Hello.
When Phalanx scientists finish researching "UFO Theory", they report that its engines to generate thrust "by injecting protons and antiprotons into the reaction chamber, then channeling this explosive force out the back of the engine".
This propulsion system is in fact highly inefficient, and it can be proven with quite a few lines of formulas. Given an UFO weighs roughly 100tons and carries 1gram of antimatter, it can accelerate to a speed no faster than 6 meters per second.
This is because of the conservation of momentum. Of course, proton - antiproton annihilation yields tremendous amounts of memory, but you can't just transform it into kinetic energy of aircraft. You must have some mass to throw away to generate thrust and thus move the opposite direction. If you just channel whatever results from annihilation (gamma-radiation at most, but there may be some other particle-antiparticle pairs) back of the engine, you will not gain more than 2mc of momentum from annihilation of 1 gram of antimatter.
UFOs just can't fly on this type of thrusters.
I think to add some scientific credibility to the game (its science fiction after all) you should equip UFOs with ion thrusters as addition to their antimatter engines.
Antimatter engines would then just transform antimatter into electric energy and provide an astonishingly powerful source of energy for thrusters, which ionize matter and then accelerate it to relativistic speeds and throw back providing thrust.
This all turned out to be very complex when i tried to conduct even the simplest of calculations to propose a scientifically-credible scheme of space-capable aircraft which would look like in-game UFO (very heavy, carrying 1 gram of antimatter as fuel and no visible mass tanks), and now i'm not sure if it's possible at all.
Still, it would be much more credible if we say it's using ion propulsion, with thrusters powered by antimatter engine, and accelerates plasma to the speeds of 1000-10000 km/s. It should utilize athmospheric air to throw away and gain thrust, just because it needs to much mass to carry along. UFO should have small mass-tanks (approximately 1 to 5 tons) to be able to maneuvre in vacuum in order to get to and from the carrier, but itself it's uncapable of interstellar or even interplanetary travel - it carries just too little exhaust mass.
This would be even good, because it would give Phalanx scientist another clue that aliens should operate from some huge orbital carrier UFO.
So, for the sake of scientific credibility, i believe that in-game texts about UFOs' propelling scheme should be updated to something like this:
The alien propulsion system is a type of rocket engine unlike any ever built on Earth. It uses energy of matter-antimatter annihilation to power ion thrusters accelerating plasma to speeds of thousands kilometers per second. In atmosphere, it can use ionized air as exhaust mass, and it also carries a mass-tank to be able to maneuvre in hard vacuum. Confusingly, amount of matter in the mass-tank is not too big, and the craft does not seems designed for interstellar travel.
