Though we don’t know what this specific test will entail, one possibility is the U.S. military’s Missile Defense Agency (MDA) is preparing to conduct its second THAAD test of the year. On July 11, 2017, the agency reported that one of the system’s interceptors had successfully destroyed a surrogate intermediate-range ballistic missile (IRBM) for the first time ever . MDA also released official video of the event, seen below.

The alert did not describe the missile system or parties who would be involved in the launch. Private contractor Alaska Aerospace Corporation manages PCSA, situated on Kodiak Island, and hosts U.S. and foreign military programs, as well as scientific research and commercial projects. The Coast Guard routinely takes parts in these events in order to secure the test range both to keep individuals away from any hazards and provide security for the often sensitive experiments.

On July 19, 2017, the Coast Guard distributed a safety notice to mariners advising them to keep away from a large section of the Pacific Ocean stretching from Kodiak Island in Alaska to Hawaii, according to an initial report by the Kodiak Daily Mirror . The message said the test launch would occur at the Pacific Spaceport Complex-Alaska (PCSA) overnight on July 29-30, 2017, but could end up rescheduled for the next two nights.

The U.S. Coast Guard has revealed upcoming plans for an unspecified missile test in Alaska. The launch site is the same one that has hosted U.S. military experiments involving the Terminal High Altitude Air Defense (THAAD) system and the announcement comes amid increased concern and warnings about North Korea and other potential enemies expanding their ballistic missile capabilities.

This launch, known as Flight Test THAAD 18, or FTT-18, was just one of two MDA planned for the U.S. government’s 2017 fiscal year, which ends on Sept. 30, 2017. There was also no public announcement of exactly when that test would occur beforehand. Still, in January 2017, in announcing the decision to use PCSA for these and future tests, MDA spokeswoman Leah Garton confirmed to Inside Defense that both THAAD launches would occur sometime in “late fiscal year 2017.” In a hearing in June 2017, U.S. Navy Vice Admiral J.D. Syring, head of MDA, said the second experiment, FTT-15, would involve collecting data on the system’s endo-atmospheric capabilities against a mock medium-range ballistic missile (MRBM) “with associated objects.” These additional items might stand in for decoys trying to throw off THAAD’s interceptor or the long-range AN/TPY-2 radar, which is essential for detecting and targeting incoming missiles. FTT-18, “in addition to previous flight testing and FTT-15 … , will demonstrate several key capabilities against longer range threats that the MDA should further explore using end-to-end modeling and simulation,” the Pentagon’s Office of the Director of Operational Test and Evaluation wrote in a 2016 review of the THAAD program’s progress. The office added that MDA and its Ballistic Missile Defense System Operational Test Agency “should plan to conduct high-fidelity modeling and simulation runs against longer range threats following the FTT-18 and FTT-15 flight test campaign, to include endgame and lethality analyses for these tests.”

AP A South Korean CH-47 Chinook flies past the first THAAD missile site in the country in April 2017.

The THAAD test and evaluation plan has already taken on a new urgency in light of North Korea’s extensive ballistic missile launches earlier in 2017. These have included the launch of the country’s first intercontinental ballistic missile (ICBM) on July 4, 2017, as well as successful demonstrations of increasingly advanced MRBM and IRBM types. This in turn had prompted complaints that the U.S. military’s missile defense test schedule was moving too slow to respond to these emerging threats. “We are not going fast. We are so risk-averse that we only test every 18 months,” U.S. Air Force General John Hyten, head of U.S. Strategic Command, told Stars and Stripes in an interview earlier July 2017. “The best way to build rockets, the best way to move fast, is to build it, test it, instrument it, learn from your failures.” So, even if the upcoming test is FTT-15, there may be concerns that THAAD both needs more testing and needs it yesterday. And while it is not clear whether THAAD would be able to handle an incoming ICBM, and the U.S. military has other missile defense systems for that purpose, it would be an important line of defense against the shorter range MRBM and IRBM types the North Korean military has showed off this year, including a stretched version of the BM-25 Musudan, also known as the Hwasong-12.

AP The Hwasong-12 on its transporter-erector.