may 14th , 2010

May 14th, 2010FMSTR

The Problem and Proposed Solution

No current, acceptable solution exists to determine liquid volume in a tank exposed to microgravity, without some form of stratification, tank

stirring or spacecraft acceleration

Normal Gravity Microgravity

An optical mass gauge is a viable option

Introduction and Background Concept Design Detailed Design Testing / Results

Source: NASA

Alternative Methods

Alternative Method Basics Requirement

Capacitive Sensor Permittivity of the cryogenic fluid is related to the volume within the tank.

Settling / Stratification

Flexible Cryogenic Temperature and

Liquid-Level Probes

A strip of silicone diodes are brought to a certain temperature. Time constants allow for

fluid volume measurement.

Settling / Stratification

Cryo-LiquidVapor

Diodes

Multipin Plug

Optical mass gauge will not require settlement or acceleration of spacecraft

Introduction and Background Concept Design Detailed Design Testing / Results

Approach:• Build prototype version of sensor• Test in laboratory (with water)• Vibration test• Flight test on a sounding rocket

Our Objective

Objectives:• Develop a sensor using an existing measurement technique to

accurately determine the liquid volume in a tank in any gravitational environment.

• Demonstrate its accuracy and reliability on board a sounding rocket mission.

Introduction and Background Concept Design Detailed Design Testing / Results

Two tanks w/ different volumes of liquid are independently exposed to Gas Cell. Amount of liquid in each can be determined; The two tanks represent fuel/fluid levels at different periods during a mission.

System Layout

Introduction and Background Concept Design Detailed Design Testing / Results

Solid Model of Flight-Ready Prototype

Power Supply

HeNe Laser

Photo Diode Detector

Valve 1

Tank 1 Tank 2

Valve 2

Piston

Gas Cell

Servo

Laser output into Fiber

Introduction and Background Concept Design Detailed Design Testing / Results

Major Design Changes

The switch from diode laser to a Helium-Neon laser

• Diode laser does not have the coherence length that we require (only 0.1 mm)• A coherence length equal to at least the sensing path length is needed ( > 5 cm)• The coherence length for a typical HeNe laser is 20+ cm

Introduction and Background Concept Design Detailed Design Testing / Results

Specifications

9.5 inches4.75 inches

Introduction and Background Concept Design Detailed Design Testing / Results

Payload occupies a half-canister (shared with UNC payload)

Specifications

Final Weight: 2.90kg (6.39 lbf)

Dimensions: 24.15 x 24.15 x 12.1 cm

Processor:• ATmega328; 1KHz sampling

rate• Memory (storage): 2GB

All wires secured with nylon harnessing.

G-switch

Introduction and Background Concept Design Detailed Design Testing / Results

Construction

Gas cell contains Air, determined that xenon or argon are not needed for accurate results in our system.

Introduction and Background Concept Design Detailed Design Testing / Results

Piston Assembly

Servo to drive piston:• 486 oz-in Torque• Titanium gears• Weight: 0.15 pounds• ~170 lbf linear force• Programmable

• Pressure test on Piston and Servo completed at 40 psi, maintained pressure

Introduction and Background Concept Design Detailed Design Testing / Results

Vibration Mount Analysis and Manufacturing

• Sierra Nevada Corp. required the team to procure its own vibration table mount

• Suggested that FEA be performed on mount to ensure the first mode is outside of the test range (>2000Hz)

• Finite Element Analysis showed the first mode was at 3943Hz

Introduction and Background Concept Design Detailed Design Testing / Results

Vibration Testing

Z-A

xis

X/Y

-Axe

s

Outcome: Vibe-Test Passed• Zero parts damaged• Optics remained in

alignment (some power loss)

Two Tests:• Sine Sweep: 10-2000 Hz• RandomResonance at: 200HzMax Accel: 25G

Introduction and Background Concept Design Detailed Design Testing / Results

Fringe Counting Methods (Method 1/3)

1 2 3 4 5

A B C D

X Y

η β

0 N

η = { location of first peak (A) }

β = N – { location of last peak (D) }

α = number of visible peaks

Fraction of sine wave before first peak:W = η / X

Fraction of sine wave after last peak:Z = β / Y

Total (fractional) fringe count:T = α + W + Z

Fractional Method

Find the fraction of sine wave that exists before the firstpeak and after the last peak.

Introduction and Background Concept Design Detailed Design Testing / Results

Fringe Counting Methods (Method 2/3)

1 2 3 4 5

A B C D

X Y

0 N

Find wavelength between first twopeaks and the last two peaks: {X , Y}

Find the mean wavelength:μ = ( X + Y ) / 2

Divide range by mean wavelength toobtain fringe count:

Total (fractional) fringe count:T = N / μ

Frequency Method #1

Find an average wavelength between the first two peaksand the last two peaks. Divide the average wavelength by the range.

Introduction and Background Concept Design Detailed Design Testing / Results

Fringe Counting Methods (Method 3/3)

1 2 3 4 5

A B C D

0 N

Find peak locations: { A , B , C , D , E }

Formulate a difference array (distancebetween each peak):D = { B – A , C – B , D – C , E – D }

Take an average (mean wavelength):μ = Mean[D]

Divide range by mean wavelength toobtain fringe count:

Total (fractional) fringe count:T = N / μ

Frequency Method #2

E

Find the average wavelength between all of the peaks.Divide the average wavelength by the range.

Introduction and Background Concept Design Detailed Design Testing / Results

Results

  Reference Tank 1 Tank 2# of Fringes 5.33 3.30 3.59

Measured Liquid Volume

(mL)= 10.33

Actual Liquid Volume (mL) = 10.53

Percent Error = 1.90%

10.33 mL

Uncertainty: +/- 0.95 mL

Introduction and Background Concept Design Detailed Design Testing / Results

Full Mission Simulation Test

Introduction and Background Concept Design Detailed Design Testing / Results

- Payload paused for 45 seconds after G-switch activation, then the system operated for 5 minutes before shutting down

- Initial pause is to prevent potential system damage during high-G environment- All data was recorded to microSD card- Results were successful (good fringe visibility)

45 seconds pause

5 minutes operation

Overall Analysis

Introduction and Background Concept Design Detailed Design Testing / Results

• Are you ready for launch? YES

• Are you happy with the results? YES

• What work still needs to be completed?

Integration with UNC to ensure both payloads will successfully fit within the canister and meet C.O.G. constraints

Lessons Learned

Introduction and Background Concept Design Detailed Design Testing / Results

- Everything takes ~5x longer than you expect

- Need a lot of time for testing due to unexpected issues

- Detailed early planning leads to success later in the project

Conclusions

• Introduced problems with measuring liquids in zero-g

• Project work completed, testing results

• Measured small liquid volume within 1.9% error

• Testing complete, ready for integration with UNC

Introduction and Background Concept Design Detailed Design Testing / Results