KPL/IK XSM Instrument kernel =========================================================================== This instrument kernel (I-kernel) contains SMART-1 X-ray Solar Monitor (XSM) optics, detector, and FOV parameters. Version and Date --------------------------------------------------------------------------- Version 2.0 -- June 09, 2005 -- Jorge Diaz del Rio, RSSD/ESA Corrected typos and spelling. Spectral Parameters section included. Version 1.0 -- April 20, 2005 -- Jorge Diaz del Rio, RSSD/ESA Filled in Instrument Overview section, provided by the XSM Team. Correction of Focal Length and Detector Size values Version 0.0 -- April 08, 2005 -- Jorge Diaz del Rio, RSSD/ESA Preliminary Version. Pending review and approval by XSM instrument team. References --------------------------------------------------------------------------- 1. ``Kernel Pool Required Reading'' 2. ``C-kernel Required Reading'' 3. ``D-CIXS/XSM EID-B'', S1-CIX-EID-3001, Issue 5.0, September 30, 2002 4. SMART-1 Frames Definition Kernel (FK), latest version. 5. Email from Juhani Huovelin (11/April/2005) 6. ``The SMART-1 X-ray solar monitor (XSM): calibrations for D-CIXS and independent coronal science''. Huovelin et all. Planetary and Space Science 50 (2002): 1345-1353. 7. ``XSM Instrument Catalogue'', S1-SUN-XSM-2-EDR-EE-3-12-V1.0 Contact Information --------------------------------------------------------------------------- Jorge Diaz del Rio, RSSD/ESA, (31) 71-565-5175, jdiaz@rssd.esa.int Implementation Notes --------------------------------------------------------------------------- Applications that need SPICE I-kernel data must ``load'' the I-kernel file, normally during program initialization. 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''. The application program may then obtain the value(s) for any IK data item using the SPICELIB routines GDPOOL, GIPOOL, GCPOOL. Routine GETFOV may also be used if the file contains instrument field-of-view (FOV) specifications. See [1] for details. This file was created, and can be updated with a text editor or word processor. Conventions for Specifying Data --------------------------------------------------------------------------- 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 SMART-1 instrument ID code, constructed using the spacecraft ID number, -238, followed by the NAIF three digit ID number for XSM detector (700). This ID is defined in [4] as follows: Instrument name ID -------------------- ------- SMART1_XSM -238700 The remainder of the keyword is an underscore character followed by the unique name of the data item. For example, the number of pixels of the FACET1 is specified by INS-238700_NUMBER_OF_PIXELS The upper bound on the length of all keywords is 32 characters. If a keyword is included in more than one file, or if the same keyword appears more than once within a single file, the last assignment supersedes any earlier assignments. Instrument Overview --------------------------------------------------------------------------- From [6]: Introduction: ------------- The X-ray solar monitor (XSM) is a calibration instrument of the 'Demonstration of Compact Imaging X-ray Spectrometer' (D-CIXS) experiment, with a separate Silicon detector unit on the SMART-1 spacecraft. The non-imaging HPSi PIN sensor has a wide field-of-view (FOV) to enable Sun visibility during a significant fraction of the mission lifetime. This is essential for obtaining calibration spectra for the X-ray fluorescence measurements by the imaging D-CIXS spectrometer. The energy range (1-20 keV), spectral resolution (about 250 eV at 6 keV, BOF), and sensitivity (about 7000 cps at flux level of 10-4 W m-2 in the range 1-8 A) are tuned to provide optimal knowledge about the solar X-ray flux on the lunar surface, matching well with the activating energy range for the fluorescence measured by D-CIXS. The independent science of the XSM will also be valuable since the XSM energy range is very sensitive to solar flares. The count rate during the top of an X1 flare will be about 35 times higher than the average quiescent count rate at solar maximum. The relative increase will be the same for an M1 flare during the SMART-1 mission, which will be closer to the next solar minimum. Since the XSM will observe the Sun as a star, and the energy range and spectral resolution are close to those of present astronomical X-ray satellites (e.g. XMM-Newton, ASCA, Chandra), we will obtain an X-ray database of the Sun which can be related with the stellar X-ray observations more easily than the data from present solar X-ray instruments. From [7]: Detector: --------- The flux of the Sun in the energy range 0.1-20 keV is very high (several hundred million photons/cm^2/s) and variable. The spectrum slope decreases very steeply with increasing energy, which means that most of the photons are concentrated in the lower energies, i.e. below 1 keV. The