This page provides an overview of the Satellites in the Quasi-Zenith Satellite System Constellation. Technical parameters of the indivdual satellites and related conventions applied within the MGEX project are summarized in the Spacecraft Characteristics section. Furthermore, a list of Events of interest for the QZSS data processing is given.
The Quasi-Zenith Satellite System (QZSS) currently comprises three satellites in an inclined geo-synchronous orbit and one satellite in geo-stationary orbit.
|Common Name||SVN||Int. Sat. ID||NORAD ID||PRN||Notes|
|QZS-1 (Michibiki)||J001||2010-045A||37158||J01||launched 2010/09/11|
|QZS-2 (Michibiki-2)||J002||2017-028A||42738||J02||launched 2017/06/01|
|QZS-3 (Michibiki-3)||J003||2017-048A||42917||J07||launched 2017/08/19|
|QZS-4 (Michibiki-4)||J004||2017-062A||42965||J03||launched 2017/10/09|
A comprehensive collection of technical information with associated references for the QZS-1 spacecraft can be obtained at ESA's eoPortal . The Cabinet Office provides QZSS Satellite Information and Operational History Information on a dedicated web site. Physical key parameters of the spacecraft are summarized below:
|Launch mass||4100 kg||4000 kg||4700 kg||4000 kg|
|Dry mass||1800 kg||1550 kg||1700 kg||1550 kg|
|Body size||2.35 m x 2.35 m x 5.70 m||2.40 m x 2.40 m x 6.20 m||2.4 m x 2.4 m x 5.4 m||2.40 m x 2.40 m x 6.20 m|
|Solar array size||n/a||n/a||n/a||n/a|
|Span width||25.25 m||19.00 m||19 m||19.00 m|
|SRP acceleration||156 nm/s2||n/a||n/a||n/a|
The QZS-1 spacecraft is equipped with a primary L-band antenna (L-ANT) for transmission of the
L1 C/A, L1C, L2C, L5, and L6 LEX signals, whereas a separate (LS-ANT) antenna is used for the
L1 SAIF signal. In addition, a laser retroreflector array (LRA) is provided to enable precise
distance measurements using satellite laser ranging.
Fig. 1 QZSS spacecraft reference system and sensor locations. Reproduced from DOI 10.1016/j.asr.2015.06.019 with permission of Elsevier; satellite image courtesy JAXA.
Phase center coordinates of the GNSS antennas and the LRA as recommended for QZS-1 processing within the MGEX project are provided in the following table. All values refer to the spacecraft coordinate system illustrated in Fig. 1. The spacecraft coordinate system is aligned with the main body axes and originates near the center of the launch adapter plane. In accord with IGS conventions, the individual axes are aligned in the following way:
- the +zIGS-axis is oriented along the boresight direction of the L-ANT antenna;
- the +yIGS-axis is parallel to the rotation axis of the solar panels and oriented such that the LRA is located in the first quadrant of the xIGS/yIGS-plane relative to the L-ANT;
- the +xIGS-axis completes a right handed system;
A machine-readable version of the phase center offset information for QZS-1 is provided as part of the IGS14 ANTEX product.
|Coordinates (w.r.t. origin)||Coordinates (w.r.t. CoM)||Reference|
|L-ANT||L1||0.0 mm||0.0 mm||+5017.8 mm||-0.9 mm||+2.9 mm||+3197.9 mm|||
|L-ANT||L2||0.0 mm||0.0 mm||+4812.8 mm||-0.9 mm||+2.9 mm||+2992.9 mm|||
|L-ANT||L5||0.0 mm||0.0 mm||+4897.8 mm||-0.9 mm||+2.9 mm||+3077.9 mm|||
|L-ANT||L6||0.0 mm||0.0 mm||+4967.8 mm||-0.9 mm||+2.9 mm||+3147.9 mm|||
|LS-ANT||L1||-1150.0 mm||-700.0 mm||+4835.0 mm||-1150.9 mm||-697.1 mm||+3015.1 mm|||
|LRA||+1150.0 mm||+550.0 mm||+4505.3 mm||+1149.1 mm||+552.9 mm||+2685.4 mm|||
|CoM (BoL)||+0.9 mm||-2.9 mm||+1819.2 mm|||
|CoM (Jul 2012)||+0.9 mm||-2.9 mm||+1819.9 mm|||
|CoM (EoL)||+0.9 mm||-3.1 mm||+1851.2 mm|||
The attitude law that describes the orientation of the QZS-1 satellite in space, depends on the elevation of the Sun relative to the orbital plane (also known as β angle):
- For |β|>20° the satellite is operated in "yaw-steering mode". Here, the +zIGS-axis is pointed to the Earth, while the yIGS-axis is oriented perpendicular to the plane made up by the Sun, Earth, and satellite. Furthermore, xIGS-axis is oriented such that the Sun is always located in the +xIGS hemisphere, while the -xIGS-axis points to "deep space" at all times to minimize heating of the onboard clocks. The QZS-1 yaw-steering mode matches the standard attitude law of the GPS, GLONASS, and Galileo satellites.
