Uranium and plutonium.

Tau Ceti is significantly younger than Sol system (at least it is in your story) so far less of the heavy radioactive elemts have decayed. Instead, there's an abundance in TC asteroid belt.

So the 'business' plan is like this:

• fly to TC with a generation ship are large fleet
• set up asteroid mining operation and self sustaining colony
• set up manufactoring base for enriched uranium and spaceships
• send back uncrewed ships with Orion-drives, fueled by the uranium you find
• these trasnport more radioactive materials to Sol where ...
• they power reactors housed in satellites beaming energy via microwave to where it's needed

This assumes that all interesting uranium deposits on earth are depleted and the rest is so diluted mining is not ecnomical.

Uranium, plutonium, thorium.

Tau Ceti is significantly younger than Sol system (at least it is in your story) so far less of the heavy radioactive elemts have decayed. Instead, there's an abundance in TC asteroid belt.

So the 'business' plan is like this:

• fly to TC with a generation ship are large fleet
• set up asteroid mining operation and self sustaining colony
• set up manufactoring base for enriched uranium and spaceships
• send back uncrewed ships with Orion-drives or thorium salt-water rockets, fueled by the radioactives you find
• these trasnport more radioactive materials to Sol where ...
• they power reactors housed in satellites beaming energy via microwave to where it's needed

This assumes that all interesting uranium deposits on earth are depleted and the rest is so diluted mining is not ecnomical.