Data Set Overview
    =================
      The data set consists of uncalibrated observations, also known as
      EDRs.

      For all the EDR products there is a detached PDS label file that
      describes the contents of one data file. Each label file will have
      the same base name as the data file it is describing, with the
      extension .LBL to denote a label file. The label file defines the
      start time and end of the observation, product creation time, and
      the structure of the binary (or ASCII) tables. Each data product
      is identified within the PDS label by a STANDARD_DATA_PRODUCT_ID
      value, shown in parentheses in the table below.

      The EPS portion of the data archive currently consists of five EDR
      data products. The EPS instrument creates all of its different
      science data packets during one observation, but the packets are
      telemetered to the ground at different times. The different formats
      of these data packets do not lend themselves to standardization
      into one EDR file format. Therefore, different EDR formats have
      been developed, each of which captures one specific data grouping
      such as spectra or PHA data. A given EDR data file will contain all
      the observations obtained on same earth day. The following table
      shows the different EPS data products. Following is a description of
      each of the current EPS EDRs. A more complete description of each
      may be found in the EPPS EDR SIS document, located in the DOCUMENT
      directory of the document volume.

      Current EPS Data Products:

        EPS Pulse Height (EPS_PULSE_HEIGHT)

          Contains Pulse Height Analysis data in binary table format. The
          PHA EDR format was changed by FSW6 on 8/18/2008 There is no
          longer a priority level associated with the PHA EDRs since the
          PHA data product is generated from PHA data packets and the
          high, medium, and low priority packets were retired.

        EPS_High Resolution Spectra (EPS_HIRES_SPECTRA)

          High resolution (energy channels) ion and electron energy
          spectra. New FS W6 EDR introduced on 8/18/2008, replaces
          EPS_HI_SPECTRA.

        EPS_Low Resolution Spectra (EPS_LORES_SPECTRA)

          Low resolution (energy channel)  ion and electron energy spectra
          and rate counters. New FSW6 EDR introduced on 8/18/2008, replaces
          EPS_MED_SPECTRA.

        EPS Summary Spectra (EPS_SUMMARY_SPECTRA)

          Contains a subset of rate counters and low resolution energy
          spectra. New FSW6 EDR introduced on 8/18/2008

        EPS Scan (EPS_SCAN_RATES)

          Contains the integrated hardware counters over four energy
          thresholds. Each threshold setting and integration lasts 1/4
          second. New FSW6 EDR introduced on 8/18/2008

      In addition to the science data, associated instrument parameters
      are included.

      EPPS Engineering and Status Data Product

        The EPPS_LONG_STATUS EDR data product contains the engineering
        and status information for the EPPS instrument. This data product
        consists of an external PDS label file and its pointer to an
        ASCII table file.  The data product is in ASCII to facilitate the
        browsing of instrument status parameters with commonly available
        text readers during mission operations. New FSW5 EDR introduced
        on 9/6/2007


    Previous Data Set Overview
    ==========================
      On 9/6/2007, version 5 of the EPPS flight software (FSW5) was
      uploaded to the MESSENGER spacecraft. FSW5 implemented several
      changes to the FIPS science telemetry. One significant change was
      the removal of FIPS housekeeping data stored in the FIPS High
      Priority Science Packet and its inclusion in the EPPS engineering
      and status data. Due to this change the EPPS_STATUS EDR has been
      replaced by the EPPS_LONG_STATUS as noted below.

      On 8/18/2008, version 6 of the EPPS flight software (FSW6) was
      uploaded to the MESSENGER spacecraft and installed on the EPPS
      instrument on 8/19/2008. FSW6 changed the packet formatting such
      that two EPS EDRs had to be retired and replaced by two new EDRs.
      Two additional EDRs had to be created to store data from two new
      instrument packets. Finally, the format for the EPS PHA EDR has
      been updated to support slight changes in the PHA data.

      Prior to these changes, the EPS portion of the data archive
      consisted of four EDR data products, which correspond to the
      different types of science data packets generated by the instrument
      at high priority, medium priority, and low priority. The EPS
      instrument created all of its different science data packets during
      one observation, but the packets were telemetered to the ground at
      different times based on priority. The different formats of the
      data packets did not lend themselves to standardization into one
      EDR file format. For example, the high priority science data packet
      contained the EPS high priority spectra, housekeeping information,
      and Pulse Height Analysis (PHA) data. Therefore, different EDR
      formats were developed, each of which captured one specific data
      grouping spectra, housekeeping information, or PHA data.

