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BalloonWinds Cracks Under Pressure

Jim Ryan

University of New Hampshire

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BalloonWindsInstrument Overview

Size: 8 8 12’

Gondola Mass: 5500 lbs

Power Requirements: 1300 W

Power System:

26 Lithium-Ion Batteries

Thermal Management:

Ice and Electric Heaters

Optical Systems:

Diode-Pumped Nd:YAG

½-meter Telescope

Direct-Detection Receivers (2)

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BalloonWindsIntegrated Instrument

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Flight Timeline

0

10

20

30

40

0 2 4 6 8 10 12 14

Time (Hr)

Altitude(km)

Flight Timeline

1. Liftoff - System Startup2. Emit Laser and Signal Fiber Alignment3. Flight Altitude Checkout4. Eight-Hour Data Collection5. Extended Data Collection (resources/weather)6. Descent

1. Liftoff - System Startup2. Emit Laser and Signal Fiber Alignment3. Flight Altitude Checkout4. Eight-Hour Data Collection5. Extended Data Collection (resources/weather)6. Descent

1 2 3 6

4 5

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Mission Objectives

1. Measure wind velocity profiles with accuracy limited by photometric return and instrument technology.

2. Confirm instrument/atmosphere model for a space-like instrument.

3. Assess subsystem scalability for space.

4. Adapt model to a space-borne instrument and compare to data requirements.

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Previous BalloonWinds Schedule

Activity Date

Crane Test 04 Jan 07

Pre-Env. Functional Test 30 Mar 07

Thermal-Vacuum Test 02 Apr 07

First Launch 14 May 07

Second Launch 04 Jun 07

Return to UNH 15 Jun 07

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Thermal-Vacuum Test

• 5 April 2007 at Kirtland AFB Phillips Lab

• Catastrophic failure occurred during initial backfill

• Damage assessment, failure analysis, redesign, and chamber reviews initiated

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External Pressure

•Vacuum at 3:30

•Target P at 3:51

•Backfill at 3:55

Internal Pressure

•Pressurized at 2:05

•Failure at 3:50

•Tracks External P

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External Pressure

•Linear decrease from pumping

•Pressure wave from explosion measured at 3:50:22

Internal Pressure

•1.21 bar initial

•Rupture at 3:50:20

•0.13 bar final

•1.07 bar differential

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Laser ChamberPre-Failure

Cross-supports

29 47 ½-inch lid(0.35-inch eff.

thickness)

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Laser ChamberPost-Failure I

Cross-supports

Lid bottom

Secondary fractures from gondola impact

Thermal insulation(yellow)

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Laser ChamberPost-Failure II

Cross-support

Lid bottom

Secondary fracturesfrom pipe interference

Fibertek Laser

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Laser ChamberPost-Failure III

Reverse angleshowing the disorder

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Laser ChamberPost-Failure IV

Fragments at thebottom of the

thermal-vacuum chamber

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Damage Assessment

• Laser chamber: Lid and walls

• GPS, attitude sensors and heaters mounted on lid were damaged

• External cooling lines were stressed

• Internal damage was minimal

• FiberTek laser and other key elements passed diagnostic testing 11 July 2007

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Failure Analysis Lid Support Structures

• Lid required additional supports to counter pressure load (19,000 lbs)

• Each cross-support was fastened to lid using 7 bolts

• Middle beam took 20-39% of total load, depending on load/lid deformation

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Failure Analysis Lid Deformation & Reaction

• Support beams much stiffer than lid

• Lid pushed against middle beam in range of 3800-7400 lbs (calc.)

• Only the two end bolts were under tension countering this load: 1800-3700 lbs each.

Lid displacement contouracting against support beams

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Change of Lid Bolts

• Small gauge bolt with insert to thread into Al.

• New through-bolt fixation.

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Failure AnalysisPull-Out Strengths

• Pull-out force for ¼-28 bolt in MIC-6 calculated to be 2100 lbs

• Measurements on two samples reported 2100 & 2700 lbs

• These values are at the lower-end of the expected 1800-3700 lbs load range

Pull-Out Strength Measurements

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Pull Test Samples

• Threads did not hold.• Too short• Too small diameter.

