May 14th , 2010
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Transcript of May 14th , 2010
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May 14th, 2010FMSTR
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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
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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
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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
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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
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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
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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
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Specifications
9.5 inches4.75 inches
Introduction and Background Concept Design Detailed Design Testing / Results
Payload occupies a half-canister (shared with UNC payload)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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