It’s unlikely that the Unha-3 will ever be used as an ICBM. Instead, North Korea has paraded what appear to be two variant road-mobile ICBMs that should have the U.S. worried. To date, these have not yet been tested, so it is not clear they “work,” but road-mobile missiles can be constantly shuttled around the country, and hidden in warehouses, tunnels, and bunkers. This makes them hard to track from satellites, thereby increasing the likelihood they would survive a strike on them. The semi-good news is that North Korea only has six untested ICBM launchers, so no matter how many missiles or warheads North Korea makes, it is constrained. In addition, the trucks needed for road-mobile ICBMs are huge, and must travel in convoys that include fuel and oxidizer trucks as well as a large number of personnel. Many of the facilities and hiding places where North Korea puts these trucks are already known, including where the trucks were adapted and a prominent ICBM missile warehouse.

The KN-08 ICBM has been paraded in Pyongyang since 2012. At first, open-source analysts found its crude workmanship unconvincing, but by 2016 North Korea demonstrated that not only is it a real ICBM, but its engine is using a more energetic fuel than previously thought. The translucent pinky-purple color of the flames seen in photos of the April 2016 engine test at Sohae are a hallmark of a fuel-oxidizer combination energetic enough to make a target not only out of the West coast of the U.S., but also Washington, DC.

The KN-14, paraded in October 2015, is a variant. It is less frequently photographed, but if it has the same engine, it can probably put at least Chicago at risk, and may even be more accurate than the KN-08.

Still, North Korea has never tested an ICBM, so there is a fair amount of educated guessing going on in and outside of several governments about when, where, and how North Korea might make its debut. The easiest way to find out would be if North Korea issued a notice to airmen, known as a NOTAM. The idea behind a NOTAM is to warn sea and aircraft of potential hazards during the flight time of the rocket. The North Koreans have done this before for their space launches, but not for their missile launches. North Korea, if you read The Atlantic, I strongly recommend that you issue one in advance of an ICBM test. By giving advanced warning, you are making it clear that you are starting a test and not restarting a war.

But North Korea is not a very trusting state, so its leaders may not issue a NOTAM for fear the U.S. or South Korea might strike the missile before it launches. There’s been a lot of talk in the U.S. about doing just this, though it is another quick way to restart a war.

Without a NOTAM to tip off observers that a launch is imminent, the next way to know what’s happening is to turn to satellite imagery. Those of us in the open-source world use commercial satellite imagery companies like Planet to get near-daily updates. Where does one start to look? One possibility is that the North Koreans will not use a transporter erector launcher (TEL) truck of the kind visible in parades, because they are scarce and it would be too damaging to the ICBM program to lose one in what will likely be a failed first test. That makes Sohae a possibility. The satellite launch site there conveniently already has everything one would want for a test—a gantry tower for stabilizing the missile, fuel, oxidizer, engineers, and communications that make it easy for Kim Jong Un to observe from afar in case of failure or preemptive strike.