Achieving Space Shuttle ATO Using the Five-Segment Booster (FSB)

12 Pages·2001·0.77 MB·English

by  Sauvageau, Donald R

AIAA 2001-3413
Achieving Space Shuttle ATO Using
the Five-Segment Booster (FSB)
Donald R, Sauvageau
Thiokol Propulsion
Brigham City, UT
FIVE SEGMENT BOOSTER
AIAA Joint Propulsion Conference
July 9-11, 2001
Salt Lake City, Utah
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,
• _- TI
01-3413
ACHIEVING SPACE SHUTTLE ATO USING THE FIVE-SEGMENT BOOSTER (FSB)
Donald R. Sauvageau
Thiokol Propulsion
Brigham City, Utah
As part of the continuing effort to identify ap- When the Phase A study was initiated, the basic
proaches to improve the safety and reliability of objective of the FSB design concept was to elimi-
the Space Shuttle system, a Five-Segment Booster nate the return to launch site (RTLS) abort mode by
(FSB) design was conceptualized as a replacement providing transatlantic landing (TAL) abort capa-
for the current Space Shuttle boosters. The FSB bility from the pad. In conjunction with achieving
offers a simple, unique approach to improve as- the basic performance objective of eliminating
tronaut safety and increase performance margin. RTLS, we also imposed the requirement of mini-
mizing the impacts on other Shuttle elements,
To determine the feasibility of the FSB, a
which entailed ensuring that the current external
Phase A study effort was sponsored by NASA and tank (ET) and pad interface control documents
directed by the Marshall Space Flight Center (ICD) were maintained as well as ensuring that
(MSFC). This study was initiated in March of there were no increases in the design driving loads
1999 and completed in December of 2000. The or environments on the orbiter. Additionally, we
basic objective of this study was to assess the fea- were to minimize the changes to the current Shuttle
sibility of the FSB design concept and also esti- reusable solid rocket booster (RSRB) hardware,
mate the cost and scope of a full-scale develop- and infrastructure, thus maximizing the utilization
ment program for the FSB. In order to ensure an of the flight-proven design materials and processes
effective and thorough evaluation of the FSB con- that are currently being successfully used on the
cept, four team members were put on contract to Space Shuttle system. The basic conceptual design
support various areas of importance in assessing approach taken for the FSB isshown in Figure 1.
the overall feasibility of the design approach.
Essentially what has been done is add a center
Thiokol was responsible for performing all of segment. As a result of the incorporation of an ad-
the motor design and overall FSB integration ef- ditional center segment, a new nozzle had to be
fort. Boeing North American conducted all of the designed to accommodate the increased mass flow
systems integration studies, which included per- rate associated with the added propellant. To main-
formance assessments and load evaluations. tain the existing interface with the ET, the forward
United Space Alliance (USA), in conjunction with attach provisions had to be changed from the cur-
United Space Boosters Incorporated (USBI) and rent forward skirt to the external surface on the
BD Systems, evaluated all of the booster element booster forward segment. Since the forward skirt
design aspects as well as the Kennedy Space Cen- no longer needs to take up the forward thrust
ter (KSC) site implications. Lockheed Martin loads, a new forward skirt was designed that was a
Space Systems Company, Michoud Operations much simpler configuration. As a result of adding
(LMSSC) was responsible for determining im- a center segment, the inert weight of the boosters
pacts to the external tank (ET) design. increased. Therefore, to ensure the same attrition
@2001 Thiokol Propulsion, Published by the American Institute of Aeronautics and Astronautics, Inc. with permission
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T rate propellant had to be included in the design.
4"61n. New Parachutes This propellant is the same formulation as that
New Forward
used in the existing Shuttle booster. The lower
Skirt
h -_t
burn rate is achieved by a slight reduction in the
NewForward
Attach iron oxide burn rate catalyst used in the basic
formulation of the propellant. The nozzle throat
diameter was also increased 5.8 inches to accom-
modate the increased mass flow rate from the
1,80( In. _ AddCenterfseIgment added center segment. The increased throat di-
ameter in conjunction with the reduced bum rate
allowed us to maintain the same maximum ex-
pected operating pressure (MEOP) that the case
hardware was originally designed for. The nozzle
exit cone was increased in length by eight inches
Four-Segment RSRB FJve-Segmen! RSRB
and diameter by three inches, corresponding with
Figure 1. Four-Segment vs.
