PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "2010-12-03, Chris Howe (RAL) V1" OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = CH1ORB INSTRUMENT_ID = C1XS OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "LOW ENERGY X-RAY SPECTROMETER" INSTRUMENT_TYPE = "SPECTROMETER" INSTRUMENT_DESC = " Instrument Overview =================== C1XS is a compact X-ray spectrometer, it also acts as the interface between the X-ray Solar Monitor instrument and the spacecraft. In the following sections a brief summary is provided of the instrument. For details see the C1XS to Planetary Science Archive ICD and the Data Handling ICD. Science Objectives ================== The table hereunder gives an overview of the scientific objectives. For more information see the EAICD. Table Summary of Scientific Objectives ---------------------------------------------------------------------- Observation | Physical parameter | Specific | Requirement | Performance ---------------------------------------------------------------------- Lunar geochemistry | Spatial distribution of | Nominal C1XS | the major lunar rock | & XSM performance | types | ---------------------------------------------------------------------- Lunar plasma | X-ray emission from | Nominal C1XS interaction | impact of solar wind | performance | electrons on night side | | of moon | ---------------------------------------------------------------------- Investigators and Other Key Personnel ===================================== Prof. Manuel Grande Dr P. Sreekumar Dr. Juhani Huovelin Mr. B. Maddison Dr. Ian Crawford Mr. C. Howe Mr. B. Kellett Dr Mahesh Anand Dr H. Andersson Dr Olivier Gasnault Prof. Andrew Holland Prof. J. N. Goswami Dr A. Shrivastava Dr Vera Fernandes Dr David Smith Dr Katherine Joy Dr Detlef Koschny Dr David Lawrence Dr S. Maurice Mrs S Narendranath Dr T Okada Dr Chris Perry Dr David Rothery Dr Sara Russell Dr C d Dr Bruce Swinyard Dr Mark Wieczorek Dr M. Wilding Instrument Specification ======================== Subsystems ---------- C1XS unit The main C1XS instrument detector head consists of a matrix of 24 X-ray sensitive Swept Charge Devices (SCDs), with collimators to define and limit the field of view (FOV), and filters to inhibit background UV and solar wind ions and electrons. Measurement of low fluxes requires a large sensitive area detector. The incident fluorescence X-rays are detected by means of an array of 24 X-ray sensitive Swept Charge Devices (SCDs). The X-rays create electron-hole pairs and charge packets within the substrate in exactly the same way as in an X-ray sensitive CCD. The SCD is a large area (100mm2) single-pixel silicon X-ray detector. It has the same readout noise, and thus energy resolution characteristics of the very best customized X-ray CCD detectors. These devices can meet the performance requirements at temperatures of 0 to - 20 deg C. But when operating in a proton radiation environment protective measures have to be taken. The trapped and solar protons can generate vacancies in the silicon detector which act as charge trapping sites which degrade the performance in particular the energy resolution. The low energy protons that actually stop in the silicon cause the most damage. The angular/spatial resolution is provided by a 6mm gold plated copper collimator mounted directly above the SCDs. The energy of individual X-rays is recorded and the event time-tagged. Depending on the telemetry capacity available the individual event data is transmitted to ground or a spectrum is accumulated on board and then transmitted. XSM unit The Solar X-ray monitor, which provides the measurement of the fluorescence excitation radiation, will measure the spectrum continuously with a 16s integration time. See XSMINSTR.CAT XSM for details. DPU unit The Data Processor Unit (DPU) has design heritage from the ROSETTA MODULUS experiments. It consists of an RTX2010 microprocessor with RAM,PROM, and EEPROM memory. The main functions of the unit are: - To receive commands from the spacecraft OBDH, - To provide control and timing synchronisation between the C1XS detectors and the Solar Monitor, - To receive data from both the C1XS detector array and the Solar Monitor, and in software to provide a software histogram data compression and time tagging, - To monitor the status and health of the instrument, and to provide housekeeping telemetry data, - To pass data from the instrument to the main spacecraft OBDH. Detector -------- C1XS Four SCDs are mounted on a ceramic substrate with the clocks and signal lines available on pins. SCD electrodes are arranged in a design that, upon clocking, will 'sweep' any charge towards a low capacitance sense amplifier located in one corner of the detector. The design of the sense amplifier is based upon that used in CCD technology, consisting of a very low capacitance sense amplifier and reset transistor, and again operates in exactly the same way as in a CCD. XSM The PIN diode is formed on a square chip and has a circular active are a. Three concentric guard rings surround the active detection area. To reduce the count rate an aperture stop made from a golden annular structure is centred on the surface of the detector. Electronics ----------- The SCD detectors are all operated in parallel under the control of a master waveform generator, located in a FPGA, which provides all the timing signals for driving the SCD electrodes, output amplifiers, the external correlated double sampling (CDS) signal processing electronics and analogue-to-digital converter (ADC). Digital control signals from the FPGA are level-shifted and buffered for driving the SCDs electrodes, again using