A powerful 70 gigawatt laser propulsion system that could accelerate an 100 kilogram object over 122 seconds to 2% of light speed (6000 kilometers per second) would also be able to fire kinetic projectiles at nuclear weapon power.
The goal of the Breakthrough Starshot program (which has $100 million in funding) is to send wafer chip spacecraft to 20% of lightspeed to probe exoplanets and other star systems. The initial $100 million would not reach that goal but a follow on program for a few tens of billions of dollar could achieve it.
Battleship naval guns can fire metal projectiles with 5000Gs of acceleration (49000 meters per second per second).
It would take 367,347 kilometers of distance to accelerate at 5000Gs to reach 2% of light speed.
The moon is 384,400 km away from the Earth.
A large moon based laser array for accelerating spaceships and probes to Mars or on interstellar missions could be pointed at the earth and about every 2 minutes be able to fire a kinetic shot to medium sized nuclear bombs.
Initial space based laser arrays should therefore start with installations on the dark side of the moon to minimize geopolitical issues by being positioned to only launch away from earth. Any ship with its own propulsion and relativistic speed capability would have vast destructive potential.
Powerful manufacturing capability in space to print large solar arrays are also powerful. Every square kilometer of solar array would be receiving about 1 gigawatt of solar power. There would then be inefficiencies converting the solar power to laser power and then inefficiencies to kinetic acceleration.
Note: This is why science fiction and science fiction movies are highly inaccurate with their portrayal of weapons. Kinetic weapons for Star Wars and Star Trek would be far more powerful than what is usually shown.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
Known for identifying cutting edge technologies, he is currently a Co-Founder of a startup and fundraiser for high potential early-stage companies. He is the Head of Research for Allocations for deep technology investments and an Angel Investor at Space Angels.
A frequent speaker at corporations, he has been a TEDx speaker, a Singularity University speaker and guest at numerous interviews for radio and podcasts. He is open to public speaking and advising engagements.