6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 1

UH/LBL 4pi Results & Plans

• Requirements & Specifications

• Preliminary look at statics & dynamics

• Initial results on carbon-fiber prototypes

• Initial results on activity & contamination

• Plans

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 2

Requirements & Specifications

• Absolute flux estimates depend strongly on fiducial volume estimate: V/V ~ 3 R/R => 3% error in fiducial volume implies ~6cm resolution near edge of balloon

• To avoid saturating error budget with 4pi alone we require R/R = 2cm for knowledge of tip position– Radial errors depend mainly on errors in pivot position, from either

global misalignment of axis, or strain of axial arm

, knowledge less crucial than R: we adopt ==6cm/R for knowledge requirement Z-component from pressure transducer, x,y from camera, mechanical

modeling Control requirements: we adopt factor of <10x knowledge

<20cm 3sigma control in all axes (goal)

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 3

Mechanical flow-down

• To minimize gravity/buoyancy torques, structure should be nearly neutrally buoyant– Minimize structural deflection: => stiff section

– Neutral buoyancy: either a heavy sealed tube section or a low-density, free-flooding tube section

• Deflection requirement => large cross section => free-flooding to avoid large inertial mass

– Internal cabling desirable => minimize tangling possibilities

– Foam-core graphite composite best choice• Highest strength-to-weight ratio, buoyancy easily controlled in tube sections

• Deployment requires short sections: ~1m or less– Section latching must be manageable in glove box

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 4

Static Load analysis

• Assumptions:– 10% of inertial boom mass (including 2kg cable)

net negative => 0.1 * 12 kg = 1.2 kg

– Source mass at boom tip = 2 kg wet weight

– Net weight supported by tensile cable with 0.6m lever arm

– 6m boom assumed (worst case—5.5m more likely)

• Tmax = 345 N in tensile cable to support static load

• Intitial finite element model tube section developed—still working on integration to larger structure – ~2.5mm deflection at boom tip for 2kg source load

0.6 m

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 5

Dynamics

• Assumptions:– Entrained water included in dynamical mass

– 6m section wet weight = 10% of 12 kg• 2 kg radioactive source assumed at tip

– <34 cPoise dynamic viscosity• Reynolds number >10 for u>3mm/s,

• => laminar flow regime, ~constant Cd ~ 1.5

• Results: – T ~ 500N adequate for initial start &

continuous motion

– Gives 0.2o per second angular velocity for worst case

• Takes ~7.5 min for 90 degrees of motion

• Boom tip velocity of 2cm/s => low turbulence

– Design cable for 5 kN (10:1 safety factor)

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 6

Control Issues

• Need a simple but robust control system with “sub-human” time constants– Classic control problem when dynamical time scale for structural

motion exceeds operator’s patience! • (eg, 56K modem download problem…)

– Control inputs: winch tension, line travel, rotary stage travel/rate

– Response of system will be very slow => require a feedback loop • prevent overdriving of winch tension

• Give indication of motion and expected time to equilibrium position

• Damp out hysteresis if possible

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 7

Details of joint design & operation

• Pivot arm provides initial offset torque to begin rotation• Tube sections approx. 4 inch diam., ~3’ long; joint still under development

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 8

Tube section coupling detail

• “Ski-boot” latching approach– 3 latches with alignment pin• Prototype already developed

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 9

Pool test plans for prototype

• Pool test: verify static/dynamic loads on full boom

• 1/3 scale test of entire assembly (full scale sections)

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 10

• Left: superposed 4pi GB over existing glove box

• Right: packing of accordion 4pi sections in glove box

4pi Glove box requirements

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 11

Activity & Contamination analysis

• [Refer to Bryan Tipton’s talk]

• Summary:

– Activity very low, not a problem

– Spectrophotometry may indicate a problem• Loss of UV transmissivity in some samples?

• Test needs to be repeated under better control

• Seems inconsistent with other reports of graphite composite tests

6/12/2002 P. Gorham/M. Rosen, Univ. of Hawaii 12

Schedule & contingency

• If graphite composite cleared, proceed with pool test – Late summer, follow immediately with engineering review of

results critical design review for production version

• Deployment of Gen-I 4pi for first calibration run by end of calendar year

• If graphite composite fails contamination tests:– Alternatives:

• double-wall Al tube sections (lots of gas-tight welding)

• Kevlar-epoxy composite another possibility

• Structural polyethylene or polypropylene?