Five-Segment the changes that had been previously qualified on
an earlier flight support motor supporting earlier
rate was achieved, new larger-diameter parachutes
Shuttle upgrade activities.
were designed to ensure that the water impact ve-
locity was the same as it is in today's boosters. Since these increased dimensions were evalu-
ated as part of the Shuttle upgrade efforts associ-
Since new metal cylinders would need to be
ated with supporting the increased pay load neces-
fabricated for the forward segment to accommo-
sary for Space Station Alpha missions, these di-
date the interface to the ET, there was flexibility
mensions were evaluated by the systems integra-
available to make the forward segment as long as
tion community and found to be acceptable from
would be needed to satisfy the overall program
both processing and clearance perspectives. Thus,
objectives. As such, a process study was con-
we were reasonably confident that this would be
ducted to determine what maximum-length for-
an acceptable design consideration for the FSB.
ward segment could be processed through the
This allowed us to compensate for some of the
Thiokol and KSC infrastructures. That study de-
reduced expansion ratio associated with the in-
termined that the forward segment could be in-
crease in throat diameter.
creased 26 inches over what the current forward
segment design provides. This allowed additional
With the added inert weight associated with
propellant to be included in the FSB concept, thus
the center segment, the water impact forces will
increasing the overall capability of the booster.
be somewhat greater than experienced by the cur-
Since the forward segment was increased 26
rent Shuttle RSRB. Therefore, with the FSB, all
inches, in order to maintain the same total booster
four stiffeners on the aft segment will be installed
length, the new forward skirt was shortened the
at KSC as opposed to the three that are currently
same 26 inches.
installed. This will provide additional cavity col-
In order to maintain the pressure capability of lapse load capability for the aft segment to ac-
the case with the added segment, a lower-bum- commodate the higher splashdown loads. We are
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alsousingstandardweightstiffenersegmentosn Motor's (RSRM), and thus their performance in
the aft segment to accommodate the higher buck- the modified environment of the FSB will be well
ling loads associated with the heavier FSB. understood and the risk associated with the design
changes will be minimal. Most of these design
To provide the necessary thrust history, we
changes are graphically depicted in Figures 1 and
needed to modify some of the propellant grain
2. The change to the 13-fin grain geometry is
geometry. The biggest change was increasing the
shown in Figure 3.
number of fins in the forward segment from the
current 11 to 13. We also changed the inhibitor The simplified forward skirt design, which
heights to tailor the thrust profile to match neces- consists of stringers with a skin welded over the
sary system performance constraints. One of the top, is also shown in Figure 3. One of the design
areas of concern with the higher mass flow rate features of this simplified skirt design is the abil-
and increased length-to-diameter ratio of the mo- ity to easily replace skin panels if they are dam-
tor is the potential for erosive burning in the bore aged as a result of splashdown loads. This skirt is
of the motor during the first second of motor op- also significantly lighter weight and lower cost
eration. To help minimize this impact, the leading than the existing skirt, which is by necessity more
edges of all center segments and the aft segment complex to facilitate the distribution of the thrust
were chamfered to provide a smoother aerody- loads for the booster. Since the thrust loads for the
namic transition between segments. With the booster on the FSB are going to be taken out on
change in inhibitor heights and grain geometry, the surface of the forward segment of the motor,
the propellant burn-back pattern also changed, the design modifications necessary to accommo-
necessitating a change in the insulation design to date that are also shown in Figure 3. The basic
accommodate the increased exposure times in approach is to have circumferential stiffeners in-
many areas of the motor. However, both the insu- tegrally machined into the case wall cylinder and
lation and the nozzle materials are exactly the a thrust post attached to the stiffener rings to
same as the current Reusable Solid Rocket transfer the loads from the booster to the ET.
FOUR-SEGMENT
FIVE-SEGMENT
• New forward • New attach case segments • Added center segment • Standard weight stiffeners
skirt (-26 In.) • Increased segment length • Insulation modification • Added stiffener ring
• New medium (26 In.) • Reduced burn rate • New nozzle
weight
parachutes • Grain/Inhibitor modification • Modlfled inhibitor helght • Increased nozzle throat
• Reduced burn rate • Leed-in chamfers on bore diameter (5.8 In.)
• Insulation modification • increase nozzle length (8 in.)
