To create a conceptual design of a tracking system of a target injected into a wet-walled, laser-fusion reactor, the influence of residual gas on the target trajectory is discussed based on a kinetic model, assuming all of the impinging molecules are adsorbed on the target surface. The model targets are a high-gain target for central ignition and a fast-ignition target with a cone as an optical guide for an additional heating laser. In the case of a fast-ignition target, tracking in the reactor might be skipped, depending on its condition, because of the heavy cone. Recent activities in fabrication of the fast-ignition target are briefly mentioned.