[FPSPACE] latest from CBS News..

Peter Pesavento eagles267@wwainc.com
Thu, 12 Jun 2003 20:34:02 -0400


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Another Feynman-esque experiment showing some interesting results....

Also, some NDE stuff wasn't done about some of the explosive bolts...

=20
CBS NEWS STATUS REPORT

a.. 07:15 p.m., 06/12/03, Update: Bolt catcher issue studied; possible =
return to flight issue; cryopumping can't explain foam shedding; update =
on foam impact test damage=20
  Accident investigators have stumbled on a potentially catastrophic =
shortcoming in the explosive bolt attachment system used to latch a =
space shuttle's boosters to its external fuel tank. While there is no =
evidence Columbia was struck by falling debris from a faulty "bolt =
catcher" during its launching Jan. 16, corrective actions almost =
certainly will be required before shuttle flights resume.
  Members of the Columbia Accident Investigation Board said today a foam =
strike during launch remains the most plausible explanation for the =
breach in the shuttle's left wing leading edge that ultimately doomed =
the orbiter and its crew during re-entry Feb. 1. One of the more =
intriguing aspects of the failure scenario is the rapidity with which a =
plume of super-heated air managed to eat its way inside during the first =
moments of Columbia's descent into the discernible atmosphere.

  The accident board today released dramatic video of a test using an =
8,000-degree arc jet that vividly illustrates just how fast a small =
breach can deteriorate into a gaping hole. Engineers fired the jet of =
super-heated air at a circular one-inch-wide hole in a strip of aluminum =
representing a wing spar, the metal structure directly behind the carbon =
composite panels making up the leading edge. Like a match flame burning =
through tissue paper from below, a one-inch hole in the plate grew to =
six inches across in just 20 seconds. The plume also burned through a =
thick wire bundle in less than one minute, in generally good agreement =
with the way the plume that burned into Columbia's wing quickly ate =
through sensor wiring once inside.

  "It's really very impressive. You cannot imagine the destructive power =
of the gases that would flow in through that hole," said Douglas =
Osheroff, a Nobel laureate in low-temperature physics and a member of =
the accident board. "It's really pretty scary to see."

  During a normal shuttle entry, the maximum temperatures experienced by =
the wing leading edges and the ship's carbon composite nose cap is 3,000 =
degrees. The temperature is moderated by the way air smoothly flows =
across the skin of the shuttle, setting up what is known as a boundary =
layer that acts as an insulator of sorts. But in a breach, no such =
protection exists and temperatures can soar much higher, "so hot that in =
fact the oxygen molecules are split into individual atoms," Osheroff =
said. "That makes them much more highly reactive."

  "It was just very impressive to see how quickly that kind of an =
atmosphere, simulating as best they could the conditions on re-entry, =
would slice through aluminum in particular," he said. "It was just =
absolutely amazing."

  Osheroff is the second Nobel prize winner to sit on a shuttle accident =
board. Richard Feynman served in that capacity for the 1986 Challenger =
disaster, performing a memorably simple experiment during an early =
hearing that showed how booster O-ring seals are affected by cold =
weather. He dipped a small O-ring into a glass of ice water, held it up =
and showed how it had stiffened, a characteristic that would have =
reduced a real O-ring's ability to work properly during cold weather. =
Challenger, of course, was destroyed by an O-ring seal failure during =
launch in cold weather.

  Today, Osheroff discussed a modest experiment of his own, carried out =
in his kitchen with about $100 in equipment, that suggests NASA has =
never understood the mechanism responsible for external tank foam =
shedding. It also suggests, to borrow a phrase from Apple Computer, that =
Nobel prize winners "think different."

  "I became rather rapidly interested in the properties of this foam," =
he said today. "It's really fascinating stuff. It's highly anisotropic, =
that is to say it's mechanical properties depend upon which direction =
you squeeze it, for instance. So I decided to do some experiments on the =
foam."

  Osheroff, with the help of a graduate student, had a metal plate =
machined to serve as a stand-in for the skin of the external tank. He =
then glued a cube of BX-250 to the plate, a sample of the same type of =
foam that came off Columbia's tank. A small hole in the plate allowed =
him to apply pressure at the interface between the foam and the metal.

