JAXA and the Geospatial Information Authority of Japan (GSI), the Ministry of Land, Infrastructure, Transport and Tourism have established a cooperative framework to provide precise orbit products for the global navigation satellite system (GNSS). The quality of the products calculated under this cooperative framework has been accepted by the International GNSS Service (IGS), and the precise GNSS products have now been made available to the public. AKIYAMA Kyohei of the Satellite Navigation Unit explains the project.

“Satellite orbit product represents the time series of satellite positions. For a navigation satellite system such as the US GPS and Japanese Quasi-Zenith Satellite System (QZSS or aka "MICHIBIKI"), the more accurate orbit product makes it possible to calculate the more accurate position on Earth (the receiver's position). That is why we have been working to improve the accuracy of orbit products.”

Among the orbit products for navigation satellites, the combined solutions calculated by the IGS is currently considered the most reliable.

“The IGS combined solutions are calculated by the IGS through combining the orbit solutions provided by various organizations around the world. Because of their extremely high accuracy, they are used, for example, to realize the terrestrial reference frame on Earth and to observe crustal movements. In other words, they play a very important role especially in earthquake-prone Japan.”

Heretofore Japan has been a "user" of the IGS combined solutions when needed. The IGS has now recognized the quality of the products calculated by JAXA and GSI, though, so Japan is in a position to contribute to the IGS combined solutions by providing its own products.

“Our GNSS products are calculated by the GSI using the GNSS orbit and clock analysis software MADOCA developed by JAXA since 2011, and JAXA makes improvements to the software based on the feedback from the GSI. The processing of the software is extremely detailed and must take into account all the forces experienced by the satellite, including not only the gravity of the Earth, Sun, and Moon, but also the radiation pressure from the sun and the Earth. Through repeated improvements based on the physics and empirical model, we have finally achieved the quality required for incorporation into the IGS combined solutions.”

This project should enable Japan to independently and reliably maintain and manage the terrestrial reference for positioning based on their own GNSS products without relying on other countries.

“I believe that navigation satellites are part of social infrastructure, and I hope we can continue to improve the quality of their orbit products.”