Russ Kepler writes:

No, not the adhesive, the foam itself. Environmentalism forced a
change of the foaming process from using a CFC agent to something
more "environmentally friendly" (and structurally inferior). If
someone is claiming otherwise, it betrays a political agenda.
Environmentalism destroyed Columbia.

I heard that, too, but was not able to find a link that didn't look
like tinfoil cap folks posted it. I'm not disputing it, just can't
find a good link - do you have one?

Yes. I wrote about this February 4, 2003, just several days after the
disaster on Feb 1st, based on Greg Katnik's analysis from 1997, and before
the culpability of the foam insulation was being promoted:

http://groups.google.com/groups?q=co...author%3Akinch

Amazingly, if you Google '"greg katnik" nasa' you get only 212 hits today.

This is the key document:

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

Which I herewith quote in its entirety below:

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.