Columbia Accident

[maxrpm]

From CNN : "A piece of foam fired at the replica at about 500 mph punched a hole 16-inches in diameter in the reinforced carbon material, as onlookers gasped at the Southwest Research Institute. "We have found the smoking gun," said Scott Hubbard, a member of the Columbia Accident Investigation Board. "

Shortly after the accident NASA said, that the piece of isolating foam which had hit Columbia´s left wing was considered no danger. I had no problems believing that - but the picture in my mind was a slowly rising shuttle just after Lift Off.
I had no idea that this lumb of isolating foam hit with 500mph!

Now, I am a pilot not an engineer, but I have experienced little birds making dents in the leading edge of my plane at speeds like 250mph.
Sure an airliner´s leading edge is not built to weather a reentry from orbit. Nevertheless I would have considered any flying structure to be endangered by anything that hit with M0,8.

Are there any experts out on the forum able to make an educated guess on the assumptions of the NASA Team about that incident on Lift Off? What theory could have made them confident that there would be no dangerous consequences for Columbia?

[PaperTiger]

What theory could have made them confident that there would be no dangerous consequences for Columbia?

The ABC network (USA) aired a special on Columbia earlier this week. I'm no engineer so won't comment about 'theories', nor will I say anything about the conclusions reached in the TV show.

Transcripts you have to pay for, but a summary of the program is available here (http://abcnews.go.com/sections/scitech/US/shuttlespecial_emails030707.html).

[wes_wall]

I too am no engineer, and the question that came to my mind:

How could the piece of foam be traveling 500 mph since if departed the tank which was traveling the same speed as the wing ? I am sure it has been published, but how fast was Columbia traveling when struck with the foam?

[Rollingthunder]

How could the piece of foam be traveling 500 mph since if departed the tank which was traveling the same speed as the wing ?

Exactly the same thing I have been wondering.

[BOAC]

You may wish to join in on THIS (http://www.pprune.org/forums/showthread.php?s=&threadid=80261) excellent thread?

[PlaneTruth]

C'mon guys!

Mass x Velocity

A piece of foam has little apparent mass but significant surface area. When exposed to a supersonic windblast it accelerates VERY quickly. For something to puncture the composite leading edge and do that much damage, it had to be moving quickly.

The Shuttle was moving well in excess of 500mph at the point the foam departed into the slipstream. Also, consider the venturi effect of the main tank and the Shuttle underside. There may be some dynamic there which produced more or less wind velocity than the actual true airspeed of the vehicle.


PT

[WideBodiedEng]

I agree with Wes Wall and Rollingthunder.
Lets say the Shuttle is travelling at 500mph. That means ALL parts are travelling at 500mph.
Now if something falls off, it slows down due to drag, but still has less (and getting lesser) forward momentum. So how much did it slow down in the distance between the falling off point and the point at which the orbiter LE caught up with it?
I would hazard a guess that it was A LOT LESS than 500 mph relative speed.
Think about it, you're overtaking another car. Its doing 80, youre doing 90. Takes a (pucker factor) while doesn't it?
I smell a cover up though of what, Bad inspection, missed damage etc, I dont know.
But I do not believe the foam was travelling at 500 relative to the wing. I DO believe that there was damage to the LE whether pre-existing and made worse by a thump from soggy foam or a tile just waiting to fail.

[TURIN]

OK here's a little experiment.

The next time you are travelling back to your hotel (down the M56/M40/Route 66, whatever) in the crew bus, get one volunteer to stick his/her head out of the skylight hatch at the back of the bus. Next get volunteer B to let go of something out of the forward skylight. Something quite light but a reasonable surface area and see how quickly said item changes velocity. For added laughs try to make the projectile sticky or wet (dyed with engineers blue would give a perfectly permenant record! :E )

The theory sounds good to me.:ok:

[kinsman]

Turin

I agree, also the thermal tiles are fragile!

