A couple of years ago Dana Andrews described a 4,000 ton interstellar colony mission vehicle to Proxima Centauri. Although his main choice of propulsion was flawed (the laser-powered ion-drive can’t accelerate as fast as assumed) the basic question remains: Could we use near-term technology to launch a 210 year mission to Proxima Centauri, at 4.24 light years?
A basic question, for all power-limited vehicles, is the minimum power-to-mass ratio needed for a given mission. The relationship is quite simple – if you carry the power-supply then the minimum is achieved when you accelerate 2/3 of the trip and coast 1/3. This means the cruise velocity is 3/2 the average velocity (i.e. if the average is 0.02c, then the cruise is 0.03c, and the delta-vee twice that, if you use rockets to brake.)
But what if you don’t use rockets or power to slow down? A magnetic-sail uses the ambient medium to shed the vehicle’s momentum against. In the interstellar medium, the braking is slow, taking decades – but at minimum power you’d be braking for 70 years on the 210 year trip anyway. Once inside the star’s asterosphere (the equivalent of the Sun’s Heliosphere) the medium is denser and braking picks up.
Of course using a magnetic-sail successfully means we need advanced knowledge of the medium between the Solar System and the target system. Breakthrough Starshot could provide such information. The sail material will be highly reflective at a specific frequency, thus could act as a laser-radar (lidar) reflective target. The material could also be charged by cosmic-rays and ultra-violet light, knocking electrons off it. A charged object responds to the magnetic-fields it encounters, thus a lidar target sail could be used to map the charged gases between the Sun and Proxima Centauri.
The chief question is: why launch before we can go quicker? A recent study of the Fermi Paradox suggests that eventually biotechnology will allow *anyone* to create a life-extinguishing super-plague and be the “Death of the Species”. While I’m not convinced it’s *likely* on biological grounds, I think as the end result is so extreme, sending isolated communities to other systems would be a prudent back-up policy. Plus, with communications technology, they will be physically isolated. They could be warned away from the specific plague sequence or develop active counter-measures.
That does leave another possible ‘plague’ that could reach down a communications beam – a ‘memeplex plague’. What if there’s an ideology so virulent it converts human hosts with 100% effectiveness? Could we defend against that possibility? I don’t know. How do brains reboot after being crashed by a mind-virus?