To save on the mass which has to be launched (which requires squaring the rocket equation), the authors of Eternity in Six Hours favor an external fixed launch system which accelerates the replicating probe including both probe and fuel for its later deceleration.
In the paper, the authors briefly list coilguns, quenchguns, laser propulsion, and particle beam propulsion as potential means of accelerating the probes. They state even though the theoretical energy efficiency of these systems could approach 100%, since one never obtains the theoretical efficiency, they assume 50% efficiency.
The question here:
Is it possible to build a launch system which launches (possibly quite large) probes to significant fractions of the speed of light?
Looking back at our paper, I think the weakest points are (1) we handwave the accelerator a bit too much (I now think laser launching is the way to go) . . .
My shallow impression is that the proposed launch systems might only represent large engineering challenges more than difficult physics/​designs breakthroughs. Coilguns have been constructed and laser propulsion has been demonstrated in the lab. What remains is a question of scale and efficiency. However, even a difference between 5% efficiency and 50% efficiency is only a single order of magnitude. Not a large difference in the overall picture here.
Launch System Feasibility Efficiency
To save on the mass which has to be launched (which requires squaring the rocket equation), the authors of Eternity in Six Hours favor an external fixed launch system which accelerates the replicating probe including both probe and fuel for its later deceleration.
In the paper, the authors briefly list coilguns, quenchguns, laser propulsion, and particle beam propulsion as potential means of accelerating the probes. They state even though the theoretical energy efficiency of these systems could approach 100%, since one never obtains the theoretical efficiency, they assume 50% efficiency.
The question here:
Is it possible to build a launch system which launches (possibly quite large) probes to significant fractions of the speed of light?
What efficiency is realistically achievable?
When contacted for comment, one of the authors, Anders Sandberg, stated:
Looking back at our paper, I think the weakest points are (1) we handwave the accelerator a bit too much (I now think laser launching is the way to go) . . .
My shallow impression is that the proposed launch systems might only represent large engineering challenges more than difficult physics/​designs breakthroughs. Coilguns have been constructed and laser propulsion has been demonstrated in the lab. What remains is a question of scale and efficiency. However, even a difference between 5% efficiency and 50% efficiency is only a single order of magnitude. Not a large difference in the overall picture here.