• System tunnel modification • Increase nozzle exit dla (3 in.)
• Insulation modification
• Reduced burn rate
• Leed-in chamfers on bore
Figure 2. FSB Design Summary
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i
59.62in.Dia Ae/At=6.55
,Joints
ET/SRB Separation
Plane
RSRM Igniter
Forward SRB Same Attach Location _ I
Thrust Post
_Field Joint
_L//Field Joint ETAttech Ring
Field Joint
Field Joint
Vew Cylinder
Segments
Field Joint
Stiffener Ring_ J
Nozz/e Exit Plane
Changes noted in italic
Figure 3. FSB RSRM Enhancements
Because of the substantial increase in throat The basic performance characteristics of the
diameter, a totally new nozzle will need to be de- FSB are shown in Figure 4. To provide a relative
signed. The new nozzle will utilize the same ma-
4,_
terials that are currently being flown on the
4,_
RSRM, but will take advantage of many of the
3,500
lessons learned from the current RSRM program
as well as those design improvements identified as
part of the Advanced Solid Rocket Motor l 2,000
(ASRM) program. This historical perspective will 1,500
enable changes to design features that will in- 1,000
eGO
crease the overall reliability of the FSB nozzle
0
relative to the current RSRM nozzle. Not because 10 20 30 40 50 80 70 80 90 100 110 120 130 140 160
Time{_c)
the current nozzle is poorly designed, but with the
Booster Performance
significant knowledge gained from recovered
5-Segment 4-Segment
hardware from flight as well as the multiple test Total ImpulN (Mlbf-sec) 365.0 296.3
MaxThrust (Ibf) 3,799,000 3,331,400
firings that have occurred, the knowledge and un- Average Thrust (Ibf) 2,843,500 2,395,000
Average Pressure 630 635
derstanding of how the RSRM nozzle performs is MEOP (psi) 1016 1016
Ispv(sec) 264.7 268.0
greater than any other nozzle design in existence. Burn _me ('_mc) 129.8 123,5
Burn Rate(InJsec) 0.343 0.368
Expansion Ratio 6.55 7.72
As such, that insight provides opportunities to en-
Throat Diameter (in.) 59.62 53.86
Initial Thrust/Weight 1.57 1.52
hance the overall reliability and robustness of the
Figure 4. FSB Design Performance
new FSB nozzle.
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reference and point of comparison, the same per-
formance characteristics for the current four-
segment RSRM are also included. To ensure that
the existing case hardware could still be used on
miATO
the FSB, note that the MEOP was constrained to
be the same. To accommodate the increased mass
188PTM
flow from the added segment, the throat diameter
I t r
was increased from 53.8 inches to 59.6 inches, 0 1OQ 200 _ 4_0
TW,e(iw=)
which resulted in a decrease in expansion ratio
from 7.72 to 6.55. This also resulted in a decrease Figure 5. Abort Modes
(one $$ME outl Results
in specific impulse from 268 to 264.7 seconds.
Because of the increased throat diameter and mass
evaluated for trajectories going to Space Station
flow rate, the thrust level increased about 500,000
Alpha. The aborts also assume that the abort is
lbf. The burn time increased from 123.5 seconds
initiated when one Space Shuttle main engine
to 129.6 seconds for the FSB. One of the key sys-
(SSME) fails and is turned off. The time indicates
tem parameters that drove the grain design for the the time at which the SSME would fail and the
FSB was the ability for the nozzle to clear the
abort mode could be initiated. The top blue bar
hold-down posts on the mobile launch platform indicates when the various abort modes could be
(MLP). In order to ensure that we maintain ade-
initiated for the current Shuttle system. The abort
quate clearance, we had to ensure that the
modes of primary interest are: return to launch site
thrust/weight ratio at liftoff was at least as high as
(RTLS), transatlantic landing (TAL), abort to or-
the current RSRM's. Note in Figure 4 that the
bit (ATO), and press to MECO (PTM). With the
FSB has a slightly higher thrust-to-weight ratio
current Shuttle boosters, if an engine fails from 0
than the current RSRM. The system level analysis to about 250 seconds, an RTLS abort could be
showed that with that thrust performance at liftoff
initiated. For the current system, the earliest that a
the FSB is able to maintain adequate clearance of
TAL abort could be initiated is approximately 120
the MLP posts and the only area of concern is an
seconds after launch. Similarly, an ATO could be
interference with the gaseous nitrogen purge
initiated at approximately 250 seconds after
which will necessitate a modification to that piece
launch. The second bar shown in green indicates
of hardware on the MLP.
