Can man colonize nearby stars? Most of the discussions of this problem seem to assume non-existent or practically impossible physics — warp drives, antimatter power sources, giant lasers that defy the law of diffraction. Is there a way to do it with technology that could actually be developed? I think so:

Step 1: Super-Telescope Survey

Build a multiple-aperture telescope in space, able to image and spectroanalyze the nearest extrasolar planets. The law of diffraction dictates that the synthetic aperture must be hundreds of kilometers or perhaps thousands. This is expensive but far cheaper than sending probes to many nearby stars.

Step 2: Robotic Probes

If suitable planets are found, send unmanned probes using fission-powered ion drives with relativistic exhaust velocities. They must be big enough to reach the star and decelerate into planetary orbit. They will be expensive and take centuries to reach their destinations, travelling at 1 or 2 percent of the speed of light. Use somewhat more efficient fusion power, if it is developed.

Step 3: Telegenomic Transmission

Once in position, the probes can receive radio transmission of human genomes of volunteers (and/or carry some onboard in digital storage). Remote growth of clones from synthesized DNA would need to be developed. Remote raising of the children would also be necessary — these would be clones of terrestrial hosts, but would of course not have the host’s memory or personality.

Radio transmission of genomes (telegenomic) allows unlimited colonization without the extreme expense of carrying human payloads. I believe it is a practical impossibility to carry living beings between stars. I also do not believe any power source beyond nuclear fission or fusion (tenths of a percent mass-conversion efficient) will ever be possible, which places severe limits on intersteller travel.