      Due to these changes the following EDR types have been retired in
      this version of the data set and will no longer be included in future
      archives:

        EPS_HI_SPECTRA, High Priority EPS Spectra (FSW6, 8/18/2008)

        EPS_HI_HOUSEKEEPING, High Priority Housekeeping (FSW6, 8/18/2008

        EPS_MED_SPECTRA, Medium Priority EPS Spectra (FSW6, 8/18/2008)

        EPPS_STATUS, EPPS Engineering and Status ()

      The following EDR types have changed in this version of the
      data set:

        EPS_PULSE_HEIGHT, EPS Pulse Height (FSW6, 8/18/2008)

      The following EDR types are new in this version of the data set:

        EPS_HIRES_SPECTRA, EPS High Resolution Spectra (FSW6, 8/18/2008)

        EPS_LORES_SPECTRA, EPS Low Resolution Spectra (FSW6, 8/18/2008)

        EPS_SUMMARY_SPECTRA, EPS Summary Spectra (FSW6, 8/18/2008)

        EPS_SCAN_RATES, EPS Scan (FSW6, 8/18/2008)

        EPPS_LONG_STATUS, EPPS Engineering and Status (FSW5, 9/6/2007)

      These changes are described in detail in the EPPS EDR SIS Document,
      contained in the DOCUMENT directory of the DOC_VOL.


    Instrument Overview
    ===================
      The EPS sensor consists of a 60-mm diameter, tuna-can-like
      cylinder, in which a start foil and stop foil, wrapped around
      opposite curved sides of the cylinder, constitute the TOF chamber.
      The detectors are arranged so that each detector senses the
      events within a given range of incidence angles. Each of the 6
      detector modules is composed of 4 pixels: large and small ion and
      large and small electron. The FIPS consists of an electrostatic
      analyzer (ESA), located at the entrance to the sensor, a
      post-acceleration chamber between the output of the ESA and the
      carbon foil, and a time-of-flight telescope. The ESA at the
      entrance to the FIPS acts as a wide-angle lens for ions. It only
      allows ions with a specific energy/charge band to enter through
      its output plane.

      See the EPPSINST.CAT file for more information and
      [ANDREWSETAL2007] for full details.


    Calibration Overview
    ====================
      This data set is NOT calibrated; it only provides the uncalibrated
      sensor measurements.


    Parameters
    ==========
      The principal parameters during normal science operations when
      observing with the EPPS are as follows:

      * EPS Medium-Priority Integration Interval (N2): This parameter
      sets the integration interval for medium-priority data (commonly
      30 s).

      * EPS High-Priority Integration Interval (N1): This parameter sets
      the integration interval for high-priority data (commonly 300 s).
      N1 is an integer-multiple of N2.

      * EPS Detector Selection: EPS possesses 24 detectors: 12 for ions
      and 12 for electrons. Half are large-pixel, and half are
      small-pixel. Only 12 detectors can be used simultaneously, so the
      operational detectors can be set by command.

      * FIPS Mode Selection: This command allows selection of the mode
      of operation: normal, burst, and pick-up ion.

      The EPPS also includes modes for testing the instrument and
      maintenance activities.


    Data
    ====
      The EPS EDR data set products are described as follows (the STANDARD_
      DATA_PRODUCT_ID value is given in parentheses). The notes provided
      in brackets give the current status of the data product in version 2
      of the data set.

      [RETIRED] The High Priority EPS Spectra EDR (EPS_HI_SPECTRA) contains
      spectral data, hardware and software rate counters in binary table
      format. Data and counter values are taken from the High Priority
      Science Packet. [RETIRED, FSW6, 8/18/2008]

      [RETIRED] The High Priority Housekeeping EDR (EPS_HI_HOUSEKEEPING)
      is an ASCII table file that contains 33 fields of housekeeping data.
      [RETIRED, FSW6, 8/18/2008]

      [RETIRED] The Medium Priority EPS Spectra EDR (EPS_MED_SPECTRA)
      contains contains spectral data, hardware and software rate
      counters in binary table format. Data and counter values are
      taken from the Medium Priority Science Packet. [RETIRED,
      FSW6, 8/18/2008]

      [NEW] The EPS High Resolution Spectra (EPS_HIRES_SPECTRA) contains
      high resolution (energy channels) ion and electron energy spectra.
      [NEW, FSW6, 8/18/2008]

      [NEW]  EPS Low Resolution Spectra (EPS_LORES_SPECTRA) contains
      Low resolution (energy channel)  ion and electron energy spectra
      and rate counters. [NEW, FSW6, 8/18/2008]

