How plausible are these concepts?
Thomas Ciesla's Centauri project utilizes a terraformed asteroid with antimatter propulsion that can travel at 30 c
Alan Holt's interstellar transport system uses two field generators and 16 field amplifiers to create a space-time bubble around a vessel
Giles Primeau's Heracles project uses muon catalyzed nuclear fusion propulsion and can reach Mars in 3 days. It uses negative muons for lower temperatures and has an isp of 1 million seconds with the ability to accelerate 1g.
Charles Orth proposes an inertial confinement fusion vehicle named VISTA. I has many high energy lasers mounted around the surface of a cone with mirrors directing beams to the detonation site at the apex. Pellets of deuterium, tritium, and hydrogen are ejected into the focus where they are detonated creating high energy plasma directed by the drive coil's magnetic field. .02 g acceleration or greater is possible and VISTA can reach Mars in 45 days. John Callas has an antimatter variation that is 1 kilometer wide and utilizes protons and antiprotons. This vehicle can make Epsilon Eridani in 100 years.