Gravity Team Total Resistance Jeff Weinell Jason Mueller Brittany Dupre
Overview • Mission Goal • Science Objectives • Technical Objectives • Science Background • Conclusion • References • Questions
Mission Goal 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.
Science Objectives • 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.
Technical Objectives Meet the design specifications provided by LAACES.
Science Background Overview Isaac Newton and his second law of motion Gravimeters (absolute and relative) Past and present gravimetry missions Atmospheric conditions
Isaac Newton 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
Theoretical Gravity Change From Newton’s second law, we can derive the theoretical change in gravity with altitude
Absolute Gravimeters 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
Relative Gravimeters • Invented by Lucien LaCoste • Zero-length spring • Previous experiments have used a variety of relative gravimeter types: • GWR T020 • GRACE • Geosat • DUCKY Ia
Lucien LaCoste Twentieth century physicist and metrologist Co-invented the modern gravimeter with Arnold Romberg Invented the zero-length spring in 1932
Zero-length Springs Exert zero force if at zero length Twisted and coiled springs create tension Can make pendulums with infinite period
GWR T020 More accurate than zero-length springs Involves levitating a super-conducting sphere in a stable magnetic field
GRACE 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
Geosat Used radio altimetry to detect momentary altitude deviations from average orbit Altitude decreases with local gravity increase Altitude increases with localized gravity decrease
DUCKY Ia A high altitude balloon payload that measured relative gravity changes Used a Vibrating String Accelerometer (VSA)
Vibrating String Accelerometer • 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
Measuring Gravity in a Dynamic Environment • 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
Eotvos Effect 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 pseudo-force
Atmospheric Conditions from Zero to 100,000 feet • 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
Conclusion • 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
References http://www.globalsecurity.org/space/systems/images/global_topo.jpg http://www.cosmosmagazine.com/features/online/1678/gravity-ball http://www2.mssu.edu/seg-vm/bio_lucien_lacoste.html http://www.currentresults.com/Weather/Texas/humidity-annual.php 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/cgi-bin/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
References (continued) http://www.microglacoste.com/fg5Principle.php http://www.jpl.nasa.gov/news/press_kits/gracelaunch.pdf http://ibis.grdl.noaa.gov/SAT/gdrs/geosat_handbook/docs/chap_1.htm http://www.srh.noaa.gov/jetstream/atmos/layers.htm http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/michel.html http://www.splung.com/content/sid/2/page/newtons_laws http://www.nasa.gov/audience/foreducators/k-4/features/F_Measuring_Gravity_With_Grace.html http://www.cleonis.nl/physics/phys256/eotvos.php http://www.leakandflowtesters.com/pressure_decay.htm http://observatory.ou.edu/Oct3-11.html http://www.centennialofflight.gov/essay/Theories_of_Flight/atmosphere/TH1G3.htm http://ethesis.helsinki.fi/julkaisut/mat/fysik/vk/virtanen/studieso.pdf http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html http://hep.physics.indiana.edu/~rickv/Standing_Waves_on_String.html http://laspace.lsu.edu/aces/BalloonCourse/Introduction/Intro%201%20-%20Overview%20of%20LA%20ACES.ppt