Crap.
I screwed up with my last post by mixing up exhaust velocity and
delta-v. Duh.

You *can* do four round trips to 100 diameters (for a size A world) and
back with 5% fuel *mass*. But it requires a very large proportion of the
fuel being converted to energy.

A round-trip to 100 diameters and back at 1G continuous acceleration
requires 13.44 G-hours or a delta-v of about 482 km/sec.

Fusion drive delta-v:
If we assume highly efficient fusion drives with an exhaust velocity of
10% of the speed of light:
delta-v = exhaust velocity x ln(initial mass/final mass)
delta-v = 0.1 x c x 0.051, using a fuel mass fraction of 5%
= 1530 km/sec

Which is a bit over 3x that needed for a 1G round trip.

The antimatter rocket:
delta-v = 0.58 x c x 0.051
= 8864 km/sec

This is almost double the needed delta-v for 4 round trips at 6G
acceleration (~4562 km/sec)

Rob O'Connor