  "The idea was to try to understand, as I increased the pressure, how =
ultimately this resulted in some sort of a fault that propagated through =
to the surface," Osheroff said. "This is important because for many =
years, people at NASA assumed, in fact, that one of the main mechanisms =
for foam shedding from the external tank was that liquid nitrogen (from =
trapped air) would somehow condense in a void or something inside the =
foam near the metal surface. And as you started getting aero heating =
(during launch), this liquid nitrogen would warm up, pressure would =
build up and it would throw foam off of the external tank.

  "What I found was that, in fact, the mechanism by which the liquid =
expands is not consistent in any way with ejection of foam from the =
surface. What it does, it tends to make a two dimensional, rather flat =
crack or fault, which propagates up to the surface and it meets the =
surface normal to the surface in almost every case. This has to do with =
anisotropic properties of the foam."

  Translation: Expanding gas in a pocket, or void, near the ultra-cold =
skin of an external tank produces linear surface cracks in the foam, it =
doesn't blow out the overlying material. In addition, calculations show =
heating due to atmospheric friction would not have had time to turn any =
pockets of liquified air into a gas by 81 seconds into flight.P> "That's =
less than 30 seconds into aero heating," Osheroff said. "Is it possible =
for the heat to propagate through the foam and actually boil off the =
liquid nitrogen that might have condensed in that brief period of time? =
... The thermal relaxation times are much too long for that."

  "So the conclusion I have reached, and that independently the people =
at Marshall Space Flight Center have reached, is that the process by =
which foam is ejected is undoubtedly a very complex one involving more =
than just cryo condensation and ejection.

  "I dare say, in fact, that these sorts of experiments which I have =
done, which were actually done in my kitchen at home for about a hundred =
dollars, are the sorts of things I think we need to see more of done. =
Specifically, experiments to try to understand the physical mechanisms =
(behind) why the foam behaves the way it does."

  In a revelation that generated quite a bit of media interest, board =
member John Barry revealed investigators are looking into apparent =
problems with the system used to capture and restrain pieces of the =
exploding bolts used to hold a shuttle's boosters to its external tank =
during launch.

  The boosters separate two minutes and five seconds or so into flight =
when explosive charges cut the massive 80-pound bolts in half. The upper =
half of a bolt is blown upward and captured in the dome of a fully =
enclosed "bolt catcher" assembly on the tank. The bottom half is =
captured by a bolt catcher on the booster.

  The bolt catchers are designed to prevent any debris from a blown bolt =
from getting into the airstream and possibly impacting the shuttle.

  "The problem we found was the original certification was done without =
the real flight hardware in 1979," Barry said. "The other thing we found =
out, this bolt that was used in STS-107 (Columbia) was done with a new =
vendor and the NDE, the non-destructive evaluation, wasn't done as well =
as it should have been.

  "They did some bolt static tests that resulted in this dome fracturing =
at a lower pressure than was anticipated," he said. "In fact, it was =
below a 1.4 safety margin. So this dome is made of aluminum and covered =
with ablative. If that comes loose, with or without that half of the =
bolt in it, it still can cause some serious risk to the orbiter. So this =
is a possible return to flight issue that we're examining."

  Complicating the picture, radar data from Columbia's launching shows =
unidentified debris separating from the shuttle 126 seconds into flight, =
right about the time of booster separation. Debris has been seen on =
radar during past missions, presumed chunks of ice, for example, and =
there is no evidence the debris seen during Columbia's flight involved =
the bolt catcher. Certainly there's no recorded data or telemetry from =
Columbia suggesting any kind of an impact 126 seconds into flight.

  But engineers cannot rule out the possibility debris may have been =
released into the airstream.

  "What we have here is a possibility that we have found another source =
of debris," said CAIB chairman Harold Gehman. "We don't have any =
evidence that it was a source of debris except the radar tracking of the =
Columbia indicated that at the time of SRB separation, 126 seconds, at a =
time when there's not supposed to be any debris, it noticed a piece of =
debris. We don't know what that was."

  He said engineers are trying to determine if a bolt catcher failure =
could "create any debris which might fall back on the wing?"

