For large instances pictures is probably the bigger consumer of space, but for small instances the database size is the bigger issue because of federation. Also, mass storage for media is cheap, fast storage for databases is not. With my host I can get 1TB of object storage for $5 a month. Attached NVMe storage is $1 per month per 10 GB.
For my small instance the database is almost 4x as large as pictrs, and growing fast.
Some satellites and rovers have used Radioisotope Thermoelectric Generators (RTGs), which are very different from a nuclear reactor. They use polonium-210, which generates heat, and that heat is converted to electricity with thermocouples. They are low power and inefficient.
To my knowledge no satellite, with an RTG, has ever used ion propulsion. Few interplanetary satellites have ever even used ion thrusters. Dawn, Hayabusa, and Deep Space 1 are the only I can think of, and they all used solar arrays.
Ion thrusters are super efficient, but produce extremely small amounts of thrust. They aren’t practical for getting large spacecraft to Mars. These proposed nuclear engines produce large thrust while have efficiency somewhere between regular chemical propulsion and ion propulsion.