Can radiation be converted to energy?

Well, a couple of things... energy being delivered *can* be through photons - it's what the sun does for Earth - and that's the form of much of the radiation we're exposed to... Gamma rays, ultraviolet, microwaves - all travel via photons, delivering energy.

Then, on the Mars right now, and on the two Voyagers, and even a couple of experiments on the moon - they used the decay from plutonium as a long-lasting battery, converting it's heat to electricity to power experiments and communications.

So, YES, Radiation can be converted to energy - or is *already* energy in many cases.

A solar sail converts sunlight into kinetic energy, if that's what you mean. It wouldn't work in interstellar space because starlight is too weak.

It is like a form of energy and yes it can, apparently a ''Black hole starship,'' is powered by a blackhole that emits hawking radiation. This radiation is used to propel the ship by means of using a parabolic reflector. Although this is simply theorized stuff, you may want to have a look on wikipedia and check it out!

Radiation IS energy!

In principle, you could make a spaceship that was powered by starlight. But the energy density is extremely low.

The energy in space has high entropy - that means it is almost completely useless.

You mean electromagnetic radiation? it is radiant energy already.