Data Set Overview  :   This data set contains Raw data taken by  the New Horizons Radio Science Experiment instrument during  the CRUISE TO FIRST KBO ENCOUNTER mission phase.   The REX instrument measures the amplitude and phase of radio signals  captured by the New Horizons high-gain antenna. The main investigation  is an occultation experiment which uses radio signals transmitted from  Earth to probe the atmosphere and ionosphere of Pluto and Charon.  Ancillary investigations include measurements of the 4 cm wavelength  radiothermal emission from planets or other radio sources. Phase data  may also be combined with Pluto encounter tracking data, derived from  the Radio Science Subsystem separately from REX and to be archived in  separate non-REX data set(s), to infer the influence of gravitational  fields on the spacecraft as it moves through the Pluto system.   The main investigation requires coordinated use of the Earth-based  transmitters and the spacecraft receiver as the two physical elements  of the REX instrument. The 'Ground Element' comprises DSN (Deep Space  Network) hardware and operations facilities on Earth, and the 'Flight  Element' includes signal processing hardware and software onboard the  spacecraft.   Unless inclusion of tuning profiles for one-way uplink transmissions is  noted below, this data set includes only samples taken and measurements  made by the REX system hardware on-board the New Horizons spacecraft --  either of one-way uplink signals or of 4cm-wavelength thermal emission.   #######################################################################  REQUIRED UNDERSTANDING: THE REX AND THE NEW HORIZONS (NH) REGENERATIVE  RANGING TRACKER [DEBOLTETAL2005] ARE   *****SEPARATE***** AND *****INDEPENDENT*****   SUBSYSTEMS THAT BOTH USE THE RADIO FREQUENCY (RF) AND TELECOMMUNICATION  SUBSYSTEMS. TRACKING DATA WILL NOT BE ARCHIVED IN REX DATA SETS.  #######################################################################   This data set contains REX observations taken during and downlinked  between Oct. 26, 2016 and Dec. 31, 2018.   The REX activities in Loads 16354 to 17331, are associated with four  tasks:   1. Solar Conjunction Observations  2. SNR Verification (e.g. Radio Path Characterization)  3. Radio path characterization (misnamed 'Total Electron Counts')  4. Bistatic Dry Run   Each of the tasks was bookended with the REX Test Patterns, that use  preset sequences with known response to compare with the REX output and  verify performance of the REX process. More details are provided in  the document/ directory in the file rex_activities_kemcruise1.pdf.   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.    Known issues in REX data  :   The following item assumes familiarity with the REX, REX terminology  and the required reading and other documentation provided with this  data set.   Time tag anomalies in ROF sequences  -----------------------------------   REX places ten incrementing time tags in each REX Output Frame (ROF).  The time tags can be used both to identify any breaks in a sequence of ROFs, and to determine the time between any two ROFs within a  sequence.   The normal sequence for time tags is to start at zero in the first ROF and increment ten times per ROF, so the first time tag of the second  ROF is 10, that of the third ROF is 20, etc. In practice, the first  and last ROFs in a sequence do not always show simple zero starts and  clean finishes, respectively, indicating data corruption in just those ROFs. There is no indication of corruption elsewhere in ROF streams,  and REX commanding ensures there are always adequate ROFs before and  after any observation, so discarding starting and ending ROFs in a  sequence based on simple inspection of time tags is the way to handle  this issue.   For more detail, refer to the REX Instrument Description section in  the SOC Instrument Interface Control Document (ICD).    Version  :  This is VERSION 2.0 of this data set.   This version includes all data from the previous version and  adds data acquired by the spacecraft between 12/07/2017 and  08/13/2018. This is the complete dataset.   TARGET_NAME values were expanded and made more consistent across all  instruments.   General statement about data set versions after V1.0  ----------------------------------------------------  The pipeline (see Processing below) was re-run on these data for each  version since the first (V1.0). A pipeline rerun usually changes the  FITS headers but not the FITS data of raw data sets. In some cases  calibrated FITS data may change because the calculated geometry of an  observation has changed. See data set version-specific sections below  for significant exceptions to this general statement, i.e. changes to  pipeline processing, calibration processing, and data delivered.   Note that even if this is not a calibrated data set, calibration  changes are listed as the data will have been re-run and there will be  updates to the calibration files, to the documentation (Science  Operations Center - Instrument Interface Control Document:  SOC_INST_ICD) and to the steps required to calibrate the data.    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.   REX_0123456789_0X7B0_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 **  : : :  REX REX 0X7B0 - 0X7B3 *   * 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)  : :  0x7b0 - REX Lossless Compressed Data (CDH 1)/REX  0x7b1 - REX Packetized Data (CDH 1)/REX  0x7b2 - REX Lossless Compressed Data (CDH 2)/REX  0x7b3 - REX Packetized Data (CDH 2)/REX    Instrument description  ----------------------   Refer to the following files for a description of this instrument.   CATALOG   REX.CAT   DOCUMENTS   REX_SSR.*  SOC_INST_ICD.*    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     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 either that the target was either a star, or that 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. The sequence identifier (REQID) 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 three additional leapseconds occurred  in at the ends of December, 2009, June, 2012 and June, 2015.  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 REX Principal Investigator:   Ivan Linscott   David Packard Building - Room 319  350 Serra Mall  Stanford, CA 94305-9515  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  may not have corresponding data products in the calibrated data set.    Data coverage and quality  :  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_REX_*.TAB. N.B. Some sequences provided may have  zero corresponding observations.   Refer to the Confidence Level Overview section above for a summary  of steps taken to assure data quality.   The Time Tag counter values included with REX data normally increment  nine times within each data file and once between consecutive frames.  However, there are sometimes anomalous departures from this behavior at  the start and end of contiguous runs of data files (see REX.CAT for a  brief discussion of such an issue related to compression). Files with  such anomalies are few compared to the total number of data files, and  excluding those files with anomalous Time Tag data from data analysis  will not significantly affect the results of the REX investigation.  Refer to the Science Operations Center/instrument interface control  document for more detail about REX Time Tags; there is adequate  information there for users to identify anomalous files.  In addition, products with Time Tag anomalies are listed in file  ERRATA.TXT provided with this data set.    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.    Review  :  This dataset was peer reviewed and certified for scientific use by  the PDS.