STS-87 Foam Impact Assessment (reposted)

http://quest.arc.nasa.gov/people/jou...s87-12-23.html

Excerpt:
------
STS-87 is Home! The Post-Flight Inspection Begins
by Greg Katnik
December 23, l997

STS-87 rolled to a stop...the extent of damage at the conclusion of
this mission was not "normal." ... During the STS-87 mission, there
was a change made on the external tank. ... Foam cause damage to a
ceramic tile?! That seems unlikely, however when that foam is combined
with a flight velocity between speeds of MACH two to MACH four, it
becomes a projectile with incredible damage potential. The big
question? At what phase of the flight did it happen and what changes
need to be made to correct this for future missions? ... It was
determined that during the ascent, the foam separation from the
external tank was carried by the aerodynamic flow and pelted the nose
of the orbiter and cascaded aft from that point. Once again, this foam
was carried in a relative air-stream between MACH two and MACH 4!
.... As this investigation continues, I am very comfortable that the
questions will be answered and the solutions applied.
------







Full article:
----------------------
FIELD JOURNAL

STS-87 is Home! The Post-Flight Inspection Begins

by Greg Katnik
December 23, l997

STS-87 rolled to a stop; the mission was complete! That statement
would be true for the flight of the Columbia, however a new mission
began when the wheels of the Columbia came to a stop -- the post
flight inspections. My division is responsible for the overall
analysis of these inspections and we insure that all changes made, due
to these inspections, do not affect other areas that may jeopardize
the flight-worthiness of the shuttle. This division does not focus on
one specific area, but analyzes all information and ensures that all
aspects are kept in balance.

Immediately after the Columbia rolled to a stop, the inspection crews
began the process of the post flight inspection. As soon as the
orbiter was approached, light spots in the tiles were observed
indicating that there had been significant damage to the tiles. The
tiles do a fantastic job of repelling heat, however they are very
fragile and susceptible to impact damage. Damage numbering up to forty
tiles is considered normal on each mission due to ice dropping off of
the external tank (ET) and plume re-circulation causing this debris to
impact with the tiles. But the extent of damage at the conclusion of
this mission was not "normal."

The pattern of hits did not follow aerodynamic expectations, and the
number, size and severity of hits were abnormal. Three hundred and
eight hits were counted during the inspection, one-hundred and thirty
two (132) were greater than one inch. Some of the hits measured
fifteen (15) inches long with depths measuring up to one and one-half
(1 1/2) inches. Considering that the depth of the tile is two (2)
inches, a 75% penetration depth had been reached. Over one hundred
(100) tiles have been removed from the Columbia because they were
irreparable. The inspection revealed the damage, now the "detective
process" began.

During the STS-87 mission, there was a change made on the external
tank. Because of NASA's goal to use environmentally friendly products,
a new method of "foaming" the external tank had been used for this
mission and the STS-86 mission. It is suspected that large amounts of
foam separated from the external tank and impacted the orbiter. This
caused significant damage to the protective tiles of the orbiter. Foam
cause damage to a ceramic tile?! That seems unlikely, however when
that foam is combined with a flight velocity between speeds of MACH
two to MACH four, it becomes a projectile with incredible damage
potential. The big question? At what phase of the flight did it happen
and what changes need to be made to correct this for future missions?
I will explain the entire process.

The questions that needed to be answered we

* what happened?

* what phase of flight did it happen in?

* why did it happen?

* what corrective action is required?

At this point, virtually every inch of the orbiter was inspected and
all hits were documented and mapped to aid in visualizing the damage.
Maps were constructed of the lower surface, the left and right
surfaces and the top surface of the orbiter. At this point, a "fault
tree" was created. The fault tree provides a systematic approach in
considering all possibilities of what may have happened. Everything
that is on the fault tree is considered to be legitimate until it is
totally ruled out. Some of the considerations were where the damage
occurred -- in the OPF, in the VAB, or on the pad before launch. These
were quickly eliminated because an inspection at T-3 ("t minus three")
hours takes place on each mission and everything was normal.

