Daredevil Nik Wallenda practices for his June 15 walk across Niagra Falls. (Ida Mae Astute/ABC)

This Friday, Nik Wallenda will attempt what's never been done before: He will walk across a cable suspended 173 feet over Niagara Falls under the dark of night on live television.

But the veteran daredevil - a seventh-generation member of the Great Wallendas, the legendary travelling family circus troupe - said the greatest challenge facing him isn't physical. It's mental.

During his practice sessions for his landmark June 15 walk across Niagra Falls, while Wallenda's feet are busy taking careful, measured steps, his mind is juggling obligations: With a stunt as big as this one - taking place across a transnational border, no less - Wallenda must make sure he's dotted his i's and crossed his t's with a host of government agencies, both American and Canadian. Then, of course, there are the logistics: Wallenda and his tiny company - it's just him, his father and an uncle - are involved in elements as basic as confirming the deliveries of fencing needed to hold back his crowd of admirers on the big day. Plus, Wallenda must be sure he politely returns the phone calls of folks like concerned state senators, news reporters and well-wishers who inquire about his health and more.

"Everything from the media to everything else - it's very distracting, very draining, at times," he said.

And so Wallenda, 33, said his biggest challenge during his training sessions is just keeping his focus. But, other than that, the stuntman said he's feeling good. He has been training in a number of venues, including Seneca Niagara Casino in Seneca, N.Y. , in conditions meant to simulate those of Niagara Falls. He's endured sprays of heavy mist from a fire hose and wind gusts of up to 44 miles per hour, courtesy of a wind machine.

Wallenda wasn't just battling the elements - he was testing his endurance. The training wire at the Seneca Falls Casino was some 1,200 feet long and 60 feet high at its high end. He often would walk up, walk down, turn around and walk back up for a total walk of 2,400 feet. The length of his walk across Niagara Falls will be 1,500 feet.

"I spent 10 days walking on a cable that would duplicate the incline that I would walk up during the second half of the walk, as well as the decline I would walk down during the first half of the walk," he said.

Wallenda said that despite all the distractions bedeviling him now, he expects to be clear-headed on the on the day of the walk.

"At that point, all of the permitting is out of the way, so I think I'll be able to focus very well," he said. "In that sort of situation, you have no choice but to focus."

Watch "Megastunts: Highwire Over Niagara Falls Live" Friday at 8 p.m. ET.