TOKYO -- Recent North Korean rocket tests have raised the possibility that Japan's current missile defenses may be rendered ineffective, forcing policymakers here to consider new options -- including a constellation of small tracking satellites and the ability to attack the missile launch itself in enemy territory.

North Korea test-fired a projectile toward the Sea of Japan on Sept. 28, later identifying it as the Hwasong-8 -- a hypersonic missile whose speed and complex trajectory would make it almost impossible for a missile shield to shoot down.

This came less than two weeks after a pair of ballistic missile test launches by North Korea on Sept. 15. The Japanese government announced shortly after the firings that the missiles had likely fallen outside its exclusive economic zone. But Tokyo did an about-face nine hours later, reporting that they had in fact landed in the EEZ. The weapons were apparently capable of changing trajectories and extending their flight distance. They were no longer following simple parabolic paths, making them hard to track.

Japan's Self-Defense Forces currently predict missile trajectories based on radar readings of launch angle and speed. The weapons are then met with a two-tier defense system: the sea-based Aegis missile shield while outside the atmosphere, followed by Patriot Advanced Capability-3 missiles as they reenter.

The system is designed for missiles traveling on a simple parabolic path, like a ball thrown in the air. But North Korea has been developing trajectory-shifting missiles in recent years that would make it much more difficult to intercept them in time or as accurately.

A low-altitude flight can also hamper tracking efforts, rendering the missile invisible when flying beyond the horizon. The Aegis system also cannot shoot down missiles unless they leave the atmosphere.

The Sept. 15 missiles reached a maximum altitude of about 50 km. The hypersonic missile tested Sept. 28 traveled at a similar altitude at five times the speed of sound or faster.

"Japan's current missile defense system will not hold" against an onslaught of hypersonic, trajectory-shifting missiles, an SDF official said.

North Korea test-fired the Hwasong-8 hypersonic missile on Sept. 28. (KCNA via Kyodo)

The first challenge is how to improve detection. Japan and the U.S. must deploy a constellation to minimize blind spots, said Tetsuo Kotani, professor of global studies at Meikai University.

"We need to increase the number of sensors in order to improve our ability to detect missiles," he said. The more eyes that look down from space, the more they can see.

The Ministry of Defense began weighing the possibility of such a satellite constellation this fiscal year. Top officials held their first meeting on the topic the day before North Korea's hypersonic missile launch.

Another challenge is intercepting the weapons -- a task that will be easiest just after they take off.

The capability to strike enemy bases -- such as hitting missile-staging areas immediately after launch to stop projectiles while still in an opponent's territory -- also emerged as a key topic during September's leadership election for the ruling Liberal Democratic Party.

Prime Minister Fumio Kishida had suggested during the campaign that he was open to the idea. "It is important that we brush up our ability to respond to missile strikes," he said.

There is some concern about whether such strikes comport with Japan's constitution, which allows only self-defense capabilities. But unlike preemptive attacks, the strikes now being debated here would occur only after it has been determined that Japan is being attacked.

Meanwhile, military technology continues its forward march. Japan will need to accelerate development at home rather depend so heavily on U.S. cooperation.

Japan's defense spending is set to increase for a ninth straight year in fiscal 2021. But the country has hesitated on major increases so far, aiming to stay at around 1% of gross domestic product. Japanese spending has risen only about 10% over the last decade, even as China's budget has more than doubled.

The latest North Korean missile test came as Japan was transitioning between governments. As its new leader, Kishida now faces a key opportunity to weigh the rapid shift in Japan's security environment and consider overhauling its defense framework.