Mina Ogawa

Farside Gravity Field of the Moon from Four-Way Doppler Measurements of SELENE (Kaguya)

The farside gravity field of the Moon is improved from the tracking data of the Selenological and Engineering Explorer (SELENE) via a relay subsatellite. The new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside. Several basins have large central gravity highs, likely due to super-isostatic, dynamic uplift of the mantle. Other basins with highs are associated with mare fill, implying basalt eruption facilitated by developed faults. Basin topography and mantle uplift on the farside are supported by a rigid lithosphere, whereas basins on the nearside deformed substantially with eruption. Variable styles of compensation on the near- and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered.

The Astro-H High Resolution Soft X-Ray Spectrometer

We present the overall design and performance of the Astro-H (Hitomi) Soft X-Ray Spectrometer (SXS). The instrument uses a 36-pixel array of x-ray microcalorimeters at the focus of a grazing-incidence x-ray mirror Soft X-Ray Telescope (SXT) for high-resolution spectroscopy of celestial x-ray sources. The instrument was designed to achieve an energy resolution better than 7 eV over the 0.3-12 keV energy range and operate for more than 3 years in orbit. The actual energy resolution of the instrument is 4-5 eV as demonstrated during extensive ground testing prior to launch and in orbit. The measured mass flow rate of the liquid helium cryogen and initial fill level at launch predict a lifetime of more than 4 years assuming steady mechanical cooler performance. Cryogen-free operation was successfully demonstrated prior to launch. The successful operation of the SXS in orbit, including the first observations of the velocity structure of the Perseus cluster of galaxies, demonstrates the viability and power of this technology as a tool for astrophysics.

Soft x-ray spectrometer (SXS): The high-resolution cryogenic spectrometer onboard ASTRO-H

We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of < 7eV in the energy range of 0.3 – 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.

In-orbit operation of the ASTRO-H SXS

We summarize all the in-orbit operations of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H (Hit- omi) satellite. The satellite was launched on 2016/02/17 and the communication with the satellite ceased on 2016/03/26. The SXS was still in the commissioning phase, in which the setups were progressively changed. This article is intended to serve as a reference of the events in the orbit to properly interpret the SXS data taken during its short life time, and as a test case for planning the in-orbit operation for future micro-calorimeter missions.

Vibration isolation system for cryocoolers of Soft X-ray Spectrometer (SXS) onboard ASTRO-H (Hitomi)

Soft X-ray Spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from micro-vibration from cryocoolers mounted on the dewar. This is mitigated for the flight model by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the flight model was verified before launch of the spacecraft in both ambient condition and thermal-vac condition, showing no detectable degradation in energy resolution. The in-orbit performance was also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the micro-vibration could degrade the cryogenic detector is shown.

Development of ultra-thin thermal shield for ASTRO-H x-ray telescopes

ASTRO-H is a general purpose X-ray observatory scheduled for launch in 2014. Two soft X-ray telescopes (SXT) and two hard X-ray telescopes (HXT) will be onboard covering energy range of 0.2 -80 keV. Thermal control of the telescope is similar to that of Suzaku, using a thermal shield (TS) placed in front of the telescope and a electric heater attached on the telescope housing. Thus it is required for a TS to have high soft X-ray transmission, low solar absorptance and a low infrared emissivity. To meet these requirement, TS should be made of thin plastic film coated by metal such as aluminum. Then most important property of TS is mechanical strength to survive various environments at the launch and in orbit. This paper describes designing of TS, method of TS production, various environmental conditions and tests, risk management of treatment of ultra-thin film of TS in the process of production, testing and assembling.

Four-way Doppler tracking for lunar gravity measurements executed by Kaguya and its relay satellite: Okina

SELENE (Selenological and Engineering Explorer) is a Japans lunar probe which was launched and injected into the lunar polar orbit in 2007. The Main Orbiter of SELENE named Kaguya has separated the Relay Satellite: Rstar (Okina). We have executed four-way Doppler measurements which determined the orbit of Kaguya aviating above the lunar far side. The ground station up-links ranging signals, and the relay satellite transponder on Rstar (RSAT-1) relays the carrier waves to Kaguya. Then the transponder on Kaguya (RSAT-2) receives the signals and returns to Rstar, and down-linked to UDSC. Three of four receivers through four-way links acquires signals and tracks Doppler frequency shift with phased lock loops. For that purpose, the receivers should be locked sequentially under the condition of large Doppler shift due to mutual velocities of three moving bodies. The receivers were designed in consideration of the above condition and system operability. Eventually, our system has realized the first case to track two fully moving links between the lunar orbiters and carried out Doppler measurements. Results of the orbit determinations for Kaguya above the lunar far side have shown the anomaly distributions of the gravity fields which could be scarcely found by the conventional two-way RARR methods.

The Result of SELENE (KAGUYA) Development and Operation~!2009-06-28~!2009-08-10~!2009-10-01~!