the abort performance capability associated with
In comparing the thrust-time history of the using the FSB as currently configured. In its cur-
FSB to the current RSRM booster's, note that rent configuration, the FSB would allow a TAL
there is a significant increase in added capability abort to be initiated off the pad with a SSME
with the FSB. That added capability could be used throttle setting of 109 percent. An ATO abort
for a number of system performance improve- could be initiated at approximately 110 seconds
ments. The key one of interest for this study is after launch with the FSB. One of the alternate
how that performance can be used to enhance the considerations for future aborts was evaluating the
overall abort capability of the Shuttle system. The various trajectory constraints that are applied in an
abort improvements afforded by the FSB are abort scenario. Some key abort trajectory con-
summarized in Figure 5. All abort modes are straints that were considered for modification are:
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•, i t L • ;
1) once an abort is initiated, fly due east as op- likely provide a more significant system safety
posed to continuing toward the high inclination enhancement than that afforded by abort mode
for a nominal SSA mission; 2) increase the angle improvements, and as such, the added capability
of attack (alpha) profile to fly a more lofted trajec- of the larger boosters would provide an even more
tory once an abort is initiated (increasing the alpha significant system safety improvement by facili-
profile results in a trajectory which forces the apo- tating other safety upgrades. The higher perform-
gee altitude of the boosters higher than what the ance capability could also allow a reduced SSME
current recoverability constraint would tolerate, throttle setting for the duration of a nominal per-
but in an abort mode the attrition rate associated formance missions, which should improve overall
with recovering the boosters is not an important system reliability. The increased capability could
criteria); 3) use or dump the OMS/RCS propellant also enable off-nominal flight conditions where
for thrust during ascent. Additionally, you would additional boost capability would be needed to
offload 42,000 pounds of liquid oxygen (LOX) compensate for degradations in other system per-
and modify the mixture ratio of the SSME to 5.87 formance attributes similar to what occurred on
to compensate for the change in the amount of the Chandra mission.
LOX. When these constraints are relaxed, the
As part of the Phase A study, a significant
current FSB would provide the ability to initiate
number of feasibility assessments were conducted
an ATO from the pad, assuming a SSME throttle
by the various FSB team members to ensure the
setting of between 109 and 112 percent. Initial
overall adequacy of the FSB design concept. A
indications are the FSB would enhance the
summary of the major feasibility assessment is-
contingency aborts and decrease the blackout
sues is contained in Table 1. With the added seg-
zones as well increasing the east coast landing
ment, there is an increase in the length-to-
windows for various abort scenarios. But the
diameter ratio of the motor as well as an increase
contingency aborts were not evaluated in detail as
in the propellant bore diameter-to-throat diameter
part of the Phase A study.
ratio, both of which contribute to increasing the
The increased capability afforded by the FSB Mach number in the bore of the motor during the
provides a significant increase in mission planning first second of motor operation. During this period
flexibility. The increased capability, as previously of time, the combined effects of increased mass
discussed, provides a significant improvement in flow and increased Mach number increase the
abort capability by providing ATO off the pad, propensity for burn rate enhancement due to ero-
which would eliminate RTLS and TAL. The sive burning. The analytical assessment conducted
equivalent payload capability of the added pay- as part of the Phase A study indicated this would
load capability of using the FSB would be ap- be nearly a 40-psi increase in maximum operating
proximately 20,000 pounds. This is in excess of pressure. Historical data shows this phenomenon
the down-weight capability the orbiter can ac- to be a consistently reproducible effect, and once
commodate. However, the added payload capabil- predicted the design could be modified to accom-
ity could accommodate other Shuttle system modate this phenomenon. As part of the Phase A
safety upgrades such as crew escape. When bal- study, subscale motor static test firings at high
ancing the overall improvement to system reliabil- length-to-diameter ratios have been conducted to
ity, concepts such as crew escape would most better understand this phenomenon.
