Data Set Overview
    =================

      This data set contains Raw data taken by the
      New Horizons Pluto Energetic Particle Spectrometer Science Investigation
      instrument during the KEM1 ENCOUNTER and KEM2 CRUISE
      mission phases.

      PEPSSI (Pluto Energetic Particles Spectrometer Science Investigation)
      is a particle telescope and a time-of-flight (TOF) spectrometer that
      measures ions and electrons over a broad range of energies and
      angles. Particle composition and energy spectra are measured for H to
      Fe from ~ 30 keV to ~1 MeV (but not all species are uniquely separated)
      and for electrons from ~30 keV to 700 keV. PEPSSI comprises a
      time-of-flight (TOF) section and a solid-state detector (SSD) array
      that measures particle energy. The combination of measured energy and
      TOF provides unique particle identification by mass and particle energy
      depending on the range: for protons from ~30 keV to ~1 MeV; for heavy
      (CNO) ions from ~80 keV to ~1 MeV. Lower-energy (>3 keV) ion fluxes are
      measured by TOF only, but without the SSD signal, providing velocity
      spectra at these energies as well. Due to storage and bandwidth
      limitations, all event data cannot be stored or telemetered to the
      ground. Instead, a round-robin algorithm is used to save Energy, TOF,
      and timing data for select events. The common data products contain
      these event and summary measurements, accumulated over fixed periods of
      86,400 seconds, with each period in a single file comprising multiple
      binary tables.  The documentation provided with this data set describes
      the data format.

      For a list of observations, refer to the data set index table. This
      is typically INDEX.TAB initially in the INDEX/ area of the data set.
      There is also a file SLIMINDX.TAB in INDEX/ that summarizes key
      information relevant to each observation, including which sequence
      was in effect and what target was likely intended for the
      observation.


    Version
    =======

      This is VERSION 1.0 of this data set.

      This version includes data acquired by the spacecraft between
      08/14/2018 and 04/10/2023. It only includes data downlinked before
      05/01/2023 and after 04/30/2022. Future datasets may include more
      data acquired by the spacecraft after 08/13/2018 but downlinked
      after 04/30/2023.

      This version includes observations from prior to, during, and after
      the ASTEROID 486958 Arrokoth (2014 MU69) encounter.

      After a lengthy hibernation period, the New Horizons spacecraft
      resumed data playback on DOY 2023_060 (March 1, 2023). The spacecraft
      collected PEPSSI data throughout its hibernation, but most of that
      data has not been downlinked yet. As a result, this version will
      contain substantial gaps in the data. These gaps will be filled in
      later versions.

      On April 10, 2022 at 10:17 UTC, the PEPSSI flight software was updated
      to version 5 (FSW5). The changes to the data are small, but the way the
      instrument is operated has changed. Refer to section 11.3.6 (Flight
      Software Version 5 Changes to Operations) in the SOC Instrument ICD
      (/DOCUMENT/SOC_INST_ICD.*) for a brief description of the changes.

      This dataset corresponds to New Horizons NAIF SPICE distribution v0007.


    Processing
    ==========

      The data in this data set were created by a software data
      processing pipeline on the Science Operations Center (SOC) at
      the Southwest Research Institute (SwRI), Department of Space Operations.
      This SOC pipeline assembled data as FITS files from raw telemetry
      packets sent down by the spacecraft and populated the data labels
      with housekeeping and engineering values, and computed geometry
      parameters using SPICE kernels.  The pipeline did not resample
      the data.


    Data
    ====

      The observations in this data set are stored in data files using
      standard Flexible Image Transport System (FITS) format.  Each FITS
      file has a corresponding detached PDS label file, named according
      to a common convention.  The FITS files may have image and/or table
      extensions. See the PDS label plus the DOCUMENT files for a
      description of these extensions and their contents.

      This Data section comprises the following sub-topics:

      - Filename/Product IDs
      - Instrument description
      - Other sources of information useful in interpreting these Data
      - Visit Description, Visit Number, and Target in the Data Labels


      Filename/Product IDs
      --------------------

        The filenames and product IDs of observations adhere to a
        common convention e.g.

