1. Why a satellite that stays put is a poor fit for Japan's cities and valleys
A "stationary" satellite really does exist. It is called a geostationary satellite. It circles high above the equator at about 36,000 km (22,000 miles), and one trip around takes about a day, the same time Earth takes to spin once. So from the ground it seems to hang at one spot, which is why TV dishes can point at one fixed place in the sky.
Japan sits well north of the equator, around latitude 35° N, so a geostationary satellite appears low in the southern sky[10]. A mountain, a tall building, or a stand of trees in that direction can block the signal. Japan's Cabinet Office, which runs the system, says that urban and mountain areas had trouble because buildings and trees blocked signals and fewer navigation satellites were in view[1]. The Cabinet Office has also pointed to farmland, where mountains and trees can get in the way in the same manner[8].
One of the engineers on the first Michibiki satellite explained the choice in a Cabinet Office interview. A positioning satellite should be seen at a high angle above the horizon. And if several satellites all sit in the same direction, as geostationary ones do, the geometry is poor and accuracy suffers. So the team wanted at least one satellite always near overhead, and for that they chose an orbit that draws a figure eight[4].
Why not simply hold a satellite over Japan? The Cabinet Office says that would be ideal, but it cannot be done, because Earth's pull and the outward force of the orbit do not point in the same direction[2]. The best available answer is a satellite that keeps moving but stays near Japan for a long time.
Quick vocabulary: the zenith is the point straight overhead. Michibiki's full name in English is the Quasi-Zenith Satellite System (QZSS). "Quasi" means "almost," because these satellites are near the zenith for hours but are not stuck there[2]. (Michibiki is a Japanese word that roughly means "guidance." Some people call the system "Japanese GPS"[1].)
2. Tilting a stationary orbit by about 40 degrees turns it into a figure eight
Take the geostationary orbit and tilt it. Now the satellite cannot stay above the equator. Over one lap it swings north of the equator, then south, then back. The Cabinet Office calls this an inclined geosynchronous orbit, and says the path traced on the ground below it is a north-south symmetric figure eight[2].
Michibiki's tilt is about 40° (JAXA lists about 40° for the first satellite), and one lap takes 23 hours 56 minutes, the same as Earth's spin[3]. A simple way to picture it is that, because the satellite takes about as long to orbit Earth as Earth takes to spin once, its path over the ground repeats roughly once a day, so the figure eight stays over about the same part of the world. That picture is my own summary, not a quote from the sources.
But Michibiki's figure eight is not the plain symmetric kind. The Cabinet Office describes it as a north-south asymmetric figure eight[2]. The next section explains what makes it lopsided, and why that helps Japan.
3. Why the satellite lingers over Japan: slow in the north, fast in the south
To make the figure eight lopsided, the orbit is stretched slightly into an ellipse, an oval. In the northern half of the figure, the satellite is farther from Earth and moves more slowly. In the southern half, it is closer and moves faster[2]. JAXA gives the first satellite's distances as roughly 32,000 km at its closest and 40,000 km at its farthest[3].
The result is that the satellite spends about 13 hours over the northern half and about 11 hours over the southern half[2]. Japan is in the northern half, so the satellite spends the longer part of each day above it.
Why slower when farther away? The Cabinet Office page states the result but not the reason. A standard way to understand it is Kepler's second law: an imaginary line from Earth to the satellite sweeps out equal areas in equal times, so when the line is long the satellite does not need to travel as far along its path. If you want a rough feel, think of a bike rolling up a hill and slowing down, then speeding up as it rolls down. A satellite is not a bike, since it never falls to the ground, so treat this only as a picture. The explanation by Kepler's law is mine, not the Cabinet Office's.
4. Three satellites take eight-hour turns, so one is always near overhead
How long does one satellite stay high in the sky? The Cabinet Office gives figures for Tokyo. One satellite in this orbit stays above 70° of elevation (elevation is the angle up from the horizon; straight overhead is 90°) for 8 hours, above 50° for 12 hours, and above 20° for 16 hours[2].
