The title sounds preatty self explanetory, but whit tech tree you coud unlock new parts and feuters(Engines, types of engine propeleant(Solid/liquid/nuclear thermal....), types of engines(pressure fed/staged/fuel generator...), manned capsules, electric parts, science instruments...). To unlock resarch nodes you will need to run science experiments on spesific locations. When the science is recovered on Droo, or the science is transmited you will recive science points whit which, as I alreaddy said woud give you ability to unlock science nodes.
(This coud be used in career mode, and career mode is NOT a suggestion of this post.)
This post has been merged into this post and this post has been marked as duplicate.