Interstellar travel is hard and complicated, yet I want to have a plausible interstellar propulsion system for my setting. Rockets are out because of the rocket equation and the horrible top speeds even if antimatter is used. Laser-sails are out because they can't slow down. Ramscoops are out because while their fuel collection rises with their velocity, drag rises with the third power of their velocity, limiting them to a top speed of 0.1c.
My idea was to combine the Ramscoop with the Laser-sail to get a system cable of reaching 0.9c with a reasonable mass ratio.
The spacecraft has a reactor, a habit, a cargo section and a large structure made of superconducting electromagnets. The structure is formed like a trumpet and protected with reflective shields, so it remains cold enough to work. It protects the spacecraft from interstellar gas, acts as a funnel for fuel and ejection mass and as a pusher plate.
The second part of the propulsion system is an array of powerful lasers in the home system. They push laser sails up to a significant fraction of lightspeed. These sails are shot at the spacecraft. As the ultra thin sails encounter the magnetic field, they break apart and turn into plasma. Encountering a ten tesla plus magnetic field at relativistic velocities tends to do that to matter. The plasma transfers its momentum and then some to the spacecraft as it is deflected.
The spacecraft could even slow down if the path ahead had been seeded with slower light-sails. It would just have to turn around. These slower light-sails would have to be deployed years before the spacecraft launches. While the spacecraft couldn't slow down with this method below the velocity of the breaking sails, its magnetic field would create even more drag to decelerate it. As soon as it is slow enough, the spacecraft is ditched and a small fusion or antimatter propelled craft with the crew, mining equipment and a self-replicating factory is deployed. These guys continue to set up basic asteroid mining and industry. Their goal is to build the same laser facilities the home system used to accelerate the propulsion sails. Once both sides can deploy the sails, a reliable travel corridor has been established.
One idea I had was to augment the sails with fusion fuel. The mag-sail would funnel the metal-carbon-fusion-fuel mixture down itself. At the deepest and tightest point of the mag-sail one would compress the plasma with stronger magnetic fields and a laser firing squad. Magneto-inertial fusion, basically. I'm not sure if this is practical, not practical or only practical during certain parts of the journey. The parts of the journey where I think such a fusion augmentation would be most useful are the final breaking phase and the end of the acceleration phase. In both instances the relative velocity between sails and mag-sail is so low that little energy is gained.
The fusion fuel that will be used is critical. The options are, assuming that both the CNO Cycle and proton-proton fusion are impractical, D+D, T+D, D+He3, He3+He3 an p+B11. D+He3 and He3+He3 are problematic as helium can't be combined with the sail in an easy manner. Any fuel tank would be destroyed by the interstellar medium. The sail itself will be more resistant to damage. p+B11 is great as both elements be connected to the sail as a layer of paint and it is neutron free. The issue is that it is 500 times harder to ignite than D+T. D+D and D+T are both neutronic, but can be ignited relatively easily and can be added to the sail as paint as well. D+T has the additional issue that the tritium will slowly disappear. No fuel stands out, all have their issues. p+B11 is probably most reasonable option assuming advanced technology.
Is the interstellar propulsion system described above realistic and reasonable? What issues might it face and how could one fix them?
