Pre-PDR Presentation
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Transcript Pre-PDR Presentation
Jeff
Weinell
Jason Mueller
Brittany Dupre
Mission
Goal
• Science Objectives
• Technical Objectives
Science
Background
Conclusion
References
Questions
We
will build a payload to measure Earth’s
gravity field as a function of altitude for
heights of up to 100,000 feet, and compare
our findings to theoretical and experimental
high altitude gravity models.
Analyze
and interpret data to find a correlation
between changes in Earth’s gravity as altitude
increases.
Compare our data to theoretical models.
Compare our data to results from previous
experiments.
Meet
the design specifications provided by
LAACES.
Isaac
Newton and his second law of motion
Gravimeters (absolute and relative)
Past and present gravimetry missions
Atmospheric conditions
Theorized
that an external force was pulling
objects towards Earth’s center
His second law states
that the net force on
an object is equal to
the instantaneous
rate of change of
that object
From
Newton’s second law, we can derive the
theoretical change in gravity with altitude
A
gravimeter is an instrument that measures
gravity
Accurate for up to about 1.1 microgal
Expensive
Hard to transport
Takes a long time for
accurate measurements
Invented
by Lucien LaCoste
• Zero-length spring
Previous
experiments have
used a variety of relative
gravimeter types:
• GWR T020
• GRACE
• Geosat
• DUCKY Ia
Twentieth
century
physicist and
metrologist
Co-invented the
modern gravimeter
with Arnold Romberg
Invented the
zero-length spring
in 1932
Exert
zero force if at zero length
Twisted and coiled springs create tension
Can make pendulums with infinite period
More
accurate than zero-length springs
Involves levitating a super-conducting sphere
in a stable magnetic field
Gravity
Recovery And Climate Experiment
Maps Earth’s gravity field every 30 days
Helps track sea levels, ocean
currents, polar ice sheets,
and Earth’s interior structure
Used
radio
altimetry to detect
momentary
altitude deviations
from average orbit
Altitude decreases
with local gravity
increase
Altitude increases
with localized
gravity decrease
A
high altitude balloon
payload that measured
relative gravity changes
Used a Vibrating String
Accelerometer (VSA)
• The VSA on the DUCKY Ia
payload detected changes in
acceleration along a single axis
• The difference between the
oscillation frequencies of the
two strings is proportional to
the acceleration along the
sensitive axis
• Gravimeters cannot distinguish
between gravitational
acceleration and acceleration due
to external forces
• It is necessary to obtain additional
acceleration measurements from
an inertial reference frame
independent of the gravimeter to
isolate gravitational acceleration
Objects
travelling east appear to experience a
decrease in gravitational acceleration
Objects travelling west appear to experience
an increase in gravitational acceleration
Vertical component of centrifugal pseudoforce
Temperature
• Decreases with altitude in the troposphere
• Increases with altitude in the stratosphere
Pressure
• Decreases as altitude increases
Humidity
• Approximately 65% in Palestine, Texas
• Weather dependent
Turbulence
• Greatest in the troposphere
Temperature,
pressure, humidity, and
turbulence will vary during balloon flight
We anticipate that gravity measurements will
be most accurate in the stratosphere
Gravity should decrease slightly with
increasing altitude
http://www.globalsecurity.org/space/systems/images/global_topo.jpg
http://www.cosmosmagazine.com/features/online/1678/gravity-ball
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http://www.ualberta.ca/~dumberry/gravity.htm
http://www.britannica.com/EBchecked/topic/242391/gravimeter
http://www.gwrinstruments.com/pdf/Geothermal_Brochure_Prod_Rev1_
4PG.pdf
http://www.cage.curtin.edu.au/~will/grav_anoms.htm
http://www-scf.usc.edu/~kallos/gravity.htm
http://www.dtic.mil/cgibin/GetTRDoc?AD=ADA202985&Location=U2&doc=GetTRDoc.pdf
http://www.jclahr.com/science/psn/zero/winding/gravity_sensor.html
http://www.merriam-webster.com/dictionary/free%20oscillation
http://www.microglacoste.com/fg5Principle.php
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TH1G3.htm
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