Data Set Overview : This data set contains Calibrated data taken by New Horizons Radio Science Experiment instrument during the PLUTOCRUISE 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. ####################################################################### #######################################################################During the Pluto Cruise mission phase, the New Horizons project performed aseries of Annual CheckOuts (ACOs), designed to determine basic functionalityand performance of the instrument complement. For REX these tests includedthe exercise of calibration test patterns, the reception of a ground-based DSNuplink signal for evaluating inflight REX system gain, linearity, stability ofthe composite uplink, USO, and REX receiver chain, characterizing the REXbandpass frequency response, and searching for any spurious signals in the REXpassband. In addition, occultations of the Earth's moon were performed in May2011 and January 2012 (ACO-5 and ACO-6) to provide example data and experiencein performing occultation inversion in preparation for the encounter atPluto/Charon.Although one-way uplink data signals were sent from the Ground Element to REX,the characteristics of those signals are not needed to analyze these REXobservations comprising instrument checkout, characterization and calibrationactivities. However, for the two Lunar Occultations, uplink data tuningprofiles are included in this data set. 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_PLUTOCRUISE.TAB. N.B. Some sequences provided may have no corresponding observations. 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. 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 1.0 of this data set. 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. Calibration : Detailed information about calibration of REX data is available in the SOC Instrument Interface Control Document (ICD) and in the NH_REX_RADIOMETER_CALIB_V4P7 calibration report in the DOCUMENT section of this data set; refer to these documents for REX calibration details. Note also that for REX data the Calibrated dataset is one version behind the Raw dataset, so for example the Calibrated dataset would be at Version 1.0 while the Raw dataset would be at Version 2.0. There was an initial delivery to the PDS of the Raw dataset before the Calibrated dataset was completed. 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-X-SPICE-6-PLUTOCRUISE-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_REX_PLUTOCRUISE.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 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, Stanford University 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. Note that the REX Raw V2.0 dataset corresponds with the REX Calibrated V1.0 dataset. The Raw data had been certified once before the calibrated data was able to be certified. 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_PLUTOCRUISE.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 calibrated radiometry values in the data products of this data set are supplied in units of dBm. The conversion to dBm includes the logarithm of a raw power value. For cases where that raw power value is zero, the logarithm function used returns the IEEE_REAL floating point special value for negative infinity (-Inf). This is correct behavior, and that IEEE_REAL special value for negative infinity is stored in the data file. However, PDS3 has no way to recognize this as negative infinity, and will instead interpret the bits in the data as -340282366920938463463374607431768211456.0, or about -3.4E+38. To deal with this, the radiometry COLUMN OBJECT will contain the VALID_MINIMUM keyword with a value sufficiently small to flag the IEEE-754 -Inf values as invalid, whether they are interpreted as the special IEEE-754 value negative infinity or as the numeric -3.4E+38. In practice, this only occurs in situations where the raw accumulated power is being initialized, or where the raw power data are zeroed because REX has been shut down before completion of a final REX Output Frame (ROF; see the ICD), or where the instrument input is a non-physical synthetic signal used to validate correct operation of the REX instrument. In all of these cases, this behavior is easily identified and will have no effect on any science analysis. 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 on December 4, 2017.