Simple: Once a player completes an entire research tree, they get a reward related to the tree:

Weapons chain:

Plasma Fusing System - Size 50, Attack +100, Attack +4%
Fuses a powerful plasma beam into your weapons, boosting your attack power

Energy Chain:

Perpetual Energy Node - Size 50, Energy +3%, Charge rate +1.
Allows the bending of normally accepted physics, for energy to recharge itself

Shield Chain:

Harmonic Vortex - Size 100, Shield +250, Shield Charge +20
A powerful shielding system, they are enormously complex, and only given to the elite pilots

Hull Chain:

Bioplating - Size 200, Hull +100, Special - allows for the hull to slowly repair itself, with a repair rate of 1 hull every 30 seconds. (2800 hull in 12 hours, balanced considering a player at the sort of rank to get it will have 10,000+ hull)
A genetically engineered organism that is resistant to most attack forms, and can regrow itself.

Defense Chain:

Wasp interceptor - Size 100, attack +100, defense +200. Visually follows ship.
An advanced interceptor, that can destroy incoming threats

Sensor Chain:

Dimensional Analyzer - Size 100, Scan + 500.
An Advanced sensor that can scan through different dimensions, notably time, that allows for the location of ship by finding where they are not.

Planetary Construction:

Captured Alien Facility - Planet structure, Size 1, Mining +5, Research +5, Artifact +5, Population +500, Attack +500, Defence +500.

A Facility that fabricates Minerals and Artifacts from nothing, it's design commonly studied by scientists.

Logistics Chain:

Base Omni-node, Base module - Special Size 1, Artifact production +300, Mineral Production +300, Research +300,
The Player who installed it may remove it back to their arty hold before leaving the legion, allowing it to be reinstalled elsewhere.

-1 Look at how over powered they are 3% extra energy thats alot extra especially for those with masses of energy but captured alien facility has to be seriously over powered size 1 for 5 of each resources and 500 pop and attk and defense and the size ratio isnt very good

defense one seems way to big for the effect. 100 size for 100 attack and 200 def?

Though I'd like to see medals for completing a research chain, I don't think modules should be the reward.
Maybe a title for completing all the chains (base stuff excluded)

I think the rewards for these are either WAY overpowered or take u way too much space.

Size: When you get these you will be a high rank and able to afford 100 decks.
Overpowed: These are just suggestion, the actual ones will probably differ - The suggestion is to actually get SOMTHING at the end of the chian, rather than these specificy.

I'm not ure getting any reward is a good idea, all you have to do to get them is spend some research, granted a lot of research, but everyone reaches that point at some point anyway.

Not sure these are needed, since the reward for completing research is the ability to buy/build whatever you just researched. That said, sure, everyone will eventually get all of these because it's just spending research, but the same can be said for the mission tier rewards, since that's just spending energy.

Yes but you have to consider the vast majority of mission tier rewards are utter crap.