  "We're just at the front end of this and we're not ready to make any =
statements about how this affects the process. The question, then, is we =
have a potential piece of debris here now. Or in a future flight. But in =
this particular case, STS-107, it's a potential that we've got a piece =
of debris.

  "Then we go back to the radar of the launch. ... And lo and behold, at =
126 seconds after launch, at the time of SRB separation, something is =
seen on the radar which indicates that there's a piece of debris ejected =
from the separation. It could be the bolt catcher. We can't prove that. =
But in an effort to positively close out the fault tree - and you =
multiply this times a thousand - you can see why this investigation has =
taken five months. So here's one we can't close out."

  But he and other board members downplayed the possibility that a =
40-pound bolt fragment could have hit Columbia without being detected by =
the shuttle's myriad sensors. The real issue is fixing the problem =
before flights resume.

  "There's no indication, in either the (recorded) OEX data that we know =
about or any of the telemetry, that something hit the wing past 120 =
seconds," Barry said.

  "What we're trying to couch here is it's very important that we =
understand all potential debris. We're not changing our working =
scenario, it's still pretty evident foam came off and hit the wing. But =
we also have to take into consideration any other future debris elements =
that could be potentially catastrophic to the orbiter."

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<DIV><FONT face=3DArial size=3D2>Another Feynman-esque experiment =
showing some=20
interesting results....</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Also, some NDE stuff wasn't done about =
some of the=20
explosive bolts...</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><!--StartFragment -->&nbsp;
<H4>
<CENTER><A name=3D"CBS NEWS STATUS REPORT">CBS NEWS STATUS=20
REPORT</A></CENTER></H4>
<P></P>
<LI><B>07:15 p.m., 06/12/03, Update: Bolt catcher issue studied; =
possible return=20
to flight issue; cryopumping can't explain foam shedding; update on foam =
impact=20
test damage</B>=20
<BLOCKQUOTE>Accident investigators have stumbled on a potentially =
catastrophic=20
  shortcoming in the explosive bolt attachment system used to latch a =
space=20
  shuttle's boosters to its external fuel tank. While there is no =
evidence=20
  Columbia was struck by falling debris from a faulty "bolt catcher" =
during its=20
  launching Jan. 16, corrective actions almost certainly will be =
required before=20
  shuttle flights resume.
  <P>Members of the Columbia Accident Investigation Board said today a =
foam=20
  strike during launch remains the most plausible explanation for the =
breach in=20
  the shuttle's left wing leading edge that ultimately doomed the =
orbiter and=20
  its crew during re-entry Feb. 1. One of the more intriguing aspects of =
the=20
  failure scenario is the rapidity with which a plume of super-heated =
air=20
  managed to eat its way inside during the first moments of Columbia's =
descent=20
  into the discernible atmosphere.</P>
  <P>The accident board today released dramatic video of a test using an =

  8,000-degree arc jet that vividly illustrates just how fast a small =
breach can=20
  deteriorate into a gaping hole. Engineers fired the jet of =
super-heated air at=20
  a circular one-inch-wide hole in a strip of aluminum representing a =
wing spar,=20
  the metal structure directly behind the carbon composite panels making =
up the=20
  leading edge. Like a match flame burning through tissue paper from =
below, a=20
  one-inch hole in the plate grew to six inches across in just 20 =
seconds. The=20
  plume also burned through a thick wire bundle in less than one minute, =
in=20
  generally good agreement with the way the plume that burned into =
Columbia's=20
  wing quickly ate through sensor wiring once inside.</P>
  <P>"It's really very impressive. You cannot imagine the destructive =
power of=20
  the gases that would flow in through that hole," said Douglas =
Osheroff, a=20
  Nobel laureate in low-temperature physics and a member of the accident =
board.=20
  "It's really pretty scary to see."</P>
  <P>During a normal shuttle entry, the maximum temperatures experienced =
by the=20
  wing leading edges and the ship's carbon composite nose cap is 3,000 =
degrees.=20
  The temperature is moderated by the way air smoothly flows across the =
skin of=20
  the shuttle, setting up what is known as a boundary layer that acts as =
an=20
  insulator of sorts. But in a breach, no such protection exists and=20
  temperatures can soar much higher, "so hot that in fact the oxygen =
molecules=20
  are split into individual atoms," Osheroff said. "That makes them much =
more=20
  highly reactive."</P>
  <P>"It was just very impressive to see how quickly that kind of an =
atmosphere,=20
  simulating as best they could the conditions on re-entry, would slice =
through=20
  aluminum in particular," he said. "It was just absolutely =
amazing."</P>
  <P>Osheroff is the second Nobel prize winner to sit on a shuttle =
accident=20
  board. Richard Feynman served in that capacity for the 1986 Challenger =

