NASA and other space programs primarily use radio waves to transfer information from spacecraft back to earth. Why don't they use gamma rays, which are more powerful?
Since radio waves have less energy than gamma rays, isn't it more likely for radio waves to get blocked by clouds, whereas gamma rays can pass through clouds?
Gamma rays are "more powerful" than radio waves only in the sense that the photon energy of the former is much higher; "gamma" radiation is usually taken to mean electromagnetic radiation arising from decays of atomic nucleusses and other nuclear processes; they have a wavelength of well less than a nanometer, whereas AM radio waves have wavelengths of hundreds of meters. A typical gamma photon energy is of the order of $1{\rm MeV}$; an optical photon is of the order of a few ${\rm eV}$ and a radio wave of the order of $10^{-8}{\rm eV}$.
Radio waves are easy to make at high powers - tens of kilowatts - with alternating electric currents produced by primitive electronic technology. They are also easy to modulate, i.e. to have a signal encoded onto them- with the same technology using sophisticated modulation schemes. The effects of such waves of even these powers on biological systems is very mild. Gamma rays of this power are hugely expensive to produced with human technology; only nuclear processes will make them. They can only be modulated by mechanical means - deflexion from mirrors and shutters, so would be useless for high speed communication - of the order of ${\rm GBps}$ which we nowadays routinely achieve with radio technology. Gamma rays of this power are utterly lethal to any biological system in their path. Moreover, their high photon energy means that they interact with and are swiftly (in comparison with radio broadcast distances) absorbed by air. They would be useless for terrestrial communications from this last point of view also. Radio waves, with their low photon energy, have very little interaction with clear air.
First, available gamma rays sources are not "more powerful" compared to electromagnetic wave transmitters, i.e., they emit much less energy/time. Second, gamma rays are extremely dangerous for the human and all other living beings. You would not survive next to such a source even when exposed only for a very short time. Third, the signal modulation and detection of gamma rays is more cumbersome than that of radio waves.
