INTAKES are the hydrogen ram scoops on the front of the spacecraft which fuel it by gathering spaceborne hydrogen. Upgrades alter the effectiveness and the profile of the vehicle; the more effectively a ship takes in fuel the more efficient its engines. The tradeoff is that, unless countermeasures are installed, this also increases the radar signature. The appearance of the ship is altered as well: more primitive intakes look like physical fan blades, others glow different colors as heat capacity increases.
MODIFIERS are a generalized slot for any kind of tech that affects the overall performance of the engine. The list includes engine coolers, exhaust systems, overdrives, afterburners, overclockers and other similar systems. Different ships can have different numbers of modifiers in a chain. The Aurora has a single modifier slot and so a pilot must decide between an afterburner and a cooler... the 300i has two, the pilot has more options.
The ENGINE is the core power plant of the ship. Engine output varies depending on manufacturer, model and type (types include Fission, Fusion, Anti-Matter, etc.) Each selection offers you a different base performance. Engine model examples: General Fusion 3000, Merlin Agena-L, Korolev Atlas III, Suncom Omega.
THRUSTERS are the end of the chain, the physical output point of the engine. They modify the overall engine output: burn at different rates, impact the range, increase or decrease the radar profile of the ship (you might pay extra for “silencer” thrusters which don’t give off such a large drive plume,) etc. Here you will see a significant visual difference: different size nozzles, different colors of thrust, etc.
THRUSTERS are defined by two values; its THRUST RATING (TR), which determines the amount thrust it can deliver. The bigger the number, the larger and more powerful the thruster. A 10 rated thruster would be used on a cruiser’s main engines, and a 1 rated thruster would be a maneuvering thruster on an RSI Aurora. You can normally fit a thruster of the same or lower rating but you couldn’t attach a 5 rated thruster to a 3 rated thruster slot. Most ships have a combination of a few higher rated thruster slots for the Main Engine thrust and at least 4, but more usually 8 lower rated thruster slots for the Maneuvering and Retro thrusters. The maneuvering thrusters are used to change the ship’s orientation as well adjust its overall velocity vector. Retro thrusters arrest the ships velocity. Frequently a front mounted maneuvering thruster will also perform retro fire duties.
The second important value for a thruster is its ARTICULATION TYPE; Fixed doesn’t move. The thrusters on the Apollo lunar lander would be classified as fixed. Then there are Jointed thrusters; these are rigid nozzles that can rotate on one or two axis. After this there are Flex thrusters; which can articulate on one or two axis, but aren’t rigid. Think of these like the nozzles on a Harrier or an F-35. Finally there are Vectored thrusters – which have vector flaps that help direct the stream of exhaust.
As an example the Hornet has one 4 rated Vectored Main Engine thruster, four 2 rated flex maneuvering jets (with the front two also performing retro duties) on the top and four 2 rated jointed thrusters on the bottom.