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6.4-min, Mass-Energy Spectra Data


Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1984-08-21 to 1985-12-24


These 6.4-min averages of data from the Medium Energy Particle Analyzer (MEPA) experiment are written on magnetic tape in SFDU format. Each physical block has a fixed length of 22528 bytes, written in English/ASCII and VAX binary representation. The volume header provides an outline of the content and structure of the entries. It is followed by an ephemeris file of many blocks, which includes the spacecraft position and velocity components in the GSE system; geographic latitude, longitude, and LT; SM latitude and MLT; and the GSE components of a model (not measured) magnetic field; each at 5-min intervals. Written next is an attitude file that includes the right ascension and declination of the direction of the spin axis, once every orbit. It is followed by an "events" file that provides information on maneuvers, data gaps, anomalous conditions, etc. The final sequence of files provides the MEPA data written as one file per day of data. Each logical record of 10948 bytes provides the 6.4-min averages of the following parameters: (a) directional fluxes of H (in 3 energy bands, 56-190, 190-600, and > 600 keV), He (in 4 energy bands, 74-240, 240-680, 680-1900, and > 1900 keV), Li (in 2 energy bands, 315-750, and > 750), C-N-O (in 4 energy bands, 137-365, 365-910, 910-2320, and > 2320 keV), and heavy ions (in 2 energy channels, 900-1340, and > 1340 keV); these fluxes, in units 1/(cm**2 s sr), are provided for each of the 32 angular sectors; (b) mass-indifferent, directional, differential fluxes in 10 energy bands covering 50-6000 keV, from each of the angular sectors, in units of 1/(cm**2 s sr kev); (c) the data in (a) and (b), averaged over all sectors; (d) proton fluxes in 10 energy channels covering 25-1350 keV, and He++ fluxes in 3 energy channels covering 1 to > 6 MeV, from each of the 32 angular sectors; (e) the data in (d), averaged over all sectors; and (f) magnetic local time and latitude, spacecraft position in GSE coordinates, and standard deviations of all averaged fluxes listed above. There has been a progressive gain drift problem since the launch, but the available data have been satisfactorily corrected. The on-board tape recorder enabled time-continous data. The documentation is thorough, and requires little or no hardcopy information.

Data are available online at

Alternate Names

  • 6.4-min, Mass-Energy Spectra


  • Space Physics: Magnetospheric Studies


  • 84-088A-02B

Additional Information



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



NameRoleOriginal AffiliationE-mail
Mr. Stuart R. NylundData ProviderApplied Physics
Mr. Robert M. CandeyGeneral ContactNASA Goddard Space Flight
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