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,'= i_
Table 1. Feasibility Assessment
Technical Issue Impact Resolution
Propellant Erosive Potential for propellant bum rate Analysis shows that pressure increase ison
Burning enhancement during first 1-2 sec of order of30 psi
burn time, resultingIn increased Subscale testingbeing conducted tovalidate
pressure analysis
Nozzle Torque Increased flex bearing stiffnessdue Evaluation conducted and noTVC redesign
tonew nozzle aggravates SRB TVC anticipated for nominal TVC operation
capability
BoosterRe-entry Increased vibroacousticandaero- Analysis indicates nomajor redesign antici-
Environments heating environments aggravates pated, willrequire requalification ofsome elec-
current SRB component and TPS troniccomponents andincreased TPS thick-
capability ness. May require shockisolation mounts for
some electronics
Aerodynamic Heating Increased aero andshiftedshock Analysis of SRB nose cone and ET indicates no
Environments heating aggravates current TPS major redesignanticipated, will requirelocalized
capability TPS thickness increases onforward SRB and
ET components. Requires analysis for all Shut-
tleelements toconfirm redesign islimitedto
components already identified
Plume-Induced Heating Increased radiation and re- Analysis ofET and singlebodypoint perele-
Environments circulation heating aggravates cur- ment indicates nomajor redesign anticipated,
rent TPS capability willrequire localized TPS thickness increases
on aftSRB and ET components. Requires
analysis for all Shuttle elements toconfirmre-
design islimitedtocomponents already identi-
fied
Pre-launch Loads and Increased weight and length en- Analysis indicates that case and skirtare ade-
Excursions hances overturningmoment which quate, will require aft skirtstructuraltesting to
aggravates current SRB aftskid, validate analysis and use ofstandard weight
case capability, and vehicle case stiffener cylinders. Requires L&Ltoin-
umbilicals clude disconnects intheir facilitymodifications
Ignition Over Pressure Increased environment aggravates Nofeasibility issues but may require some re-
and MLP Plume Im- liftoff loads and SRB thermal curtain design during development program. Changes
pingement and MLP capability incomponent vibration levelsTBD
Environment
LiftoffLoads Increased environment drivenby Assessment by ETand SRB currently in-work.
FSB lOP, whichaggravates vehicle, Request more extensive analysis toidentify
attach, theorbiterwingandorbiter additional orbiterimpacts
components
Liftoffclearance With Increased FSB weight and nozzle Will requiresystem controlbiasingand modifi-
MLP length required higherthrust to cationstoGN2 purge lineonly
weightto clear MLP hold-down
posts
FCS Liftoffand Flight Changes instabilityaggravates ac- No major redesign anticipated, willrequire re-
Stability ceptable flex criteria tuned bending filters and software architecture
1stStage Ascent Loads Increased high Qand max g loads Analysis shows localized ET structurethickness
aggravate current ET structuralca- increases required. Changes Incomponent
pabilityand theorbiterwingand vibration levels notexpected. Orbiter impacts
fuselage loads willbe addressed byupdates totheflightenve-
lope
Pre-separation Loads Increased loadaggravates current Redesign ofseparation boltwillbe needed dur-
SRB fwd separation boltcapability ingdevelopment
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Table 1. Feasibility Assessment (cont)
Technical Issue Impact Resolution
BoosterSeparation Changesinboosterlength,mass AnalysisshowsthatFSB meets3_clearance
Clearance propertiesandthrusttail-offchanges requirements
clearancecharacteristics
BoosterSplashdown Increasedboosterinerwteightin- Redesignparachuteswithlargerdiameterto
Loads creasessplashdownloads reducedescent velocityandwaterimpactloads.
Usestandardweightcylindersforaftsegment
KSCFacilityModification MajormodificationstoexistingSSV Outyearmanifestplanwillneedtobeadjusted
processingfacilitieswouldbeoccur- tocreatefacility"downtime"toallowfacility
dngduringperiodswithflightrates modificationstooccur
at7to8flightperyear
VABQuantityDistance FSBwillincreasethequantityof Furtherevaluationisrequired
propellantintheVAB,therebyin-
creasingtheinhabitedandinterline
buildingdistance
With the new nozzle's larger throat and larger In viewing Figure l, notice that the nose-
exit cone, the overall spring rate and torque associ- tip of the FSB is 30 feet farther forward than the
ated with the nozzle design, aggravates the overall current booster' s. This creates a different aerody-
capability of the thrust vector actuation (TVA) sys- namic environment and shock wave interaction
tem. However, the flex torque of the FSB nozzle is than is currently experienced. The aerodynamic
less than that of the current RSRM nozzle due to
changes create a more severe environment for the
replacing the flex boot with a beating protector. An booster nose cone as well as some increased aero-
analysis was conducted that indicated the current heating on the ogive portion of the ET. Both of
TVA system has sufficient capability to meet the these areas can be accommodated by adding TPS
system performance requirements, with the new to compensate for the more severe aero-heating
nozzle, under nominal flight conditions where both environment. With the higher mass flow rate and
hydraulic power units are operating on each SRB. increased burn time, the plume-induced heating
environment and the recirculation environment
With the increased capability of the FSB, the
also become more severe. Both of these effects
trajectory after booster separation results in a
higher apogee than the current boosters. This re- can also be compensated by localized increases in
TPS on the ET as well as the booster.