         PEP_0123456789_0X691_ENG.FIT
         ^^^ ^^^^^^^^^^ ^^^^^ ^^^\__/
         |        |       |    |  ^^
         |        |       |    |   |
         |        |       |    |   +--File type (includes dot)
         |        |       |    |      - .FIT for FITS file
         |        |       |    |      - .LBL for PDS label
         |        |       |    |      - not part of product ID
         |        |       |    |
         |        |       |    +--ENG for CODMAC Level 2 data
         |        |       |       SCI for CODMAC Level 3 data
         |        |       |
         |        |       +--Application ID (ApID) of the telemetry data
         |        |          packet from which the data come
         |        |          N.B. ApIDs are case-insensitive
         |        |
         |        +--MET (Mission Event Time) i.e. Spacecraft Clock
         |
         +--Instrument designator


      Note that, depending on the observation, the MET in the data filename
      and in the Product ID may be similar to the Mission Event Time (MET)
      of the actual observation acquisition, but should not be used as an
      analog for the acquisition time.  The MET is the time that the data are
      transferred from the instrument to spacecraft memory and is therefore
      not a reliable indicator of the actual observation time.  The PDS label
      and the index tables are better sources to use for the actual timing of
      any observation.  The specific keywords and index table column names for
      which to look are

        * START_TIME
        * STOP_TIME
        * SPACECRAFT_CLOCK_START_COUNT
        * SPACECRAFT_CLOCK_STOP_COUNT


        Instrument   Instrument designators              ApIDs **
        ===========  ==================================  =============
         PEPSSI       PEP                                0X691 - 0X698 *

         * Not all values in this range are in this data set
         ** ApIDs are case insensitive

         There are other ApIDs that contain housekeeping values and
         other values.  See SOC Instrument ICD (/DOCUMENT/SOC_INST_ICD.*)
         for more details.


        Here is a summary of the types of files generated by each ApID
        (N.B. ApIDs are case-insensitive) along with the instrument
        designator that go with each ApID:


         ApIDs   Data product description/Prefix(es)
         =====   ===================================
         0x691 - PEPSSI High Priority Science (long integration)
         0x692 - PEPSSI Medium Priority Science (short integration)
         0x693 - PEPSSI Low Priority Science (Up to 500 PHA events)
         0x694 - PEPSSI Low Priority Science (Up to 500 PHA events)
         0x695 - PEPSSI High Priority Science Diagnostic Mode data
         0x696 - PEPSSI Medium Priority Science Diagnostic Mode data
         0x697 - PEPSSI Diagnostic Mode Event data
         0x698 - PEPSSI Diagnostic Mode Event data

     For historical reasons, PEPSSI products always use an ApID of '0x691'
     in the filename. Each product actually contains all the data types
     (ApIDs) available for that day.

     ApIDs '0x693' and '0x694' are combined during ground processing.
     So are ApIDs '0x697' and '0x698'.


      Instrument description
      ----------------------

        Refer to the following files for a description of this instrument.

        CATALOG

          PEPSSI.CAT

        DOCUMENTS

          PEPSSI_SSR.*
          SOC_INST_ICD.*
          NH_PEPSSI_V###_TI.TXT  (### is a version number)


      Other sources of information useful in interpreting these Data
      --------------------------------------------------------------

        Refer to the following files for more information about these data

          NH Trajectory tables:

            /DOCUMENT/NH_MISSION_TRAJECTORY.*   - Heliocentric

          PEPSSI Field Of View definitions:

             /DOCUMENT/NH_FOV.*
             /DOCUMENT/NH_PEPSSI_V###_TI.TXT



      Visit Description, Visit Number, and Target in the Data Labels
      ---------------------------------------------------------------

      The observation sequences were defined in Science Activity Planning
      (SAP) documents, and grouped by Visit Description and Visit Number.
      The SAPs are spreadsheets with one Visit Description & Number per row.
      A nominal target is also included on each row and included in the data
      labels, but does not always match with the TARGET_NAME field's value in
      the data labels.  In some cases, the target was designated as RA,DEC
      pointing values in the form ``RADEC=123.45,-12.34'' indicating Right
      Ascension and Declination, in degrees, of the target from the
      spacecraft in the Earth Equatorial J2000 inertial reference frame.
      This indicates that either the target was a star, or the
      target's ephemeris was not loaded into the spacecraft's attitude and
      control system which in turn meant the spacecraft could not be pointed
      at the target by a body identifier and an inertial pointing value had
      to be specified as Right Ascension and Declination values.  PDS-SBN
      practices do not allow putting a value like RADEC=... in the PDS
      TARGET_NAME keyword's value. In those cases the PDS TARGET_NAME value
      is set to CALIBRATION.  TARGET_NAME may be N/A (Not Available or Not
      Applicable) for a few observations in this data set; typically that
      means the observation is a functional test so N/A is an appropriate
      entry for those targets, but the PDS user should also check the
      NEWHORIZONS:OBSERVATION_DESC and NEWHORIZONS:SEQUENCE_ID keywords in
      the PDS label, plus the provided sequence list (see Ancillary Data
      below) to assess the possibility that there was an intended target.
      These two keywords are especially useful for STAR targets as often
      stars are used as part of instrument calibrations, and are
      included as part of the sequencing description which is captured
      in these keywords.