      [NEW] EPS Summary Spectra  (EPS_SUMMARY_SPECTRA) contains a subset
      of rate counters and low resolution energy spectra. [NEW, FSW6,
      8/18/2008]

      [NEW]  EPS Scan (EPS_SCAN_RATES) contains the integrated hardware
      counters over four energy thresholds. Each threshold setting and
      integration lasts 1/4 second. [NEW, FSW6, 8/18/2008]

      [CHANGED] The EPS Pulse Height EDR (EPS_PULSE_HEIGHT) contains
      Pulse Height Analysis data in binary table format. The PHA data
      product is generated from the high, medium, or low priority
      science packet. The priority level will be identified within the
      PDS label. [CHANGED, FSW6, 8/18/2008)

      [CHANGED] The High Priority FIPS Spectra EDR (FIPS_HI_SPECTRA)
      contains spectral and velocity distribution, hardware and software
      rate counters in binary table format. Data and counter values are
      taken from the High Priority Science Packet. [CHANGED, FSW5,
      9/6/2007]

      [RETIRED] The EPPS Status EDR contains engineering and status
      information for the EPPS instrument. The data product is in ASCII
      to facilitate the browsing of instrument status parameters with
      commonly available text readers during mission operations.
      [RETIRED, FSW5, 9/6/2007]

      [NEW] The EPPS Engineering and Status EDR (EPPS_LONG_STATUS),
      contains engineering and status information for the EPPS
      instrument. The data product is in ASCII to facilitate the
      browsing of instrument status parameters with commonly available
      text readers during mission operations.  [NEW, FSW5, 9/6/2007]

Confidence Level Overview
   =========================
     The EPPS EDR data are the least processed data set released for the
     EPPS.  Data presented here are an accurate representation of the EPPS
     data as received from the spacecraft, with minimal timing and no
     spatial processing.


   Review
   ======
     The EPPS EDR was reviewed internally by the EPPS team prior to
     release to the PDS. PDS also performed an external review of the
     EPPS EDR.


   Data Coverage and Quality
   =========================
     Data reported are the minimally processed data received from the
     spacecraft during the following mission phases: Launch, Earth_Cruise,
     Earth Flyby, Venus 1 Cruise, Venus 1 Flyby, Venus 2 Cruise,
     Venus 2 Flyby, Mercury 1 Cruise, Mercury 1 Flyby, Mercury 2 Cruise,
     Mercury 2 Flyby, Mercury 3 Cruise, Mercury 3 Flyby, Mercury 4 Cruise,
     Mercury Orbit, Mercury Orbit Year 2, Mercury Orbit Year 3, Mercury
     Orbit Year 4, and Mercury Orbit Year 5.  These mission phases are
     defined as:

                            Start time          End time
      Phase Name            Date (DOY)          Date (DOY)
      -------------------   -----------------  -----------------
      Launch                03 Aug 2004 (216)  12 Sep 2004 (256)
      Earth Cruise          13 Sep 2004 (257)  18 Jul 2005 (199)
      Earth Flyby           19 Jul 2005 (200)  16 Aug 2005 (228)
      Venus 1 Cruise        17 Aug 2005 (229)  09 Oct 2006 (282)
      Venus 1 Flyby         10 Oct 2006 (283)  07 Nov 2006 (311)
      Venus 2 Cruise        08 Nov 2006 (312)  22 May 2007 (142)
      Venus 2 Flyby         23 May 2007 (143)  20 Jun 2007 (171)
      Mercury 1 Cruise      21 Jun 2007 (172)  30 Dec 2007 (364)
      Mercury 1 Flyby       31 Dec 2007 (365)  28 Jan 2008 (028)
      Mercury 2 Cruise      29 Jan 2008 (029)  21 Sep 2008 (265)
      Mercury 2 Flyby       22 Sep 2008 (266)  20 Oct 2008 (294)
      Mercury 3 Cruise      21 Oct 2008 (295)  15 Sep 2009 (258)
      Mercury 3 Flyby       16 Sep 2009 (259)  14 Oct 2009 (287)
      Mercury 4 Cruise      15 Oct 2009 (288)  03 Mar 2011 (062)
      Mercury Orbit         04 Mar 2011 (063)  17 Mar 2012 (077)
      Mercury Orbit Year 2  18 Mar 2012 (078)  17 Mar 2013 (076)
      Mercury Orbit Year 3  18 Mar 2013 (077)  17 Mar 2014 (076)
      Mercury Orbit Year 4  18 Mar 2014 (077)  17 Mar 2015 (076)
      Mercury Orbit Year 5  18 Mar 2015 (077)  30 Apr 2015 (120)

     No EPPS data were collected during Venus_1_Flyby phases.  The EPPS
     was on for brief periods during the other six mission phases.
     During these planned operational periods, the EPS sensor on the EPPS
     did not have high voltage enable, hence no Time-of-flight data and
     only spectra data were collected.  The EPS was turned on for the
     Venus_2_Flyby and to be remained on throughout the remainder of the
     mission phases.  EPPS data were collected during the Mercury_1_Flyby.

