urn:nasa:pds:context:instrument:dawn.vir 1.0 1.11.0.0 Product_Context 2018-12-28 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.dawn instrument_to_instrument_host De Sanctis, M. C., A. Coradini, E. Ammannito, G. Filacchione, M.T. Capria, S. Fonte, G. Magni, A. Barbis, A. Bini, M. Dami, I. Ficai-Veltroni, and G. Preti, VIR Team, The VIR Spectrometer, Space Sci Rev, doi:10.1007/s11214-010-9668-5, 2010. reference.DESANCTISETAL2010 C.T. Russell, F. Capaccioni, A. Coradini, M.C. de Sanctis, W.C. Feldman, and 11 others, Dawn Mission to Vesta and Ceres - Symbiosis between terrestial observations and robotic exploration, Earth, Moon, and Planets, Vol 101, pp. 65-91, 2007, doi:10.1007/s11038-007-9151-9 reference.RUSSELLETAL2007 VISIBLE AND INFRARED SPECTROMETER Imager Spectrometer not applicable not applicable Instrument Overview =================== VIR is an imaging spectrometer having moderate spectral resolution that combines two data channels in one instrument. The two data channels, Visible (spectral range 0.25-1 micron) and Infrared (spectral range 0.95-5 micron), are committed to spectral mapping and are housed in the same optical subsystem. The instrument is composed by the Optics Module (OM), the Proximity Electronic box (PEM), housed inside the Optics Module, and the Main Electronic box (ME). The proximity electronic box (PEM) contains all the electronics needed to interface the Main Electronics, to drive the FPAs, the scan mirror and the cover mechanism and to perform the acquisition and conversion of the science and housekeeping data. The Main Electronics manages the operation of the two channels, gathers data and housekeeping information, stores the data, performs data compression, controls the cryo-cooler and interfaces the instrument with the S/C. A complete description of the instrument and its performance can be found in [BINIETAL2005]. Technical Description ===================== The optical concept is inherited from the visible channel of the Cassini Visible Infrared Mapping Spectrometer (VIMS-V) and from the Rosetta Visible InfraRed Thermal Imaging Spectrometer(VIRTIS). This concept matches a Shafer telescope to an Offner grating spectrometer to disperse a line image across two FPAs. The optical subsystem is housed inside the Cold Box of the Optics Module. The spectrometer has the ability to point and scan along the direction perpendicular to the slit. VIR can be divided in three modules: the Optical Head, the Proximity Electronics Module and the Main Electronics. VIR OPTICAL HEAD ---------------- The Optical Head contains the following items: - telescope optical components, mountings and optical bench, and scan unit - spectrometer optical components, mountings and housing - internal calibration system - slit and shutter mechanism - visible detector assembly - infrared detector assembly - external and internal baffles - cover unit - radiators The VIR optical system is a Shafer telescope matched through a slit to an Offner grating spectrometer. The Shafer consists of 5 mirrors mounted on an aluminum optical bench. The primary mirror is a scanning Beryllium mirror driven by a torque motor. The bench is machined from a single aluminum alloy billet and acts both as a cold plate and optical support structure, mounted on the ledge of the Cold Box. The Offner spectrometer consists of a mirror and a spherical convex diffraction grating housed in an aluminum structure that is flange mounted to the telescope. PROXIMITY ELECTRONICS --------------------- The Proximity Electronics consists of the following items: - box structure - mother board and connectors - CCD boards - IR board - scan mirror and cover board MAIN ELECTRONICS DESCRIPTION ---------------------------- The ME is physically separated from the Optics Module. It consists of the Digital Processing Units (DPUs), the S/C interface control units, the power supply for all the sub-units of the instrument excluding the cryocooler, the interface units and the coolers electronics. The DPU, S/C interfaces, instrument interfaces are also called DHSU (Data Handling and Support Unit). The VIR sub-systems (PEM, coolers, covers and scan mirror) are switched on/off by means of the Power Distribution Unit (PDU) of the ME/power supply unit, controlled by the DHSU. The main tasks of the DHSU are: - acquire, pre-process, compress and format the science and calibration data - control and power switch the sub-systems, the coolers and the Covers - health check the instrument and provide the operational status of VIR to the S/C - execute uplink and downlink activities to and from VIR - interpretate and execute the telecommands - manage and synchrone the activities between VIR and the S/C - store the science data in the instrument Mass Memory (2 Gbit), before downloading to the S/C solid state recorder. Scientific objectives ===================== A Multispectral Imager - covering the range from the near UV (0.25 micron) to the near IR (5.0 micron) and having moderate to high spectral resolution and imaging capabilities - is an appropriate instrument for the determination of global (size, shape, albedo, etc.), and local (mineralogical features, topography, roughness, dust and gas production rates, etc.) properties of Vesta and Ceres. The primary scientific objectives of VIR during the Dawn mission are: - to study the mineralogy of Vesta and Ceres, and their environment - to determine the nature of rock-forming minerals and their relative abundances - to measure the temperature of their surfaces - to generate physiographic maps of the surfaces Secondary objectives are: - provide synthetic maps of the surface - merge data from different instruments through data fusion Techniques - identify gaseous species emitted by the surface and physical Condition of the exosphere- if any. Calibration measurements ======================== Before the integration of the VIR experiment on the DAWN spacecraft a full calibration of the instrument has been performed to completely characterize the instrumental performances. The fundamental calibrations necessary to correctly retrieve the scientific information from VIR data are: 1- Geometric calibration: measurement of IFOV, FOV and in field distorsions; 2- Spectral calibration: correlation between spectral dispersion axis of the focal planes with wavelength; 3- Spatial calibration: evaluation of the flat-field matrices necessary to homogenize the focal planes responses; 4- Radiometric calibration: determination of the Instrument Transfer Function (ITF), that allows to convert digital numbers (DN) in physical units of spectral radiance (W m-2 micron-1 sterad-1). These quantities, continuously checked during the flight at each switch on of the experiment, are used in the data pipeline before the scientific analysis. Principal Investigator ====================== Maria Cristina De Sanctis Istituto Nazionale di Astrofisica, Rome References ========== - C.T. Russell et al., 'Dawn Mission to Vesta and Ceres', Earth, Moon and Planets 101, 65-91, 2007 - M.C. De Sanctis, et al., 'The VIR Spectrometer', Space Sci Rev, doi:10.1007/s11214-010-9668-5, 2010