Tatsuaki Okada

The Hayabusa will rendezvous 25143 Itokawa, an S (IV)-class near-earth asteroid, in September to October, 2005. The XRS is among the remote sensing instruments aboard. We present here the main objectives of the XRS observation. The XRS will determine major elemental composition of surface of the asteroid. Elemental variation will be surveyed by asteroid rotation in longitudinal direction, maybe with spatial resolution of 60 degrees. The XRS always detect such major elements as Mg, Al, Si, and S, but it also can do for higher atomic number elements such as Ca and Fe, especially during the occurrence of solar flare. Furthermore, microscopic roughness of the surface is informed by observation at various solar phase angles due to particle size effect in X-ray fluorescence. Since thermal design of the XRS has been well calibrated, thermal radiation intensity off the asteroid surface will be estimated by monitoring the temperature profile during descent of the spacecraft for asteroid touchdown.

SELENE XRS will determine major elemental composition of lunar surface. In this study, we will introduce the intelligent observation system of XRS with onboard computer-control.

XRS ( X-Ray fluorescence Spectrometer ) which will be installed on SELENE , will observe x-ray fluorescence emitted from the lunar surface and quantify the major elemental composition of the lunar surface. Determination accuracy for major elemental composition of the lunar surface can be enhanced by comparing spectrum from the lunar surface with one from the standard sample. In this study , we attemped to evaluate the accuracy of elemental composition ratio acquired by this method.

The SELENE (SELenological and Engineering Explorer) is a Japanese lunar polar orbiter with 14 scientific instruments. The XRS is to map major elemental composition in 20km spatial resolution, to provide the clue to understanding the lunar evolution. Energy resolution and efficient detection area of the XRS has been much improved by using arrays of Si CCD with 100cm² detection area and ultra-thin beryllium window for better transparency at low energy. We present the specification, performance and current status of the XRS and method of remote X-ray spectrometry.

The first global remote X-ray and gamma-ray spectrometry have been proposed for the Bepi Colombo mission, to map abundances of major and radioactive elements on the surface of Mercury. The Mercury Planetary Orbiter (MPO) that orbits around the relatively low altitude (400 x 1500 km) appropriate for surface global mapping. We present the outlines of X-ray and Gamma-ray spectrometers that have been designed with new technologies such as the X-ray detector using GaAs array on ASIC as well as the low-power stirling cryostat for pure germanium Gamma-ray detector.

We have been studying the instrumentation onboard the lander and rover for a lunar geological exploration with the SELENE-B that demonstrates the next generation technologies of a pin-point and soft landing on planetary surfaces of scientific interest and an autonomous controlled scientific rover. In this mission, imaging spectroscopy and multi-band imagery will characterize the target site around a crater central peak and gamma-ray spectrometry will measure radioactivity along the rover's track. Lunar rocks and soils at the target crops or around the lander are selected to brush up and grind for detailed analyses by microscopy and x-ray fluorescence/diffraction method. The systematic configuration of instruments is also introduced.

The SELENE (SELenological and Engineering Explorer) is a Japanese lunar polar orbiter and performs lunar global mapping with more than 10 scientific instruments. The XRS will map major elemental composition in 20km spatial resolution and provide the clue to understanding the lunar evolution. For that purpose, the XRS has been designed to improve energy resolution and efficient detection area. Then the X-ray detector has arrays of CCD with 100cm² detection area, and is kept below -50C by radiation cooling. Ultra-thin beryllium window are developed for better transparency at low energy. We present the specification and the current status of the XRS as prepared for the interface test, as well as the plan of pre-flight tests and observation plan.

We present the results of initial operation, the current status, and the future observation plan of the X-ray fluorescence spectrometer (XRS) onboard Hayabusa, which was launched with the fifth M-V launch vehicle on May 9th, 2003. The XRS observes X-rays characteristic of elements excited by solar irradiation, to determine major elemental composition of asteroid Itokawa (1998SF36). Then we classify the S-class asteroid and prospect the degree of evolution processes. During the two-year long cruising phase, the XRS are checked out its function and the detectors against radiation damage, and observes X-ray bodies such as super nova remnants or active galactic cores as well as cosmic backgrounds of X-rays for in-flight calibration. The XRS also monitors solar X-rays using the standard sample. Flight demonstration of the newly developed onboard computer proves usability for more than 20 days.

