The second satellite of the Quasi-Zenith Satellite System (QZSS)—the Japanese version of the Global Positioning System (GPS)—is scheduled for launch on June 1, and it promises to measure a position on the ground with higher accuracy.
The QZSS is a four-satellite system, and the Japanese aim to put it in full-scale operation starting next fiscal year. It is expected to bring about major changes in society, such as its application to autonomous driving.
The GPS is a positioning satellite widely used in car navigation systems and smart phones. The radio signals transmitted from the satellites are received by GPS receivers, which can determine the distance from the satellites by measuring the amount of time they take to receive the signals.
At least three satellites are required in order to determine a position, and a fourth satellite to determine the current time. Therefore, determining a position usually requires four satellites in total.
“Michibiki” is the Japanese version of the GPS. It has those four satellites.
Satellites have been launched one by one from the Tanegashima Space Center (Kagoshima Prefecture) in H2A rockets. The first satellite has been in operation since 2010. The third and the forth satellites are scheduled to be launched within 2017.
The GPS developed by the United States has been used around the world. However, because it was originally made for military use, if the US restricts its use due to issues like international conflicts, other countries using the GPS will be severely affected. This is why Europe has been developing its own satellites, and Japan has also decided to launch its own new satellite system back in 2011 to stop being dependent on the US.
Reaching 6-cm accuracy
There are around 30 satellites orbiting the earth, but they are not always flying above Japan. When a satellite is far away, sometimes radio signals cannot be received from directly overhead. Tall building and mountains can reflect or interfere with the signals, which leads to inaccuracies in positional information or makes it impossible to locate a position at all.
Michibiki adopts a special trajectory called the Quasi-Zenith orbit that is designed to lengthen the amount of time satellites fly directly overhead Japan. The orbit is oval-shaped like a geostationary orbit but tilted, and the satellites move in a figure-8 pattern.
They reach their highest altitudes at 39,000 km above ground so that they can stay in space longer. With one satellite, the average flight time above Japan is about 8 hours. Therefore, three satellites will allow 24-hour satellite coverage.
With GPS, errors in position determination are usually smaller than 10 meters, but with an additional Michibiki satellite, the positioning will improve to a few meters. When all four Michibiki satellites begin their operation in April 2018, the accuracy will improve to 1 meter. By using electronic reference points on the ground to correct the measurement errors, accuracy will further improve to 6 cm. The aim is to launch seven satellites by fiscal 2023, and to achieve 6-cm accuracy without the GPS that is currently being used.
Economic Effect of 2 Trillion Yen
It is anticipated that Michibiki will bring innovation to the IT industry and will be useful to various businesses and to disaster prevention. The Cabinet Office commented “it would serve as a trump card for the creation of next-generation services such as automation and labor saving.”
In the past, driverless tractors on farms came with the risks of running over the crops with their tires. However, in an experiment conducted after the launch of the first Michibiki satellite, tractors with 30-cm-wide tires were able to run safely through rice plants that were spaced 40 cm apart.
Distinguishing the individual lanes on the roads may be impossible with the current GPS and its positioning accuracy; with Michibiki, it will become possible. This would be useful for autonomous driving. Other experiments with Michibiki have also been conducted, such as carrying baggage to remote islands using a small driverless aerial drone or measuring the exact distances run in a marathon.
The third satellite will be put into a stationary orbit and will be equipped with useful functions in the event of a disaster. With it, even if communication networks shut down, people would still be able to alert disaster prevention organizations on the whereabouts and the safety of their loved ones.
The government hopes to export systems and receivers to Southeast Asia and Oceania, regions under QZSS system coverage. The economic effect is estimated at more than 2 trillion yen in 2020 when the Tokyo Summer Olympics will be held.
Professor Shinichi Nakasuka of Tokyo University, the chairperson of the Committee on National Space Policy, pointed out that “combined with great ideas, this (Michibiki) will have great potential.”
On the other hand, there are unresolved issues, such as how to put receivers to use in wider range of fields. Convincing society with the convenience the system offers seems to be the key to success.
Takeo Kusaka is a senior staff writer of the Sankei Shimbun Science News department
(Click here to read the original report in Japanese.)