There are no radio telescopes in space because
A) no one has built an antenna large enough to reach astronomical objects yet
B) radio telescopes are too fragile and expensive to make to put into space
C) there is too much radio noise in space, so a radio telescope won't work out there
D) radio waves penetrate Earth's atmosphere so there is no need to put one in space
E) you need an array, like the VLA to detect ANY radio radiation, so it is just not realistic to put an entire array in space
