I ran across this blog post, which presented a design for a spacecraft capable of generating a magnetic field big enough to protect all of Mars from solar particle radiation. The design uses a 415 megawatt nuclear reactor to power a 57 ton copper solenoid.
Since I am working on a proposal for a mission to demonstrate a powerful magnetic sail technology, (called a plasma magnet) I went ahead and did a back-of-the-calculator estimate on what it would take to get similar performance.
If scaling relations for the plasma magnet hold up to thousands of kilometers, then a set of coils 14 meters in diameter, made of aluminum, with about 1 ton of mass would only need 600 kilowatts of electrical power to create a Mars-sized magnetosphere. This is only 12 times what the ISS solar array would produce at Mars.
The only problem I can see is that a magnetic sail this large would generate almost 300 kilonewtons of thrust. You’d probably have to attach it to a small asteroid to keep it balanced on the Lagrange point.
If it really is possible to give Mars a magnetosphere with currently existing technology and a few BFR flights (and my cubesat mission would go a long way towards showing that), then would it be worthwhile for a colonization project to do this early on? I’ve seen conflicting opinions on how dangerous solar activity is for people on the surface.