 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 pseudo- force

 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

       4PG.pdf    bin/GetTRDoc?AD=ADA202985&Location=U2&doc=GetTRDoc.pdf  

       4/features/F_Measuring_Gravity_With_Grace.html     TH1G3.htm     %20Overview%20of%20LA%20ACES.ppt