X-ray fluorescence spectrometer (XRS) onboard HAYABUSA (MUSES-C) spacecraft that was launched by the fifth M-V launch vehicle on 9 May 2003. The XRS has plans to observe supernova remnants (SNR), active galactic nuclei (AGN) and cosmic X-ray backgrounds for in-flight calibration and scientific observation during the transfer and return phase. When HAYABUSA spacecraft performed tests of the ion electric propulsion system (IES) and its heater control system, the XRS observed spectra were noisy. This study shows method of reducing heat noise.

X-ray spectrometer onboard HAYABUSA spacecraft has a standard sample to perform comparative analysis. Comparing with the X-rays from the standard sample and asteroid surface, the dependency of induced X-ray, solar X-rays, is reduced [1].<BR>It takes more than 2 years to reach the Asteroid, and the temporal variance of the XRS performance is investigated periodically by the observation of the X-rays from Cosmic X-ray Backgrounds, astronomical X-ray bodies, and the standard sample.<BR>From 28 May 2003 to 30 May 2003, just after the launch of HAYABUSA, XRS observed an X-ray source: SCO-X1 [2]. The observation continued two days due to the initial checkout. Fortunately, an X.1 class solar flare happened during this term. The spectra from the standard sample were composed of Ca and Si line spectra together with Mg, Al, and Si line spectra. These data is available for the XRS in-flight calibration: energy gain and intensities. In addition, model parameter is determined by this data.<BR>Yamamoto et al reported that the energy calibration, comparison of the energy flux between GOED 10 and XRS, and the comparison of the observation and calculation using thess data [3]. The energy calibration of the line spectra: Mg, Al, Si, Ca, and Fe, was determined within 1% accuracy comparing with ⁵⁵Fe calibration data before launch. Temporal variation of energy flux obtained by XRS showed the consistency with that obtained by GOES 10 satellite. Moreover, the model calculation was performed and compared with the observation. The comparison showed the background noise in the energy range 0.5-3keV clearly existed. This noise was serious problem to determine the intensities of Mg, Al, and Si X-ray fluorescence spectra.Therefore, we report here the method to remove this background noise, and the effect of the method.<BR>[1] Okada, T., Fujiwara, A., Tsunemi, H., and Kitamoto, S. 2000. X-ray fluorescence spectrometer onboard MUSES-C, Adv. Space Res. 25, 345-348.<BR>[2] Arai et al, 2003. Proc. ISAS Lunar Planet. Symp.<BR>[3] Yamamoto et al, 2003. Proc. ISAS Lunar Planet. Symp.<BR>

Unmanned lunar geologic exploration of a crater&rsquo;s central peak to investigate subsurface layering is discussed. Rover-lander corporative mission is executed. From a lander which is within 500m from the frank of the central peak, a rover should make a round-trip to the frank and bring samples back to the lander. Multi-band camera, gamma-ray spectrometer, rock-coring mechanism, sampling and transportation mechanism should be on board the rover. Detailed analyses of the returned samples including microscopic spectroscopy and X-ray spectrometry and diffraction should be done in the lander.

We are developing X-Ray fluorescence spectrometer onboard MUSES-C which will be launched in 2002. Charge-coupled device (CCD) is used to detect X-Ray fluorescence from the surface of asteroid. We have made an apparatus to evaluate the CCD with various conditions. We will report about this apparatus and the performance of CCD itself when temperature and driving pulse voltage are varied.

We are developing an X-Ray fluorescence Spectrometer (XRS) onboard the asteroid probe MUSES-C. Variation of solar X-rays must be considered to analyze major elements quantitatively. XRS observes solar X-rays indirectly using a standard sample. Therefore X-rays from a planetary surface can be calibrated with those from a standard sample in addition to investigation of the spectra and intensities of solar X-rays. We make a model of solar X-ray flux and simulate X-rays observed from a standard sample under various solar conditions. We estimate inversely solar X-rays with calculated emissions and investigate suitable integration times.

We are developing an X-Ray fluorescence Spectrometer (XRS) onboard the asteroid probe MUSES-C. XRS contains 5 CCD chips. XRS will not carry in-flight calibration sources. Therefore we will observe cosmic X-ray objects for the calibration with XRS during the cruise. We performed numerical simulation of observing some known X-ray objects. Those simulations were run with exposure time about 3 hours, based on the best-fit models to the ASCA SIS spectra.

We are developing an XRF/XRD instrument for future planetary landing probes. Using this CCD-based device, major elemental and mineral composition is determined through x-ray fluorescence and diffraction method. We have designed and fabricated a miniaturized laboratory model with a two-dimensional CCD. We considered a geometric configuration of the CCD and samples to improve precision of measurement. We investigated a method of onboard data analysis to decrease an amount of telemetry data. We report results of measurements and analyses for XRF and XRD of major minerals.