SAMPEX Data Arrive at NSSDC

Volume 12, Number 1, March 1996
by R. Parthasarathy

The Solar Anomalous Magnetospheric Particle EXplorer (SAMPEX) is the first in NASA's relatively low-budget, fast-track series of Small Explorer class of spacecraft. It was launched on July 3, 1992, to provide cosmic ray fluxes at the polar cap and radiation belts fluxes. Special emphasis was on the particles in the 6-20 atomic mass unit (AMU) range where the fluxes are known to have an "anomalous excess." This anomalous component is believed to result from cool, neutral interstellar atoms entering the heliosphere, being ionized (at low ionization levels) and then swept out to the heliospheric boundary where they are accelerated to tens of MeV/nucleon and finally diffusing back into the inner heliosphere.

The SAMPEX spacecraft appears here in final launch configuration.

The University of Maryland provides the science coordination and many data processing and management functions for SAMPEX. Dr. Glenn Mason there is the single official principal investigator. SAMPEX carries four instruments provided by co-investigators at various sites:

LICA is a time-of-flight instrument that measures mass and energy in the range below 12 MeV/nucleon. The other three are dE/dX telescopes. HILT covers 4-170, MAST 7-450, and PET 18-270 MeV/nucleon. PET has an electron channel in the range 0.4-30 MeV, while the lowest energy channel in LICA is sensitive to MeV electrons also. Directional resolution is good enough that some of the instruments enable atomic charge state determination via model computations of cut-off rigidity. Further information is available from the SAMPEX project's World Wide Web (WWW) page at URL and from NSSDC's SAMPEX page at URL .

Raw Level-0 data are electronically transferred from Goddard's institutional data capture facilities to the University of Maryland SAMPEX Office. That office then inserts some ancillary parameters (orbit/attitude, etc.) and distributes the resultant level 1 (L-1) data to the individual co-investigator teams, where higher level (L-2) data products are derived.

The full-resolution L-1 data, written in the CalTech-developed Tennis format on a University of Maryland VAX/VMS computer, are stored at NSSDC on erasable optical disks. Each disk typically holds 12 days of data in one-day files. At present these disks are accompanied by minimal documentation since in the near-term users of this data product are expected to interact with SAMPEX Principal Investigator Dr. Glenn Mason at the University of Maryland ( These L-1 data are not casually usable; many channels of housekeeping data must be carefully scrutinized before the raw counts from any channel during any of the 6-s time bins may be converted into rates or fluxes. It is anticipated that prior to the end of the SAMPEX mission, sufficient supporting material will have been provided by the University of Maryland to NSSDC to support use of these L-1 data by persons not otherwise associated with SAMPEX.

Currently, four L-2 data products are being provided to NSSDC by the University of Maryland. These are arriving in ASCII format over the Internet and are becoming accessible from the NASA Data Archive and Distribution Service (NDADS):

The 30-sec data are managed as one-day files, and the polar cap averaged data are managed as monthly files. Multiple NDADS access paths are supported. Users can use on the Web the Space Physics data Catalog (SPyCAT) at URL Via the older E-mail-based Automated Retrieval Mail System (ARMS), users may send E-mail to ARCHIVES@NSSDCA.GSFC.NASA.GOV and enter in the Subject line REQUEST SAMPEX "DATASET NAME". In the main body users should enter the Entry IDs (EID) for the desired day(s) or month(s) on successive lines, and the word document as the final line if documentation is needed. Relevant values for DATASET NAME and for EID are given in the following table:


SAMPEX_30S_FLUX_ASCII YYYYDDD 	133 variables, 	18 MeV/n channels, 4.0 MB

SAMPEX_30S-RATE_ASCII YYYYDDD 	392 variables, 	50 MeV/n channels, 9.5 MB

SAMPEX_POLCAP_FLUX_ASCII YYYYMM	58 variables, 	18 MeV/n channels, 630 KB

SAMPEX_POLCAP_RATE_ASCII YYYYMM	313 variables, 	50 MeV/n channels, 3.0 MB

Currently, the FLUX data are being cast in Common Data Format (CDF); when available for access their names will remain the same as in the ASCII files except "_CDF" will replace "_ASCII."

By mid-April 1996 NSSDC expects to have the L-2 ASCII data available at least to the middle of 1993.

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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 21 Nov 1996 [EDG]