may 14th , 2010
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May 14th , 2010. FMSTR. Introduction and Background Concept Design Detailed Design Testing / Results. The Problem and Proposed Solution. - PowerPoint PPT PresentationTRANSCRIPT
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