The greatest challenge is the sheer size of the radio search needed to look for signals ( effectively spanning the entire visible universe ), the limited amount of resources committed to SETI, and the sensitivity of modern instruments.
12.
At that time Doxsey specified that ( 1 ) repeated radio searches, especially during the high X-ray luminosity state of Her X-1, should be made and ( 2 ) there was a clear need for a better position determination for Her X-1.
