There are three different modes that you can play the game in: Career, Science, and Sandbox. When you start a new game, you’ll be asked which mode you want to play in. You can’t change a game’s mode once it starts, but you can have multiple different games going at the same time:
In Sandbox mode, all parts are unlocked, and you don’t have to pay for them. Sandbox mode gives you a free-play environment for going to space.
In Science mode, you need to gather science points, which you spend at the Research and Development building to unlock parts for your rockets.
In Career mode, you need to manage your finances, pay for parts, hire astronauts, and upgrade your facilities, in addition to unlocking new parts for your vessels by gathering science.
In this chapter, we’ll focus on Career mode, because both Science and Sandbox mode are just simpler versions of Career mode and can be played the same way.
When you’re playing in Career mode, you start with a very basic Kerbal Space Center and a very limited selection of rocket parts, and your crew is limited in what it can do. On top of this, your rockets are no longer free: you’ll need to pay for them. Over time, you’ll accept contracts from various organizations that want you to achieve certain goals, such as collecting data from a particular spot on a planet, or rescuing a Kerbal who’s stuck in orbit.
The central piece of the Career mode is the science system. When you start a new game, you’ll ...