The Spacesuit is what you wear in Lunacraft. There are 3 slots: the Helmet, the Battery, and the Jetpack.
The different slots in the Spacesuit
Despite there being a Helmet Slot, it is not very clear what it does. It either hasnt been updated, or wasnt meant to be there. However, it has been noted that if you place Notchium in that slot, you can take two more hits from White Astronauts, but every other metal seems to have no effect.
The Battery Slot is where your sources of energy go. You start with the Battery which is the worst, but you can also use the Power Crystal, which is the second best, and the Energy Orb, which is the best. Doing this recharges your suit faster and increases the speed of which you run.
The Jetpack Slot is where the Jetpack goes. Each level (Jetpack v1, v2, and v3) increases the speed of your accent into the air, and gives you more fuel for flying before you run out. Additionally, if the Battery Slot has something better in it, such as an Energy Orb, your Jetpack will recharge faster.