a result, several large pieces were loosened and broke off in "dynamically critical" areas, meaning areas where there is a high dynamic pressure during the atmospheric phases of flight. The redesign has apparently made this risk minimal, but with all of the ice buildup from the rain hitting the supercooled tank, cracks formed and pieces broke off, although none were very large.
Basically, the solution to preventing ET foam separation is to fuel the shuttle and then launch within 24 hours. This happened most of the time, so the foam shed was very small in nature and thus posed no threat to the shuttle. The concern is when launch gets delayed for many days and possibly weeks (as has occured before). The only way to prevent that would be to defuel the ET whenever there will be a delay, but it's a dangerous and time consuming process, so they'd rather not do that unless they were going to take the Shuttle off the pad and back to the VAB.
Basically, the solution to preventing ET foam separation is to fuel the shuttle and then launch within 24 hours. This happened most of the time, so the foam shed was very small in nature and thus posed no threat to the shuttle. The concern is when launch gets delayed for many days and possibly weeks (as has occured before). The only way to prevent that would be to defuel the ET whenever there will be a delay, but it's a dangerous and time consuming process, so they'd rather not do that unless they were going to take the Shuttle off the pad and back to the VAB.
This sounds typical of safety regulations pertaining to industrial substances. Another classic example is refrigerants. Fo years "R12" was used as the working fluid for most refrigerators, cooling and aircon systems. R12 however, if allowed to escape (which it does eventually either through failure of the system or neglect or breaking of the appliance gives off CFCs which harm the environment. So R12 was replaced by R134a aka "Klea". Klea is great for not contributing to the CFC problem but instead causes acid rain or some other problem... but thats ok because there isnt a regulation on that yet
I was an engineer with Martin Marietta for ten years from 1981 to 1991. I worked as a Staff Propulsion Engineer on the External Tank (ET) during much of that time. At Martin - NASA's Prime Contractor for the ET - the Propulsion & Thermal depts worked closely together (cryogenic propellants - insulation) so I have a pretty detailed knowledge of the STS ET and its 'foam' ('TPS' - 'Thermal Protection System' in the formal terminology).
I'm afraid that Chris's note is so full of factual errors that I must offer a rebuttal.
Firstly, the adhesion of the insulation didn't change significantly when the process changed. The foam has always come off in chunks and, due to the inherent design and inherent variables in the chemistry, it always will. All that has really changed is:
1. There are more inspections & more pull-tests on the foam to find voids, so limiting the amount which falls of in big pieces.
2. Some areas of 'SLA' (Super Lightweight Ablator) and shaped foam pieces around certain areas of the tank have been either removed or greatly reduced in size so as to reduce the hazard to the Orbiter on the ascent.
Chris is quoting a good story about the effects of changes in TPS chemistry in the late '80s, but I'm afraid it isn't true. We were losing pieces of insulation from before STS-1 (it came off during a propellant loading test prior to launch) and on every flight since. Often there were 'dings' on Orbiter tiles ascribed to debris from the ET, but, prior to the Feb 2003 loss of Columbia, nobody thought that the Orbiter could be seriously damaged in that way.
The ET is cleared for up to 12 tanking/detanking events, and the practical limitation is fatigue in certain areas of the metal tanks themselves, rather than the TPS. There is little or no deterioration of the bondline between the foam and the metal skin after the first tanking. There is no paint finish as such on the tank - the surface is chemically passivated prior to TPS application.
The reason the first ET was painted (actually, the first two flight articles, plus the various test ETs) was that the white paint protected the TPS from UV light which would damage the foam's surface thermal properties, since the first tanks would spend up to a year on the pad during Shuttle system testing prior to launch. The foam (known to us as NCFI - North Carolina Foam Insulation - amaze your friends with this!) starts out as a cream colour when first applied and gradually darkens with UV exposure; after about 3-4 months it is a reddish-brown and doesn't seem to darken much further. All our testing indicated that no deterioration of the foam other than the surface colour and an increased 'powderiness' of the surface resulted from the paint's elimination.
A further error in Chris's piece - the ET CANNOT 'be left tanked for more than a week'. The propellants are LH2 and LOX, the insulation will prevent some, but not all, heat ingress and if you leave the propellants in there, the tanks will be empty after less than a couple of days. After a scrub for the day, we drain the propellants (it takes about 8 hours, and is a very safe and normal procedure; I helped develop some of them) and recover them to the LH2 & LOX dewars by the side of the pad; even then, we lose about 40% of the propellants due to boiloff. We then retank the next day. It is possible, although not entirely desirable (from the point of view both of losses and propellant thermal conditioning) to keep the cryogens on board for a 24-hour turnaround, but no longer.