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Failure AnalysisFailure Sequence I

• Pull-out occurred at an end of the middle support beam

• Same-side bolts on neighboring beams let go

• Unsupported lid then fractured

• 4 end-bolts recovered with evidence of pull-out

• 5th end bolt was released by a crack

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Failure AnalysisReconstructed Lid Fragments

Pull-out locations

Primary fracture line

Secondary fractures

GPS & Attitude plate(damaged)

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Failure AnalysisConclusions

• Material selection (cast aluminum) was the primary cause of the failure– Poor strength required additional support– 3% elongation caused brittle fractures

• Inaccuracies in the stress analysis– Failed to predict inadequate lid strength, which

lead to the addition of cross-supports– Failed to predict pull-out of the cross-support

bolts

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Laser Chamber RedesignThinking outside the box…

Rectangular Cylindrical Feasible Feasible

Aluminum Steel Lighter Stronger

Reuse mounting scheme Gondola interference

Simpler implementation Easier access

Engineering costs Schedule

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Laser Chamber RedesignDesign Comparison I

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Laser Chamber RedesignDesign Comparison II

Material: Cast Aluminum MIC6 Wrought Aluminum 6061-T6Ultimate Strength: 166 MPa 310 MPaYield Strength: 105 MPa 275 MPaElongation at Break: 3% 12%Lid thickness (M/R) 0.5 (0.065) 2.25 (0.25)Lid/base attachment Inserted threads Through boltsWeight ~200 lbs ~400 lbs

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Chamber ReviewsCoolant Tank

Material 304L Stainless SteelVolume (empty) 18 cubic feetDesign Pressure 18.75 psigTest Pressure (Hydrostatic) 28 psigAssembly Test Pressure (Pneumatic) 22.5 psig (1.5 MEOP)

Electronics ChamberMaterial 304L Stainless SteelVolume (empty) 30 cubic feetDesign Pressure 18.75 psigTest Pressure (Hydrostatic) 28 psigAssembly Test Pressure (Pneumatic) 22.5 psig (1.5 MEOP)

Interferometer ChamberMaterial 304L Stainless SteelVolume 14 cubic feetDesign Pressure 16.5 psigAssembly Test Pressure (Pneumatic) 22.5 psig (1.5 MEOP)

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Revised BalloonWinds Schedule

Activity Start Date

Laser Chamber CDR 01 Aug 07

Re-Integration 29 Oct 07

Leave UNH 17 Mar 08

Thermal-Vacuum Test 27 Mar 08

First Launch 05 May 08

Second Launch 27 May 08

Return to UNH 09 Jun 08

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Thermal ChamberDesignASME Pressure Vessel Code usedDesign validated using COMPress SoftwareMaterial 304L Stainless Steel24” Diameter 10 GA shell (.1345”)ASME Flanged and Dished headsVolume (empty) 18 cubic feetDesign Pressure 18.75 psigMaximum Expected Operating Pressure (MEOP)

~15psig

FabricationWelded cylinder, Flanges and HeadsFestival City Fabricators, Stratford ONT, CA

Code approved pressure vessel manufacturer

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Thermal Chamber

TestingProof/Leak Test (Hydrostatic) 28 psig

Functional/Leak testing UNH (Pneumatic) 16.5 psig (1.1 MEOP)

3 Complete pressure cycles to date.

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Electronics ChamberDesignASME Pressure Vessel Code usedDesign validated using COMPress SoftwareMaterial 304L Stainless Steel

36 Diameter 10 GA shell (.1345”)ASME Flanged and Dished headsVolume (empty) 30 cubic feetDesign Pressure 18.75 psigMaximum Expected Operating Pressure (MEOP)

~15psig

FabricationWelded cylinder, Flanges and HeadsFestival City Fabricators, Stratford ONT, CA

Code approved pressure vessel manufacturer

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Electronics Chamber

TestingProof/Leak Test (Hydrostatic) 28

psig

Functional/Leak testing UNH (Pneumatic) 16.50 psig (1.1 MEOP)

3 Complete pressure cycles to date.

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Interferometer ChamberDesignMaterial 304L Stainless Steel20 Diameter 12 GA shell (.105”)Flat Heads with weight relief .625 thickVolume (empty) 18 cubic feetDesign Pressure 16.5 psig **Maximum Expected Operating Pressure (MEOP) ~15psig

FabricationWelded cylinder and flanges Shell made by Hollis Line Machining Hollis NH

Code approved pressure vessel manufacturerHeads made by Advance Group Ann Arbor MI

TestingLeak Test (Helium and Nitrogen) 16.3 psigFunctional/Leak testing UNH (Pneumatic) 16.5 psig (1.1

MEOP)

**Verified by mathematical analysis and OptiVessel Code

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• Anyone want to golf on Thursday?

• See this space for details.

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Laser ChamberDesignMaterial MIC 6 Aluminum (Cast)

Beams (added after initial lid deformation) 6061T6

Rectangular 29 x 45 x 13Volume (empty) 9.5 cubic feet

Design Pressure ?

Maximum Expected Operating Pressure (MEOP) ~15psig

FabricationWelded side walls and O-ring seal top and bottom

Advance Group Ann Arbor MI

TestingLeak Test (Helium and Nitrogen) 16.32 psig

Functional/Leak testing UNH (Pneumatic) 16.2 psig

FailureLid failed in TVAC at a differential pressure of 16.5 psig

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Laser ChamberFailure Analysis