May 14th, 2010
FMSTR
Introduction and Background
Concept Design
Detailed Design
Testing / Results
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
An optical mass gauge is a viable option
Normal Gravity
Source: NASA
Microgravity
Introduction and Background
Concept Design
Detailed Design
Testing / Results
Alternative Methods
Alternative Method
Basics
Capacitive Sensor
Requirement
Permittivity of the cryogenic fluid is related to
Settling /
the volume within the tank.
Stratification
Flexible Cryogenic
A strip of silicone diodes are brought to a
Settling /
Temperature and
certain temperature. Time constants allow for Stratification
Liquid-Level Probes
fluid volume measurement.
Multipin Plug
Vapor
Cryo-Liquid
Diodes
Optical mass gauge will not require
settlement or acceleration of spacecraft
Introduction and Background
Concept Design
Detailed Design
Testing / Results
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.
Approach:
• Build prototype version of sensor
• Test in laboratory (with water)
• Vibration test
• Flight test on a sounding rocket
Introduction and Background
Concept Design
Detailed Design
Testing / Results
System Layout
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.
Introduction and Background
Concept Design
Detailed Design
Testing / Results
Solid Model of Flight-Ready Prototype
Servo
Power Supply
Tank 1
Photo Diode
Detector
Tank 2
Piston
Valve 1
Valve 2
HeNe Laser
Laser output
into Fiber
Gas Cell
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
Payload occupies a half-canister
(shared with UNC payload)
9.5 inches
4.75 inches
Introduction and Background
Concept Design
Detailed Design
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
G-switch
All wires secured with
nylon harnessing.
Testing / Results
Introduction and Background
Concept Design
Detailed Design
Construction
Gas cell contains Air,
determined that xenon or
argon are not needed for
accurate results in our
system.
Testing / Results
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
Two Tests:
•Sine Sweep: 10-2000 Hz
•Random
Resonance at: 200Hz
Max Accel: 25G
Introduction and Background
Concept Design
Detailed Design
Testing / Results
Fringe Counting Methods (Method 1/3)
Fractional Method
η = { location of first peak (A) }
X
Y
A
B
1
2
3
β = N – { location of last peak (D) }
C
D
4
5
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
N
0
η
β
Find the fraction of sine wave that exists before the first
peak and after the last peak.
Introduction and Background
Concept Design
Detailed Design
Testing / Results
Fringe Counting Methods (Method 2/3)
Frequency Method #1
X
Find wavelength between first two
peaks and the last two peaks: {X , Y}
Y
A
B
1
2
3
C
D
4
5
Find the mean wavelength:
μ=(X+Y)/2
Divide range by mean wavelength to
obtain fringe count:
Total (fractional) fringe count:
T=N/μ
0
N
Find an average wavelength between the first two peaks
and 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)
Frequency Method #2
Find peak locations: { A , B , C , D , E }
A
B
C
D
E
1
2
3
4
5
Formulate a difference array (distance
between each peak):
D = {B –A,C –B ,D –C ,E –D }
Take an average (mean wavelength):
μ = Mean[D]
Divide range by mean wavelength to
obtain fringe count:
Total (fractional) fringe count:
T=N/μ
0
N
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
# of Fringes
5.33
Tank 2
3.30
Measured
Liquid Volume
(mL)
3.59
= 10.33
Actual Liquid
Volume (mL)
= 10.53
Percent
Error
= 1.90%
10.33
mL
Introduction and Background
Concept Design
Detailed Design
Testing / Results
Full Mission Simulation Test
5 minutes operation
45 seconds pause
- 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)
Introduction and Background
Concept Design
Detailed Design
Testing / Results
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
Introduction and Background
Concept Design
Detailed Design
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
Testing / Results
Introduction and Background
Concept Design
Detailed Design
Testing / Results
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