NASA Technical Reports Server (NTRS) 20030065843: Enhanced Large Solid Rocket Motor Understanding Through Performance Margin Testing: RSRM Five-Segment Engineering Test Motor (ETM-3)

12 Pages·7.6 MB·English

by  NASA Technical Reports Server (NTRS)

AlAA 2003-4958
Enhanced Large Solid Rocket Motor
Understanding Through Performance
Margin Testing - RSRM Five-Segment
Engineering Test Motor (ETM-3)
Hal Huppi, Mark Tobias, and James Seiler
A TK Thiokol Propulsion
I
{Brigham City, UT
AlAA Joint Propulsion Conference
-
July 21 23,2003
Huntsville, Alabama
For permission to copy or to republish, contact the American Institute of Aeronautics and Astronautics,
1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344.
ENHANCED LARGE SOLID ROCKET MOTOR UNDERSTANDING
THROUGH PERFORMANCE MARGIN TESTING -
RSRM FIVE-SEGMENT ENGINEERING TEST MOTOR (ETM-3)
Hal Huppi, Mark Tobias, and James Seiler*
ATK Thiokol Propulsion
Brigham City, Utah
ABSTRACT INTRODUCTION
The Five-Segment Engineering Test Motor (ETM-3) is During the last 2% years (2001 through 2003), NASA
an extended length reusable solid rocket motor MSFC and ATK Thiokol have jointly designed, veri-
(RSRM) intended to increase motor performance and fied, and produced a five-segment Engineering Test
internal environments above the current fou-segment Motor (ETM-3). The focus of this endeavor has been
RSRM flight motor. The principal purpose of ETM-3 is on providing the opportunity for learning and im-
to provide a test article for RSRM component margin provement. Challenging a new generation of people
testing. As the RSRM and Space Shuttle in general (i.e., SRM technical personnel) is an investment for the
continue to age, replacing obsolete materials becomes Space Shuttle program in not only maintaining and
an ever-increasing issue. Having a five-segment motor enhancing current capabilities, but also providing pos-
that provides environments in excess of normal opera- sibilities for future upgrade enhancements.
tion allows a mechanism to subject replacement mate-
rials to a more severe environment than experienced in The current Space Shuttle RSRM is a post Challenger
flight. Additionally, ETM-3 offers a second design data (late 1980’s) derivative of the original SRM designed
point from which to develop and/or validate analytical back in the 1970s. The design and analysis engineers of
models that currently have some level of empiricism today were not involved in the original design activi-
associated with them. These enhanced models have the ties; therefore, the opportunity to build upon the suc-
potential to further the understanding of RSRM motor cessful trial and error works of their predecessors is of
performance and solid rocket motor (SRM) propulsion primary importance towards enhancing a new genera-
in general. Furthermore, these data could be leveraged tion’s understanding for the new century. Today’s en-
to support a five-segment booster (FSB) development gineers have used the ETM-3 activities to accomplish
program should the Space Shuttle program choose to that goal and set the stage for testing the largest SRM
pursue this option for abort mode enhancements during to date. The ETM-3 static test article configuration
the ascent phase. A tertiary goal of ETM-3 is to chal- (Table 1) will increase motor performance and internal
lenge both the ATK Thiokol Propulsion and NASA environments above the current four segment motor
MSFC technical personnel through the design and and thus provide a mechanism for margin testing of
analysis of a large solid rocket motor without the bene- RSRM components.
fit of a well-established performance database such as
the RSRM. The end result of this undertaking will be a Techniques have been improved for exercising and
more competent and experienced workforce for both upgrading RSRM and ETM-3 analytical models and
organizations. Of particular interest are the motor de- design methods. Technical skill enhancement has been
sign characteristics and the systems engineering ap- accomplished in the following areas: propellant formu-
proach used to conduct a complex yet successful large lation, ignition transient modeling, erosive burning,
motor static test. These aspects of ETM-3 and more computational fluid dynamics (CFD), fluid structural
will be summarized. interaction (FSI), loads allocations, structures, thermal,
material recession, instrumentation, and the T-97 test
stand facilities. Testing of the RSRM design well out-
side its intended performance environment will demon-
02003, ATK Thiokol Propulsion, a Division of ATK Aerospace Company
Published by the American Institute of Aeronautics and Astronautics, Inc., with permission
* Authors are RSRM chief systems engineer, ballisticslgraind esign supervisor, and ETM-3 project engineer; respectively.
