Planet hoppers are miniature rockets that are easy to launch, but can only carry players. An optional setting, enabled by default, allows travel directly between planets skipping space platforms entirely.
Mods introducing new content into the game.
Transportation of the player, be it vehicles or teleporters.
The description says that it only transports the player, but in fact it also holds an item.
This slot is a base game constraint. As noted in the launcher description, any items in the cargo slot will be voided.