The Technology tree allows the player to unlock more advanced parts for constructing variously level craft. It is a branching tree structure composed of nodes, each containing a set of one or more parts. Previously collected Science points have to be spent to research a node, which then unlocks its parts for use in the Editor. Funds may also be involved in unlocking individual parts depending on the difficulty settings.
The tree is accessible via the Kerbal Space Center Research and Development Facility's “Technology” tab. As part of the Science system, the Technology tree is not available in Sandbox Mode; instead all parts are automatically unlocked. All other modes begin with the initial node “Start” unlocked. Each node beyond it has a prerequisite node or nodes which must be unlocked before it can be researched. Unlocking the entire tree requires 18 468 Science including the hidden nodes, but 16 918 without. Before difficulty modifiers, there are 392 019.3 Science points available from experiments, and 6 055.8 from recovered vessels.
There are two additional placeholder nodes in the stock game which are included in the table below, but have no parts currently assigned to them. The nodes appear towards the end of the Tech Tree, and are only displayed in-game when a mod is installed which use them. These nodes are: Nanolathing, costing 550 Science, and Experimental Motors, costing 1000 Science. While these cannot be unlocked via research, it is technically possible to unlock them via Green Monoliths.
The technology tree is displayed as a horizontal branching tree structure, with low tech research nodes on the left and higher tech nodes on the right. The root node of the technology tree, Start, is on the leftmost side of the tree and is unlocked by default in all new Career Mode games.
By conducting missions and collecting Science, the player may spend their Science points on available research nodes. In Career mode, depending on the difficulty settings, funds may also be required to unlock each part in the node. Only nodes that have had their dependencies unlocked are displayed on the technology tree. As the player unlocks more nodes, higher tech nodes will become available until the eighth tier of the tree is reached.
Most research nodes have dependencies upon earlier, lower technology nodes. For example, the General Rocketry node requires that the Basic Rocketry node is unlocked before the player may spend 20 Science points to unlock its parts. Some nodes have multiple dependencies that require several nodes to be unlocked before they become available. There are also research nodes that have multiple dependencies, but most only require one of them to be unlocked prior to becoming available. Within the stock tech tree, Nuclear Propulsion and Ion propulsion are the only nodes that require all dependencies.
In Career Mode there is also a further restriction depending on the level of the research facility. The starting building allows only nodes under 100 Science points, the mediocre allows up to 500 Science points, and the final facility has no limits. (These restrictions can be put into Science Mode by editing the save file to reduce the building level)
- This research has multiple other requirements