NSSDCA ID: PSSB-00721
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 JUPITER 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. For the Jupiter encounter mission phase, SDC collected no science data during the Jupiter flyby, as the requisite spacecraft configuration prevented SDC from operating. There were some very sparse data taken from December, 2006 through April, 2007, and some of very short (or zero) duration after the Jupiter flyby from April, 2007 through June, 2007. 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_JUPITER.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 3.0 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 and to the steps required to calibrate the data. SDC updates for JUPITER Data Sets V3.0 ============== Updated the electronics box temperature calibration; the full calibration, including all model parameters and coefficients, is described in [JAMESETAL2010]. Updated the dust impact velocity calculation to use the Ecliptic J2000 reference frame, instead of the Earth Mean frame, to estimate Keplerian orbits; this was a small correction as the spacecraft trajectory is generally near the line to the first point of Aries. Added the stimulus calibration table, in file DOCUMENT/SDC_STIM_Vnnnn.TAB, so the user can assess when these operations may have generated false positive events. SDC updates for JUPITER Data Sets V2.0 ============== None of the formats for the Calibrated data have changed. The data files look the same, including the data formats. The changes were improvements to the processing code. There were 3 changes made to the code: Change to dust impact velocity assumption ----------------------------------------An assumption is needed for the the dust impact velocity to calculate its mass. Before this update the pipeline used only the normal component of the total velocity between the dust and instrument (assuming the particle is in Keplerian orbit). Now this has been changed to the total relative velocity of the particle (still assumed to be in Keplerian orbit) and the instrument. Using multiple sensors for temperature correction ------------------------------------------------There are two thermistors on the analog board. The analog board temperature is used for calibrating a particular channel on the board. Before this update, for a given channel the temperature of the closest thermistor to a that channel. Now a linear fit to the temperatures is used. New charge-velocity-mass calibration curve -----------------------------------------The calibrated data contains the mass of the particle. The charge to mass curve used to be Q=3.18E17*m^1.3*v^3.0 where m is the mass, Q is the charge and v is the relative speed. This was the Simpson-Tuzzolino curve. The new curve is a function of detector temperature as well: Q=(1.15E15+6.75E12*T)*m^1.052*v^2.883 where T is the temperature. A paper with this new calibration curve was published in 2010 [JAMESETAL2010]. 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. ALI_0123456789_0X0AB_ENG_1.FIT ^^^ ^^^^^^^^^^ ^^^^^ ^^^ ^__/ | | | | | ^^ | | | | | | | | | | | +--File type (includes dot) | | | | | - .FIT for FITS file | | | | | - .LBL for PDS label | | | | | - not part of product ID | | | | | | | | | +-- Version number from the SOC | | | | (Science Operations Center) | | | | | | | +--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 * For those datasets where the NH project is delivering CODMAC Level 1 & 2 data (REX & PEPSSI), ENG and SCI apply to CODMAC Level 1 & 2 data, respectively. 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 the documentation 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 /DOCUMENT/NH_TRAJECTORY.* - Jupiter-centric 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-JUPITER-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_JUPITER.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; that is, some sequences may have failed to execute due to spacecraft events (e.g. safing) and there will be observations associated with those sequences. No attempt has been made during the preparation of this data set to identify if any, or how many, such empty sequences there are, so it is up to the user to compare the times of the sequences to the times of the available observations from the INDEX/INDEX.TAB table 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-j-sdc-2-jupiter-v3.0/
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 |