National Aeronautics and
Space Administration

Lyndon B. Johnson Space Center
Houston, Texas
77058

RADM Richard H. Truly
Associate Administrator for Space Flight
NASA Headquarters
Code M
Washington, DC 20546


Dear Admiral Truly:

The search for wreckage of the Challenger crew cabin has been
completed.  A team of engineers and scientists has analyzed the
wreckage and all other available evidence in an attempt to
determine the cause of death of the Challenger crew.  This letter
is to report to you on the results of this effort.

The findings are inconclusive.  The impact of the crew
compartment with the ocean surface was so violent that evidence
of damage occurring in the seconds which followed the explosion
was masked.  Our final conclusions are:

--the cause of death of the Challenger astronauts cannot be
positively determined;

--the forces to which the crew were exposed during Orbiter
breakup were probably not sufficient to cause death or serious
injury; and

--the crew possibly, but not certainly, lost consciousness in the
seconds following Orbiter breakup due to in-flight loss of crew
module pressure.

Our inspection and analyses revealed certain facts which support
the above conclusions, and these are related below:

The forces on the Orbiter at breakup were probably too low to
cause death or serious injury to the crew but were sufficient to
separate the crew compartment from the forward fuselage, cargo
bay, nose cone, and forward reaction control compartment.  The
forces applied to the Orbiter to cause such destruction clearly
exceed its design limits.

The data available to estimate the magnitude and direction of
these forces included ground photographs and measurements from
onboard accelerometers, which were lost two-tenths of a second
after vehicle breakup.

Two independent assessments of these data produced very similar
estimates.  The largest acceleration pulse occurred as the
Orbiter forward fuselage separated and was rapidly pushed away
from the external tank.  It then pitched nose-down and was
decelerated rapidly by aerodynamic forces.  There are
uncertainties in our analysis; the actual breakup is not visible
on photographs because the Orbiter was hidden by the gaseous
cloud surrounding the external tank.  The range of most probable
maximum accelerations is from 12 to 20 G's in the vertical axis. 
These accelerations were quite brief.  In two seconds, they were
below four G's; in less than ten seconds, the crew compartment
was essentially in free fall.  Medical analysis indicates that
these accelerations are survivable, and that the probability of
major injury to crew members is low.

After vehicle breakup, the crew compartment continued its upward
trajectory, peaking at an altitude of 65,000 feet approximately
25 seconds after breakup.  It then descended striking the ocean
surface about two minutes and forty-five seconds after breakup at
a velocity of about 207 miles per hour.  The forces imposed by
this impact approximated 200 G's, far in excess of the structural
limits of the crew compartment or crew survivability levels.

The separation of the crew compartment deprived the crew of
Orbiter-supplied oxygen, except for a few seconds supply in the
lines.  Each crew member's helmet was also connected to a
personal egress air pack (PEAP) containing an emergency supply of
breathing air (not oxygen) for ground egress emergencies, which
must be manually activated to be available.  Four PEAP's were
recovered, and there is evidence that three had been activated. 
The nonactivated PEAP was identified as the Commander's, one of
the others as the Pilot's, and the remaining ones could not be
associated with any crew member.  The evidence indicates that the
PEAP's were not activated due to water impact.

It is possible, but not certain, that the crew lost consciousness
due to an in-flight loss of crew module pressure.  Data to
support this is:

--The accident happened at 48,000 feet, and the crew cabin was at
that altitude or higher for almost a minute.  At that altitude,
without an oxygen supply, loss of cabin pressure would have
caused rapid loss of consciousness and it would not have been
regained before water impact.

--PEAP activation could have been an instinctive response to
unexpected loss of cabin pressure.

--If a leak developed in the crew compartment as a result of
structural damage during or after breakup (even if the PEAP's had
been activated), the breathing air available would not have
prevented rapid loss of consciousness.

--The crew seats and restraint harnesses showed patterns of
failure which demonstrates that all the seats were in place and
occupied at water impact with all harnesses locked.  This would
likely be the case had rapid loss of consciousness occurred, but
it does not constitute proof.

Much of our effort was expended attempting to determine whether a
loss of cabin pressure occurred. We examined the wreckage
carefully, including the crew module attach points to the
fuselage, the crew seats, the pressure shell, the flight deck and
middeck floors, and feedthroughs for electrical and plumbing
connections.  The windows were examined and fragments of glass
analyzed chemically and microscopically.  Some items of equipment
stowed in lockers showed damage that might have occurred due to
decompression; we experimentally decompressed similar items
without conclusive results.

Impact damage to the windows was so extreme that the presence or
absence of in-flight breakage could not be determined.  The
estimated breakup forces would not in themselves have broken the
windows.  A broken window due to flying debris remains a
possibility; there was a piece of debris imbedded in the frame
between two of the forward windows.  We could not positively
identify the origin of the debris or establish whether the event
occurred in flight or at water impact.  The same statement is
true of the other crew compartment structure.  Impact damage was
so severe that no positive evidence for or against in-flight
pressure loss could be found.

Finally, the skilled and dedicated efforts of the team from the
Armed Forces Institute of Pathology, and their expert
consultants, could not determine whether in-flight lack of oxygen
occurred, nor could they determine the cause of death.


Joseph P. Kerwin

Last Updated Sunday, January 29 2006 @ 10:37 AM MST