EDIT: Apparently the accepted physics has changed, and we now use the convection model for generating planetary magnetic field, not the dynamo model. Next thing you know people will be telling me Pluto is no longer a planet. (end edit)
Obviously, my first thought was to hit Mars with Ceres, on PPV the mission would pay for itself, sadly the Boffins would never let that happen.
Using ion drives with (H2O or bi-products) as reaction mass, move Ceres to Mars orbit (they are already in nearby orbits) to act as a moon, to restart the magnetic field on mars, so an atmosphere could be maintained indefinitely. Ceres could also act as a resupply base, due to low escape velocity and abundant water (assuming any survives the trip) Mars has abundant water in any case.
I need help with calculating how much thrust for how long would be needed. I know time is relevant. I'd like a time frame within my remaining lifetime say 30 years. Even just some rough numbers and a picture of how it would work would be nice. Then we can have a goal for how many and how powerful our ion engines would need to be.
Ceres is ~1/3 water so that's our maximum reaction mass. And I know it's going to take a bunch of Ion drives using current tech.
I'm new at orbital mechanics, so which direction to fire the ions in order to drop Ceres to a lower orbit and speed it up? Eventually it would need to achieve near Mars orbit for capture. Google doesn't have any nifty info graphics on lowering orbits, everything covers getting into orbit from earth or transferring to a higher orbit.
Ceres has a much smaller ratio of mass- Mars:Ceres than our own Earth:moon, so Ceres would need to initially orbit very close to Mars in order to get the dynamo spinning again. Later on Ceres could be moved farther out again once the proper field strength is achieved.
Ceres is spinning rather fast (~9 hour day), so ion drives would need to be placed around the planet and fire as the dwarf planet rotates. Placing them at the equator on gimbals would allow full control for orbital corrections.
Orbital inclination would need to be adjusted as well, most likely.
I feel transferring Ceres to act as a moon for Mars is the best solution, forget about using nukes to spin up the core, or giant magnets... give it a moon and forget about it for the next billion years.
That last problem is there may be a liquid ocean deep under the surface, so too much thrust would shift the core, the net force would need to be balanced against that, (if there is a liquid layer), so as not to cause catastrophic imbalance.
I know it's a big problem, but the reward would be a maintenance free magnetic field on Mars, leading to a rich, possibly breathable, atmosphere (with proper mixture).