[Humabout]

The issue, Eric, is that constant acceleration transfers naturally achieve higher delta-vs than impulse transfers. And the higher your acceleration, the more delta-v such a transfer takes. So if you have a 0.1g acceleration drive running nonstop, it eats more delta-v than a 0.01g accel drive between The Same Orbits. Thus, lower accel drives tend to use less fuel, regardless of isp.

Kreios, I never said anything about restartability. I addressed throttle-ability. Modern rocket engines can't operate below about 30% max thrust. They can turn off and fire back up. Heck, JPL is looking at using the auxiliary thruster on Voyager 1 for attitude control after its been mothballed for 40 years. But they can't run it at 10% thrust.

The reason that matters is that you can't dial back a 1g drive down to 0.005g to get a lower delta-v transfer that doesnt take over a decade to get to Saturn (Hohhman). This is inherent to the drives and presents an unintuitive challenge when analyzing costs.

Ultimately, you want to cost transfers by ($/ton)(ton/dv) or ($/dv). Thus, the more dv, the more money, and then you can balance transit time (crew wages, maintenance costs, etc.) against the cost of fuel to get a ballpark transit time and cost per transit. Spreadsheets are your friend here.