aae450 spring 2009 mass savings and finite element analysis (fea) preparation for orbital transfer...
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AAE450 Spring 2009
Mass Savings and Finite Element Analysis (FEA) Preparation for Orbital Transfer Vehicle (OTV)
100 gram Case
Tim ReboldSTRC
[Tim Rebold] [STRC]
[1]
AAE450 Spring 2009
Mass Savings
[Tim Rebold] [STRC]
*Not to scale
Savings1. Skin panel reduction
2. Reduced OTV diameter to match Lunar Lander
3. Attachment interface being separated
4. Modified truss and electronic floor beam dimensions
[2]
Skirt / Payload Attach Fitting (PAF)
A-A
Added supports stiffenstringers for mounting equipment
Standard launch vehicle (Dnepr) interface
Lander
AA
Ø = 2.06 m
Mass Reduced Mass reduction: 27.73 kg (59% reduction) Total Structural Mass: 49.37 kg (excluding 14.3 kg thermal control) finert = 0.22
AAE450 Spring 2009
FEA Preparation
[Tim Rebold] [STRC]
Model– Thin wall & beam elements model structural
components– Lumped masses represent non-structural
components Concerns
– Assumption used to size truss frame was based on capability to only carry axial loads
• Moments might produce yielding stresses– Stresses at joints and connections– Axial and lateral modes (resonant
frequencies)• Can stiffen skirt until requirements are
satisfied– Vibrations transmitted to electronics and solar
array structure
[3]
AAE450 Spring 2009
References
[Tim Rebold] [STRC]
(1) Delta II Payload Planners Guide
http://snebulos.mit.edu/projects/reference/launch_vehicles/Delta/DELTA_II_User_Guide_Update_0103.pdf
(2) Skullney, W.E. Fundamentals of Space Systems. 2nd Edition. Ch. 8, pp.465-564 Oxford University Press, 2005.
(3) “Properties of Materials.” 2009. Purdue University. http://www.lib.purdue.edu/eresources/wts/result.html?WTSAppName=Lib_edupackk
(4) Sun, C.T. Mechanics of Aircraft Structures. New York: John Wiley and Sons, 2006.
(5) Dnepr User’s Guide http://snebulos.mit.edu/projects/reference/launch_vehicles/DNEPR/Dnepr_User_Guide.pdf
(6) Larson, W.J. Spacecraft Structures and Mechanisms. Microcosm, Inc. , 1995
[4]
AAE450 Spring 2009
Future Work FEM analysis
– Obtain better approximation of center of mass and inertia values– Perform modal analysis to see if OTV meets stiffness
requirements placed on launch vehicle payloads– Perform stress and strain analysis for various load cases– Ensure all components will be protected from a dynamic
environment
[Tim Rebold] [STRC][5]
AAE450 Spring 2009
Arbitrary Payload Case Variables
– OTV payload (Lander) : Expected to scale linearly– Number of engines & propulsion system size : Increases
structural support but should be scaled relatively linearly– Solar Array size : Increased structural support mass and will
most likely be scaled exponentially
[Tim Rebold] [STRC][6]
AAE450 Spring 2009
Mass Savings Summary
[Tim Rebold] [STRC][7]
MASS SAVINGS (kg)
Components Old New Reduction Savings (%)
E-MOD floor beams 7.07 3.80 3.27 46
E-MOD floor overlay 4.88 3.52 1.36 28
Shear / Skin panels 13.82 3.91 9.91 72
Propulsion support frame
4.30 2.07 2.23 52
Stringers / Stiffeners 6.28 6.07 0.21 3
PAF release 10.75 0 10.75 100
Total 47.10 19.37 27.73 59
Aluminum 6061-T6 material selected for all structural elements
Abbreviations• E-MOD: Electronics Module
AAE450 Spring 2009
Structural and Thermal Budgets
[Tim Rebold] [STRC][8]
MASS (kg)Components
E-MOD floor beams & overlay 7.32
Shear / Skin panels 3.91
Propulsion support frame 2.07
Stringers / Stiffeners 6.07
Integration (Lander and propulsion module) 22*
Fasteners (welds, rivets, bolts, adhesives) 8*
E-MOD thermal control 11.1
Propulsion thermal control 3.2
Total (structures) 49.37
Total (thermal) 14.3
TOTAL 63.67*Estimates
AAE450 Spring 2009
Dimensions - OTV
[Tim Rebold] [STRC]
*Not to scale
[9]
Skirt / Payload Attach Fitting (PAF)
1.8 m
x
0 m
1.45 m
0.95 m
Lander
Ø = 2.06 m
Skin panels removed
Stiffener / C-Channels
AAE450 Spring 2009
Integration Ring Dimensions
[Tim Rebold] [STRC]
*Not to scale
Lander
[10]
Ø = 2 cm (6 equally spaced over C-Channels)
2.00 m
3.6 cm
Mass = 5.93 kg
1 cm
AAE450 Spring 2009 [Tim Rebold] [STRC]
*Not to scale
[11]
1 cm
Payload Attach Fitting Dimensions
6 cm
2.12 m
Ø = 4 cm (8 equally spaced)
Cross Section
3.6 cm
1 cm
6 cm
1 cm
14.8 cm
A-A
Webthickness = 4 mm
Mass = 40.08 kg
A
A
AAE450 Spring 2009
Dimensions – C-Channels
[Tim Rebold] [STRC]
*Not to scale
[12]
Stringer / StiffenerCross-Section
2.75 cm
3 mm
3.5 cm
Cross sectional area = 0.000252 m2
Length = 1.45 mMass = 1.0114 kgρ = 2768 kg/m3
Why a C-Channel?• Easy access for making connections to other members• Provides a relatively high moment of inertia
AAE450 Spring 2009
Dimensions – Propulsion Support
[Tim Rebold] [STRC]
*Not to scale
Electronics Module
[13]
0.36 m
0.65 m
0.57 m
0.20 m
Ø = 0.58 m
0.30 m (includes 1 cm clearance over Xenon tank)
0.50 m
0.90 m
0.66 m
OTV Base
AAE450 Spring 2009
Dimensions – Propulsion Support Frame
[Tim Rebold] [STRC][14]
1
4
32
Member1234
t (mm)0.773.20.51.52
h (cm)0.752.200.750.75
b (cm)0.752.200.750.75
th
b
bWeld
Propulsion truss frame
Stringer / StiffenerCross-Section
Weld
Might need to thicken flange to tolerate local stresses
Pinned joint
AAE450 Spring 2009
Dimensions – Electronic Module
[Tim Rebold] [STRC]
*Not to scale
[15]
0.05 m, Floor beam height
6 beams spanning from OTV stiffeners oflength 0.57 m
Electronics Module
0.03 m
Ø = 0.25 m
Thin (0.5 mm) floor skin
Beams welded to thin (mm’s) circular ring
Components not placed under lander nozzle and above floor lacking beam supports
0.50 m
AAE450 Spring 2009
Dimensions - Electronic Module Floor Support
[Tim Rebold] [STRC][16]
t
b
h
Electronic Modulefloor beam supports
PCDU
PSU
Thin 0.5 mm floor overlaysbeam supports
Battery DC / DCConverter
Acronyms• PCDU: Power Conditioning Distribution Unit• PSU: Power Supply Unit
Electronic Module Support
No. Beams t (mm) b (cm) h (cm)
6 2.9 2.5 5.0
b Weld
Electronic Modulefloor beam supports
Stringer / StiffenerCross-Section
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