The day national security planners feared and anticipated arrived this month when Kim Jong Un's regime successfully tested an intercontinental ballistic missile theoretically capable of hitting Alaska. But with the North's threat looming larger than ever, the high ground for U.S. ICBM defenses might not be ground at all.

Space-based missile defense has caused political scuffles and faced skepticism in the halls of Washington since the Reagan administration's ill-fated Strategic Defense Initiative, more infamously known as Star Wars.

Now, the concept is getting new life as North Korea's fast-paced pursuit of nuclear ICBMs has spurred talk of more missile defense in general. Lawmakers on Capitol Hill see an opening this year to push forward with the long-debated expansion of America's missile shield in space, including sensors and even interceptors reminiscent of President Reagan's proposal.

Both the House and Senate have agreed in their annual defense policy bills that the U.S. should pursue what Sen. Dan Sullivan, R-Alaska, calls the "unblinking eye," an array of orbiting satellite sensors that could collect high-quality launch data on future ballistic missiles from North Korea or other adversaries.

The tracking data could be used to better direct existing defenses on the ground, from regional defense on the Korean peninsula such as the Lockheed Martin Terminal High Altitude Area Defense system, or ground-based interceptors on the West Coast. Sullivan spearheaded legislation in the Senate's National Defense Authorization Act that would provide $27.5 million toward the development, launch, and demonstration of the space-based sensor layer.

Kim Jong Un "is aggressively testing the frontiers of their capability and learning and we need to be doing that as well," Sullivan told the Washington Examiner.

Sullivan rallied bipartisan backing on his bill and says he has the support of top generals and military officials. The recently departed commander of the Missile Defense Agency, Vice Adm. James Syring, has pointed to space tracking as a need, and President Trump, as a candidate, said he supported new missile defense capabilities in space.

"At some point soon, our nation must commit to deployment of a global space-based sensor system with discrimination capability," Gen. John Hyten, the head of U.S. Strategic Command, testified to the Senate in April.

Trump has ordered the Pentagon to conduct a Ballistic Missile Defense Review, which will likely include space-based sensors, by the end of the year.

Previous administrations have also seen the need for sensors, but plans never made it off the drawing board, says Thomas Karako, director of the Missile Defense Project at the Center for Strategic and International Studies.

"I think this would be a tremendous step forward, and I think it's important to keep in mind … space sensors are not just about long-range missile defense, but they would improve the lethality and effectiveness of every interceptor family in the ballistic missile defense system," Karako said.

The land-based sensors that now form the backbone of the U.S. missile defense system have difficulty with the curvature of the Earth and seeing threats over the horizon. With space sensors "you get birth-to-death tracking … you get more specific tracking data to really help tell your interceptors where to go and what to kill," he said.

Lawmakers in the House agree the department should consider the new layer of missile defense, and have also gone further. The House NDAA directs the Pentagon to begin tests on the space-based interceptors, first envisioned by Reagan and fought over for years in the chamber.

"This is a profound step forward," Rep. Trent Franks, R-Ariz., who sponsored the legislation, told the Washington Examiner. "This is a true paradigm shift in the direction of a new capability."

The House NDAA would put $30 million into creating a "test bed" to try out hardware in space that could shoot down incoming North Korea ballistic missiles, similar to the U.S.'s existing ground-based interceptors at Fort Greely, Alaska, and Vandenberg Air Force Base in California.

Asked which contractors might bid on sensors and interceptors, Karako says it's hard to say at this point.

"It probably depends on how MDA shapes up the contract, and either way it would presumably be a competition in which most of the primes get involved. That might means Lockheed, Northrop, Raytheon, and probably others," he said

The U.S. has struggled to develop its ground interceptor capabilities for two decades — an ability invariably described as hitting a bullet with a bullet — with a number of failures and re-calibrations along the way. In May, the system reached a milestone by successfully shooting down a test ICBM, but remains in development.

Franks, a long-time member of the House Armed Services Strategic Forces subcommittee, successfully got an amendment added to the NDAA that allows the military to test the fledgling technology in space, what he called the "biggest step since Reagan" in preventing a nuclear strike on the U.S.

"A space-based missile defense layer is an idea I think whose time has come, at least in terms of initiating it so that if the moment should arrive when we need that capability, and I think that's where missile warfare is heading, that we have done our homework within the right timeframe," he said.

The interceptors and test bed are far from a new idea in the House, or Washington, and Franks says he has been debating the issues for more than a decade. But Franks and other proponents made progress in last year's NDAA by allowing the Pentagon to study the idea.

"This year, we are actually starting to build and do some prototypes and some things like that to begin to see what we think is a tangible possibility for space-based missile defense," he said.

There is widespread and longstanding doubt about the viability of space-based interceptors. The Union of Concerned Scientists has said they would be enormously expensive and ineffective at stopping ballistic missiles from North Korea or other adversaries.

"Many hundreds of orbiting space-based interceptors are required to defend against just one or two missiles — an extremely expensive approach," according to the nonprofit advocacy group.

The government's last major effort toward deploying interceptors ended during the Clinton administration, says Michaela Dodge, a policy analyst who specializes in missile defense at the Heritage Foundation.

"That's over 20 years ago, so today we could do it much better if we wanted to, but so far we haven't had political will to proceed with this type of deployment," Dodge said.

Such a system would theoretically allow the so-called kill vehicles, the section of the interceptor that collides with the incoming ballistic missile, to reach its target faster than the existing interceptors at Fort Greely and Vandenberg, she says.

"Ultimately, we talk about a layered missile defense system, but the layer that we are missing is the space-based missile defense layer," Dodge said. "So I think it's a good thing that the House looks into that and takes a step to establish the test bed too."