[Aussierotor]

The foam would have to be stronger than my 6 pack beer carrier lol

[Rollingthunder]

Right then, piece of foam insulation comes loose - a rather fragile piece of material even with a hard backing - perhaps more fragile than insulating tiles (ceramic?) - enters slipstream and decelerates from launch vehicle speed of around 500 mph - or something certainly below the speed of sound at that point. Foam is likely to fragment in violent slipstream - if it doesn't it indicates impact in a second or two lessening speed of impact. Full piece or fragment thereof strikes leading edge of wing at something less than vehicle speed. Test indicated foam fired at test tiles at 500 mph. Still don't understand.

[witchdoctor]

Bear in mind that at 500mph it produced a 16 inch diameter hole - that is huge. If it was travelling slower, it may still have produced a hole several inches in diameter which could well have been significant enough to have produced the effects we all witnessed. Either way, a fairly hefty piece of foam hit the l/e with a considerable velocity and I don't find it difficult to believe that this was the cause of the damage.

[slingsby]

Interupted airflow over a damaged wing/tile area at 500mph, damage initially assessed maybe as ok at the time. But then the shuttle, while still in the atmosphere accellerates through the sound barrier and and upwards through lower mach numbers, the airflow into the damaged area would have increased and possibly removed more of the tiles as it accellerated. Aerodynamics engineers, surely you could shed some light about the forces inflicted on the shuttle after its impact. Could a larger area of damage been caused by the disrupted airflow after the initial impact/damage.

The question of shuttle costs v scientific value has been covered enough. If companies want to pay, let them, I for one have yet to see this vehicle in operations and would dearly like to experience viewing a launch.

[Desert Dingo]

Some other reports suggest that the piece of foam may have become saturated with water and hit the wing not as a light bit of foam, but as a great lump of ice. :ugh:

Quote...........
At launch the Columbia’s left wing was hit by a piece of foam insulation from the main fuel tank, at a speed of around 480 MPH. Urgent analysis done while the craft was still in orbit concluded that the likelihood of serious damage was slight. However, the video recording of this impact shows it to be very hard indeed with an explosive spray of what looks to be more than just foam. It almost certainly was, probably containing a large amount of ice. The piece was estimated to be around 51 cm x 41cm x 15 cm and would have weighed around 1.2kg if only foam. However, if it were saturated with water (ice) it would have weighed around 29kg, a far more dangerous scenario. The Columbia had been sitting for weeks on the launch pad, out in the freezing weather. It seems incredible that some sort of shelter is not provided to prevent water freezing on and in the Shuttles’ with the attendant risk of mechanical damage due to the expansion of the ice. This is probably what caused the foam to come loose.

Recent test impacts with foam fired at a shuttle wing at 768 ft/sec or 523 MPH showed that not only was the surface deformed by the impact, but also a main rib in the wing failed with a clearly visible five-inch crack through the carbon reinforced material. The crack extended across the rib lock and onto the panel surface. This panel is a high-carbon heat shield. A crack or hole in it means almost certain destruction of the shuttle upon re-entry.

[simfly]

I tend to agree with above, if it is the(se) tiles which were the cause, you can clearly see from the footage how hard they hit the Columbia's wing, obvioulsly deccelerated very fast after seperation from the fuel tank. :oh:

[Flash2001]

As I posted on the other forum, the mass of the particle should drop out of the energy equation to a first approximation anyway. The total energy, which is the total ability to do damage, will be equal to the average force due to dynamic pressure times the distance travelled along the airframe.

[OVERTALK]

Possibly more productive to talk about fixes:

Subject: NASA May Not Be Able to Prevent Shuttle Foam Loss
I think that my idea of a sacrificial leading
edge would fly.(an aerodynamic fairing that would quickly
burn away uniformly during the heat of re-entry, yet
protect the RCC tiles during the ride into orbit). Think
plain fibreglass - or a more reliably ablative and
heat-affected compound.

As it would be effectively a leading-edge
extension, it would increase wing chord slightly - and so
improve glide performance in the event of a sub-orbital
abort.

If NASA was concerned about it not burning away
uniformly during re-entry they could, whilst in orbit, utilize shielded
mild detonating cord (MDC - such as used to remove
fighter canopy plexiglass prior to ejection). The MDC (a directed
energy device) would blow it off along the length of each
leading edge - leaving the RCC intact.