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strate its robustness and shed light on component re- The ETM-3 static test article is a unique end-item con-
sponse to reduced margin conditions. Pre- and post-test figuration that will not be flown. It is being used as a
data from these areas can be used to enhance and vali- mechanism to overtest RSRM component hardware
date models and analysis techniques with a second and materials and to provide insight into a larger SRM
large SRM data point. The data can also be used to with a greater lengtwdiameter (L/D) ratio, higher inter-
support a FSB development program should the Space nal Mach number, and a larger internal static pressure
Shuttle program choose to pursue this option for ascent drop down the bore (Table 2 and Figure 1).
abort mode enhancements.” 2*3 *4 ,
Table 2. ETM-3 vs. RSRM Key Parameters
Table 1. ETM-3 Component Overview
Key Comparison
RSRM 1- D ETM-3 1- D
Parameters
ETM-3 Design
I 1
Component Sarneas Modified New Reference Burn Rate (IDS) 0.368 Reduced
LID Ratio 23.08 28.42
Static Pressure Droo (osia) 135.2
I I I I
Max Mach No. 0.39 0.44
I I 1 I
Maximum Vacuum
Thrust (Mlbf) 3.145 3.65
I
Specific Impulse 268.4 267.5
I
Web Time (sec) 111.1 114.8
Action Time (sec) 123.5 127.8
PROGRAM REQUIREMENTS Web Time Avg
Pressure (psia) 733.2
The RSRM top level margin test program requirements Web Time Avg Mass
Flow Rate (Ibmlsec) 9,746 11,652
applicable to ETM-3 consist of the following:
1) Do not destroy the motor or the test stand
2) Maintain reusability of the metal hardware
3) Obtain margin test data
4) Enhance analytical modeling capability
Similar Head-End Pressure
as RSRM
Preserves 1,016 psia MEOP
Increased Web Time
Due to Additional Center
Slightly Steeper Tailoff
200
~ Increased Web Time Average
100 Pressure
07
0 20 40 60 80 100 120 140 160
Time (sec)
Figure 1. ETM-3 Design TIM (D-TIM) Predicted Performance: Comparison to RSRM Block Model
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The ETM-3 project has been structured to mitigate the associated products were scheduled into the 2% year
overall concern of a potential negative impact to the window per an ETM-3 Milestone Logic Flow (Figure
RSRM flight motors. Design verification is based on 2). Project planning dictated that evolution of verifica-
pre-test activities that support test readiness (subscale tion phase products would be tracked primarily in the
testing and analysis) and not on post-test performance. following areas: Requirements, Verification Plan,
The joint MSFC and ATK Thiokol team has orches- Configuration, Safety and Mission Assurance
trated critical reviews that have scrutinized the design (%MA), and the T-97 test stand.
verification process. The process has consisted of tak-
ing exceptions to the current RSRM requirements, al- Once the point design was established, changes to the
locating unique loads, and performing necessary design current RSRM static test requirements via a Contract
activities (subscale testing and analysis) that provided End Item (CEI) addendum became necessary in order
component verification compliance. This was all done to accommodate the unique changes of ETM-3 (Figure
to manage the inherent risks and enhance the positives 3). Lead component design engineers were designated
that ETM-3 has to offer. to assist in developing a preliminary requirements as-
sessment matrix and component verification logic
flows. These logic flows were later integrated at the
SYSTEMS ENGINEERING APPROACH
motor level to produce an ETM-3 Project Road Map
(PRM) that was color-coded by component (Figure 4).
