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 --------------------------------------------------------------- The TEXT_KERNEL_ID stores version information of loaded project text kernels. Each entry associated with the keyword is a string that consists of four parts: the kernel name, version, entry date, and type. MIXS I-kernel Version: \begindata TEXT_KERNEL_ID += 'MPO_MGNS V0.0.1 28-FEB-2013 IK' \begintext Change Log History: Version 0.0.0 -- February 28, 2013 -- Richard Moissl Initial draft. References --------------------------------------------------------------- 1. "Kernel Pool Required Reading" 2. "C-kernel Required Reading" 3. "MGNS EID, Part B", BC-EST-RS-02516 , February 29, 2012 4. BepiColombo Frames Definition Kernel (FK), latest version. 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 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. Naming Conventions --------------------------------------------------------------- All names referencing values in this I-kernel start with the characters 'INS' followed by the NAIF Bepicolombo MPO spacecraft ID number (-69) 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-69300_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. MGNS Description --------------------------------------------------------------- [TBD] "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 be used to map the relative abundances of different elements and will help to determine if there is ice at Mercury's poles, which are never exposed to direct sunlight." [TBD] Gamma ray sensor description here [TBD] [TBD] Neutron sensors description here [TBD] MGNS Field of View Specification --------------------------------------------------------------- [TBD] "The FOV of this instrument should be considered to be along a centerline parallel to the S/C Z axis, covering the full solid angle subtended by the Mercury crust at the S/C." [TBD] "The Sensor units detect neutrons and gamma rays from all directions (4*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 [TBC] 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." [TBC] [TBD] "To first order, the MGNS requires no SPICE FOV cutoff, and its boresight is defined by a vector from the S/C centerline to the subsatellite point. 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." [TBC] 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. [TBC] \begindata INS-690300_HALF_DIST = ( 0.00000005, -0.00033641, 0.92072971, 98.64754679 ) INS-69300_HALF_DIST_UNITS = 'KM' INS-69300_MAX_ALT = 1600 INS-69300_MAX_ALT_UNITS = 'KM' \begintext Also defined here is a reference vector to 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-69300_REFERENCE_VECTOR = ( 0.0, 0.0, 1.0 ) \begintext Platform ID --------------------------------------------------------------- \begindata INS-69300_PLATFORM_ID = ( -69000 ) \begintext NAIF ID Code to Name Mapping --------------------------------------------------------------- \begindata NAIF_BODY_NAME += ( 'MPO_MGNS' ) NAIF_BODY_CODE += ( -69300 ) \begintext