    Ancillary Data
    ==============

      The geometry items included in the data labels were computed
      using the SPICE kernels archived in the New Horizons SPICE
      data set, NH-J/P/SS-SPICE-6-V1.0.

      Every observation provided in this data set was taken as a part of a
      particular sequence.  A list of these sequences has been provided in
      file DOCUMENT/SEQ_PEPSSI_*.TAB.  In addition, the
      sequence identifier (ID) and description are included in the PDS label
      for every observation.  N.B. While every observation has an associated
      sequence, every sequence may not have associated observations.  Some
      sequences may have failed to execute due to spacecraft events (e.g.
      safing).  No attempt has been made during the preparation of this data
      set to identify such empty sequences, so it is up to the user to
      compare the times of the sequences to the times of the available
      observations from INDEX/INDEX.TAB to identify such sequences.


    Time
    ====

      There are several time systems, or units, in use in this dataset:
      New Horizons spacecraft MET (Mission Event Time or Mission Elapsed
      Time), UTC (Coordinated Universal Time), and TDB Barycentric
      Dynamical Time.

      This section will give a summary description of the relationship
      between these time systems.  For a complete explanation of these
      time systems the reader is referred to the documentation
      distributed with the Navigation and Ancillary Information
      Facility (NAIF) SPICE toolkit from the PDS NAIF node, (see
      http://naif.jpl.nasa.gov/).

      The most common time unit associated with the data is the spacecraft
      MET.  MET is a 32-bit counter on the New Horizons spacecraft that
      runs at a rate of about one increment per second starting from a
      value of zero at

        19.January, 2006 18:08:02 UTC

      or

        JD2453755.256337 TDB.

      The leapsecond adjustment (DELTA_ET = ET - UTC) was 65.184s at
      NH launch, and the first four additional leapseconds occurred
      at the ends of 12/2009, 06/2012, 06/2015, and 12/2016.
      Refer to the NH SPICE data set, NH-J/P/SS-SPICE-6-V1.0, and the
      SPICE toolkit documentation, for more details about leapseconds.

      The data labels for any given product in this dataset usually
      contain at least one pair of common UTC and MET representations
      of the time at the middle of the observation.  Other portions
      of the products, for example tables of data taken over periods
      of up to a day or more, will only have the MET time associated
      with a given row of the table.

      For the data user's use in interpreting these times, a reasonable
      approximation (+/- 1s) of the conversion between Julian Day (TDB)
      and MET is as follows:

        JD TDB = 2453755.256337 + ( MET / 86399.9998693 )

      For more accurate calculations the reader is referred to the
      NAIF/SPICE documentation as mentioned above.


    Reference Frame
    ===============


      Geometric Parameter Reference Frame
      -----------------------------------

      Earth Mean Equator and Vernal Equinox of J2000 (EMEJ2000) is the
      inertial reference frame used to specify observational geometry items
      provided in the data labels.  Geometric parameters are based on best
      available SPICE data at time of data creation.


      Epoch of Geometric Parameters
      -----------------------------

      All geometric parameters provided in the data labels were computed at
      the epoch midway between the START_TIME and STOP_TIME label fields.



    Software
    ========

      The observations in this data set are in standard FITS format
      with PDS labels, and can be viewed by a number of PDS-provided
      and commercial programs. For this reason no special software is
      provided with this data set.


    Contact Information
    ===================

      For any questions regarding the data format of the archive,
      contact

      New Horizons PEPSSI Principal Investigator:

      Ralph McNutt, Jr.

      Johns Hopkins University
      Applied Physics Laboratory
      Space Department
      11100 Johns Hopkins Road
      Room MP3-E116
      Laurel, MD   20723
      USA

Confidence Level Overview
    =========================
      During the processing of the data in preparation for
      delivery with this volume, the packet data associated with each
      observation were used only if they passed a rigorous verification
      process including standard checksums.

      In addition, raw (Level 2) observation data for which adequate
      contemporary housekeeping and other ancillary data are not available
      may not be reduced to calibrated (Level 3) data.  This issue is raised
      here to explain why some data products in the raw data set,

        NH-A-PEPSSI-2-KEM2-V1.0,

      may not have corresponding data products in the calibrated data set,

        NH-A-PEPSSI-3-KEM2-V1.0.


    Data coverage and quality
    =========================
      Every observation provided in this data set was taken as a part of a
      particular sequence.

