don't run out of quantums.
Edit, within the next couple of missions Liu will award you with the Phased Plasma Torps, those are much more effective against Kessok, until then, conserve your quantums, Photons work just fine against the odd Keldon, also there are a couple of different points throughout the game where you can find additional quantums. in the mission where you find the damaged freighter, scan it and you will receive a fresh load of quantums, later on there is a point where you rendezvous with the Geronimo, if you scan them, McCray will give you some of his.