An executive order said the United States faced a “catastrophic threat” from advanced aerial weapons. But a defense system like Israel’s may not be feasible in the country, which is more than 400 times larger.

President Donald Trump’s Monday night executive order on the creation of an “Iron Dome for America” calls for much more than the air defense system Israel utilizes. The order calls for “a next-generation missile defense shield” to protect the homeland.

The first Trump administration floated a space weapon concept in March 2018: a neutral particle beam in space. But it ultimately shelved the idea because of the massive amount of power needed to destroy a missile with directed energy.