After these and many other considerations were eliminated, the focus
was placed on the ascent, orbit and re-entry phase of the mission.
Because of the fore and aft flow characteristics of the damage sites,
and the angle of penetration, the ascent phase seemed most likely. The
orbit phase of flight was eliminated because the characteristics of
these types of hits (most likely meteorites or space debris) occur in
a random pattern and direction. Re-entry was eliminated because the
"glazing and re-glassifying" of the tiles due to heat upon re-entry (a
normal process) indicated that the damage had occurred prior to this
phase. The fault-tree was now pointing to the ascent phase.

The pictures that were taken by cameras mounted in the orbiter
umbilical began to give the first clues. These cameras are designed to
turn on during the solid rocket booster (SRB) separation, and turn off
after the separation is complete, thereby recording the event. This
process occurs once again when the external tank separates from the
orbiter. The initial review of these photographs did not reveal any
obvious damage to the external tank. No foam missing, no "divots"
(holes) and no material loss. Everything appeared normal.

The SRBs were then focused on for the answers. After inspection of the
SRBs, no clues were found. In fact, the solid rocket boosters looked
to be in great condition. Where to now? The external tank photographs
were magnified and reviewed once again. This time some material loss
was noted, but not in a significant degree. The attention was now
focused on the crew cabin cameras. These cameras gave more of a side
view of the external tank as it tumbled back to Earth. These
photographs revealed massive material loss on a side of the external
tank that could not be viewed by the umbilical cameras!

Where are we now? One of the questions had now been answered. The
ascent phase of flight was when the damage occurred. With the
information provided by the photography and the mapped flow of damage,
a logical reason could be established as to "what" happened. It was
determined that during the ascent, the foam separation from the
external tank was carried by the aerodynamic flow and pelted the nose
of the orbiter and cascaded aft from that point. Once again, this foam
was carried in a relative air-stream between MACH two and MACH 4!

Now the big question -- why? The evidence of this conclusion has now
been forwarded to Marshall Space Flight Center (MSFC) because this is
the design center for the external tank. MSFC will pursue the cause of
damage. Here are some descriptions of some of the considerations:

* The primer that bonds the tank foam to the metal sub-stream was
defective and did not set properly. This was eliminated as a cause
because the photography indicated that the areas of foam loss (divots)
did not protrude all the way down to the primer.

* The aerodynamics of the roll to "heads up." The STS-87 mission was
the first time this maneuver had ever been completed.

* The STS-86 mission revealed a similar damage pattern but to a much
lesser degree than STS-87. The STS-86 tile damage was accepted ruled
as an unexplained anomaly because it was a night launch and did not
provide the opportunity for the photographic evidence the STS-87
mission did. A review of the records of the STS-86 records revealed
that a change to the type of foam was used on the external tank. This
event is significant because the pattern of damage on this flight was
similar to STS-87 but to a much lesser degree. The reason for the
change in the type of foam is due to the desire of NASA to use
"environmentally friendly" materials in the space program. Freon was
used in the production of the previous foam. This method was
eliminated in favor of foam that did not require freon for its
production. MSFC is investigating the
consideration that some characteristics of the new foam may not be
known for the ascent environment.

* Another consideration is cryogenic loading, specifically hydrogen
(-423 degrees Fahrenheit) and oxygen (-297 degrees Fahrenheit). These
extreme temperatures cause the external tank to shrink up to six (6)
linear inches while it is on the pad prior to launch. Even though this
may not seem much when compared to the circumference of the external
tank, six inches of shrinkage is significant.

This is where the investigation stands at this point in time. As you
can imagine, this investigative process has required many hours and
the skills of many men and women dedicated to the safety of the
shuttle program. The key point I want to emphasize is the process of
investigation, which is coordinated amongst many people and considers
all possibilities. This investigation has used photography, telemetry,
radar coverage during the launch, aerodynamic modeling, laboratory
analysis and many more technical areas of expertise.

