https://www.popularmechanics.com/military/weapons/a25938090/star-wars-light-trump-missile-defense/Finally, the big one: space-based missile defense, first proposed in the 1980s under the Strategic Defense Initiative. According to the report, the Pentagon “will study development and fielding of a space-based missile intercept layer capable of boost-phase defense.” These defenses would be satellites armed with interceptor rockets or, down the road, lasers. Pointed at down at the Earth, they would be alerted by a network of sensors to missile launches and swiftly knock down missiles before those missiles could release their warheads.
This, too, faces many complications. First, the U.S. would need to develop and maintain a constellation of missile-sensing interceptor sats in low Earth orbit. Developing, building, and launching this constellation would be very expensive at a time when the defense budget is expected to remain flat or even drop in the near future, meaning the Department of Defense would need to cut other programs to fund it.
Adversaries could simply build more missiles to overwhelm this expensive system, or develop other weapons such as cruise missiles or hypersonic weapons. And more fundamentally, there's the issue of breaking the informal taboo on militarizing space. It could come back to haunt the U.S. as other countries also deploy orbital weapons.