  disaster, performing a memorably simple experiment during an early =
hearing=20
  that showed how booster O-ring seals are affected by cold weather. He =
dipped a=20
  small O-ring into a glass of ice water, held it up and showed how it =
had=20
  stiffened, a characteristic that would have reduced a real O-ring's =
ability to=20
  work properly during cold weather. Challenger, of course, was =
destroyed by an=20
  O-ring seal failure during launch in cold weather.</P>
  <P>Today, Osheroff discussed a modest experiment of his own, carried =
out in=20
  his kitchen with about $100 in equipment, that suggests NASA has never =

  understood the mechanism responsible for external tank foam shedding. =
It also=20
  suggests, to borrow a phrase from Apple Computer, that Nobel prize =
winners=20
  "think different."</P>
  <P>"I became rather rapidly interested in the properties of this =
foam," he=20
  said today. "It's really fascinating stuff. It's highly anisotropic, =
that is=20
  to say it's mechanical properties depend upon which direction you =
squeeze it,=20
  for instance. So I decided to do some experiments on the foam."</P>
  <P>Osheroff, with the help of a graduate student, had a metal plate =
machined=20
  to serve as a stand-in for the skin of the external tank. He then =
glued a cube=20
  of BX-250 to the plate, a sample of the same type of foam that came =
off=20
  Columbia's tank. A small hole in the plate allowed him to apply =
pressure at=20
  the interface between the foam and the metal.</P>
  <P>"The idea was to try to understand, as I increased the pressure, =
how=20
  ultimately this resulted in some sort of a fault that propagated =
through to=20
  the surface," Osheroff said. "This is important because for many =
years, people=20
  at NASA assumed, in fact, that one of the main mechanisms for foam =
shedding=20
  from the external tank was that liquid nitrogen (from trapped air) =
would=20
  somehow condense in a void or something inside the foam near the metal =

