Data Set Overview : This data set contains Raw data taken by the New Horizons Alice Ultraviolet Imaging Spectrograph instrument during the KEM1 ENCOUNTER mission phase. PERSI-Alice (P-ALICE; also ALICE) is a spectrograph on the New Horizons spacecraft that is sensitive to extreme and far UltraViolet (UV) light (520-1870 Angstroms). The ALICE instrument comprises a telescopic optics section and a spectrograph section that includes a diffraction grating and a photosensitive two-dimensional (2-D) detector. The optics and diffraction grating physical arrangement configure one detector dimension as a spatial dimension and the other as spectral. ALICE has two separate entrance apertures that feed light to the telescope section of the instrument: the AirGlow Channel (AGC) aperture; the Solar Occultation Channel (SOCC) aperture. Both apertures pass light to the detector through a lollipop-shaped slit comprising two contiguous sections: a narrow, rectangular slit with a Field Of View (FOV) of 0.1 by 4.0 degrees; a fat, square slit with FOV 2.0 x 2.0 degrees. ALICE has two data-taking modes: PixelList mode records each detector/photon event location (pixel i.e. spectral and spatial), interleaved with time sequence events (hacks), allowing sub-second resolution of the photon events; histogram mode summarizes the per-pixel photon event counts into a 2-D histogram over all detector pixels, collected over an extended time which can range from a few seconds to several days. From both modes, the common data product is the histogram (derived on the ground in the PixelList case), which is functionally equivalent to a spectral-by-spatial spectrogram (2-D image); other data products are also provided and described 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_ALICE_*.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. This version includes data acquired by the spacecraft between 08/14/2018 and 12/31/2018. It only includes data downlinked before 01/01/2019. Future datasets may include more data acquired by the spacecraft after 08/13/2018 but downlinked after 12/31/2018. This version includes high voltage (HV) dark tests, and Airglow observation of 2014MU69. 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. ALI_0123456789_0X4B0_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 ** : : : ALICE ALI 0X4B0 - 0X4B7 * * 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) : : 0x4b0 - ALICE PixelList Lossless (CDH 1)/ALI 0x4b1 - ALICE PixelList Packetized (CDH 1)/ALI 0x4b4 - ALICE PixelList Lossless (CDH 2)/ALI 0x4b5 - ALICE PixelList Packetized (CDH 2)/ALI 0x4b2 - ALICE Histogram Lossless (CDH 1)/ALI 0x4b3 - ALICE Histogram Packetized (CDH 1)/ALI 0x4b6 - ALICE Histogram Lossless (CDH 2)/ALI 0x4b7 - ALICE Histogram Packetized (CDH 2)/ALI Notes: ------ 1) CDH 1 and CDH 2 refer to the spacecraft redundant Command and Data Handling systems in general, and here specifically to their respective Solid State Recorders (SSRs) 1 and 2, where ALICE data be stored and prepared for downlink. ALICE can send data to SSR 1 or to SSR 2, or, for mission-critical data, to both redundantly. ALICE shares its channel to the SSRs with the Long-Range Reconaissance Imager (LORRI), so both instruments cannot store data simultaneously. ALICE has the capability to store histogram data to instrument-internal storage, and to transfer it to the SSR(s) later; such an operation is called a Held Histogram, and it allows ALICE to take data at the same time that LORRI is taking and writing data to the SSR(s). 2) Packetized and Lossless refer to the method used on-board to convert raw, high-speed instrument data on the SSR to low-speed data ready for downlink. The conversion process is generally referred to as compression, even though Packetized conversion does not reduce the data volume In practice, PixelList data always use Packetized compression. Histogram data may use Packetized or Lossless compression. Depending on the actual data contents, Lossless compression reduces data volume by 60 to 90% or more; for nominal science data a factor of 3 or more is normal. Lossless compression is used whenever possible to reduce downlink data volume. There is no difference, between Packetized and Lossless compression, in the resultant FITS files after processing by the Science Operations Center (SOC) data pipeline. Instrument description ---------------------- Refer to the following files for a description of this instrument. CATALOG ALICE.CAT DOCUMENTS ALICE_SSR.* SOC_INST_ICD.* NH_ALICE_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 ALICE Field Of View definitions: /DOCUMENT/NH_FOV.* /DOCUMENT/NH_ALICE_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. 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. Specifically for ALICE observations, any observation that has an observation description or sequence ID that includes the words dump or held will usually have N/A as its target, but that indicates the observation was actually taken as part of an earlier sequence and held held locally in instrument memory (i.e. a Held Histogram; see the Notes in the Data section below), and the Dump sequence represents the commands that transferred the instrument data onto the spacecraft Solid-State Recorders (SSRs). In the cases of Held Histograms, the user should check the previous sequence in the sequence list. For other cases note that if the characters _P_, _C_, or _PC_ are in the sequence ID, then the intended target was likely Pluto, Charon, or Pluto and Charon together, respectively. 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 ALICE Principal Investigator: S. Alan Stern Southwest Research Institute (SwRI) Department of Space Studies 1050 Walnut Street, Suite 400 Boulder, CO 80302 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, NH-A-ALICE-2-KEM1-V1.0, may not have corresponding data products in the calibrated data set, NH-A-ALICE-3-KEM1-V1.0. Data coverage and quality : Every observation provided in this data set was taken as a part of a particular sequence. Refer to the Confidence Level Overview section above for a summary of steps taken to assure data quality. The lollipop-shaped fuzz in images of some ALICE spectra, seen as high signal levels at the box end of the slit around Hydrogen Lyman-alpha (H Lya) wavelengths, is due to a characteristic of the detector and aperture. To make the Micro Channel Plate (MCP) more sensitive to UV light, it was coated with potassium bromide (KBr) photocathodes from 520 to 1180 Angstrom and with cesium iodide (CsI) photocathodes from 1250 to 1870 Angstrom. A vertical strip - a spectral band of 70 Angstrom centered at ~1216 Angstrom - of the MCP was masked and left uncoated to reduce the sensitivity of the detector to H Lya radiation. In the slit portion of the aperture (0.1deg wide x 4deg high), the diffraction grating keeps the strong H Lya line within that uncoated band. However, in the 2x2 degree box portion of the aperture designed to capture the Sun during occultations, the H Lya spreads out beyond the uncoated 70-Angstrom band over another ~55 Angstroms of more sensitive photocathode-coated detector on either side. The quantum efficiencies of the photocathode- coated surfaces are about an order of magnitude more sensitive to H Lya wavelengths than the bare, uncoated glass, which gives rise to high signal levels from the box area of the slit i.e. the lollipop fuzz. The Alice team plans to provide an update to their calibration for the second KEM Cruise 1 delivery. The current calibration uncertainty is 5 percent for data around and post the Pluto encounter. The calibration change is due to the gain sag during that encounter, particularly from the Solar Occultation. 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.