PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2004-01-13; J. Diaz del Rio (ESA). v1.0" RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 1994-12-31 NOTE = "GIOTTO Particle Impact Analyzer (PIA) dust mass spectra of 1P/Halley" END_OBJECT = TEXT END This dataset contains data obtained through the efforts of the International Halley Watch (IHW) Disciplines and the Lead Center. From the original compact disk (one of a 2-disk set), several datasets have been created, one for each instrument of each spacecraft. The data contained in this dataset contains the data taken by the Giotto PARTICLE IMPACT ANALYZER Experiment (PIA). The dataset contains also documentation included in the original disk. The PDS formatted data have been placed in the DATA subdirectory while the original FITS files are in the EXTRAS subdirectory. In addition to the data themselves, the disks contain a wide variety of supporting files and tools for the Archive user; the major categories are documentation, ephemeris information, searchable tables and indices, and software (source code as well as executable modules). These have been organized in three principal directories one level below the root: DOCUMENT, INDEX, and SOFTWARE. The EXTRAS directory contains the original splitted FITS files. Original Format The data for these files were received as a series of FITS files, each of which consisted of spectra of a single mode. Amplitude-triggered samples in the spectra were indicated by an "X" following the sample. Reformatting at SBN The following changes were made to the data: o A program was written to parse the headers and spectra and convert the ASCII values to binary form. Parameter values were ordered to facilitate comparison between the MPI and IKI submissions for the VEGA missions, which used the same instrument (PUMA). o Flagged amplitudes, followed by an "X" in the text file, were indicated in the binary file as a additional byte set equal to 1 for flagged amplitudes, 0 otherwise. This is the same system used for the IKI VEGA submissions. o All spectra of the same mode were collected into a single, fixed- length table. o The original order of the spectra in the FITS files, as well as the order of the text files themselves, was preserved in the combined mode tables. This order was assumed to be chronological. Known Anomalies/Problems: o Little or no explanation was available for some of the parameters in the spectrum headers. This is indicated in the DESCRIPTION part of the PDS label for these datasets. o It has not yet been possible to translate the times in this file, which are apparently in units of spacecraft clock time, to UT. o In the received FITS file numbered 40, the final spectrum in the file (sequence number 2991, event number 46698, time 48110) was truncated. It is not clear if only this last spectrum was lost or if other spectra might have followed since the NAXIS1 and NAXIS2 values from the header indicate more data. The incomplete spectrum was omitted entirely from the binary table. o Two mode 1 spectra were found which contained an odd number of bytes in the spectrum. In mode 1 the number of bytes should be even, as each sample in the spectrum consists of a time sample byte and an amplitude sample byte. In these cases the single byte was assumed to be a time value and a null amplitude byte was appended to the spectru . o In working with these files it was noted that many spectra exhibited strange features, including: - parameter values but no spectrum bytes (i.e., zero-length spectra) - repeating time values of 255 (the maximum possible time) - repeating amplitude values of 127 (the maximum possible) - repeating values of 32 (ASCII code for blank) o There was a failure in the instrument during the fly-by. The following is taken directly from the FITS file header which was attached to the text files: "During the actual flyby two out of six multiplier-amplifiers failed, yielding incorrect amplitude information in the mass spectra channel; to obtain partial correction for amplitude, use F(a), where F(0) = 0 F(20) = 49 F(1...4) = a*2 + 21 F(21) = 52 F(5...8) = a + 25 F(22) = 57 F(9...14) = a + 26 F(23...25) = 3*(a-23) + 62 F(15,16) = a + 27 F(26...83) = a + 4a F(17...19) = a + 2b F(84...127) = 128 NOTE: Despite this correction the amplitude ranges 1...22 and around 51...65 are incomplete." No further documentation of this problem was available. Specifi- cally, it seems likely the "2b" in the equation for F(17...19) was intended to be "28". For more information about the data please contact the Small Bodies Node of the Planetary Data System at the Astronomy Dept., University of Maryland E. Grayzeck, Jr. D. Klinglesmith III Small Bodies Node of IHW Team Member for Planetary Data System Large-Scale Phenomena Astronomy Department Laboratory for Astronomy and Solar Physics University of Maryland Code 684.0 For more information about the dataset please contact the Planetary Data Archive (PSA) of the European Space Agency at the European Research and Technology Center (ESTEC), Noordwijk, The Netherlands. Jorge Diaz del Rio Joe Zender ESTEC/ESA ESTEC/ESA jdiaz@rssd.esa.int joe.zender@rssd.esa.int