variability, on the other hand, is concentrated in the higher energies because it is mainly caused by changes in the high temperature components of the solar spectrum (originating in active regions and flares). This means that tuning the low energy limit for the XSM is very important to achieve reasonable count rates. Nevertheless, even by cutting out the invariable low energy part of the flux below 1 keV, the detector will receive high photon fluxes requiring a very small active detector area. The lower limit for the energy range is determined by the external X-ray windows and the surface contact layers of the detector, with a minor effect by the very thin dead layer of Si on the detector surface. The optimal energy pass band is acquired with a 25 micron Beryllium window. The standard design includes an aluminium contact of 500 nm thickness, and the estimated Si dead layer is 200 nm. The co-added effects of these lead to a band pass with 10% efficiency at about 1 keV. The upper limit of the energy range for the HPSi Pin-detector depends on the thickness of the detector, which dominates the upper energy limit via the QE. The thickness, 0.5 mm, of the standard Si diodes manufactured by Metorex, are well-suited fro this purpose. The range extends to about 20 keV with well sufficient QE for our purpose. The inefficient charge collection in the edge area of the detector is handled by manufacturing a larger detector bulk with the edge area covered by an aperture stop of gold. Simulations with various flare intensities show that the optimal area size not covered by the golden ring is about 1.5 mm in diameter, and the optimal thickness is 125 to 500 microns. Electronics: ------------ The electronics of the XSM consists of 1) pre-amplifier stages and shaping amplifier, which are in the sensor unit box and 2) an electronics board in the main D-CIXS instrument box, which includes further stages of the signal processing electronics. The electrical and data interfaces connect the XSM with the D-CIXS. There will be no direct electrical or data interfaces from the XSM to the spacecraft. Performance and field of view: ------------------------------ The detector features will, according to simulations, yield about 1 cps in the solar activity minimum (i.e. sunspot cycle minimum), about 200 cps in the solar maximum (i.e. average sunspot cycle maximum), and about 7000 cps during an X1 flare (a strong flare). Class X10 flares have been detected, and photon count rates above 10000 cps are therefore not ruled out. From these we can set the requirement for the dynamic range of the detector. The optimisation of that range should, however, be done simultaneously with that of the energy resolution. Technically, there is a clear trade-off between these goals since high dynamic range, and capability to handle very high count rates, will inevitably lead to a loss of energy resolution and to an intolerable event pile-up. Therefore, the requirement for the energy resolution has to be about 230 eV at 6 keV. This is quite sufficient for a good spectral analysis with the capability of resolving the major spectral lines expected in the lower energy part of the spectrum (thin thermal plasma spectrum). The resolution will also be comparable to those of the instruments on the other X-ray missions (XMM-Newton, Chandra, SRG). The suitable number of equally spaced energy channels in the range 1-20 keV is 512, leading to at least 3-4 channels per resolution element. The dynamic range will be optimized by using a hardware technique to compensate for the detector dead time losses. This will also lead to significantly decreased amount of signal pile-up. The estimated fraction of piled up events will be about 1% at the signal level of 20000 cps. The X-ray flux from the Sun will overwhelmingly dominate the signal in the energy range of the instrument over the sky background, or any other possible source simultaneously in the FOV. In fact, the open aperture of the detector should be maximized in order to have the Sun in the field of view for a sufficiently large range of attitudes. Thus, the instrument requires no collimation or focusing system (telescope), and the full aperture of the detector will be used. Energy resolution: ------------------ The XSM detector is a PIN-diode made of high purity silicon. Its initial energy resolution will be about 250 eV at 5.9 keV at the beginning of the SMART-1 mission. Bombardment of solar protons and cosmic particles will deteriorate the operation of the PIN-diode by degrading the energy resolution. This radiation damage will cause higher leakage current across the PIN-diode, which will be the dominant noise source in the system. Mounting Alignment --------------------------------------------------------------------------- Refer to the latest version of the SMART-1 Frames Definition Kernel (FK) [4] for the D-CIXS/XSM reference frame definitions and mounting alignment information. Field-of-View Layout --------------------------------------------------------------------------- This section illustrates the FoV of the XSM detector with respect to the XSM instrument. The computations required to obtain the FoV are also described here. XSM is a single crystal detector, i.e. composed of 1 single pixel. The detector is circular having a diameter of 1.5 mm. The collimating aperture is also circular, with a diameter of 3.6 mm. The distance between the collimating aperture and detector is 2.0 mm. |<----- 3.6mm ----->| | | | | ==`. FoV .'