     EPS High Ion Sector 1 and 5 have malfunction detectors and do not
     produce any data product.

     The lowest energy channel (32 to 55 keV) on the High Ion Sector 3
     and 5 have periodic high count that are due to flight software
     interaction with the instrument and should not be used.  User of
     EPS data should consult with the instrument team at JHU/APL to
     verify the quality of specific data in certain time interval prior
     to publication.

     During orbital phase, a certain sector in the EPS field-of-view has a
     direct view of the sunlit side of the planet. During these periods, the
     single event data (Fast, Scanned, etc) may be susceptible to photon
     contamination. The science event data (all rate and spectra data) have
     additional on-board software processing that should eliminate this
     photon contamination.  But the user should always consult with the
     instrument team at JHU/APL to verify the quality of specific data prior
     to publication.

     During spacecraft noon-midnight orbits, EPS instrument temperature can
     raise to level that affect the low energy channels.  We have noticed
     during some of these orbits, the temperature induced noise render
     those energy channels below 100 keV to be useless.  In addition, the
     higher than normal temperature also induced a data 'drop-out' where the
     count in all rate drops by factor during one integration period and
     remain so for a few minutes to hours.  The EPS team is currently
     investigating the cause of this 'drop-out'.  Users should always consult
     the instrument team at JHU/APL to verify the quality of specific data
     prior to publication.

     During orbital phase, EPS routinely switches between large and small
     pixel on both the ion and electron detector.  User should check the
     pixel size flag in the data to know which pixel the detectors are using.

     On 18 Aug 2008 (231), a new Flight Software (FSW) was uploaded to EPPS.
     This new FSW (v6) enhances the energy resolution for EPS and adds a high-
     resolution proton distribution data packet on FIPS. Description of these
     new data products are included in the FMT file.  In addition, the new
     FSW v6 fixed the data spikes in the EPS data (as mentioned in the
     previous paragraph). As always, user of the EPS data should consult with
     the instrument team at JHU/APL to verify the quality of specific data
     prior to publicaion.

     On 18 August 2009 (230), another new FSW was uploaded to EPPS.  This new
     FSW (v7) only affects the FIPS data.

     In the nominal flight configuration, the FIPS sensor on the EPPS
     field-of-view will not measure the solar wind.  Periodically, the
     spacecraft will rotate such that the FIPS field-of-view can detect
     the nominal radial flowing solar wind.  These periods typically lasted
     less than 3 hours and are identified as:

                        Start time         End time
     Phase Name         Date (DOY)         Date (DOY)
     ----------------- ----------------   ----------------
     Earth_Cruise      05 Apr 2005 (105)  05 Apr 2005 (105)
     Earth_Flyby       02 Aug 2005 (214)  02 Aug 2005 (214)
                       07 Aug 2005 (219)  07 Aug 2005 (219)
     Venus_1_Cruise    27 Feb 2006 (058)  27 Feb 2006 (058)
                       06 Sep 2006 (249)  10 Sep 2006 (253)
     Venus_1_Flyby     No Data
     Venus_2_Cruise    01 Mar 2006 (060)  01 Mar 2006 (060)
     Venus_2_Flyby     05 Jun 2007 (156)  05 Jun 2007 (156)

     There are gaps in the EPS scan spectra (EPS_SCAN_SPECTRA) products
     inclusively spanning 2014-078 through 2014-083 and 2014-246 through
      2014-254.

     There are data gaps in the EPS scan spectra (EPS_SCAN_RATES) products
     inclusively spanning 2014-334 to 2014-350 (production halted to reduce
     data volume during a low speed downlink during a solar conjunction),
     2014-352 to 2015-022 (production halted for a high voltage check), and
     2015-092 to end of mission on 2015-120 (production halted to reduce
     solid state recorder load during a solar conjunction).

   Limitations
   ===========
     This data set is minimally processed data.  The data are received
     from the spacecraft telemetry and ingested into the MESSENGER
     Science Operations Center (SOC).