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OCR for page 33
NATIONAL RESEARCH COUNCIL
COMMISSION ON ENGINEERING AND TECHNICAL SYSTEMS
2101 Constitution Avenue Washington, D. C. 20418
COMMITTEE ON NASA SCIENTIFIC
AND TECHNOLOGICAL PROGRAM REVIEWS
Panel on Redesign of Space Shuttle
Solid Rocket Booster
The Honorable James C. Fletcher
Administrator
National Aeronautics & Space Administration
400 Maryland Avenue, S.W., Room 7137
Washington, DC 20546
Dear Jim:
November 20, 1987
I am pleased to submit herewith the fifth interim report
of the National Research Counci1's Panel for the Technical
Evaluation of the Redesign of the Space Shuttle Solid Rocket
Booster. Since our last report, the Panel has conducted two
formal meetings and members have met with the redesign team
during three test readiness reviews, three technical
interchanges, and the DM-8 hot firing.
In contrast to our previous getters, which have dealt with
the SRB program as a whole, this report addresses only the
test program in preparation for first flight. The test pro-
gram is progressing well and has had some notable successes in
recent months. A consequence has been heightened confidence
in the baseline design. As additional tests are successfully
carried out, the need to continue even the current minimal
effort on contingent designs for first flight diminishes.
The overall testing program, including subscale tests,
short-duration simulations, and full-duration firings, repre-
sents a commendably extensive effort--certainly large compared
with that which preceded the first Shuttle flight and very de-
manding of resources. When completed, it is reasonable to
anticipate that the design and performance of the joints and
insulation of the Shuttle SRM will be better understood than
those of any other large solid rocket motor. The timing of
the program, working toward the next launch in June 1988, is
"tight" and the Panel approaches with great reluctance sugges-
tions which could impose additional items or time constraints
on the effort.
33
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to serve government and other organizations
OCR for page 34
Letter to the Honorable James C. F1 etcher
—2—
Nonetheless, our review of the test program has leg us to
conclude that it couth be further improved in a few signifi-
cant aspects, which we commend to your attention:
o Despite a formal designation of the primary and
secondary O-rings as the redundant seals, the designs
of both the case-to-case field and case-to-nozzle
joints use bonded insulation upstream of the primary
O-ring to contain combustion gases within the motor.
This characteristic of the designs emphasizes the
importance of understanding how this insulation works
as a j oint seal. In addition to the work already
planned, we recommend an evaluation of the seal ing
characteristics of the designs, inch uding the
respective flaps and adhesives, as functions of
temperature ~ def ormation rates, exposure to varied
environments, and aging.
O Because both the case-to-case j oint and the case-to-
nozzle joint feature unvented designs, attention is
re qu ired to a s sure that the pert ormance o f the pr i -
mary and secondary O-rings is evaluated in the test
program. We concur with the decision for a timely
fur 1-scale, full-duration motor firing in which
pressurization of the primary O-ring in both j oints
is ensured. With no similar tests of the secondary
O-rings planned on full-duration motors, we believe
that the number of such tests planned for the
short-duration simulation test articles shout ~ be
increased. Furthermore, measures taken to ensure
that the O-rings experience pressure in the respec-
tive tests also prevent the pretest application of
pressure in the usual way to seat the O-rings in the
proper direction. Special care will therefore be
required in these tests to be sure that the primary
and secondary O-rings are properly seated before
firing.
o Because O-ring leakage can occur and not leave
discernible traces in fired hardware and since the
timing of leakage cannot be evaluated by post-test
inspection, we recommend that the pressure both
immediately upstream of the primary and between the
primary and secondary O-rings in both the case-to-
case field and case-to-nozzle joints be routinely
measured in all ground tests, including full-scale
firings.
34
OCR for page 35
Letter to the Honorable James C. Fletcher
o The repetitive tests planned to demonstrate how to
make an effective insulation bondline in the case-to-
nozzle joint by assembly and disassembly are very
important. In addition, we believe that there should
be at least one test each in which the case-to-nozzle
and the case-to-case field joints are assembler,
leak-tested, disassembled, cleaned-up, reassembled,
and fired before first flight to simulate in advance
an operation that may well be requ i red a fter flight
articles are delivered to the launch site ~ This
latter type of test could be accomplished in short-
duration simulation tests in the Joint Environment
Simulator (JES), Nozzle Joint Environment Simulator
(NJES), and/or the Transient Pressure Test Article
(TPTA).
While most of these recommendations relate to the manner
in which presently planned tests are to be carried out or to
measurements to be made, some of the recommendations require
additional testing on TPTA, JES, or NJES hardware. Recog-
nizing the severe time constraints already imposed on these
test units, the Panel recommends that if the schedule of test
activities before the next flight is not sufficiently flexible
to accommodate our recommendations for additional tests, con-
sideration be given to providing the necessary room in the
test program by deferring some of the testing now planned for
so-called "manufacturing defects."
In closing, I am again pleased to congratulate NASA for
the high degree of profess tonal ism and dedication of the
redesign team. We are grateful for the informative technical
presentations and discussions which have f acid itated our
task.
S incerely,
H. Guyford Stever
Chairman
cc: Adm. Richard H. Truly
Panel Members
35
OCR for page 36
Representative terms from entire chapter:
honorable james