==----- || `. .-. .' || ^ || `. ' ` .' || | Distance between collimating || `. .' || 2.0mm aperture and detector pixel || `.' || | || .' `. || v |`====!.' `.!===='|----- `=====|=========|=====' |=========| |<-1.5mm->| 2.0 FoV = 2 x ( 90 - ATAN -------------- ) = 103.7848 degrees. 1.8 + 0.75 This diagram illustrates the XSM FOV layout in the XSM reference frame. ^ +Xxsm | | --- .__|__. ^ .' | `. | / | \ | . | . | ~104 deg | x-------------> +Yxsm | . +Zxsm . | \ / v `. .' --- ` --- ' | ~104 deg | Boresight (+Z axis) |<----------->| is into the page | | Optics Parameters --------------------------------------------------------------------------- This section contains assignments specifying the XSM optics parameters. The XSM optical parameters are included in the data section below, taken from [3] and [5]: --------------------------------------- parameter XSM --------------------------------------- Focal Length, mm 0.58823581 (1) Number of pixels 1 Detector shape circle Detector size, mm 1.50 IFOV, rad/pixel 1.8113867 (2) Field of view (rad) Nominal 1.8113867 (2) --------------------------------------- (1) XSM has a circular detector of 1.5 mm diameter and a circular FoV of 51.8924 Degrees half cone. The concept of a focal length with respect to the XSM optics is not applicable, although it is possible to define a ``virtual'' focal length. The ``virtual'' focal length can be computed as: 0.75 F = ------------- = 0.58823581 mm tan(alpha) where 0.75 corresponds to the detector radius and alpha is the half cone FoV angle. (2) XSM has a field of view of 51.8924 degrees half cone angle, and it is a single pixel detector, therefore IFOV = FOV. These values are provided in the assignments below, with the same units as in the table. \begindata INS-238700_FOCAL_LENGTH = ( 0.58823581 ) INS-238700_DETECTOR_SIZE = ( 1.50 ) INS-238700_NUMBER_OF_PIXELS = ( 1 ) INS-238700_FOV_ANGULAR_SIZE = ( 1.8113867 ) INS-238700_IFOV = ( 1.8113867 ) \begintext FOV Definitions --------------------------------------------------------------------------- This section contains assignments defining the FOV. These definitions are based on the XSM detector and optics parameters provided in this section, along with the previous section and are provided in a format consistent with/required by the SPICE (CSPICE) function GETFOV (getfov_c). The XSM FOV is defined as a cone with a half angle of 51.8924 degrees. It is defined with respect to the SMART1_XSM frame. The boresight vector is a unit vector along the +Z axis of the frame and the cross-reference vector is a unit vector along the +X axis the frame. \begindata INS-238700_FOV_FRAME = 'SMART1_XSM' INS-238700_FOV_SHAPE = 'CIRCLE' INS-238700_BORESIGHT = ( 0.0 0.0 1.0 ) INS-238700_FOV_CLASS_SPEC = 'ANGLES' INS-238700_FOV_REF_VECTOR = ( 1.0 0.0 0.0 ) INS-238700_FOV_REF_ANGLE = ( 51.8924 ) INS-238700_FOV_CROSS_ANGLE = ( 51.8924 ) INS-238700_FOV_ANGLE_UNITS = 'DEGREES' \begintext Spectral Parameters --------------------------------------------------------------------------- This section contains assignments specifying XSM spectral resolution parameters. Parameter Unit Comments / precision ------------ ------ -------------------------- Energy resolution (1) eV 250 @ 6 keV Time resolution s 16 Energy range keV 1.0 ... 20.0 keV Number of channels number 512 Read out dead time s 0.000005 (1) The Energy resolution is a parameter that varies with respect to time along the mission. Therefore this parameter is not provided in the data section, although it is described in the table. The value provided in the table refers to the one obtained at the beginning of the mission. Due to degradation of the detector, this value is changing (requires calibration before and after each measurement). These values are provided in the assignments below, with the same units as in the table. \begindata INS-238700_INTEGRATION_TIME = ( 16 ) INS-238700_ENERGY_RANGE = ( 1.0 , 20.0 ) INS-238700_NUMBER_OF_CHANNELS = ( 512 ) INS-238700_READOUT_DEAD_TIME = ( 0.000005 ) \begintext Platform ID --------------------------------------------------------------------------- This number is the NAIF instrument ID of the platform on which the instrument is mounted. XSM is mounted directly on the spacecraft. \begindata INS-238700_PLATFORM_ID = ( -238000 ) \begintext