As this investigation continues, I am very comfortable that the
questions will be answered and the solutions applied. In fact, some of
the solutions are already in progress. At present the foam on the
sides of the tank is being sanded down to the nominal minimum
thickness. This removes the outer surface, which is tougher than the
foam core, and lessens the amount of foam that can separate and hit
the orbiter.

---------

Stuf4 wrote:

http://quest.arc.nasa.gov/people/jou...s87-12-23.html

Excerpt:
------
STS-87 is Home! The Post-Flight Inspection Begins
by Greg Katnik
December 23, l997

STS-87 rolled to a stop...the extent of damage at the conclusion of
this mission was not "normal." ... During the STS-87 mission, there
was a change made on the external tank. ... Foam cause damage to a
ceramic tile?! That seems unlikely, however when that foam is combined
with a flight velocity between speeds of MACH two to MACH four, it
becomes a projectile with incredible damage potential. The big
question? At what phase of the flight did it happen and what changes
need to be made to correct this for future missions? ... It was
determined that during the ascent, the foam separation from the
external tank was carried by the aerodynamic flow and pelted the nose
of the orbiter and cascaded aft from that point. Once again, this foam
was carried in a relative air-stream between MACH two and MACH 4!



A simple trajectory design change can blow the foam debris away from the
Orbiter, instead of blowing the blizzard of debris towards the Orbiter.
From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack. Changing the
angle of attack to -2 degrees in this region would rotate the relative wind
on the Orbiter by 4 degrees. Essentially, blowing the foam away from the
bottom of the Orbiter instead of towards it.

Craig Fink

In article . net,
Craig Fink wrote:

A simple trajectory design change can blow the foam debris away from the
Orbiter, instead of blowing the blizzard of debris towards the Orbiter.
From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack. Changing the
angle of attack to -2 degrees in this region would rotate the relative wind
on the Orbiter by 4 degrees. Essentially, blowing the foam away from the
bottom of the Orbiter instead of towards it.

What would that do to the aeroloading on the wings?

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
"Heisenberg might have been here."
~ Anonymous

"Craig Fink" wrote in message
ink.net...
| Stuf4 wrote:
|
| http://quest.arc.nasa.gov/people/jou...s87-12-23.html
|
| Excerpt:
| ------
| STS-87 is Home! The Post-Flight Inspection Begins
| by Greg Katnik
| December 23, l997
|
| STS-87 rolled to a stop...the extent of damage at the conclusion of
| this mission was not "normal." ... During the STS-87 mission, there
| was a change made on the external tank. ... Foam cause damage to a
| ceramic tile?! That seems unlikely, however when that foam is combined
| with a flight velocity between speeds of MACH two to MACH four, it
| becomes a projectile with incredible damage potential. The big
| question? At what phase of the flight did it happen and what changes
| need to be made to correct this for future missions? ... It was
| determined that during the ascent, the foam separation from the
| external tank was carried by the aerodynamic flow and pelted the nose
| of the orbiter and cascaded aft from that point. Once again, this foam
| was carried in a relative air-stream between MACH two and MACH 4!
|
|
|
| A simple trajectory design change can blow the foam debris away from the
| Orbiter, instead of blowing the blizzard of debris towards the Orbiter.
| From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack. Changing
the
| angle of attack to -2 degrees in this region would rotate the relative
wind
| on the Orbiter by 4 degrees. Essentially, blowing the foam away from the
| bottom of the Orbiter instead of towards it.
|
| Craig Fink
Now my memory may be faulty, but did this not come up as a non starter
because of the extra drag, though small, menaing that fule for some orbits
was a bit near the limit?

Sounds to me that someone on the flight team assumed from this sort of
report, that this problem was understood and fixed etc etc, but then, we
have been here before..

The whole story of the foam simply cries out ' we ain't as smart as we think
we are', and let us hope this time, a lesson about not dismissing
'unlikely' events is made the right way next time.

Brian

--
Brian Gaff....
graphics are great, but the blind can't hear them
Email:
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Craig Fink wrote:
A simple trajectory design change can blow the foam debris away from the
Orbiter, instead of blowing the blizzard of debris towards the Orbiter.
From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack. Changing the
angle of attack to -2 degrees in this region would rotate the relative wind
on the Orbiter by 4 degrees. Essentially, blowing the foam away from the
bottom of the Orbiter instead of towards it.