In order to orchestrate a successful design verification
A high-fidelity schedule definition (utilizing each PRM
phase, early upfront planning was a key activity that
block) was also created for tracking and status pur-
could not be overlooked. An ATK Thiokol-dedicated
poses. Weekly systems integration telecons with MSFC
planning team was established consisting of a program
and internal component team meetings were also util-
manager, a project engineer, and a systems engineer
ized to discuss PRM progress and action item closures.
with like counterparts at NASA-MSFC. Major events
Figure 2. ETM-3 Milestone Logic Flow
(MSFC RSRM Project and Independent Reviews) and
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A Verification Plan was formalized which documented
the proposed testing and analysis activities that were
linked to the PRM. ETM-3 unique changes and RSRM Four MSFC Project Reviews
demonstration changes received a change interaction 0 Kick-off
assessment in both the engineering and system safety
0 Project Requirements
communities. Also, S&MA risk assessment studies and
Integrated Failure Modes & Effects Analyses (IFEMA) 0 Preliminary Design
were performed. Final Engineering Change Packages 0 Design
(ECP) containing all verification documents were ap-
One MSFC Independent Review
proved by MSFC. In order to accommodate the ex-
tended length ETM-3, T-97 test stand tooling and
facility modifications were necessary (Figure 5).
I I
Modified Propellant Formulation to
Reduce Burn Rate (all segments) Hardware (all segments)
IStandard R SRM Igniter I I
Added Center Segment
I I I
Chamfered Propellant
and center segments)
Thickened Aft Inhibitor
Figure 3. ETM-3 Unique Changes
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Figure 4. ETM-3 Project Road Map (PRM)
Modifications in Shaded Boxes
otter Turn-around
Forward Reaction
N, Trailers
Figure 5. T-97 Tooling and Facility Modifications
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MOTOR / COMPONENT DESIGN over RSRM (Table 2 and Figure 1). In some cases
CHARACTERISTICS these increases are substantial. These increased envi-
ronments have been characterized and assessed by the
The enhanced performance of ETM-3 is achieved pri- various component disciplines.
marily by the addition of a RSRM center segment.
However, added motor performance has been achieved In order to handle the increase in head-end pressure
with a throat diameter increase and the incorporation of that the additional center segment provides, the RSRM
an extended aft exit cone (EAEC) (Figure 6). The reference burn rate has been reduced. This has been
EAEC was previously tested on Flight Support Motor accomplished with minor alterations to the TP-H1148
No. 5 (FSM-5) as an RSRM enhancement, although it Type IV propellant formulation. Iron oxide type, am-
was never implemented as part of the flight baseline monium perchlorate (AP) unground-to-ground ratio,
configuration. Parameters such as average pressure, and ground AP particle size have been optimized to
maximum thrust, mass flow rate, centerline Mach provide the lower bum rate. The changes have resulted
number, pressure and thrust integrals have all increased in a TP-H1148 Type VI1 classification.
Throat Plane Shifted Aft
Throat Diameter Increased
----_-_-._ --_--.- .---- .--._-- .-____
._._-..
-..-- -.-
/./. --.
-..
-0.- 1..
0-
,/' . a ' \..
,/' *.'
,i
*.' --- --- *- '
------ -- -_- - --- --- - ---D iameter Increased I
- ------------ - - - -
*. ' --- - ,/*
\.. '.. - .=:.===3 /." ,/'
...
.-. -..
