Barbara Selby                                  February 28, 1989
Headquarters, Washington, D.C.       Embargoed until 11 a.m. EST

Jerry Berg
Marshall Space Flight Center, Huntsville, Ala.


RELEASE:  89-25

SHUTTLE TILE DAMAGE STUDY COMPLETED; "GO" FOR DISCOVERY FLIGHT 


     A NASA review panel, investigating the damage to the orbiter 
Atlantis' thermal protection system during the STS-27 mission, 
found that the most probable cause was ablative insulating 
material from the righthand solid rocket booster nose cap 
dislodging and striking the orbiter about 85 seconds into 
flight.  

     The Shuttle was traveling at approximately two and one-half 
times the speed of sound.  At that speed, tests and analyses have 
demonstrated that material breaking away from forward portions of 
the vehicle can result in debris striking the orbiter with enough 
force to damage the tiles.  

     Following its landing on Dec. 6, 1988, inspection revealed 
that Atlantis had sustained slightly more than 700 individual 
tile impacts.  The damage was concentrated on the lower surface 
tiles of the righthand side.  One complete tile was found missing 
from the damaged area below the crew compartment, and an 
insulation panel was missing from the right orbital maneuvering 
system (OMS) pod.

     In its effort to understand how the damage occurred, the 
review team gathered extensive physical evidence by examining the 
Atlantis vehicle, reviewing prelaunch inspection records and 
procedures, assessing tracking camera footage and interviewing 
Atlantis' flight crew.  They studied the flight hardware design 
and build records and conducted laboratory tests on the damaged 
tiles, looking for bits of the damaging debris material.

     In addition to such tests and analyses, the finding 
concerning the most probable cause was based on:

     o  A determination that several manufacturing process 
variables on the right booster nose cap were very near their 
specification limits; and,

     o  The discovery of minute bits of the booster nose cap 
insulation material and paint embedded in the damaged tiles and 
OMS pod blankets.

     The review team also reported that debris from other 
sources, including repaired external tank insulation and cork 
material covering the solid rocket motor joints, may have caused 
minor tile damage.

     The team's findings do not pose any constraint for launching 
Discovery on the STS-29 mission, according to the report.  A 
major reason for concluding that the STS-29 hardware is ready to 
fly stems from an improvement made to the suspect insulating 
material covering the booster nose caps.

     The suspect material, known as Marshall Sprayable Ablator 
(MSA), was used in its original formulation for nose caps up to 
and including the STS-27 mission.  Following fabrication of the 
STS-27 nose caps, changes were made in the material's properties, 
manufacturing process and application.  The result was an 
improved product designated MSA-2.  The changes have been shown 
to produce stronger bonds between the insulating material and the 
surface on which it is applied.  

     The first boosters to be fabricated with the improved 
material are those for the upcoming STS-29 flight.  This new 
material recently was subjected to additional strength tests, 
called "pull tests," and successful completion of those tests has 
further bolstered confidence that the material will perform 
successfully.

     Despite the team's belief that the change in nose cap 
insulation material will prevent severe tile damage in the 
future, the report recommended several other steps toward further 
understanding and to minimize minor damaging debris on future 
flights.  The recommended steps include:

     o  Expanding an existing operations team to monitor and 
report on this critical area for all future flights; 

     o  Selectively performing the pull tests on SRB nose cap 
insulation material prior to future flights;

     o  Inspecting the joint cork material which externally 
covers solid rocket motor field joints to make sure there are no 
low density inclusions in the material (such inclusions, if 
found, normally are repairable);

     o  Reviewing design criteria and searching for process 
enhancements to further minimize debris potential; and, 

     o  Assigning more data-gathering sources, such as additional 
cameras, for future flights.  If and when tile damage does occur, 
such additional sources would yield more data and other evidence, 
thus providing a better basis for establishing the causes.

     The review panel was chaired by John W. Thomas of Marshall 
Space Flight Center.  Other members include Jay Honeycutt of the 
NSTS Program Office, NASA Headquarters (alternate chairman); Jack 
Nichols, James Earle, James Hester, Keith Henson and Dewey 
Channell of the Marshall Space Flight Center; Marion Coody, 
Robert White, Gary Coen and Don McMonagle of the Johnson Space 
Center; and Charles Stevenson and Judith Kersey of the Kennedy 
Space Center.