- For |β|<20° the satellite is operated in "orbit normal mode". While the +zIGS-axis is again pointed towards the center of the Earth, the +yIGS-axis is held perpendicular to the orbital plane and parallel to the orbital angular momentum vector. The +xIGS-axis is roughly oriented in anti-flight direction.
Further details and the mathematical formulations of the QZS-1 attitude modes are provided in  and .
Satellite property information and operational history information of tnewer IGSO satellites QZS-2 and QZS-4 as well as the GEO satellite QZS-3 are/will be provided by the Cabinet Office in different documents available at a specific website. These documents include information about reference frames, attitude law, mass and center of mass, antenna phase center corrections, geometry, group delays, and transmit power.
References Kogure S., priv. comm. (20 July 2012)
 QZS-1 ILRS SLR Mission Support Request Form - Retroreflector Information
 Ishijima Y., Inaba N., Matsumoto A., Terada K., Yonechi H., Ebisutani H., Ukawa S., Okamoto T., "Design and Development of the First Quasi-Zenith Satellite Attitude and Orbit Control System", Proceedings of the IEEE Aerospace Conference, March 7-14 2009, Big Sky, MT, USA, (2009). DOI 10.1109/AERO.2009.4839537
 Montenbruck O., Schmid R., Mercier F., Steigenberger P., Noll C., Fatkulin R., Kogure S., Ganeshan A. S. (2015) GNSS satellite geometry and attitude models. Advances in Space Research 56(6):1015-1029. DOI 10.1016/j.asr.2015.06.019
 Cabinet Office (2017) QZSS Satellite Information
List of events before 2017.
|2017/02/17||08:49 - 09:16||QZS-1||J01||Mode change YS to ON||DLR analysis|
|2017/03/27||07:59 - 08:28||QZS-1||J01||Mode change ON to YS||DLR analysis|
|2017/04/07||10:13 - 23:21||QZS-1||J01||ON mode, slow yaw exit (4h)||DLR analysis|
|2017/04/08||15:15 - 18:36||QZS-1||J01||ON mode due to orbit maneuver||DLR analysis, NAQU 2017008 - 010|
|2017/04/09||16:17 - 18:36||QZS-1||J01||ON mode due to orbit maneuver||DLR analysis, NAQU 2017008 - 010|
|2017/06/01||QZS-2||J02||Launch of QZS-2|
|2017/06/27||10:17 - 12:37||QZS-2||J02||First L5 signal transmission||CONGO/MGEX monitoring|
|2017/07/27||22:00||QZS-2||J02||Start of regular broadcast ephemerides transmission||CONGO/MGEX monitoring|
|2017/08/19||QZS-3||J03||Launch of QZS-3|
|2017/08/20||09:42 - 10:06||QZS-1||J01||Mode change YS to ON||DLR analysis|
|2017/09/10||~09:00||QZS-3||J07||Start of signal transmission||CONGO/MGEX monitoring|
|2017/09/15||09:05||QZS-2||J02||QZS-2 declared usable||NAQU 2017074|
|2017/09/25||Afternoon||QZS-1||J01||Start of transmission outage||CONGO/MGEX monitoring|
|2017/09/26||Afternoon||QZS-1||J01||End of transmission outage||CONGO/MGEX monitoring|
|2017/10/09||22:01||QZS-4||J03||Launch of QZS-4||NAQU 2017091|
- QZS-1 operational history information is as well as. complementary information on the current status of QZSS is provided at the QZSS web site of the Cabinet Office. This site also provides the QZSS Interface Specification and Notice Advisory to QZSS Users (NAQU) messages.
- Supplementary information related to Michibiki-1 can also be found at the QZSS project web site of JAXA.
- QZSS employs distinct PRNs for the L1 SAIF SBAS signal (PRN(SAIF) = 183, 184, ...) and the other ranging signals (PRN(std) = 193, 194,...). In order to ensure a unique RINEX satellite number for each QZSS satellite, it is recommended to consistently use the satellite number "Jnn" with n = PRN(std)-193=PRN(SAIF)-183. Use of an SBAS RINEX satellite number "Snn" with nn = PRN(SAIF)-100 is deprecated.
- The experimental remote synchronization system for an onboard crystal oscillator (RESSOX) of QZSS aims at the use of a ground-controlled low cost oscillator onboard a GNSS satellite as an alternative to a high-performance atomic frequency standard.