  surface. And as you started getting aero heating (during launch), this =
liquid=20
  nitrogen would warm up, pressure would build up and it would throw =
foam off of=20
  the external tank.</P>
  <P>"What I found was that, in fact, the mechanism by which the liquid =
expands=20
  is not consistent in any way with ejection of foam from the surface. =
What it=20
  does, it tends to make a two dimensional, rather flat crack or fault, =
which=20
  propagates up to the surface and it meets the surface normal to the =
surface in=20
  almost every case. This has to do with anisotropic properties of the=20
foam."</P>
  <P>Translation: Expanding gas in a pocket, or void, near the =
ultra-cold skin=20
  of an external tank produces linear surface cracks in the foam, it =
doesn't=20
  blow out the overlying material. In addition, calculations show =
heating due to=20
  atmospheric friction would not have had time to turn any pockets of =
liquified=20
  air into a gas by 81 seconds into flight.P&gt; "That's less than 30 =
seconds=20
  into aero heating," Osheroff said. "Is it possible for the heat to =
propagate=20
  through the foam and actually boil off the liquid nitrogen that might =
have=20
  condensed in that brief period of time? ... The thermal relaxation =
times are=20
  much too long for that."</P>
  <P>"So the conclusion I have reached, and that independently the =
people at=20
  Marshall Space Flight Center have reached, is that the process by =
which foam=20
  is ejected is undoubtedly a very complex one involving more than just =
cryo=20
  condensation and ejection.</P>
  <P>"I dare say, in fact, that these sorts of experiments which I have =
done,=20
  which were actually done in my kitchen at home for about a hundred =
dollars,=20
  are the sorts of things I think we need to see more of done. =
Specifically,=20
  experiments to try to understand the physical mechanisms (behind) why =
the foam=20
  behaves the way it does."</P>
  <P>In a revelation that generated quite a bit of media interest, board =
member=20
  John Barry revealed investigators are looking into apparent problems =
with the=20
  system used to capture and restrain pieces of the exploding bolts used =
to hold=20
  a shuttle's boosters to its external tank during launch.</P>
  <P>The boosters separate two minutes and five seconds or so into =
flight when=20
  explosive charges cut the massive 80-pound bolts in half. The upper =
half of a=20
  bolt is blown upward and captured in the dome of a fully enclosed =
"bolt=20
  catcher" assembly on the tank. The bottom half is captured by a bolt =
catcher=20
  on the booster.</P>
  <P>The bolt catchers are designed to prevent any debris from a blown =
bolt from=20
  getting into the airstream and possibly impacting the shuttle.</P>
  <P>"The problem we found was the original certification was done =
without the=20
  real flight hardware in 1979," Barry said. "The other thing we found =
out, this=20
  bolt that was used in STS-107 (Columbia) was done with a new vendor =
and the=20
  NDE, the non-destructive evaluation, wasn't done as well as it should =
have=20
  been.</P>
  <P>"They did some bolt static tests that resulted in this dome =
fracturing at a=20
  lower pressure than was anticipated," he said. "In fact, it was below =
a 1.4=20
  safety margin. So this dome is made of aluminum and covered with =
ablative. If=20
  that comes loose, with or without that half of the bolt in it, it =
still can=20
  cause some serious risk to the orbiter. So this is a possible return =
to flight=20
  issue that we're examining."</P>
  <P>Complicating the picture, radar data from Columbia's launching =
shows=20
  unidentified debris separating from the shuttle 126 seconds into =
flight, right=20
  about the time of booster separation. Debris has been seen on radar =
during=20
  past missions, presumed chunks of ice, for example, and there is no =
evidence=20
  the debris seen during Columbia's flight involved the bolt catcher. =
Certainly=20
  there's no recorded data or telemetry from Columbia suggesting any =
kind of an=20
  impact 126 seconds into flight.</P>
  <P>But engineers cannot rule out the possibility debris may have been =
released=20
  into the airstream.</P>
  <P>"What we have here is a possibility that we have found another =
source of=20
  debris," said CAIB chairman Harold Gehman. "We don't have any evidence =
that it=20
  was a source of debris except the radar tracking of the Columbia =
indicated=20
  that at the time of SRB separation, 126 seconds, at a time when =
there's not=20
  supposed to be any debris, it noticed a piece of debris. We don't know =
what=20
  that was."</P>
  <P>He said engineers are trying to determine if a bolt catcher failure =
could=20
  "create any debris which might fall back on the wing?"</P>
  <P>"We're just at the front end of this and we're not ready to make =
any=20
  statements about how this affects the process. The question, then, is =
we have=20
  a potential piece of debris here now. Or in a future flight. But in =
this=20
  particular case, STS-107, it's a potential that we've got a piece of=20
  debris.</P>
  <P>"Then we go back to the radar of the launch. ... And lo and behold, =
at 126=20
  seconds after launch, at the time of SRB separation, something is seen =
on the=20
  radar which indicates that there's a piece of debris ejected from the=20
  separation. It could be the bolt catcher. We can't prove that. But in =
an=20
  effort to positively close out the fault tree - and you multiply this =
times a=20
  thousand - you can see why this investigation has taken five months. =
So here's=20
  one we can't close out."</P>
  <P>But he and other board members downplayed the possibility that a =
40-pound=20
  bolt fragment could have hit Columbia without being detected by the =
shuttle's=20
  myriad sensors. The real issue is fixing the problem before flights=20
resume.</P>
  <P>"There's no indication, in either the (recorded) OEX data that we =
know=20
  about or any of the telemetry, that something hit the wing past 120 =
seconds,"=20
  Barry said.</P>
  <P>"What we're trying to couch here is it's very important that we =
understand=20
  all potential debris. We're not changing our working scenario, it's =
still=20
  pretty evident foam came off and hit the wing. But we also have to =
take into=20
  consideration any other future debris elements that could be =
potentially=20
  catastrophic to the =
orbiter."</P></BLOCKQUOTE></LI></DIV></BODY></HTML>

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