"Galactic cosmic radiation damage to human beings is one of the most limiting design criteria for a spaceship," he said. "Right now, from what we know, we cannot shield a human being to the level that the safety people tell us we would need."
"[BTE Dan] starts with reasonable technical information, ion engines and nuclear power and those sorts of things," said James Gilland, a researcher at the Ohio Aerospace Institute who studies space propulsion. "But when he extrapolates them in power and size, everything breaks down. You can't just linearly scale this stuff. I disagree with his statement that we have the technology now to do this. We don't."