Sabrina, thanks for the topic

Technical writing may be quite complicated issue for an ordinary freelancer. By saying that, I mean that one need to have some good experience in particular technical sphere or even a degree. I know one freelancer who has degree in engineering so he is really skilled in technical writing.
It also depends on the purpose of such writing: whether you write magazine article or you write instruction for some hi-tech device.
In case you write magazine article about difference between intercontinental ballistic rockets on liquid and solid fuel you might not need engineering education. You can just research the matter through appropriate resources.