Complex sentence: These attempts were unable to detect any emission due to technical limitations of the instruments and the discovery of the radio reflecting ionosphere in 1902 led physicists to conclude that the layer would bounce any astronomical radio transmission back into space, making them undetectable.
Split into simpler sentences: These attempts were unable to detect any emission due to technical limitations of the instruments. The discovery of the radio reflecting ionosphere in 1902, led physicists to conclude that the layer would bounce any astronomical radio transmission back into space, making them undetectable.