This might simply mean that using power from the power plant, e.g. to power the manoeuvre drive, consumes inconsequential fuel compared to idling the power plant.HG'79, p17-18 wrote:A power plant uses fuel equal to 1% of the ship's tonnage every four weeks, regardless of actual power drain; this usage is primarily to maintain the fusion bottle and other housekeeping functions. Other fuel requirements are considered inconsequential.
There is a problem: it's certainly too little reaction mass.
E.g. the Free Trader; It uses 10 Dt = 10 tonnes of hydrogen for four weeks, or 4 g/s. If we say that inconsequential is 1%, then we use around 40 mg/s reaction mass to achieve 1 G ≈ 10 m/s² acceleration. So in 1 s 40 mg of reaction mass would increase the ships speed by 10 m/s.
By conservation of momentum MrVr = MsVs, so the velocity of the ejected reaction mass would need to be Vr = MsVs/Mr ≈ 1000000 × 10 / 0.00004 = 2.5 × 10¹¹ m/s = 250 million km/s or about 1000 times the speed of light.
At this energy level we have to consider energy rather than velocity. At close to lightspeed MrVr = MsVs would be Mr = MsVs / Vr ≈ 1000000 × 10 / 300000000 = 33 g of pure energy which by E=mc² is 3 × 10¹⁵ J which in 1 s is 3 PW = 3000000 GW. Obviously this can be produced by neither a fusion rocket nor the power plant.
Even if we could eject the reaction mass at close to lightspeed we would need several thousand times more reaction mass.
I would argue that reaction drives that use no noticeable reaction mass are even more magical than gravitic drives.