Length Increased -.Re-
----.. ----._-- --.__-._ - -_- __-_ -. ___ --.- ------.- _ *__..---- //--/
Figure 6. ETM-3 Nozzle and EAEC
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The ETM-3 grain configuration is similar to previously susceptible to this flow-driven event. These forward
fired RSRMs with the primary exception of leading facing steps protrude into the free stream flow acting as
edge propellant grain chamfers on the center and aft flow restrictors. Local pressure gradients develop
segments (Figure 7). These chamfers are nominally across the forward facing propellant comer, which
sized in the radial and axial directions. Previous design promotes grain deformation toward the centerline of
iterations considered a smaller sized chamfer. Detailed the motor. If port velocities are high enough and the
FSI analyses indicated additional margin against unre- propellant modulus low enough, unrestrained deforma-
strained propellant deflections could be gained with a tions can develop leading to motor failure from over
larger chamfer. Hence, the larger sized chamfer was pressurization. The increased mass flow rate and port
adopted as the baseline grain geometry. The chamfers velocity of the ETM-3 design aggravates these condi-
were cast in place via new tooling rings that bolt to the tions. Consequently, the forward facing propellant cor-
existing center and aft casting pit mold plates and inter- ners have been chamfered as mentioned above. These
face with the current casting cores (Figure 8). chamfers significantly reduce local pressure gradients
and minimize the inward deflections of the propellant
I grain. A detailed assessment of this phenomenon has
Propellant Leading
been performed for the ETM-3 grain design.6
Edge Chamfer (aft and
center segments)
The nitrile butadiene rubber (NBR) inhibitor height for
Change
each center segment has been modified to accommo-
date the propellant chamfer. These inhibitors are now
the same height as the aft segment NBR inhibitor. The
aft segment inhibitor is short enough to handle the in-
creased propellant radius and the mold tooling is easily
adaptable for use with the center segment casting op-
eration. Since trace shape tailoring is unimportant for
ETM-3, this was deemed the most straightforward,
Inhibitor
Thickened AI^ innibitor
economical design solution.
Figure 7. ETM-3 Grain Chamfers and Inhibitors The ETM-3 case insulation profile has been changed
from RSRM for the center and aft segments. The for-
The propellant chamfers are necessary to mitigate the ward segment profile remains the same as RSRM. In-
potential for a phenomenon known as “bore choking.” sulation thicknesses for the aft and center segments
Segmented SRMs with forward facing grain steps are have been increased to account for longer exposure
times and increased mass flow rates. The
- aft dome carbon fiber (CF)-EPDM / NBR
insulation thickness ratio was also in-
creased. This was accomplished by reduc-
I Motor Case ing the NBR thickness and replacing it
with staged CF / EPDM to maintain the
design profile (Figure 9).
MOTOR / COMPONENT
VERIFICATION SUMMARY
All ETM-3 predicted margins (including
those less than RSRM) have been justified
through performance and environments
requirements definition, com-ponent veri-
fication tests and analyses, and both ATK
Thiokol and MSFC review processes. De- ,
pitted in Figure 10 is an example of the
Figure 8. ETMS Propellant Grain Chamfer
magnitude of documentation that was
Cast Tooling
submitted to MSFC during the design re-
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STA A STA A
Dome
Raw CF-EPDM
RSRM Aft Dome Insulation Configuration ETM-3 Aft Dome Insulation Configuration
Figure 9. RSRM vs. ETMS Aft Dome CF-EPDM / NBR Thickness Ratio Increased
view period. In some areas updates to the documents Per the verification plan, major motor or component
were prepared to support delta design activities and compliance activities were performed in the following
final component change submittals. Tied to the RSRM areas:
challenged and/or modified requirements per the CEI
Grain design and motor performance predictions
0
ETM-3 addendum and verification plan, a summary of
Propellant formulation testing
compliance rationale is contained in each applicable Ignition transient predictions
document and compiled in a motor level CEI verifica- Erosive burning test and analysis’
tion compliance matrix. CFD analysis8-’
FSI analysis6
Motor Requirements Test StandlFa cilities
Requirements
CPWI-36WE TWR-74468 0
Environments
CFW1-3600 Addendum L TWR-74579 A
\
TWR-74579A TWR-74580 A
TWR-74580 A
c
Test StandlFacilities
uullltJulmllr ’ Verification Plan
TWR-15723-067
I I I
L
Propellant Nozzle
System Safety
ECP SRM-3599 TR12631 ECP SRM-3593 TWR-74454
TWR-74361
TWR-74422
TWR-74391 TWR-74423
TWR-74409 TWR-74424
TWR-74437 TWR-74425
-TWR-74438 TWR-74426
TWR-74439 TWR-74427
TWR-74597 1
Supports multiple components
TWR-74598 I ’
Matrix
TWR-74459
Figure IO. ETM-3 Design Review Verification Submittals
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0 Internal environments and mass properties ance for axial pressure drop determination, ignition