Japan’s first large lunar explorer was launched by the H-IIA rocket on September 14, 2007 and had been in observation operation from December 21, 2007 to June 11, 2009(JST). This explorer named “KAGUYA (SELENE: SELenological and Engineering Explorer)” has been keenly anticipated by many countries as it represents the largest lunar exploration project of the post-Apollo program. The lunar missions that have been conducted so far have gathered a large amount of information on the Moon, but the mystery surrounding its origin and evolution remains unsolved. KAGUYA investigate the entire moon in order to obtain information on its elemental and mineralogical distribution, its geography, its surface and subsurface structure, the remnants of its magnetic field and its gravity field using the scientific observation instruments. The results are expected to lead to a better overall understanding of the Moon’s origin and evolution. Further, the environment around the Moon including plasma, the electromagnetic field and high-energy particles will also be observed. The data obtained in this way is of great scientific value and is also important information in the possibility of utilizing the Moon in the future. This paper describes the highlight of KAGUYA development and operation with some newly developed engineering achievements including a separation mechanism of sub-satellites from main orbiter as well as the latest scientific accomplishment of KAGUYA. Keyword: SELENE, KAGUYA, H-IIA, JAXA, moon, origin and evolution, ground system, GIS, YouTube, WMS, EPO. KAGUYA SATELLITE SYSTEM OVERVIEW KAGUYA consists of a main orbiter at about 100km altitude and two sub-satellites (Relay Satellite named “OKINA” and VRAD Satellite named “OUNA”) in lunar polar orbit. The main orbiter is also called as KAGUYA. The main orbiter weight at the launch is about 2.9 tons and the size of its main body is 2.1m 2.1m 4.8m. This satellite is 3 axis stabilized and the panel (+Z panel) on which mission *Address correspondence to this author at the SELENE Project, Japan Aerospace Exploration Agency, Tsukuba, 305-8505, Japan; E-mail: sobue.shinichi@jaxa.jp instruments heads are installed is pointed to the gravity center of the Moon. About 3.5 kilo watt is the maximum power produced by a solar paddle. The surface of the KAGUYA is covered with the black color conductive MLI (multi-layer thermal insulators) for conductivity requirement of plasma observation instrument (PACE). The on-orbit configuration of the Main Orbiter is shown in Fig. (1) [1-3]. KAGUYA MISSION PROFILE The Lunar transfer orbit which contributes to reduction of mission risk via two phasing loops around the Earth was adopted. KAGUYA was inserted into a polar elliptical orbit at a perilune altitude of 100 km of lunar. The two subThe Result of SELENE (KAGUYA) Development and Operation Recent Patents on Space Technology, 2009, Volume 1 13 satellites (OKINA and OUNA) were separated from the main orbiter at an apolune of 2,400 km and 800 km respectively. Finally the main orbiter reached the circular orbit at about 100 km altitude and the inclination of polar circular orbit is 90 deg. The apolune altitude of OKINA is determined to measure the gravity field anomaly on the far side of the Moon through relaying the Main orbiter s-band signal effectively. The apolune altitude of OUNA is selected for the low order gravity model coefficient measurements using radio sources on the OKINA and OUNA by VLBI method. When OKINA and OUNA separating from the main orbiter, the spin rotation power were added. This subsatellite separation mechanism which gives the rotational and the translational force simultaneously was originally developed for JAXA’s micro-lab satellite. To consider power generation, octagonal prism shape was selected for subsatellites. All faces of satellite are covered with the solar cells, and each sell produces about 70 watt powers. KAGUYA mission profile is shown in Fig. (2). OKINA was impacted to the far side of the Moon on February 11, 2009 and gravity anomaly observation at the far side of the Moon was successful completed. Fig. (1). The on-orbit configuration of the main orbiter. Lift off Separation from H -IIA Rate Dumping Solar Array Paddle Deployment Sun/Star Capture, High Gain Antenna Deployment Altitude Control of Perigee Lunar Elliptical Orbit Insertion Altitude of Perilune about 100 km

Vibration isolation system for cryocoolers of soft x-ray spectrometer on-board ASTRO-H (Hitomi)

Abstract. The soft x-ray spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from microvibration from cryocoolers mounted on the dewar. This is mitigated for the flight model (FM) by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the FM was verified before launch of the spacecraft in both ambient condition and thermal-vacuum condition, showing no detectable degradation in energy resolution. The in-orbit detector spectral performance and cryocooler cooling performance were also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the microvibration could degrade the cryogenic detector is shown. Lessons learned from the development to mitigate unexpected issues are also described.

Design of the time assignment system for ASTRO-H and its performance before launch

The ASTRO-H, which will be launched in 2015, is the sixth in a series of Japanese X-ray satellites. It is an international mission led by JAXA in collaboration with NASA and ESA, aiming to observe astrophysical objects in the X-ray band from 0.5 to 600 keV. One of the important scientific goals is to understand physical processes in the extreme environments of active and variable astrophysical objects, such as black holes, neutron stars, binary star, and active galactic nuclei. Therefore, a fast timing capability is a key requirement for the mission. According to numerical estimates of scientific performance, absolute times of X-ray events are required to have an accuracy of 300 μs to achieve minimum scientific goals and an accuracy of 30 μs is desired as a goal. The satellite carries a GPS receiver to get the accurate time information, which is distributed from the central computer on board through the large-and-complex SpaceWire network. Distributions of time information are shared in the same lines used for communications of telemetry and commands, and thus propagation delays and jitters affect the timing accuracy of the payload instruments. Further six items are identified as sources of timing errors and are measured on ground to be used in the calibration by off-line software. The time-assignment tasks in the off-line software packages are designed to be common for all the scientific instruments, although the hardware designs for finer timing resolutions are different by the instruments. Measurements of propagation delays in the flight configuration on ground and in-orbit calibration plans are described. The detail description will be submitted to the IEEE TNS paper in near future. This work demonstrates a good example of care points for space-use instruments in the hardware-and-software designs and calibration measurements in order to achieve a fine timing resolution at the micro second order with the middle-sized satellites using the SpaceWire (IEEE1355) network.