Each satellite stays above 70° for 8 hours. A day has 24 hours, and the three satellites are spaced so that they take turns, about 8 hours each, so at least one is above 70° at any moment. It is near the zenith, but, as the Cabinet Office stresses, it does not stay at the exact zenith[2].
The Cabinet Office also describes what you would see from near Tokyo if you could watch the three satellites all day: they appear one after another from the south-southeast horizon, make a slow loop near the top of the sky, then head down toward the south-southwest. Near Tokyo they do not drop below the horizon, but skim it and rise again[2]. (They are far too faint to see with your eyes.)
In a canyon of buildings, the southern sky is often blocked while the sky straight above is open. A satellite near the zenith can send its signal through that gap.
5. Keeping the figure eight in shape: the first satellite's 13 years
Can a satellite just be launched and left alone? The first Michibiki was launched on September 11, 2010, on an H-IIA rocket from the Tanegashima Space Center, on an island in southern Japan. About two weeks later it was in its figure-eight orbit, it moved to regular operation in December 2010, and it ended its work on September 15, 2023, after 13 years[4].
Keeping the orbit takes upkeep. For a navigation satellite, firing thrusters disturbs the orbit and interrupts service for a while, so the engineers wanted to fire them as little as possible. According to the interview, the first satellite needed an orbit correction only about once every 180 days, and one of the engineers said no earlier Japanese satellite had such a low frequency[4].
6. Why Japan is still adding satellites, and what happened to number five
A figure eight only works if there are enough satellites. The service began in November 2018 with four: three in the figure-eight orbit and one geostationary satellite[5]. Satellites 2, 3 and 4 were launched in 2017, and a replacement for the first satellite followed in October 2021[9].
The goal is seven. The plan adds one satellite each in the figure-eight orbit (number 5), a geostationary orbit (number 6), and a third kind called quasi-geostationary orbit (number 7). The Cabinet Office says that with seven, at least four Michibiki satellites would always be above Japan, so Michibiki alone could keep positioning going without help from other countries' navigation satellites[5]. Satellite 6 was launched in February 2025[9], and its services began in July 2025[10].
Then came a setback. On December 22, 2025, an H3 rocket carrying satellite 5 failed. The second stage's second engine burn did not start properly and stopped early, so the satellite did not reach its orbit, and no radio signal from it was received[8]. Ordinary positioning service was not affected, because it is normally used together with GPS and other countries' satellites. Without them, Michibiki alone would be less stable[8].
On August 11, 2026, an H3 rocket launched satellite 7. JAXA reports that it separated about 29 minutes after liftoff and was placed in its designated orbit[6]. That was not yet the end of the trip: the minister in charge said it would move to its final orbit and spend a few months in testing before operation begins[7].
So, in the sources I read in October 2026, the system was not yet at seven working satellites. The figure-eight group was one short, because the fifth satellite was lost. Looking further ahead, the government aims for an eleven-satellite system that keeps working even if any one satellite fails[7]. The Cabinet Office said a satellite called number 8 was being built for the eleven-satellite plan, and when asked whether it could replace number 5, answered that it could not say yes or no yet[8].
Try It Yourself: Compare How Much Sky You Can See
- Measure the sky with your fist. Stay in a safe place away from traffic, and keep the Sun out of your eyes. In daylight, hold your fist upright at arm's length. One fist is about 10° tall. Look at a street with tall buildings and at an open park. How many fists tall is the clear sky to the south? Is the sky straight above open even where the south is blocked? Never look at the Sun, and watch for traffic. Stop only where it is safe.
- Read the originals. The Cabinet Office's English page on QZSS[1] gives the overview. Its Japanese page on the orbit[2] has the 13-hour and 11-hour figures and the elevation numbers. The interview with the first satellite's engineers[4] tells the design story.