normally Ion engines in the real world would get you accelerations of 1/10000 of a G. A Star frontier ADF is equal to 1 G, so the fact that they can get you a single g of acceleration is miracle.. As i see it the atomic drives and ion drives of SF Universe do not use standard Rocket Mechanics and Physics, as even the atomic rocket prolong 1 G acceleration is physically impossible. Since Tachyons exist in SF universe, it likely that both engines actually use these FLT particles to create a tachyon rockets Consider the central problem of rocketry: how can one burn fuel at a high enough exhaust velocity to provide reasonable thrust without an unreasonable expenditure of energy. This is the dilemma that plagues our space program, and the solutions we have developed are not very good. So let's consider a device that makes great quantities of E =0 tachyons and uses them as the infinite velocity exhaust of a "rocket". Within the constraints of the conservation laws of physics, we can make all the tachyons we want for free, provided we make them in neutrino-antineutrino pairs to conserve spin and lepton number. Momentum conservation is not a problem because we want and need the momentum kick derived from emitting the neutrino-antineutrino pair. This leaves us to deal with energy conservation The paradox here is that with a high-momentum exhaust of tachyons produced at no energy cost and beamed out the back of our space vehicle, the vehicle would seem to gain kinetic energy from nowhere, in violation of the law of conservation of energy. The solution to this paradox (as can be demonstrated by considering particle systems) is that the processes producing the tachyons must also consume enough internal energy to account for the kinetic energy gain of the system. Thus, a tachyon drive vehicle might be made to hover at no energy cost (antigravity!), but could only gain kinetic energy if a comparable amount of stored energy were supplied, from the atomic power plant or ion engine in the form of particles. Electrons or hydrogen ions from the ion engines are very low mass and energy, while the fragments from atomic fission are at least hundreds to thousand of time more massive . So the power output is what matters the Tachyon thrust amplifier of an Ion engine are very likely max out, so they are limited on the amount of real thrust they can provide, while an Atomic engines' Amplifiers very likely operating at a diminish power level to prevent the reactor from becoming unstable. Adding Ion engines may not help as they are drawing on the ship electrical power ( remember they are not atomic reactors) So ship with out reactor would be limited in it power output and usage.