sults in increased vibroacoustic and aero-heating
environments, which must be accommodated dur- By adding a segment to the booster, the pre-
ing the re-entry portion of the booster recovery. launch twang loads increase because of the added
The Phase A analysis indicated that these in- mass and length. These loads can be accommo-
creased or more severe environments can be ac-
dated in the booster by using standard weight
commodated by increasing the thermal protection stiffeners in the aft segment. The aft skirt was also
system (TPS) and adding shock attenuation evaluated for these increased loads and was found
mounts for some of the electronic components that to be acceptable with a minor decrease in margin
would be subjected to the more severe vibroacous- of safety over the current configuration, but still
tic environment.
within the system specification requirements.
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f r
J ;, L"u
Ignition over pressure (lOP) and plume envi- ance specification. The FSB provides higher loads
ronments associated with ignition increase the than the current booster, which will aggravate the
thermal and structural loads on the RSRB thermal negative margin. As such a new separation bolt
curtain and MLP, both of which can be accom- will be required if a FSB is integrated into the
modated with minor design changes. The IOP also Shuttle system. The new separation bolt, however,
creates a higher load on the vehicle attach as would be designed to meet the desired factor of
well as down wing load on the orbiter, both of safety for the booster system and as such would
which need to be evaluated in more detail in fu- slightly increase the reliability of the FSB relative
ture studies. to the current boosters.
As discussed earlier, the clearance of the nozzle
The current plan is to use the same booster
during liftoff with the MLP indicated there is a separation motors (BSM) that are currently flying
slight interference with the gaseous nitrogen purge on the existing boosters and not change them
line, which will require some modification. By when integrated into the FSB. An analysis was
incorporating the FSB on the Shuttle system, there conducted to determine if the existing BSMs
is going to be a change in the basic flight control could provide adequate clearance during separa-
system. The Boeing Integration team evaluated the tion taking into account the increased mass and
impact of the FSB on the flight control system and changes in moment of inertia for the FSB. The
determined the only change that would be required separation analysis indicated the FSB does meet
would be that some of the notch filters within the
all of the 3-sigma clearance requirements speci-
guidance system would require modification, with fied for the Shuttle system.
the changes required being within the capability
With the increased mass of the FSB, there is a
and flexibility of the current system.
potential for increasing the splashdown loads when
The increased capability afforded by the FSB
the booster impacts water. To facilitate the in-
increases the loading during the high dynamic pres-
creased mass for the FSB, a larger diameter para-
sure (Q) and maximum acceleration (G) regimes of
chute was designed that would ensure the impact
the ascent flight profile. These do provide increased
velocity for the FSB would be the same as the cur-
loads to the orbiter and ET. The increased loads to
rent boosters. This new parachute would be made
the ET were evaluated and can be accommodated
of newer lightweight materials as well as more
by localized increases in thickness to various struc-
refined design approaches that have been devel-
tural elements. All of the structural element modifi-
oped since the original booster parachutes were
cations can be accommodated within the existing
designed. The new design approach has already
component fabrication methodologies primarily by
been demonstrated with two drop tests using the
removing less material from the basic billet for
current Shuttle boosters. The larger diameter para-
each of the components. This results in a slight in-
chutes with the improved material will be able to
crease in inert weight but no change in the basic
package within the current volume available in the
component design or fabrication.
existing frustum. Modifying structural thicknesses
The current forward attach bolt that holds the of load.carrying elements and changing TPS
booster to the ET has a negative margin relative to thicknesses can accommodate the total impact on
the desired factor of safety in the booster perform- the ET of the increased thermal loads and struc-
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