KPL/IK PHEBUS 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 MPO Probing of Hermean Exosphere By Ultraviolet Spectroscopy (PHEBUS). Version and Date ----------------------------------------------------------------------------- Version 0.5 -- May 26, 2021 -- Alfredo Escalante Lopez Corrected MPO_PHEBUS_SLIT_75 cross angle aperture. Version 0.4 -- March 9, 2020 -- Marc Costa Sitja, ESAC/ESA Rafael Andres, ESAC/ESA Corrected MPO_PHEBUS_SLIT_100 cross angle according to [7]. Version 0.3 -- December 18, 2018 -- Marc Costa Sitja, ESAC/ESA Removed PHEBUS full scan FOVs. Version 0.2 -- August 6, 2018 -- Marc Costa Sitja, ESAC/ESA Corrected reference vectors for all FoVs. Version 0.1 -- May 18, 2018 -- Marc Costa Sitja, ESAC/ESA Eric Quemerais, LATMOS/IPSL Redefined Field of View definitions for the on-going first review. Version 0.0 -- January 10, 2017 -- Marc Costa Sitja, ESAC/ESA First draft. Pending review from the PHEBUS instrument team and the BepiColombo SGS. References ----------------------------------------------------------------------------- 1. ``Kernel Pool Required Reading'' 2. ``Frames Required Reading'' 3. ``C-Kernel Required Reading" 4. BepiColombo MPO Spacecraft Frames Definition Kernel 5. ``BepiColombo PHEBUS - Instrument User Manual'', PHEB_UM_INST_111107_1_LATMOS, Issue 1, Release 1, Draft 4, 15th October 2015 6. JIRA Action ``AI-TM1-SGS/PHE-08: SGS and PHEBUS to define measured position for scanner'' https://issues.cosmos.esa.int/bepicolombo/browse/PHE-12 Consulted on 18th May 2018. 7. Email communication from E. Quemerais ``BC-PHEBUS field of view and line of sight definition'' which includes the document ``PHEBUS FoV Definition for spice kernels''. Contact Information ----------------------------------------------------------------------------- If you have any questions regarding this file contact the ESA SPICE Service 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 ----------------------------------------------------------------------------- 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 [2] for more details. This file was created and may be updated with a text editor or word processor. * SPICEPY 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 ----------------------------------------------------------------------------- Data items are specified using ''keyword=value'' assignments [1]. All keywords referencing values in this I-kernel start with the characters `INS' followed by the NAIF MPO instrument ID code, constructed using the spacecraft ID number (-121) followed by the NAIF three digit ID number for one of the SIXS data item. These IDs are as follows Instrument name ID -------------------- ------ MPO_PHEBUS -121430 MPO_PHEBUS_ZERO -121431 The remainder of the name is an underscore character followed by the unique name of the data item. For example, the PHEBUS boresight direction in the MPO_PHEBUS frame (see [2]) is specified by: INS-121430_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. Overview ----------------------------------------------------------------------------- From [5]: The PHEBUS instrument is a UV spectrometer covering the spectral range going from 50 nm to 315 nm with two additional narrow bands in the visible around 404 nm (K line) and 422 nm (Ca line). Photons from the source (exosphere of Mercury) are collected by a SiC primary mirror installed inside a one-degree of freedom rotating mechanism (360 degrees). The primary mirror focuses the photons on a slit. Spectrometric information is obtained by the use of two gratings sharing the same pupil. Photons going through the slit are scattered according to their wavelength onto two separate intensified cross-delay anode detectors. One detector (labelled EUV) covers the 55-155 nm wavelength range. The second one (labelled FUV) covers the 145-315nm wavelength range. The two intensifiers based on Micro-Channel Plates use high voltages at values around 3600-5000 V. The two visible narrow spectral bands are obtained by two prisms on the side of the FUV detector that feed two identical Photo-Multiplier Tubes. The high voltage level that is necessary for these PMT is around 1000 V. They are called NUV Ca and NUV K detectors. The aim of