The nuclear energy is released at the Sun’s center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength.

Firstly, spacecraft carries its mission in very severe environment, including varied temperature ranging hundreds centigrade, electromagnetic interference, high-energy cosmic radiation particles etc.

The nuclear energy is released at the Sun's center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength.