KPL/IK MGNS Instrument Kernel ============================================================================= This instrument kernel (I-kernel) contains references to mounting alignment, operating modes, and timing as well as internal and FOV geometry for the BepiColombo - Mercury Gamma-Ray and Neutron Spectrometer (MGNS). Version and Date ----------------------------------------------------------------------------- Version 0.3 -- May 10, 2024 -- Ricardo Valles Blanco, ESAC/ESA Decreased 90 degrees half-angles to 89.99994 degrees limit. Version 0.2 -- February 1, 2023 -- Alfredo Escalante Lopez, ESAC/ESA Ricardo Valles Blanco, ESAC/ESA Marc Costa Sitja, NAIF/JPL Added instrument sensors descriptions and references. Added instrument Field-of-view. Fixed typos for PDS4 Bundle release version 1.0. Version 0.1 -- July 05, 2016 -- Marc Costa Sitja, ESAC/ESA Updated BEPICOLOMBO MPO IDs from -69 to -121. Removed kernel name and version assignment. Version 0.0 -- February 28, 2013 -- Richard Moissl, ESAC/ESA Initial draft. References ----------------------------------------------------------------------------- 1. ``Kernel Pool Required Reading'', NAIF. 2. ``Frames Required Reading'', NAIF. 3. ``MGNS EID, Part B'', BC-EST-RS-02516 , November 14, 2017 4. BepiColombo Frames Definition Kernel (FK), latest version. 5. ``The Mercury Gamma-Ray and Neutron Spectrometer (MGNS) Onboard the Mercury Planetary Orbiter of the BepiColombo Mission'', I.G. Mitrofanov, A.S. Kozyrev, 29 January 2009. 6. ``The Mercury Gamma-Ray and Neutron Spectrometer (MGNS) Onboard the Mercury Planetary Orbiter of the BepiColombo Mission: Design Updates and First Measurements in Space'', I.G. Mitrofanov, A.S. Kozyrev, 21 July 2021. Contact Information ----------------------------------------------------------------------------- If you have any questions regarding this file contact SPICE support at ESAC: Alfredo Escalante Lopez (+34) 91-8131-429 spice@sciops.esa.int or NAIF at JPL: Boris Semenov +1 (818) 354-8136 Boris.Semenov@jpl.nasa.gov Implementation Notes ----------------------------------------------------------------------------- This file is used by the SPICE system as follows: programs that make use of this frame kernel must "load" the kernel normally during program initialization. Loading the kernel associates the data items with their names in a data structure called the "kernel pool". The SPICELIB routine FURNSH loads a kernel into the pool as shown below: FORTRAN: (SPICELIB) CALL FURNSH ( frame_kernel_name ) C: (CSPICE) furnsh_c ( frame_kernel_name ); IDL: (ICY) cspice_furnsh, frame_kernel_name MATLAB: (MICE) cspice_furnsh ( 'frame_kernel_name' ) PYTHON: (SPICEYPY)* furnsh( frame_kernel_name ) In order for a program or routine to extract data from the pool, the SPICELIB routines GDPOOL, GIPOOL, and GCPOOL are used. See [1] for more details. This file was created and may be updated with a text editor or word processor. * SPICEYPY is a non-official, community developed Python wrapper for the NAIF SPICE toolkit. Its development is managed on Github. It is available at: https://github.com/AndrewAnnex/SpiceyPy Naming Conventions ----------------------------------------------------------------------------- All names referencing values in this I-kernel start with the characters 'INS' followed by the NAIF BepiColombo MPO spacecraft ID number (-121) and then followed by a NAIF three digit code for the MGNS detector (300) The remainder of the name is an underscore character followed by the unique name of the data item. For example, the MGNS boresight direction in the MPO_MGNS frame (see [2]) is specified by: INS-121895_BORESIGHT The upper bound on the length of the name of any data item identifier 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. Description ----------------------------------------------------------------------------- From [5, 6]: The Mercury Gamma-ray and Neutron Spectrometer (MGNS) on board BepiColombo Mercury Planet Orbiter is designed to observe and study the gamma-ray and neutron emissions of Mercury. The MGNS is a multifunctional scientific instrument, comprising one gamma-ray spectrometer and four neutron detectors. The sensor unit of the gamma-ray spectrometer consists of one 3 by 3 inches high energy resolution inorganic scintillator crystal, i.e. CeBr3, whereas the sensor unit of the neutron detectors consists of three 3He gas-filled tubes and one stilbene organic scintillator crystal with plastic scintillator as its anticoincidence shield. The design of MGNS is adapted from that of the HEND neutron detector which operates on board the NASA 2001 Mars Odyssey mission. MGNS is a Russian-made and Russian-funded contribution by the Russian Federal Space Agency (ROSCOSMOS) to the BepiColombo ESA and JAXA collaborative mission. The MGNS has one detector (SCD/G) for gamma rays and four detectors (SD1, SD2, MD and SCD/N) for neutrons. This instrument will detect gamma rays and neutrons that are emitted by radioactive elements on Mercury's surface or by surface elements that have been stimulated by cosmic rays. It will determine the subsurface composition with a spatial resolution of 400 km comparable with the relief features on Mercury and sufficient for testing composition anomalies at large impact basins on the planet. It will also determine of regional distribution of volatile depositions on the polar areas of Mercury, which are permanently shadowed from the Sun and to provide a global map of hydrogen abundance. The gamma-ray spectrometer of the MGNS is based on a 77 mm diameter, 78 mm thick circular cylinder of CeBr3 viewed by a Hamamatsu R1307-13, 76 mm diameter Photo Multiplier Tube (PMT). The original Flight Model with LaBr3 crystal was replaced before launch by the Flight Spare Model incorporating the CeBr3 crystal increasing sensitivity for the natural radioisotope of 40K by a factor of 6. The exposure time could be evaluated, as the sum of all time intervals, when the MPO flies above the pixel along the predicted elliptical orbit. The mapping stage of MPO is assumed to be 1 Earth year. Assuming a pixel size of about 400 km on the surface, which corresponds to the MPO altitude at the pericenter of the orbit. The choice of neutron detectors is based on the current understanding of the neutron leakage flux from Mercury and on the available heritage of neutron sensors. 3He proportional counters LND 2517 having a diameter of 12.7 mm, length of 94 mm and pressure of 6 atm, were used for SD1, SD2 and MD. These counters are most sensitive to thermal and epithermal neutrons. The counter of SD1 has a surrounding Cd shield, which absorbs all neutrons below the threshold of 0.4 eV. The counter of SD2 has no shield and detects both thermal and epithermal neutrons. The difference between counts from SD2 and SD1 corresponds to thermal neutrons. Detector MD is surrounded by a thick polyethylene enclosure inside the Cd shield. An external Cd shield rejects external thermal neutrons, and polyethylene moderates external neutrons epithermal and high-energy neutrons. Detector SCD/N uses a stilbene crystal of size 30 cm diameter and 40 cm thickness for the detection of high-energy neutrons. The stilbene sensor is surrounded by a plastic scintillator, which reject external protons. Mounting Alignment ----------------------------------------------------------------------------- Refer to the latest version of the BepiColombo Frames Definition Kernel (FK) [2] for the MGNS reference frame definitions and mounting alignment information. FOV Definitions ----------------------------------------------------------------------------- MGNS does not have fields of view in the traditional sense. The MGNS instrument has five uncollimated detectors: three detectors based 3He counter, one sensor for high energy neutrons detector and gamma-ray spectrometer. These sensors take science measurements with a 2*Pi steradian field of view. The MGNS Instrument has no aperture and does not require holes in the spacecraft MLI. Please note that the FOV reference and cross angles are defined with half angle values. The half-angle values have been set to the maximum FOV angular radius limit of 89.99994 degrees. The following FOV definition corresponds to the NAIF Body Names: MPO_MGNS. \begindata INS-121895_NAME = 'MPO_MGNS' INS-121895_BORESIGHT = ( 1.000, 0.000, 0.000 ) INS-121895_FOV_FRAME = 'MPO_MGNS' INS-121895_FOV_SHAPE = 'CIRCLE' INS-121895_FOV_CLASS_SPEC = 'ANGLES' INS-121895_FOV_REF_VECTOR = ( 0.000, 0.000, 1.000 ) INS-121895_FOV_REF_ANGLE = ( 89.99994 ) INS-121895_FOV_ANGLE_UNITS = 'DEGREES' \begintext The effective FOV of this instrument should be considered to be along a center line parallel to the S/C Z axis, covering the full solid angle subtended by the Mercury crust at the S/C. The Sensor units detect neutrons and gamma rays from half-sphere directions (2*Pi sr). For mapping in orbit around Mercury, the MGNS has an effective field-of-view defined by the solid angle subtended by Mercury, which will change as a function of time throughout each orbit due to spacecraft altitude changes. Centered on the nadir direction, this angle is described by a half-cone angle given by theta = arcsin[1/(1+h/R)], where R is the radius of Mercury (2440 km) and 'h' is the spacecraft altitude, assuming the planet is spherical. The orbits will be elliptical, with the closest distance of about 400 km defining the largest cone (and the most sensitive measurements, having the highest measured flux). By this formula, the sensor response to the planet is limited to a half-cone angle of 67.55 degrees. The footprint will be distorted and reduced in intensity by attenuation of S/C components when the S/C Z-axis is not pointed at the planet, but the GRS will retain substantial response at most S/C attitudes. A footprint intensity function has been derived based on isotropic response that has a maximum at the subsatellite point and decreases to zero at the limb. At some circle radius between the subsatellite point and the limb, half of the intensity will be inside the circle, defined as the "1/2 distance". A simple representation of the footprint will be used, in which intensity is constant over this "1/2 distance" and zero outside. This "1/2 distance" (a curved path on the Mercury surface) can be computed for any altitude from a 3rd-order polynomial in altitude, the coefficients of which can be read from keywords. Beyond a certain altitude, the response will be dominated by background. No footprint will be computed for altitudes greater than this altitude, which can be read as a keyword. The footprint intensity function 'y' is described by the following third order polynomial: y = 0.00000005*x*x*x - 0.00033641*x*x + 0.92072971*x + 98.64754679 where 'x' is the spacecraft altitude in kilometers and 'y' is the 1/2 distance in kilometers. The polynomial coefficients of the footprint intensity function and the maximum altitude are captured in the following keywords. \begindata INS-121895_HALF_DIST = ( 0.00000005, -0.00033641, 0.92072971, 98.64754679 ) INS-121895_HALF_DIST_UNITS = 'KM' INS-121895_MAX_ALT = 1600 INS-121895_MAX_ALT_UNITS = 'KM' \begintext Also defined here is a reference vector to the instrument X-axis, nominally coaligned with the spacecraft Z-axis, provided for the convenience of analysis software. It is used for performing dot products with the spacecraft velocity vector. \begindata INS-121895_REFERENCE_VECTOR = ( 0.0, 0.0, 1.0 ) \begintext End of IK file.