Yeah, the total run-scan function could be fairly short:

  (defun run-scan (antenna scan)
    "Perform a scan on this antenna. Return a scan log."
    (let* ((slew-time (move-to antenna (scan-position scan)))
           (on-source-time (delay antenna (scan-length scan))))
      (setf (antenna-last-duration antenna) (+ on-source-time slew-time))
      (make-scan-log scan slew-time on-source-time)))