Clark's wife and the six other astronauts were killed in the final minutes of their 16-day scientific research mission aboard Columbia.
Clark, now 59, said he turned to alcohol in the aftermath of Columbia. If it wasn't for his son, he doubts he would have gotten through it.
'He's the greatest kid ever,' Clark said in a phone interview from Houston. 'He cares about people. He's kind of starting to get his confidence, but he's not at all cocky.'
Iain is set to graduate this spring from a boarding school in Arizona; he wants to study marine biology at a university in Florida.
After the accident, Iain insisted to his father: 'I want to invent a time machine.' If he could go back in time, the child reasoned, he could warn his mother about the fate awaiting her.
'He asked me why she didn't bail out, that kind of stuff, because he knew she had been a parachutist,' Clark recalled.
The tragic end to NASA's 113th shuttle flight prompted President George W. Bush to take action. He announced in 2004 that the three shuttles left would stop flying in 2010 once they finished delivering pieces of the International Space Station.
The shuttles resumed flying with new safety measures in place and eked out an extra year, ending on No. 135 in 2011.
Kalpana Chawla's husband, Jean-Pierre Harrison, who also has remarried, published a biography titled The Edge of Time in 2011.