circuitry already developed for CCD applications. The video signal from each SCD is taken to a CDS Signal Processor via a preamplifier. The signal processor performs the correlated double sampling and A/D conversion. The digitised data is fed through the FPGA which performs data thresholding in the digital domain, and thus provides the first stage of data reduction by only passing on those data that are above a predefined, but programmable threshold. From the FPGA, the data are passed to the Data Processor Unit (DPU). XSM The electronics of the XSM consists of pre-amplifier stages and shaping amplifier, which are in the sensor unit box, and an electronics board in the main C1XS instrument box, which includes further stages of the signal processing electronics. The electrical and data interfaces connect the XSM with the C1XS. There are no direct electrical or data interfaces from the XSM to the spacecraft. FOV --- C1XS C1XS has a planar array of 24 SCD, the field of view (FOV) is 28 deg. XSM 52 deg half cone angle (the angle between the rotational symmetry axis and the surface of the cone.) providing an overall FOV of 104 deg. Compression ----------- One of the C1XS instruments modes/data gathering modes (Type 006) uses Run Length Encoding (RLE) compression was used. This mode was not used during instrument operations. Software -------- The on-board software is responsible for the control of the C1XS & XSM experiments. It collects science and housekeeping data from the experiments and forwards these to the spacecraft. Temperature sensors, voltage monitors, and Spacecraft Power Supply Current monitor is conditioned and digitised on demand from the DPU via the internal backplane bus. The housekeeping parameters are given in C1-C1X-RAL-ICD-0002 Data Handling ICD and are one of the data products in the data set. It receives, interprets and executes telecommands for the experiments The software is designed to allow the most effective collection and transmission of science data by C1XS and XSM consistent with instrument survivability and with the external constraints on resources placed on the instrument. Energy resolution ----------------- C1XS 0.8-20keV range with a resolution of 85 eV at 1.25 keV XSM 1.2-20keV range with a resolution of 200 eV at 5.9 keV Mechanical design ----------------- The C1XS instrument weighs 5.56 kg and has physical dimensions of approximately 250 mm wide by 150 mm tall by 190 mm deep (with the door closed). It is functionally and thermally divided into two parts. The larger section is the electronics module. This module contains the instrument main power switching and conditioning circuits, the switched mode power supply and five circuit boards. The circuit boards are arranged side-to-side, and are held in place with wedge-locking card guides. The electronics enclosure is a thick-walled (4 mm) aluminium box, which acts as the instrument second section is the detector module. This houses the swept charge device (SCD) X-ray detectors together with their associated drive electronics radiation shielding and cooling interface. Three SCD modules plug into the detector module. Each module contains two strips of SCDs with 4 SCDs in each strip. The SCD strips are mount ed on a 3 mm copper and a 6 mm tantalum heatsink, which is thermally isolated from the rest of the module. The tantalum is included for proton shielding but also provides additional thermal mass. The coppe r protrudes from the bottom of each SCD module to allow the external radiator to be connected to the instrument via a heatpipe. To constrain the detector field of view, a machined copper collimator is mounted above each detector. It provides an angular acceptance of 28 deg, from the 100 km orbit of Chandrayaan-1 the C1XS field of view is equivalent to a 50 km square on the surface of the Moon. The C1XS interface to the spacecraft is via the electronics module and the instrument is bolted down to the Chandrayaan-1 spacecraft deck using 4 screws to provide a good thermal interface between the instrument and the spacecraft panel/radiator. Operational Considerations -------------------------- The SCD temperatures must be less than -5 deg C to obtain reasonable SCD performance. Calibration ----------- The data contained within this archive is uncalibrated. Platform Mounting ----------------- see INSTHOST.CAT for details and drawing. Operating Modes / Data Collecting Modes --------------------------------------- XSM The XSM instrument has a single operating mode. On transistion to operating mode the detector views a calibration source for 300 s. The source is removed from the detector field of view for the duration of the science data collection. 300 s prior to leaving operating mode the calibration source is placed in the field of view. C1XS The C1XS instrument has three operating modes: 1) Standby; Housekeeping data is produced 2) Operating; The SCD are powered up and science data collected. 3) Resting; The instrument is waiting for the SCD temperatures to be below -5 degC. Acronyms and Abbreviations ========================== C1XS Chandrayaan-1 X-Ray Spectrometer ISRO Indian Space Research Organisation ESA European Space Agency SCD Swept Charge Device FOV Field Of View XSM X-ray Solar Monitor ASIC Application Specific Integrated Circuit DPU Data Processing Unit OBDH On Board Data Handling CDS Correlated Double Sampling ADC Analogue to Digital Converter CCD Charge-Coupled Device FPGA Field Programmable Gate-Array RLE Run Length Encoding eV Electron Volt keV Kilo Electron Volt " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "Howe_et_al_2009_1" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END