A Japanese H-IIA rocket screamed away from the country’s Tanegashima Space Center on Thursday, dispatching an innovative satellite into orbit to join a constellation of spacecraft enhancing the availability and accuracy of Global Positioning System navigation services over the Japanese Islands and Asia-Pacific Region.
The 53-meter tall H-IIA rocket took flight at precisely 0:17:46 UTC, lifting off the ground powered by its cryogenic main engine and a pair of Solid Rocket Boosters that did most of the work for the first minute and a half of the flight before dropping away. H-IIA relied on its cryogenic core stage for six and a half minutes before the second stage took over for a pair of burns – first into a Low Earth Parking Orbit ahead of a critical re-start to boost the 4,000-Kilogram satellite into an elliptical transfer orbit.
Known as QZS-2, Japan’s second Quasi-Zenith Satellite departed the upper stage 28.5 minutes after launch, embarking on a mission to join the first QZS satellite in a specialized Geosynchronous Orbit to be followed by the QZS-3 and 4 satellites later this year to bring the constellation to operational strength in order to open for business by mid-2018.
The Quasi Zenith Satellite System (QZSS) takes a unique spot in the world’s navigation satellite systems in that it augments a foreign satellite constellation in a twofold manner: a) by acting as a member of the GPS constellation and transmitting GPS-compliant navigation signals, and b) relaying augmentation signals generated on the ground to allow receivers to factor corrections into their position calculation to improve location accuracy.
Traditional augmentation systems such as the U.S. Wide Area Augmentation System only provide augmentation signals, but in Japan’s specific case the issue was not only to increase GPS accuracy but also enhance its availability, especially in the country’s urban canyons where tall buildings can block GPS signals and cause outages when not enough satellites are sufficiently high to allow a user on the ground to compute its position which requires inputs from four satellites.
To accomplish this, QZSS hosts three satellites transmitting GPS navigation signals from a specialized Tundra orbit that allows one satellite to be at very high elevation for the entire Japanese territory at any given time (increasing the odds that a full set of four GPS transmitters is available for a user on the ground).
Plans for QZSS first started out in 2002 when development work was initiated by an industry consortium in Japan which later dissolved and the project continued under supervision by JAXA. The U.S. provided clearance for Japan to use the GPS navigation bands in 2006 and the first QZS satellite lifted off atop an H-IIA in October 2010 on a proof-of-concept mission.
Taking up residence in its high-altitude perch, the QZS-1 satellite – nicknamed Michibiki-1 (to guide, to show the way) – entered a multi-month signal characterization and optimization phase. By July 2011, the all signals coming from the satellite were set to healthy and studies showed GPS accuracy with augmentation messages from QZS-1 increased by a factor of up to 2.5.
With the concept for QZSS proven, JAXA contracted Mitsubishi Electric for a total of $526 million to build three additional satellites – two of which will join QZS-1 in Tundra orbit to create 24/7 coverage over Japan while QZS-3 will be headed into a normal Geostationary Orbit from where it can deliver augmentation services to the entire Asia-Pacific Region. The complete four-satellite constellation is expected to be in orbit by the end of the year and begin operations next year.
Based on the flight-proven DS-2000 satellite platform, QZS-2 stands 6.5 meters tall and has a launch mass of 4,000 Kilograms, including 370kg for the navigation payload. At the heart of the navigation package sits a pair of redundant Rubidium Atomic Clocks that provide the ultra-stable timing needed for the generation of the navigation signal that is transmitted via an L-Band antenna.
QZS-2 transmits navigation signals in the