NSSDCA ID: PSSB-00754
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 Calibrated data taken by New Horizons Student Dust Counter instrument during the PLUTOCRUISE mission phase. The mission of the SDC is to analyze the size and distribution of Interplanetary Dust Particles (IDPs) along the New Horizons 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. SDC was designed to detect events for particles down to about one picogram at Pluto [BAGENALETAL2016]; that detection limit is lower than 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. The channels in the binary table for raw data are numbered from 0 to 13; the channel in the binary table for calibrated data are numbered from 1 to 14. 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 (channel number 10 in raw data; channel number 11 in calibrated data) are still processed but should be ignored. SDC Data Summary ================ In the years following the Jupiter encounter, designated as the PLUTOCRUISE mission phase, SDC collected science data intermittently during hibernation. There were also Annual Checkouts (ACOs), STIM calibrations, Noise calibrations, and an anomaly in November, 2007. SDC's main science data collection periods are during hibernation. During ACOs, science data date are taken intermittently but the user must be careful in analyzing this since there is usually more activity on the spacecraft than during hibernation. STIM and Noise refer to scheduled calibrations and are done with a regular cadence of one per year after the Jupiter encounter; they occurred sporadically in the early years of the mission. Refer to the sequence tables, and/or the PDS data label keywords NEWHORIZONS:SEQUENCE_ID and NEWHORIZONS:OBSERVATION_DESC, to identify and remove calibration data from any science analysis. Note that some SDC data files have the same stop and start time and a zero exposure time. The reason for this is that the start and stop time for SDC data files are the event times for the first and last events in the files, so for files that contain a single event, these two values are identical. SDC was designed to take advantage of the quiet state of the spacecraft during non-encounter mission phases, especially hibernation. Various active spacecraft operations cause mechanical shocks that are picked up by the polyvinylidene fluoride (PVDF) sensors and registered by SDC as science events. This is particularly true during three-axis pointing and active spin mode when the spacecraft frequently fires short bursts of the attitude thrusters. However because the thruster-induced events are often frequent enough to violate the SDC autonomy rule B (section 3.4.2 of Horanyi et al. (2008) [HORANYIETAL2008]), during some spacecraft maneuvers many SDC detector channels are switched off, by autonomy processing, for prolonged periods. Level four data reduction (referred to in section 4 of Horanyi et al. (2008) [HORANYIETAL2008]) is used to filter out any events that appear within a second of any thruster firing, thereby allowing science recovery between firings. The science team anticipates that the techniques and results of such Level four processing will be provided in future, higher-level data sets. Autonomy rules can also affect SDC threshold settings; threshold settings are designed to keep the SDC detection limit above a noise floor. Refer to the SDC instrument catalog, file CATALOG/SDC.CAT, and Horanyi et al. (2008) [HORANYIETAL2008], for descriptions of threshold parameters and how they affect instrument behavior and recorded data. STIM (Stimulus) and Noise (Noise floor) refer to scheduled calibrations and are done with a regular cadence of one per year after the Jupiter encounter; they occurred sporadically in the early years of the mission. Refer to the sequence tables, and/or the PDS data label keywords NEWHORIZONS:SEQUENCE_ID and NEWHORIZONS:OBSERVATION_DESC, to identify and remove calibration data from any science analysis. N.B. The duration of the off, as well as the on, periods must be considered in making any calculation of average dust detection event rates. During spacecraft checkout activities in first six months of the Post-Launch mission phase, spacecraft activity was high and these autonomous off/on transitions occurred quite frequently, there were several periods, some weeks or months long, where SDC was either completely off, or on for only hours or minutes at a time. Later on during the Launch phase, and much later during the Pluto Cruise phase, the autonomy levels for turning off channels were relaxed, and the transition to more frequent hibernation operations meant that autonomous off/on transitions occurred less frequently. All per-channel off and on transitions, whether initiated by autonomy or by spacecraft on/off commands to the entire instrument, are recorded for the entire mission to-date in a PDS TABLE file that is provided with all SDC data sets; updated versions will be provided as the mission progresses. The high frequency of off/on transitions, as described in the previous paragraph, is apparent in this PDS TABLE. As of early 2014, there have been no events caused by large particles observed in any of these data sets; this has been noted as exceptional by peer reviewers of SDC data sets. The science team agrees and this topic is an active discussion within the science team; the science team anticipates that this will be addressed in some future delivery of SDC data sets. 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_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. Version ======= This is VERSION 2.0 of this data set. The pipeline (see Processing below) was re-run on these data for each version since the first (V1.0). As a result, ancillary information, such as observational geometry and time (SPICE), may be updated. This will affect, for example, the calibration of the data if parameters such as the velocity or orientation of the target relative to the instrument, or the recorded target itself, have changed. See the following sections for details of what has changed over each version since the first (V1.0). Note that even if this is not a calibrated data set, the 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. SDC updates for Pluto Cruise Data Sets V2.0 ============== The previous Pluto Cruise data sets' deliveries (V1.0) went through peer review in December, 2014. When subsequent versions of those data sets were being delivered, some with additional data (from August, 2014 through January, 2015) before all of those previous liens were resolved, the previous data sets were left as is, with those liens folded into the newer data sets. New observations added with this version (V2.0) include ongoing cruise observations from August, 2014 through January, 2015. Other changes for this version were re-running of the ancillary data in the data product, updated geometry from newer SPICE kernels, minor editing of the documentation, catalogs, etc., and resolution of liens from the December, 2014 review, plus those from the May, 2016 review of the Pluto Encounter data sets.i 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. 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 | | 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 ** =========== ================================== ============= SDC SDC 0X700 * 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) ===== =================================== 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. 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. 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_SDC_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 occured 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 docmentation, 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 SDC Principal Investigator: Mihaly Horanyi, 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-x-sdc-3-plutocruise-v2.0/
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. Brian Carcich | General Contact | Cornell University | carcich@astro.cornell.edu |