KPL/IK GALA Instrument Kernel =============================================================================== This instrument kernel (I-kernel) contains the GAnymede Laser Altimeter (GALA) optics, detector and field-of-view (FOV) paramters. Version and Date ------------------------------------------------------------------------------- Version 0.1 -- January 31, 2016 -- Jorge Diaz del Rio, ODC Space Preliminary version. Pending review by the GALA instrument and JUICE Science Operations Working Group team. Version 0.0 -- July 24, 2013 -- Marc Costa Sitja, ISDEFE/ESA Initial Release. References ------------------------------------------------------------------------------- 1. ``Kernel Pool Required Reading'' 2. ``C-kernel Required Reading'' 3. JUICE Frames Definition Kernel (FK), latest version. 4. ``The Ganymede Laser Altimeter (GALA) on ESA’s JUICE mission: Overview of the instrument design.'', Lingenauber, K. et al. Contact Information ------------------------------------------------------------------------ If you have any questions regarding this file contact SPICE support at ESAC: Marc Costa Sitja (+34) 91-8131-457 mcosta@sciops.esa.int, esa_spice@sciops.esa.int or NAIF at JPL: Boris Semenov (818) 354-8136 Boris.Semenov@jpl.nasa.gov Implementation Notes ------------------------------------------------------------------------------- Applications that need SPICE I-kernel data must ``load'' the I-kernel file, normally during program initialization. The SPICE routine FURNSH loads a kernel file into the pool as shown below. CALL FURNSH ( 'frame_kernel_name' ) -- FORTRAN furnsh_c ( "frame_kernel_name" ); -- C cspice_furnsh, frame_kernel_name -- IDL cspice_furnsh( 'frame_kernel_name' ) -- MATLAB Loading the kernel using the SPICELIB routine FURNSH causes the data items and their associated values present in the kernel to become associated with a data structure called the ``kernel pool''. Once the file has been loaded, the SPICE routine GETFOV (getfov_c in C, cspice_getfov in IDL and MATLAB) can be used to retrieve FOV parameters for a given instrument or structure. The application program may obtain the value(s) for any other IK data item using the SPICELIB routines GDPOOL, GIPOOL, GCPOOL (gdpool_c, gipool_c, gcpool_c in C, cspice_gdpool, cspice_gipool, cspice_gcpool in IDL and MATLAB). See [1] for details. This file was created with, and can be updated with a text editor or word processor. Naming Conventions and Conventions for Specifying Data ------------------------------------------------------------------------------- All names referencing values in this IK file start with the characters `INS' followed by the NAIF JUICE spacecraft ID number (-907) followed by a NAIF three digit ID code for one of the GALA sensors. This is the full list of names and IDs for the GALA sensors described by this IK file: JUICE_GALA_RXT -907120 The remainder of the keyword name is an underscore character followed by the unique name of the data item. For example, the GALA Receiver Unit boresight direction in the JUICE_GALA_RXT frame is specified by: INS-6907620_BORESIGHT The upper bound on the length of the name of any data item is 32 characters. If the same item is included in more than one file, or if the same item appears more than once within a single file, the latest value supersedes any earlier values. Instrument Description and Overview ------------------------------------------------------------------------------- From [4]: The GAnymede Laser Altimeter (GALA) is a laser altimeter for studying the tidal deformation of Ganymede and the morphology and topography of the surfaces of the icy satellites Europa, Callisto and Ganymede. GALA contributes to the exploration of the surface morphology and physical properties of Ganymede, Europa and Callisto, to the determination of their interior structures from a combination of shape, topography and gravitational field data, to the exploration of the satellites’ physical surface properties, and to their formation and evolution especially with respect to subsurface water oceans. By measuring the time-of-flight of a laser pulse transmitted from the instrument, backscattered at the satellite's surface, and detected in the instrument’s receiver telescope, height profiles are obtained in along-track direction. Combining many of these tracks, the local, regional, and global topography of Ganymede are derived. From the pulse-spreading of the returned pulse the surface roughness on the scale of the laser footprint (order of a few tens of meters depending on S/C altitude) can be obtained. Additionally, information on the albedo at the laser wavelength (1064 nm) can be gained from the intensities of the transmitted and returned pulses. GALA is one of the JUICE instruments focusing on the characterisation of Ganymede’s subsurface water ocean. By obtaining not only good spatial coverage but also temporal coverage with laser ground-tracks the tidal deformation of Ganymede’s ice