d 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 L1, L2 and L5 bands which are processed by ground-based receivers like any other GPS signal. Augmentation messages are not generated onboard the satellite but on the ground through monitoring of GPS signal variability by an array of ground stations across Japan and surrounding regions which detect GPS clock errors and other factors like signal delay caused by changes in Earth’s ionosphere.
Correction data for these varying factors is uplinked to the QZS satellite which immediately re-transmits it to any enabled receiver in its footprint which can then apply the corrections to its navigation solution to yield a more accurate location, on average with one-meter accuracy.
QZSS delivers the L1-SAIF (Sub-meter class Augmentation with Integrity Function) that is compatible with the U.S. Wide Area Augmentation System, plus an L1-SAIF+ signal that allows receivers to acquire GPS position lock faster and provides space for messages for disaster relief. Additionally, an experimental signal designated L-EX is compatible with the European Galileo satellite constellation coming on line by the end of the decade.
QZS-4 will be an identical carbon copy of the second satellite and complete the three-satellite constellation that allows one of the satellites to be almost directly overhead (zenith) as seen from a user in Japan. The QZS-3 satellite will be slightly heavier, weighing in at 4,700 Kilograms, and aiming for a 15-year mission in the traditional Geostationary Orbit from where it can relay augmentation messages to a large area.
Called upon for the launch of QZS-2 was Japan’s trusted H-IIA rocket that debuted back in 2001 and has flown 33 times prior to Thursday’s mission, logging 32 successful missions.
Standing 53 meters tall, the launch vehicle consists of a stack of two four-meter diameter stages, each powered by a single liquid-fueled engine, plus two SRB-A3 Solid Rocket Boosters on the first stage to deliver the initial kick needed to send the satellite toward its high-energy orbit. At liftoff, H-IIA weighs 285 metric