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Gravity Probe B 2-s averaged Level 2 data


Availability: At NSSDC, Ready for Electronic Access


This data collection consists of Level 2 data from the Gyroscope Drift Rate Experiment of the Gravity Probe B (GP-B) mission. GP-B was designed to study certain aspects of Einstein's general theory of relativity through the use of precision gyroscopes in Earth orbit. The primary objective of the Gyroscope Drift Rate Experiment was to measure two relativistic effects on nearly perfect gyroscopes.

Level 2 Data Definition: Level 2 data is more than a transformation of Level 1 telemetry data. Level 1 data, along with data from outside sources and combinations of Level 1 data goes through Science Ops pre-processing algorithms to become Level 2 data averaged on 2 second centers. * A select subset of the Level 1 data is sent to Science Ops. Filters are applied and some additional calibrations are made to the data via pre-processing. * Other data, such as GPS ephemeris data and Laser Ranging data, are combined with the telemetry (Level 1) data, and some monitors from the Level 1 data are joined together through pre-processing algorithms. Some filtering (lowpass and Kalman filtering for example) and FFT's may be applied. * All data is averaged on two-second centers. After all pre-processing algorithms are accomplished, the resulting data set is put into the Level 2 database. * Level 2 data is considered the cleanest, most complete science data set. It is a starting point for analysis.

Gravity Probe B data was stored in a SYBASE database during the operational phase of the mission. The Level 2 Database was a Sybase client-server database that held Level 2 data, its meta-data, and the Orbit Determination Database. When it came time to archive data for long-term preservation, the information from each of the SYBASE database tables was output to CDF files. For each CDF file, another file with the same file name but with a file extension of .SUM was also created. This file contains metadata related to the SYBASE database select used to form the associated CDF file.

Alternate Names

  • Level 2 data, 2-s average


  • NASA Space Science Data Coordinated Archive


  • Astronomy: General Relativity
  • Astronomy: Gravity Waves

Additional Information



Questions or comments about this data collection can be directed to: Coordinated Request and User Support Office.



NameRoleOriginal AffiliationE-mail
Ms. Jennifer SpencerData ProviderStanford
Dr. C. W. EverittGeneral ContactStanford
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