>>14005784An in depth answer would be more like an essay, to be brief robots need a power supply which is self contained, they need either hermetically sealed or differentially coated joints and friction surfaces because two like metals can spontaneously fuse in vacuum, the delicate parts like power supplies, computers, etc need insulation and radiation shielding, and the whole thing should be built to operate under extreme thermal stress. In LEO the lit side of an object can get as hot as if it were inside an commercial oven while the shaded side can be -200F.
As to robots on a planet, it depends on the planet you put the robot on, but generally they will always need some way to generate heat to keep their electronic systems functioning, a self-contained power supply, and a means of locomotion that doesn't require regular maintenance, since there are currently no facilities to repair or refurbish them.
>How tricky are rockets?Also depends on their function, in some ways rockets are a lot easier than they used to be because a lot of the fundamental issues have been learned out at this point in time, a lot of the difficulty comes with optimizing a rocket to complete it's goal as best as possible.
>Why are they so complex?A rocket is an extreme balancing act of various kinds of engineering and design tradeoffs. Rockets have to harness extremely violent and powerful chemical reactions to fly, and yet the machinery to do so has to be as light as humanly possible, tanks have to withstand many atmospheres of pressure internally, and significant compressive forces at the peak of atmospheric drag, but they have to be as light and thin as possible to save on dry mass. Propellants should be as dense as possible to allow tanks to be smaller, but also burn as efficiently as possible, etc.
You're working with a machine that operates in an environment of extremes, extreme heat, extreme mechanical stress, extreme cold, extremely high pressures, and so on.
