"Can deliver resources and creates temporary storage for 24 hours on a remote planet." in-game description
The Supply Pod is a ship that lands on the surface of your planet and acts as temporary storage. You can send 1 supply pod per day per planet to any inhabited planet. "Per day" means "per 24 hour period."
There are five levels of supply pods that can be built starting at level 10 of the Planetary Command Center. Supply Pods also have cargo hold, and will take some resources with them to the surface of the planet. However, be ready to use the supply pod when it arrives, because you'll only have that storage for 24 hours. Therefore, they are quite useful in helping to colonize new planets, and in rescuing comrades who have been snarked into oblivion. The amount of storage the Supply Pod has depends on the level of the ship built. As of update 3.0899, supply pods have different speeds. The smaller the pod, the faster.
Supply Pods deploy at a level equivelent to the storage building size. For example a Supply Pod 4 deploys at level 20. After the 24 hours, they blow up, leaving a crater of the same level. (5, 10, 15, 20 or 25).
Warning: An incoming supply pod needs a place to land. If you have all 121 spaces on a planet filled, the supply pod will not deploy. Instead, it will silenty destruct itself.
A supply pod will use a plot, but you do not have to have available plots. If at zero plots, you'll have -1 plots available after the supply pod deploys. Note the difference between plots and spaces.
Supply Pods when sent will deduct resources from the sending colony, however, the supply pod will not carry more than what was available at the sending colony.