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

AAE450 Spring 2009

FEA – Set Up

[Tim Rebold] [STRC][17]