Something about my mass model of “Daedalus” didn’t sit right with me, so I recomputed the tankage from first principles. The percentages were more like 5%, thus meaning a slightly slower fastest time – 71.58 years with an initial mass of 281,181 tonnes.
While “Daedalus” can cruise at 0.12-0.14c, meaning speedy trips to Alpha Centauri, compared to the above, the problem is that there’s no way of stopping at such speeds – finite tank mass means an infinite mass of propellant would be required.
I went on to compute the performance of a magnetic sail equipped vehicle and got quite an encouraging result – which I’ll post here after the Symposium presentation itself, which is in a matter of days. Traveling to Alpha Centauri via fusion rocket in sub-50 years will be an immense engineering challenge, so one hopes better options will arise. Jonathan Vos Post has a paper online which is a good example of the extreme performance required for very rapid flybys – a perfectly efficient fusion motor, a five stage vehicle, and a mass-ratio of ~100,000 means a flight in ~9 years or so. Wildly unrealistic, but illustrative of the effort needed.
To do better will need something better than rockets, but not necessarily more powerful than fusion energy.