shell along Ganymede’s orbit around Jupiter will be measured. From the tidal signal (expressed in terms of the radial tidal Love number h2), the presence of an ocean can be verified. While the tidal signal is expected on the order of several meters in case of a subsurface ocean. Without an ocean, this signal will be few tens of centimetres only. To realize measurements of tidal response, the instrument will collect data to analyse intersecting ground-tracks at different tidal phases. From h2, the extension of Ganymede’s ice shell can be constrained, especially when combined with measurements of the tidal potential by the radio science experiment (3GM). GALA will contribute to the exploration of the surface morphology and physical properties of Ganymede, Europa and Callisto. Combining stereo-data sets from the camera (JANUS) with altimetry data will provide topography and digital terrain models that are essential for geological analysis as well as for interpretation of the reflected radar signals of the RIME instrument. GALA uses the “direct-detection” (classical) approach of laser altimetry. The instrument emits laser pulses at a wavelength of 1064 nm by using a actively Q-switched Nd:Yag laser. The detector measures the emission time of each pulse. The returning laser pulse is refocused onto a silicon avalanche photodiode (APD) through back-end optics. The APD-signal is then amplified, sampled and fed to a digital range finder. The data is passed to a digital processing unit, which controls the operation of the complete instrument and communicates with the spacecraft. Main instrument characteristics are summarized in the following Table: Table: GALA baseline instrument parameters ----------------------------------------------------------------------- Parameters Value Comments ----------------------------------------------------------------------- Laser wavelength 1064.3 mn With error of +/-0.2nm ----------------------------------------------------------------------- Pulse Energy 17 mJ ----------------------------------------------------------------------- Pulse length 6 ns ----------------------------------------------------------------------- Pulse repetition rate 1 to 30 Hz Variable ----------------------------------------------------------------------- Collimator aperture 45x60 mm ----------------------------------------------------------------------- Beam divergence 100 nrad Full cone ----------------------------------------------------------------------- Spot size on the surface 50 m In 500km orbit ----------------------------------------------------------------------- Receiver telescope diameter 250 mm F/1 telescope ----------------------------------------------------------------------- Primary mirror diameter >260 mm ----------------------------------------------------------------------- Obscuration ratio 0.13 small as possible ----------------------------------------------------------------------- Focal length 1.5m ----------------------------------------------------------------------- Distance from primary mirror 158.4 mm less than 170 mm to secondary mirror ----------------------------------------------------------------------- Field of View (FOV) 450 mrad ----------------------------------------------------------------------- Backend Optics (BEO) 1x TBD projective magnification ----------------------------------------------------------------------- Incidence angle to BPF 1.65 deg less than 3 deg ----------------------------------------------------------------------- Altitude resolution ~10 cm At optimal conditions ----------------------------------------------------------------------- Operation ranges < 1000 to Depending on different < 1300 km albedo values ----------------------------------------------------------------------- Mounting Alignment ------------------------------------------------------------------------------- Refer to the latest version of the JUICE Frames Definition Kernel (FK) [3] for the GALA reference frame definitions and mounting alignment information. GALA Laser Head and Transmitter parameters ------------------------------------------------------------------------------- TBD; need consultation with GALA instrument team GALA Optics and Detector parameters ------------------------------------------------------------------------------- TBD; needed consultation with GALA instrument team GALA Receiver Telescope Field of View Definition ------------------------------------------------------------------------------- The GALA Receiver Telescope (RXT) Field of View (FOV) is defined as a 225 mrad half-angle cone centered on the +Z axis of the JUICE_GALA_RXT frame. \begindata INS-907120_FOV_FRAME = 'JUICE_GALA_RXT' INS-907120_FOV_SHAPE = 'CIRCLE' INS-907120_BORESIGHT = ( 0.000, 0.000, 1.000 ) INS-907120_FOV_CLASS_SPEC = 'ANGLES' INS-907120_FOV_REF_VECTOR = ( 0.000, 1.000, 0.000 ) INS-907120_FOV_REF_ANGLE = ( 0.250 ) INS-907120_FOV_ANGLE_UNITS = 'RADIANS' \begintext