May 14th, 2010 FMSTR. The Problem and Proposed Solution No current, acceptable solution exists to determine liquid volume in a tank exposed to microgravity,

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


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.


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


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


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


Specifications

9.5 inches4.75 inches


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


Construction

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


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


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


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


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.



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.



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.


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


Full Mission Simulation Test


- 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


• 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


- 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


Documents

May 14th, 2010 FMSTR. The Problem and Proposed Solution No current, acceptable solution exists to determine liquid volume in a tank exposed to microgravity,