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Flight Vehicle Structural Design Processes
for a Common Bulkhead and a Multipurpose
Crew Vehicle Spacecraft Adapter
Pravin K. Aggarwal and Patrick V. Hull
NASA/MSFC
SciTech, 5-9 January 2015
Kissimmee, FL
MSA: Design Overview
MPCV/Orion
MPCV/MSA Joint
ORION Responsibility
(MSA)
MPCV Stage
Adapter
MSFC DCSS/MSA Joint
ORION Responsibility
Delta IV DCSS
MSA: Design Overview
• Primary Structure
• Single Piece Fwd & Aft Rings
• Conical Isogrid Panels
• All Welded Construction
• Secondary Structure
• Diaphragm & Doghouse
• Electrical Panels Fwd Ring Electrical Panel Conventional FSW
• Access Panel Covers
Isogrid Barrel
Panels
Access
Cover
Self Reacting FSW
MSA Diaphragm
Aft Ring
MSA: Design Overview
Isogrid Nodes
Access Panel (2 Plcs)
Fwd Ring
Aft Ring Diaphragm Interface
MSA: Pocket Parameter Optimization
MSA: Historical Comparison
Ref: Heineman Jr., W.: “Design Mass Properties II: Mass Estimating and Forecasting for Aerospace
Vehicles Based on Historical Data,” Report No. JSC-26098, NASA Johnson Space Center, Houston, TX,
November 1994.
MSA: Design Overview
Common Bulkhead: Design Overview
Ares I Upper Stage
Common Bulkhead
LH2 Tank
LO2 Tank
Ares I Upper Stage 5.5m diameter
Pressurized Structure
Ares I
Common Bulkhead: Design Overview
Bond Lines
CB FWD Dome
(LH2 side)
Bolted Flange
Honeycomb
Core
CB AFT Dome
(LO2 Side)
Seal Plate
Match Drilled
Shear Fasteners Segmented
bolting ring
Common Bulkhead Design Overview
LH2 Side Bond Surface Area
(Bonded Area Only)
CB Core Volume
LOX Side Bond Surface Area
(Bonded Area Only)
Total CB Inside Volume
Bolting Ring to Seal
Plate Volume
Common Bulkhead: Thermal Gradient
Thermal stress across a common bulkhead is a major contributor to the driving load case [1]
Problem: Thermal mismatch along with pressure differential define the driving loads for a common bulkhead.
There is a significant temperature gradient across the common bulkhead. The CB FWD dome temperature = -423F,
CB aft dome temperature = high temperature ullage pressurant
Solution:
Core must have low thermal conductivity and sufficient shear strength
Choose dome and core thicknesses to balance thermal effect and structural efficiency
Hold tight tolerance on domes skin thickness for thermal stress effects
Reduce LO2 ullage pressurant temperature through additional chilled helium ullage pressurant
Common Bulkhead Sizing for min facesheet = 0.050"
2400
AL 2014
AL 2014 with MPS temp reduction mass
2350
Al-Li 2195
Al-Li 2195 with MPS temp reduction mass
2300 AL 2219
2250
2200
CB Estimated Mass (lbs)
2150
2100
2050
2000
1: “Structural Design Considerations for 1950
the Storage of Liquid Hydrogen in a Space
Vehicle” Sagata, note error in thermal 1900
stress equation
1850
1800
-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200 220
AFT Facesheet Temperature (F)
Common Bulkhead: Trades
Trade Study Example
Sandwich vs. Machined / stiffened dome
Composite Common Bulkhead Machined / Stiffened Common Bulkhead
Mass Lighter Heavier
System Impact Core volume thermal conditioning Easier to mount auxiliary hardware to LO2 side
Design Complexity No exterior dome insulation required Simplified dome design
Complex core bonding to domes Isogrid machined spun form dome and joint ring
Manufacturing and
Hermetic seal weld around joint forging
Assembly
Match drilling of bolting ring Complex insulation installation
Elliptical vs. Spherical Cap
Common Bulkhead: Trades cont.
Stability Trades for common bulkheads
Pressure Stabilized: Must maintain positive pressure on concave
side of bulkhead
Structurally Stable: Designed for negative pressure
Designed for 1g acceleration for loss of pressure during testing
Designed for 4+g acceleration flight loads
• Ares was design for a loss of pressure in aft tank, this protects for inadvertent
venting during testing and flight
Fail Safe FOS: 1.0 for loss of pressure failure?
Common Bulkhead: Core Volume Thermal Conditioning
Design Issue: Maintaining and verifying common bulkhead volume integrity can be
operationally difficult and costly
Problem: Core volume environment. It is necessary to maintain a pure core volume absent of any
air ingestion and provide the ability to check medium for any dome leaks.
To protect bondline during shelf life (moisture absorption)
Prohibit core pressurization during testing
Prevent mixing of propellants
Provide thermal insulation
Solution:
On pad operational access
Quantify leak rate of bulkhead then determine pad stay time based on total allowable pressure decay (small
volume compared to tankage)
Monitor core from initial leak test through T0
LCC: Excessive common bulkhead core volume pressure
Core volume monitored with pressure transducers
If leakage does occur post T0
Some ambient air with a typical atmospheric humidity (0.026lbmH2O/ lbmDry Air ) will be ingested into the
core volume at subatmospheric pressure
The moist ambient air ingestion would be short lived as atmosphere depressurization occurs,
immediately following this event, the moist air ingestion will be of short duration
Atmospheric pressure decays rapidly on ascent
Moisture ingestion at its maximum level is not catastrophic
Common Bulkhead: Tanking
Tanking generates temperature and pressure gradients across a common bulkhead
A common bulkhead configuration can require additional operational constraints than a separate
tank configuration
The following tanking sequence is based on a “sandwich” common bulkhead
conceptual design, similar to the heritage S-IVB and S-II designs
Facilities tanking first
LOX followed by LH2
Common Bulkhead driven impacts
Minimize T across common bulkhead
Design is structurally sensitive to cryo-loading anomalies
Potential launch turnaround delays
Operational procedures for on-pad “core” purging
A different, more complex purge method may be applied for a Common Bulkhead to eliminate
cryopumping or accumulation of haz gas levels.
Purge effluent may be analyzed for haz gas prior to launch