NASA May Not Be Able to Prevent Shuttle Foam Loss, Board Says
July 11 (Bloomberg) -- NASA may
not be able to prevent some fuel-tank insulating foam
from falling off and striking the space shuttle during
its launch, the likely trigger for Columbia's
destruction, and is trying to find a way to get rid of it
in future missions, investigators said today.
The foam's construction and the
way it is manually sprayed onto the area known as the
bipod ramp, where the shuttle is connected by struts to
the fuel tank, could reduce the strength of the
insulation and lead it to break off, the Columbia
Accident Investigation Board said in a 189-page ``working
scenario'' posted to its Web site.
A chunk of foam suspected of
puncturing Columbia's left wing was shed from the bipod
area, according to investigators.
``It may not be possible to
control a manual process well enough to preclude defects
in the bipod ramp,'' the board wrote.
That finding is pushing the
National Aeronautics and Space Administration toward
eliminating the foam from the tank-shuttle connector, an
accident board member said today.
``A possibility is don't let
any bipod ramps come off and hit the wing leading edge,
which is where I think NASA is headed,'' Scott Hubbard,
who run's the agency's Ames Research Center in
California, told reporters today in Washington. ``One
answer is just don't ever let this happen again by
eliminating the source. I believe they are redesigning
the bipod ramp to completely take out the foam.''
NASA encases the tank in foam
to prevent ice formation and maintain the temperature of
the liquid oxygen and liquid hydrogen stored inside, the
propellants for the shuttle's main engines.
Destruction Demonstrated
The destructive power of foam
fragments was demonstrated this week at the independent
Southwest Research Institute in San Antonio, Texas, where
a 1.6-pound foam piece fired at a mockup of the shuttle's
wing edge tore a 16-inch hole in the heat shielding.
Hubbard said investigators had
found the ``smoking gun'' after the test Monday. The hole
would have let atmospheric gases as hot as 3,000 degrees
Fahrenheit stream into the interior of the wing during
reentry, melting its structure and eventually forcing the
shuttle to veer out of control and break apart, about 40
miles above Texas. All seven astronauts aboard were
killed.
The Southwest Research tests
``support the theory'' the left wing was damaged by the
foam impact, the board said. The board's ``scenario''
report estimates the size of the hole in Columbia was
smaller, about 6 to 10 inches in diameter.
Retired Admiral Harold Gehman,
the board's chairman, said during a press briefing in
Washington that the panel has completed its probe and is
writing its final report on the shuttle's destruction,
set for release in mid-August.
NASA might need to treat
shuttles as developmental vehicles in order to prevent
future problems that could lead to their destruction,
board members said today.
`R&D Vehicle'
``A lot of this boils down to
not treating the shuttle as operational, but as an R&D
vehicle,'' said Brigadier General Duane Deal, a commander
with the U.S. Air Force's 21st Space Wing. ``You need to
treat each launch as the first launch, each orbit as the
first orbit and each reentry as the first reentry.''
Gehman said that meant there
would have to be more scrutiny of the vehicles as they
are prepared for launch and during their missions. ``You
are always on the lookout for tiny little differences,
you're suspicious of tiny little differences,'' he said.
The main mission of the shuttle
is to deliver crews and building materials to the
International Space Station, the largest space project,
and to repair the orbiting Hubble Space Telescope. A
Houston-based joint venture of Boeing Co. and Lockheed
Martin Corp. prepares the shuttles for launch.
Last Updated: July 11, 2003

[DrSyn]

For the info of WideBodiedEng and any others who may have not followed the investigation in depth, the Shuttle stack was accelerating through about Mach 2.6 at the time the foam segment detached. Its impact speed at the leading edge was accurately determined from high-speed film to be around 500 mph. Both the released videos of the event clearly show that the impact was forceful.

Also, do not confuse tiles with RCC sections and tank foam. Tiles are not at issue in this accident.

[STS]

Just to let anyone know who is interested not just in the Columbia investigation but space matters in general, one of the best resources on the net is http://www.nasawatch.com

I know many of you probably know that, but if you haven't had a look at the site, it contains links to a heck of a lot of information and is updated virtually daily. I've always found it pretty useful.