the PHEBUS instrument is to observe sources (emission lines from atoms and ions) in the exosphere of Mercury or in the interplanetary medium, the surface of Mercury (only on the night side) but also to observe stars (mainly for calibration and degradation characterization purposes) or comets if opportunities arise. The scanning mechanism allows to select the pointing direction without moving the spacecraft. This will allow us to obtain vertical profiles in the exosphere of Mercury independently of the spacecraft attitude. Some operations will be performed in the normal Nadir pointing mode. Others, like star calibration, will require inertial pointing of the platform. PHEBUS will observe the interplanetary medium on a regular basis from the orbit of Mercury (emissions of hydrogen at H Lyman alpha and H Lyman beta, and helium HeI 58.4 nm). These interplanetary emissions will always be superposed to the Hermean exospheric signal and will have to be removed to retrieve the exospheric component. These observations will provide information on the distribution of H and He atoms in the interplanetary medium. If the possibility arises, PHEBUS will study comets that will cross the observation plane of PHEBUS which is parallel to the MPO orbit plane. Finally, at the end of the mission and assuming that the observation is safe enough for the instrument, PHEBUS will observe the emissions from the solar corona (H Lyman alpha 121.6nm, H Lyman beta 102.5 nm, and possibly the helium corona at 30.4 nm at second order). The instrument is basically composed of two combined spectrometers (FUV and EUV) operating in the spectral range of [55; 315 nm] and two NUV channels dedicated to the calcium and potassium lines measurement. The ranges are defined as follow: - EUV channel: from 55 nm to 155 nm - FUV channel: from 145 nm to 315 nm - NUV channels: - NUV Ca: 422 nm (calcium line) - NUV K: 404 nm (potassium line) A scanning mirror takes the light from the exosphere above the limb onto the entrance slit of the spectrometers with a minimum of reflections in order to maximize the UV count rate of MCP detectors (Micro Channel Plate). As long-term orbital stability may not be guaranteed, this scanning mirror is required: - to maintain the line-of-sight close to the limb during long integration time sequences, - to make the search and monitoring geometry less dependent on the MPO orbit, - to extend the vertical range of scanning. The PHEBUS instrument consists of two units: - PHEBUS Main Unit (internal with external protrusion) - PHEBUS Parking Bracket . The Parking Bracket is a passive and external unit whose purpose is to occlude the aperture of the baffle during the non-operational phases. Main Unit: ---------- The Main Unit - which represents the active part of the instrument itself - consists of several subsystems all included inside a single box. Its external protrusion (the baffle protrudes out of the spacecraft) is also called the Front End. The front end subsystem is composed of: - A baffle - An entrance mirror - A scanner mechanism (including a shutter) The Baffle: ~~~~~~~~~~~ The baffled entrance tube defines the 25.4 mm diameter aperture, and suppresses the internal stray light. The requirements on the baffling performance are fierce since the Hermean surface delivers up to 10E7 Rayleigh per spectral bin (at 300 nm, 10E6 Rayleigh at 200 nm). It provides a guard angle of +/-8.3 degrees. As the baffle is an external assembly, it is covered with MLI. The Entrance Mirror: ~~~~~~~~~~~~~~~~~~~~ The entrance mirror collects the light from the exosphere above the limb and directs it to the spectrometer. It is an off-axis parabolic primary telescope mirror made of SiC (sintered substrate + CVD polished layer) with a 170 mm focal length. The Scanning Mechanism: ~~~~~~~~~~~~~~~~~~~~~~~ The scanner mechanism allows the baffle and the mirror to rotate 360 degrees around the instrument. The assembly composed of the baffle and the mirror can be moved to a parking position in front of the Parking Bracket which occludes the baffle entrance. The scanner mechanism includes also an electromechanical shutter which is normally open. A light sensor using Si photodiodes, internal to the