NSSDCA ID: PSSB-00790
Availability: Archived at NSSDC, accessible from elsewhere
This description was generated automatically using input from the Planetary Data System.
Data Set Overview ================= This data set contains Raw data taken by New Horizons Student Dust Counter instrument during the PLUTO mission phase. The mission of the SDC is to analyze the size and distribution of Interplanetary Dust Particles (IDPs) along the New Horizon trajectory to the Kuiper Belt. SDC comprises twelve thin, permanently polarized polyvinylidene fluoride (PVDF) plastic film sensors, with a combined area of about 0.1 m**2, mounted on the top surface of a support panel and normal to the spacecraft ram direction (flight velocity). In addition, there are two reference sensors, identical to the top surface sensors, mounted on the back side of the detector support panel and protected from any dust impacts, used to monitor background noise levels. An impacting IDP causes a depolarization charge when it penetrates the PVDF film on one of the sensors. That charge is then measured by that sensor's electronics (channel); if the measurement is above a preset level, the instrument records and stores the event for later downlink. The level preset is adjusted based on in-flight Noise Floor Calibrations, and there are extensive autonomy rules adjusting SDC behavior, even turning channels off for up to thirty days at a time, to avoid overloading the storage system with noise. Some time between instrument delivery to the spacecraft and launch, the detector on one channel began exhibiting symptoms of degraded electrical contacts to the PVDF; data from that channel (11) are still processed but should be ignored. SDC was designed to detect events for particles down to about one picogram at Pluto; that detection limit is lower earlier in the mission where the spacecraft velocity was higher. The SDC instrument has a temperature- and velocity-dependent calibration, first converting the raw measurement to charge, then converting charge to particle mass. The common data product is a binary table of downlinked event data: time; sensor channel; magnitude; threshold magnitude. Associated data products are housekeeping data such as instrument temperatures for calibration and near-in-time spacecraft thruster events, which may induce false positives i.e. SDC events not caused by IDPs. During the Pluto Charon Encounter mission phase starting in January, 2015, there were several sub-phases: three Approach sub-phases, (AP1, AP2 and AP3); a CORE sequence for the Pluto flyby on 14.July, 2015 (Day Of Year 195), sometimes also referred to as NEP (Near-Encounter Phase); three Departure sub-phases (DP1, DP2, DP3). For this first SDC delivery for the Pluto mission phase, this data set includes all SDC data through late-July, including all encounter data. SDC was turned on throughout Approach. It was powered off then on periodically when needed for spacecraft power reasons or for trajectory correction maneuvers, and the channels were turned off and on around the start of DSN tracks that contained tweakups, as per normal operations. The thresholds were updated and set higher for Pluto making SDC less sensitive to dust hits - on April 9th, 2015 (DOY 099), then set back to Cruise threshold settings on July 30th (DOY 211). 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_SDC_PLUTO.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. 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 Operation Center (SOC) at the Southwest Research Institute (SwRI), Department of Space Studies. 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. SDC data calibration is a two-step process: raw data numbers from a particle impact are converted to a charge, and the charge is converted to a particle mass via the ground calibrations obtained at a dust acceleration facility. Refer to the provided documentation for more information. The latest calibration procedure is described in James et al., (2010) [JAMESETAL2010]. 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. SDC_0123456789_0X700_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 | | | +--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 =========== ================================== ============= SDC SDC 0X700 * Not all values in this range are in this data set 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 along with the instrument designator that go with each ApID: ApIDs Data product description/Prefix(es) ===== =================================== 0x700 - SDC Science Data/SDC Instrument description ---------------------Refer to the following files for a description of this instrument. CATALOG SDC.CAT DOCUMENTS SDC_SSR.* SOC_INST_ICD.* NH_SDC_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 SDC Field Of View definitions: /DOCUMENT/NH_FOV.* /DOCUMENT/NH_SDC_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 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. The PDS standards 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. 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-PLUTO-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_SDC_PLUTO.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) over this dataset is 65.184s. 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 SDC Principal Investigator: Mihaly Horany, LASP, University of Colorado Mihaly Horanyi Laboratory for Atmospheric and Space Physics University of Colorado Boulder, CO 80302-0392 USA
These data are available on-line from the Planetary Data System (PDS) at:
https://pdssbn.astro.umd.edu/holdings/nh-p-sdc-2-pluto-v1.0/
Questions and comments about this data collection can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. Mihaly Horanyi | Data Provider | University of Colorado | horanyi@colorado.edu |
Dr. Joseph Peterson | General Contact | Southwest Research Institute | joe@boulder.swri.edu |