WASHINGTON – President Donald Trump is expected to announce on Tuesday the concept he wants for his future Golden Dome missile defense program — and while it would not be the most expensive option that the Pentagon had offered, it would still cost taxpayers tens of billions of dollars and take years to make a reality.

If realized, the system would mark the first time that the U.S. would put weapons in space, which could be fired to destroy an incoming missile during flight.

Trump also is expected to announce that Gen. Michael Guetlein, who currently serves as the vice chief of space operations, will be responsible for overseeing Golden Dome’s progress.

Golden Dome is envisioned to include ground and space-based capabilities that are able to detect and stop missiles at all four major stages of a potential attack: detecting and destroying them before a launch, intercepting them in their earliest stage of flight, stopping them midcourse in the air, or halting them in the final minutes as they descend toward a target.

For the last several months, Pentagon planners have been developing options — which a U.S. official described as medium, high and “extra high” choices, based on their cost — that include space-based interceptors.

The administration picked the “high” version, with an initial cost ranging between $30 billion and $100 billion, according to the official, who spoke on condition of anonymity to detail plans that have not been made public.

The difference in the three versions is largely based on how many satellites and sensors in space would be purchased, and for the first time, space-based interceptors.

The White House and the Pentagon didn’t immediately respond to requests for comment.

The Congressional Budget Office estimated this month that just the space-based components of the Golden Dome could cost as much as $542 billion over the next 20 years. Trump has requested an initial $25 billion for the program in his proposed tax break bill now moving through Congress.

The Pentagon has warned for years that the newest missiles developed by China and Russia are so advanced that updated countermeasures are necessary. Golden Dome’s added satellites and interceptors — where the bulk of the program’s cost is — would be focused on stopping those advanced missiles early on or in the middle of their flight.

The space-based weapons envisioned for Golden Dome “represent new and emerging requirements for missions that have never before been accomplished by military space organizations,” Gen. Chance Saltzman, head of the U.S. Space Force, told lawmakers at a hearing Tuesday.

China and Russia have put offensive weapons in space, such as satellites with abilities to disable critical U.S. satellites, which can make the U.S. vulnerable to attack.

But there’s no money for the project yet, and the program overall is “still in the conceptual stage,” newly confirmed Air Force Secretary Troy Meink told senators Tuesday.

While the president picked the concept he wanted, the Pentagon is still developing the requirements that Golden Dome will need to meet — which is not the way new systems are normally developed.

The Pentagon and U.S. Northern Command are still drafting what is known as an initial capabilities document, the U.S. official said. That is how Northern Command, which is responsible for homeland defense, identifies what it will need the system to do.

The U.S. already has many missile defense capabilities, such as the Patriot missile batteries that the U.S. has provided to Ukraine to defend against incoming missiles as well as an array of satellites in orbit to detect missile launches. Some of those existing systems will be incorporated into Golden Dome.

Trump directed the Pentagon to pursue the space-based interceptors in an executive order during the first week of his presidency.