Is it really necessary to have a lander to perform radio-astronomic observations in moon's shadow? Isn't it easier to have an orbiting spacecraft instead and perform observation while it's orbiting behind the moon?

Very readable explanation of why and how useful a dark-side lunar radio telescope would be.

TLDR: As a result of expansion of the universe, over 13B years the wavelength of neutral hydrogen signals has been stretched from 21cm to 'tens of meters'. On Earth, this part of the spectrum is cluttered with noise from Earth and Sun. For 14 days at a time...not a problem on the dark-side.