In Operation

Project Topics


December 20, 2012 Updated

MICHIBIKI: Current status of rubidium atomic clock 2

The First Quasi-Zenith Satellite “MICHIBIKI” is equipped with two rubidium atomic clocks, Clock 1 for the operation system and Clock 2 for the spare system, to construct the redundant structure. The former is currently used for generating positioning signals.
At 2:40 a.m. on Dec. 19 (Japan Standard Time), we found an anomaly in Clock 2, and we have not been able to restore its normal operations. We keep generating and providing positioning signals normally using Clock 1 while investigating the anomaly cause and studying countermeasures.

Overview


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Quasi-zenith Satellite System (QZSS) watching Japan from above


As mobile phones equipped with car navigation or GPS (*1) have become widespread, positioning information using satellites is imperative to our lives. To specify a location, we need to receive signals from at least four satellites. However, in some urban or mountainous areas, positioning signals from four satellites are often hampered by kyscrapers or mountains, and that has often caused significant errors.
The QZSS consists of a multiple number of satellites that fly in the orbit passing through the near zenith over Japan. By sharing almost the same positioning signals for transmission with the currently operated GPS as well as the new GPS, which is under development in the U.S., the system enables us to expand the areas and time duration of the positioning service provision in mountainous and urban regions in Japan.
Furthermore, the QZSS aims at improving positioning accuracy of one meter to the centimeter level compared to the conventional GPS error of tens of meters by transmitting support signals and through other means.
In order to have at least one quasi-zenith satellite always flying near Japan's zenith, at least three satellites are necessary. The first quasi-zenith satellite "MICHIBIKI" carries out technical and application verification of the satellite as the first phase, then the verification results will be evaluated for moving to the second phase in which the QZ system verification will be performed with three QZ satellites

Future improvement by the QZSS

Some of you who usually use car navigation may feel that the current system has enough functionality. However, the satellite positioning system is not just for car navigation. It is imperative for mapping, measurements for construction work, monitoring services for children and senior citizens, automatic control of agricultural machinery, detecting earthquakes and volcanic activities, weather forecasting and many other applicable fields. Therefore, an improvement in accuracy and reliability is called for from various areas. New service using more accurate positioning data may be born when positioning accuracy is further improved by the QZSS thus we can capture location information with an error of within one meter.

Future MICHIBIKI activity

The MICHIBIKI was launched by the H-IIA Launch Vehicle No. 18 on September 11, 2010. After being injected into the quasi-zenith orbit, the MICHIBIKI is now under a three-month initial functional verification. Then, its technical and application verification will be carried out in cooperation with concerned organizations. (During the verification, we can receive signals from the MICHIBIKI. However, in the early stage, we will place an alert flag as we verify the accuracy of information contained in its signals. To use the MICHIBIKI, please use a special receiver, which is specially processed to not exclude MICHIBIKI data from your positioning calculation even though an alert flag is in effect. In addition, please be aware that positioning accuracy may deteriorate compared to that using only the GPS.)
You cannot receive MICHIBIKI signals through a commercially available GPS receiver such as a car navigation system, but you can do so by modifying a conventional device. We heard that there are some machines that can receive MICHIBIKI signals by improving software. JAXA and related organizations are now promoting receiver manufacturers to cope with MICHIBIKI signal reception.

Major Characteristics

International Designation Code 2010-045A
Launch Date 20:17, September 11, 2010 (JST)
Launch Vehicle H-IIA Launch Vehicle No.18
Location Tanegashima Space Center
Shape 2 box shape with wing-type solar array paddles
2.9m in depth x 3.1m in width x 6.2m in height
(Length between the tips of the paddles: 25.3m)
Weight Approx. 4000kg
Orbiter Quasi-Zenith Orbit
Altitude Approx. 32000 - 40000km
Inclination Approx. 40 degrees
Period 23 hours 56 minutes