0 Loads and environments transient modeling, static test loads, case behavior sub-
0 Internal acoustics / pressure dynamics jected to gravity loading, and material recession (in-
0 Case structures analysis hibitor, aft dome insulation, and EAEC ablatives).
0 Propellant, Liner, Insulation (PLI) structural Internal field joint pressure gages and aft dome and
analysis
EAEC recession gages are being used for the first time
0 Nozzle structural analysis
on a full-scale static test. ETM-3 will be the most
0 Nozzle torque / vectoring analysis
highly instrumented full-scale static test motor in
0 Insulation thermal design
0 Nozzle char and erosion analysis
0 Nozzle joint thermal analysis ETM-3 Instrumentation
0 Motor joints and seals assessment Summary by Gage Type
0 System Safety review 618 total gages
(633 total channels, 257 stand
BENEFITS SUMMARY
0 47 pressure gages (24 standard)
0 29 force (load) gages (44 channels,
After the ETM-3 test and the follow-on evaluations,
30 standard)
predicted RSRM environments and margins will be 0 167 temperature gages (89 standard)
better understood. Table 3 contains an overview of the 0 45 acceleration gages (IO standard)
ETM-3 CEI exceptions and predicted margins that per- 0 160 strain gages (56 standard)
mit a second motor environmental design point and 0 11 event gages (11 standard)
0 36 displacement gages (12 standard)
over testing of RSRM hardware and materials. 0 8 voltage (command) gages (8 standa
0 8 current gages (8 standard)
ETM-3 will be fired in the T-97 static test facility. The 0 6 interlock gages (6 standard)
T-97 aft test stand has been relocated to accommodate 0 33 radiometer (heat flux) (3 standard)
the ETM-3 increased motor length and a portion of the
anticipated FSB length (Figure 5). During the test,
RSRM history with a total of 618 gages.
thrust and pressure data will be recorded. Additional
extensive instrumentation, both internal and external,
Table 4 contains an overview of the RSRM related
will be used to help in understanding motor perform-
topics and analyses that are clearly being tested and
Table 3. ETM-3 CEI Exceptions I Predicted Margins
PMBT 40"-90°F 55"-82"F Lower end for PLI SF
Upper end for MEOP
Performance Table II 1 Addendum L Table II +5 sec, +65 psia avg pressure
1
Pressure Seals No erosion Erosion of nozzle joints 3 Predicted ~50%a fter Joint 4
and 4 primary acceptable primary groove depth reduced
Nozzle Liner Design -- Design to minimize pocketing High temperature carbonized
material used in throat region
Environments -- Larger mass flow and New loads accounted for in
DreSSure droD comDonent analvsis
Case Safety Factors 1.4 1.3 for joint pins 0.12 margin (pins, operation)
(SF) Actual properties/dimensions 0.16 margin (buckling) 1.4 SF
for buckling and operation 0.02 margin (operation) 1.4 SF
Insulation 2.0 factory joints 1.5 over factory joints Actual factory joint SFs >1.5
Decomposition SFs
1.5 aft dome 1.3 in aft dome Actual aft dome SFs >I. 5
__
Propellant SFs None PMBT exception only
Nozzle SFs Char/erosion equation 600°F isotherm within CCP Isotherm well within CCP
1.5 for flex boot 1.3 for flex boot 0.14 thermal margin
AEC I. 5 in. AEC 12 in. charred Virgin material remaining
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