The Orbiter's own on-board propellants (comparatively small tanks, in the Orbiter itself, for use during orbit insertion, on-orbit, de-orbit and reentry) are entirely different storable propellants, normally loaded up to 3 weeks prior to launch.
Sorry for such a long post, but I want to correct any misunderstandings here.
Oh, and to answer Andy's question - no it wouldn't, the (titanium dioxide) paint was pretty thin. BTW it would not be acceptable engineering practise to use the tensile strength of a coat of paint to hold a structure together!
For Garry:
Also, something most people don't know is that the command which releases the hold-down bolts at T-0 is the same command which ignites the Solid Rocket Boosters. Think about that - the boosters are not actually lit when the last hold-down is released. We never liked that, but then liquid propulsion guys don't like solids for so many reasons!
Cheers,
Kevin
I'm afraid that Chris's note is so full of factual errors that I must offer a rebuttal.
Firstly, the adhesion of the insulation didn't change significantly when the process changed. The foam has always come off in chunks and, due to the inherent design and inherent variables in the chemistry, it always will. All that has really changed is:
1. There are more inspections & more pull-tests on the foam to find voids, so limiting the amount which falls of in big pieces.
2. Some areas of 'SLA' (Super Lightweight Ablator) and shaped foam pieces around certain areas of the tank have been either removed or greatly reduced in size so as to reduce the hazard to the Orbiter on the ascent.
Chris is quoting a good story about the effects of changes in TPS chemistry in the late '80s, but I'm afraid it isn't true. We were losing pieces of insulation from before STS-1 (it came off during a propellant loading test prior to launch) and on every flight since. Often there were 'dings' on Orbiter tiles ascribed to debris from the ET, but, prior to the Feb 2003 loss of Columbia, nobody thought that the Orbiter could be seriously damaged in that way.
The ET is cleared for up to 12 tanking/detanking events, and the practical limitation is fatigue in certain areas of the metal tanks themselves, rather than the TPS. There is little or no deterioration of the bondline between the foam and the metal skin after the first tanking. There is no paint finish as such on the tank - the surface is chemically passivated prior to TPS application.
The reason the first ET was painted (actually, the first two flight articles, plus the various test ETs) was that the white paint protected the TPS from UV light which would damage the foam's surface thermal properties, since the first tanks would spend up to a year on the pad during Shuttle system testing prior to launch. The foam (known to us as NCFI - North Carolina Foam Insulation - amaze your friends with this!) starts out as a cream colour when first applied and gradually darkens with UV exposure; after about 3-4 months it is a reddish-brown and doesn't seem to darken much further. All our testing indicated that no deterioration of the foam other than the surface colour and an increased 'powderiness' of the surface resulted from the paint's elimination.
A further error in Chris's piece - the ET CANNOT 'be left tanked for more than a week'. The propellants are LH2 and LOX, the insulation will prevent some, but not all, heat ingress and if you leave the propellants in there, the tanks will be empty after less than a couple of days. After a scrub for the day, we drain the propellants (it takes about 8 hours, and is a very safe and normal procedure; I helped develop some of them) and recover them to the LH2 & LOX dewars by the side of the pad; even then, we lose about 40% of the propellants due to boiloff. We then retank the next day. It is possible, although not entirely desirable (from the point of view both of losses and propellant thermal conditioning) to keep the cryogens on board for a 24-hour turnaround, but no longer.
The Orbiter's own on-board propellants (comparatively small tanks, in the Orbiter itself, for use during orbit insertion, on-orbit, de-orbit and reentry) are entirely different storable propellants, normally loaded up to 3 weeks prior to launch.
Sorry for such a long post, but I want to correct any misunderstandings here.
Oh, and to answer Andy's question - no it wouldn't, the (titanium dioxide) paint was pretty thin. BTW it would not be acceptable engineering practise to use the tensile strength of a coat of paint to hold a structure together!
For Garry:
It pretty much IS like 'CTRL E'. After that point (T minus 31 seconds), the launch control computer is in charge and decides whether to continue or abort. Manual intervention is possible after this point, but only to stop the launch, not to correct anything. When you get down to the last few seconds, it takes a brave individual to hit 'STOP', as you don't know for sure when the computer's going to stop it.Garry Russell wrote:..............Auto start sequence, what's that?...CTRL E? :roll:
Garry
Also, something most people don't know is that the command which releases the hold-down bolts at T-0 is the same command which ignites the Solid Rocket Boosters. Think about that - the boosters are not actually lit when the last hold-down is released. We never liked that, but then liquid propulsion guys don't like solids for so many reasons!
Cheers,
Kevin