Before leaving the Overworld in a Rocket, creating a few Buckets of Fuel is necessary. Enough to leave Earth and eventually return to it. Creating Fuel is a simple process, requiring Oil and a Fuel Refinery.
Creating Rocket Fuel requires Oil. After installing Ad Astra, Oil Wells can be found spawning in your world, specifically in the oceans. They should be easy to find with a high render distance as they tower over the sea’s surface.
They spawn pretty commonly. However, if you struggle to find an Oil Well, it can also be found using the locate command. In-game, enter /locate structure ad_astra:oil_well
Before heading towards an Oil Well, bring plenty of Buckets. This will reduce the need to take additional future trips and ensure you have enough fuel to return to the Overworld after a mission.
To collect the Oil, hold an Empty Bucket. Then right-click the individual oil spots located around the Oil Well. There should easily be enough to collect at least 20 Oil Buckets. Check below the water, too, as other oil spots can be found there.
Using an Oil Refinery
A Fuel Refinery will need to be crafted to convert Oil into Rocket Fuel. These require a Furnace, 2 Buckets, and 6 Steel Plates. To obtain Steel Plates, place Iron Ingots inside a Blasting Furnace to obtain Steel Ingots. Then place Steel Ingots inside a Crafting Table alongside a Hammer (provided by Ad Astra).
A Fuel Refinery also requires power, which can be done by placing it next to a Coal Generator or connecting them over multiple blocks using Steel Cables. When right-clicking a Fuel Refinery, the following interface appears.
Buckets of Oil should be placed in the top-left slot (1). Empty Buckets will then be placed into the output slot (2). The Oil-bar will begin to fill up, with it able to hold 3 Buckets worth of oil at a time. As long as the machine receives power, Oil will be converted into Rocket Fuel, and the bar on the right will fill up.
The Empty Buckets can be removed from the output slot (2) and moved into the top-right slot (3). Finally, the Buckets of Fuel will enter the bottom-right slot (4) and can be collected.
Fueling a Rocket
When a Rocket is placed on a Launch Pad, sneak and right-click it to open the Rocket’s inventory. Fuel Buckets can be added to the top-right slot, and Empty Buckets will be returned to the bottom left.
A Rocket can hold 3000mL of Fuel, equivalent to 3 Buckets at a time. With it loaded, you can stand inside the Rocket and hold SPACEBAR to begin your ascent into space. Make sure to take additional Rocket Fuel with you, as well as a Launch Pad so you can return to the Overworld.