OK, so what are the effects on the rest of the stack? On the
trajectory? On payload? Abort options?

It's not near as simple as you'd like to believe.

D.
--
The STS-107 Columbia Loss FAQ can be found
at the following URLs:

Text-Only Version:
http://www.io.com/~o_m/columbia_loss_faq.html

Enhanced HTML Version:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Corrections, comments, and additions should be
e-mailed to , as well as posted to
sci.space.history and sci.space.shuttle for
discussion.

Herb Schaltegger wrote:

Craig Fink wrote:

A simple trajectory design change can blow the foam debris away from the
Orbiter, instead of blowing the blizzard of debris towards the Orbiter.
From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack. Changing the
angle of attack to -2 degrees in this region would rotate the relative wind
on the Orbiter by 4 degrees. Essentially, blowing the foam away from the
bottom of the Orbiter instead of towards it.

What would that do to the aeroloading on the wings?

The elevon schedule will need to be adjusted. There is a lot more to
this story than meets the eye, but suffice it to say this change will
likely be implemented.

From Herb Schaltegger:
Craig Fink wrote:

A simple trajectory design change can blow the foam debris away from the
Orbiter, instead of blowing the blizzard of debris towards the Orbiter.
From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack. Changing the
angle of attack to -2 degrees in this region would rotate the relative wind
on the Orbiter by 4 degrees. Essentially, blowing the foam away from the
bottom of the Orbiter instead of towards it.

What would that do to the aeroloading on the wings?

Craig, I agree with Herb that load relief limitations would be a
significant constraint. The margin is thin as it is right now, so
I've heard. I would be surprised if a 4deg alpha shift could be done
without ripping the wings off.

To increase payload performance, the orbiter had been designed to be
more gossamer than robust which means that safety margins along many
axes are thin.


~ CT

Herb Schaltegger wrote:

In article . net,
Craig Fink wrote:


A simple trajectory design change can blow the foam debris away from the
Orbiter, instead of blowing the blizzard of debris towards the Orbiter.
From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack. Changing the
angle of attack to -2 degrees in this region would rotate the relative wind
on the Orbiter by 4 degrees. Essentially, blowing the foam away from the
bottom of the Orbiter instead of towards it.


What would that do to the aeroloading on the wings?


Break them

aero_engineer wrote:

Herb Schaltegger wrote:

Craig Fink wrote:

A simple trajectory design change can blow the foam debris away from
the Orbiter, instead of blowing the blizzard of debris towards the
Orbiter. From Mach 2 to 4 the Shuttle flys a +2 degree angle of attack.
Changing the angle of attack to -2 degrees in this region would rotate
the relative wind on the Orbiter by 4 degrees. Essentially, blowing the
foam away from the bottom of the Orbiter instead of towards it.

What would that do to the aeroloading on the wings?

The elevon schedule will need to be adjusted. There is a lot more to
this story than meets the eye, but suffice it to say this change will
likely be implemented.

Elevon, probably not a problem after the high loads region. I would think
the biggest problem would be with engine out design. Larger negative angles
of attack are used in this region to loft the vehicle so that flight path
angle doesn't fall off too much. This would eat into the available lofting
that the vehicle can peform with an engine out. If it is too much, the
nominal trajectory may need to be slightly lofted.

Craig Fink

Stuf4 wrote:



Craig, I agree with Herb that load relief limitations would be a
significant constraint. The margin is thin as it is right now, so
I've heard. I would be surprised if a 4deg alpha shift could be done
without ripping the wings off.

To increase payload performance, the orbiter had been designed to be
more gossamer than robust which means that safety margins along many
axes are thin.



The Shuttle already flys more negative angles of attack than -2 degrees in
this region for engine out trajectories. This is after the high loads
region, and the Shuttle actually flys angles of attack of around -5 degrees
during the high loads region (Max Q).

Craig Fink