      Refer to the Confidence Level Overview section above for a summary
      of steps taken to assure data quality.

      For PEPSSI, electron detector channels are dominated by cosmic rays
      in post-Jupiter mission phases.

      The PEPSSI data are considered suspect for the first forty
      minutes after an instrument power-on event, called a Bad Time
      Interval (BTI); this file lists those time windows. The entire
      Post-launch commissioning mission phase is also considered a
      BTI.

      See the Science Operations Center - Instrument Interface Control
      Document (ICD - found at DOCUMENT/SOC_INST_ICD*.*) and the BTI TABLE
      file for more detail.

      The PEPSSI Time Of Flight only (TOF-only) Pulse Height Analysis (PHA)
      event data may show differences in the 'N2 data' and 'N3 data' taken
      simultaneously but using different collection algorithms.  Refer to
      the instrument description in the PEPSSI instrument catalog
      (PEPSSI.CAT) under 'Data sampling and priority for TOF-only data'
      in the 'Operational modes' section.

      Some subset of the PHA event data is noise or other instrumental
      artifacts.  PHA events with parameters outside the stated instrument
      sensitivity limits (see the SPECIFICATIONS section in the PEPSSI
      instrument catalog file) should be ignored, or, at the very least,
      used with extreme caution.

      It should be noted that the Primary HDU and the first 5 extension
      HDUs (the Image HDUs containing spectrograms) of the level 3 data
      are 'quick-look' or 'browse' products only.  They are constructed
      with one minute averages for the whole mission, so that, if the data
      collection period (the DT in the table in the FLUX extension) is not
      an even multiple or factor of 1 minute, the spectrogram image will
      exhibit aliasing artifacts.  Further, the second extension, the
      Helium spectrogram includes the Alpha source channels (see above).
      In short, the Image HDUs in the level 3 data are not for scientific
      use but for browsing or quick-look purposes and for researchers to
      determine if they are able to correctly read the data in the table
      extensions.

      Please see the 'Data Validity' section of PEPSSI.CAT for details
      regarding information on channels which should be excluded from
      analysis.



    Observation descriptions in this data set catalog
    =================================================

      Some users will expect to find descriptions of the observations
      in this data set here, in this Confidence Level Note.  This data
      set follows the more common convention of placing those
      descriptions under the Data Set Description (above, if the user is
      reading this in the DATASET.CAT file) of this data set catalog.


    Caveat about TARGET_NAME in PDS labels and observational intent
    ===============================================================

      The downlink team on New Horizons has
      created an automated system to take various uplink products, decode
      things like Chebyshev polynomials in command sequences representing
      celestial body ephemerides for use on the spacecraft to control
      pointing, and infer from those data what the most likely intended
      target was at any time during the mission.  This works well during
      flyby encounters and less so during cruise phases and hibernation.

      The user of these PDS data needs to
      be cautious when using the TARGET_NAME and other target-related
      parameters stored in this data set.  This is less an issue for the
      plasma and particle instruments, more so for pointing instruments.
      To this end, the heliocentric ephemeris of the spacecraft, the
      spacecraft-relative ephemeris of the inferred target, and the
      inertial attitude of the instrument reference frame are provided
      with all data, in the J2000 inertial reference frame, so the user
      can check where that target is in the Field Of View (FOV) of the
      instrument.

      Finally, note that, within the FITS headers of the data products,
      the sequence tables, and other NH Project-internal documents used
      in this data set and/or inserted into the data set catalog,
      informal names are often used for targets instead of the canonical
      names required for the TARGET_NAME keyword.  For example, during
      the Pluto mission phase, instead of the TARGET_NAME '15810 ARAWN
      (1994 JR1)' there might be found any of the following:  1994JR1;
      1994 JR1; JR1.  For all values where the PDS keyword TARGET_NAME
      is used (e.g. in PDS labels and in index tables), the canonical,
      PDS-approved names are used (if not, please bring this to the
      attention of PDS so it can be rectified).  However, within the
      context of this data set, these project abbreviations are not
      ambiguous (e.g. there is only one NH target with 'JR1' in its
      name), so there has been, and will be, no attempt to expand such
      abbreviations where they occur outside formal PDS keyword values.


    Superseded KEM1 files
    ===============================================================

      Thirteen PEPSSI data files in the KEM1 mission phase were incomplete
      until newer data was received from the spacecraft. New versions of
      these files are included in the raw and calibrated PEPSSI datasets.

      Refer to the document/superseded_files_*.tab file for the affected
      filenames and product IDs for KEM1 and KEM2 datasets.


    Review
    ======
      This dataset was peer reviewed and certified for scientific use by
      the PDS.