scanner mechanism, activates the shutter to cut the light path in case of wrong pointing. The scanner mechanism is a worm drive gearing system. It is used during each observation. The main specifications of the scanner are summarized below: - 360 degrees free rotation - Positioning accuracy 0.1 degrees - Speed (measured under gravity conditions - Scanner QM model): From 24,5 deg/s to 27.0 deg/s according to the selected moment - MAXON motor The Spectrometer: ~~~~~~~~~~~~~~~~~ The spectrometer subsystem is composed of: - One entrance slit - Two gratings: - EUV grating - FUV/NUV grating - Four detector assemblies: - FUV detector - EUV detector - NUV K detector - NUV Ca detector The entrance slit (horizontally oriented) selects the spectral and spatial resolutions. The instrument has a ~0.1 x 2 degrees FOV while the spectral resolution is ~1 nm in the EUV range and ~1.5 nm in the FUV range. The entrance slit is mounted on a specific 90 degrees rotating mechanism allowing to position the slit across the light flux (for exosphere measurement) or to remove it in order to increase the FOV (calibration on stars). The EUV spherical holographic diffraction grating covers the spectral range from approximately 55 to 155 nm with 2726 lines/mm. It is equipped with a dedicated heater used for in-flight decontamination purpose. The EUV detector consists of a 2-D photon-counting micro channel plate detector Z-stack + V-stack (5 stages), matching the optical spectrum. The size of the detector active area is ~ 40 x 20 mm2 containing 1024 x 512 pixels (spectral x spatial). The 2 degrees slit is imaged onto the central pixels (~ 6.6mm height) while the remaining pixels are used for dark current monitoring. The pixel format allows for Nyquist sampling with a spectral resolution of 1 nm and a spatial resolution of 1 degree. The EUV detector covers the 55-155 nm wavelength range. A CsI photocathode is used in order to remove at best stray-light from longer wavelengths. This CsI photocathode is sensitive to ambient air and moisture. For this reason, a small vacuum chamber is built around the EUV detector focal plane, and the focal plane shall be maintained under vacuum (less than 1.10-1 mbar) until the launch thanks to the PGSE. The FUV detector is very similar to the EUV one and operates within the range [145-315] nm. As the EUV detector, the FUV detector is maintained under vacuum. As the MgF2 is not opaque at the FUV wavelengths (above 115nm) the FUV window is made of that material and seals the vacuum chamber without requiring neither a mechanism to open it nor a pumping system. A solar blind photocathode of CsTe is used in order to protect the detector against stray light. Both NUV channels (NUV Ca and K) are very similar. Each NUV channel uses a set of two mirrors to deviate the specific rays of potassium (for NUV K, 404.7 nm) and calcium (for NUV Ca, 422.8 nm) from the spectrum dispersed by the FUV grating. A photomultiplier tube (Hamamatsu R3550P/SEL) operated in photon-counting mode is used on each channel to measure the intensity of each line. Parking Bracket Unit: --------------------- During instrument non-operational phases, the baffle is parked in front of a bracket so that the baffle aperture is protected from the space outer light environment. The parking bracket is an external unit. It is made of golden aluminium, and its face exposed to the highest fluxes is covered with OSR. The following table summarizes the instrument optics, performances and resolution: Parameter | Units | Value/Description Remarks -------------------------+---------------+---------------------------- Optics | | | | Aperture | mm | 25.4 Focal length | mm | 170 Focal number | | N/A Field of view | degrees | 2 x 0.1 Central obstruction | % | Pixel IFOV | microrad | 650 Spectral range | nm | [55-315] + 404 + 422 Filter bandwidth | | Spectrometers | nm | 1 NUV channel | nm | 10 Spectral Channels | | 2050 Spectral dispersion | Pix/nm | Mirror efficiency | % | 25 Mirror Material | | SiC Mirror Grating | | SiC and Pt and Coating | | | | Sensor (RAE) | | | | Pixel lines | # | 512 Per detector Pixels per line | # | 1024 Per detector Pixel pitch | microrad | 78 Peak quantum | | efficiency | | EUV | % | 55 FUV | % | 15 Full well capacity | # e- | 4000 Scale per pixel | | At Periherm | m/px | 2500 At Apoiherm | m/px | 5000 Smear | px/s | Exposure time | ms | 10 to 108 | | Resolution | | | | Spectral resolution | nm | delta(landa) = 1 Angular resolution | microrad/px | 650 Spatial resolution | m/pixel | 25 to 50 | | Mounting Alignment ----------------------------------------------------------------------------- Refer to the latest version of the BepiColombo Frames Definition Kernel (FK) [4] for the PHEBUS reference frame definitions and mounting alignment information. PHEBUS Apparent Field-of-View Layout ----------------------------------------------------------------------------- The instrument Field of View is defined by the spectrometer slit size (5.67 x 0.283 mm). With a focal length of 170 mm, it corresponds to ~ 2 x 0.1 degrees projected on the horizon. Nevertheless the FoV sizes can be classified by the % of the total energy of the FoV contained in the rectangular zone [6]: With Slit: / |x| le 0.05 deg / |x| le 0.20 deg 75% -: 100% -: \ |y| le 1.00 deg \ |y| le 1.15 deg Without Slit: / |x| le 0.60 deg / |x| le 0.93 deg 75% -: 100% -: \ |y| le 1.21 deg \ |y| le 1.65 deg This diagram illustrates the PHEBUS apparent FOV in the MPO PHEBUS (MPO_PHEBUS) reference frame. ^ +Yphebus (along slit) | | | +-|-+ --- | | | ^ ---->| | |<---- 0.1 degrees | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +Xphebus (cross slit) | | | | <------------x | | 2 degrees | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |___| _v_ PHEBUS boresight (+Zphebus) is into the page FOV Definitions --------------------------------------------------------------------------- This section contains assignments defining the PHEBUS spectrometer FOVs. These definitions are based on the spectrometer parameters provided in the previous sections and are provided in a format consistent with/required by the SPICE TOOLKIT function GETFOV. PHEBUS (MPO_PHEBUS) FOVs: ~~~~~~~~~~~~~~~~~~~~~~~~~ The PHEBUS FOVs are defined within a rectangle pyramid with an along slit angle of 2 degrees and a cross slit angle of 0.1 degrees. They are defined with respect to the MPO_PHEBUS reference frame. The boresight and cross-reference vectors are unit along the +Z axis and the +X axis of the frame, respectively. Please note that the FOV reference and cross angles are defined with half angle values. The following FOVs definitions correspond to the NAIF Body Names: MPO_PHEBUS_SLIT_75, MPO_PHEBUS_SLIT_100, MPO_PHEBUS_75 and MPO_PHEBUS_100. \begindata INS-121431_NAME = 'MPO_PHEBUS_SLIT_75' INS-121431_BORESIGHT = ( 0.000 0.000 1.000 ) INS-121431_FOV_FRAME = 'MPO_PHEBUS' INS-121431_FOV_SHAPE = 'RECTANGLE' INS-121431_FOV_CLASS_SPEC = 'ANGLES' INS-121431_FOV_REF_VECTOR = ( 0.000 1.000 0.000 ) INS-121431_FOV_REF_ANGLE = ( 1.000000 ) INS-121431_FOV_CROSS_ANGLE = ( 0.05000 ) INS-121431_FOV_ANGLE_UNITS = 'DEGREES' INS-121432_NAME = 'MPO_PHEBUS_SLIT_100' INS-121432_BORESIGHT = ( 0.000 0.000 1.000 ) INS-121432_FOV_FRAME = 'MPO_PHEBUS' INS-121432_FOV_SHAPE = 'RECTANGLE' INS-121432_FOV_CLASS_SPEC = 'ANGLES' INS-121432_FOV_REF_VECTOR = ( 0.000 1.000 0.000 ) INS-121432_FOV_REF_ANGLE = ( 1.150000 ) INS-121432_FOV_CROSS_ANGLE = ( 0.2000 ) INS-121432_FOV_ANGLE_UNITS = 'DEGREES' INS-121433_NAME = 'MPO_PHEBUS_75' INS-121433_BORESIGHT = ( 0.000 0.000 1.000 ) INS-121433_FOV_FRAME = 'MPO_PHEBUS' INS-121433_FOV_SHAPE = 'RECTANGLE' INS-121433_FOV_CLASS_SPEC = 'ANGLES' INS-121433_FOV_REF_VECTOR = ( 0.000 1.000 0.000 ) INS-121433_FOV_REF_ANGLE = ( 1.210000 ) INS-121433_FOV_CROSS_ANGLE = ( 0.600000 ) INS-121433_FOV_ANGLE_UNITS = 'DEGREES' INS-121434_NAME = 'MPO_PHEBUS_100' INS-121434_BORESIGHT = ( 0.000 0.000 1.000 ) INS-121434_FOV_FRAME = 'MPO_PHEBUS' INS-121434_FOV_SHAPE = 'RECTANGLE' INS-121434_FOV_CLASS_SPEC = 'ANGLES' INS-121434_FOV_REF_VECTOR = ( 0.000 1.000 0.000 ) INS-121434_FOV_REF_ANGLE = ( 1.650000 ) INS-121434_FOV_CROSS_ANGLE = ( 0.930000 ) INS-121434_FOV_ANGLE_UNITS = 'DEGREES' \begintext Optical Parameters ----------------------------------------------------------------------------- TBD. Detector Parameters ----------------------------------------------------------------------------- TBD. End of IK file.