"Crossing the Threshold is a carefully considered, insightful narrative that should interest anyone and everyone who cares about the future of spaceflight."
"Crossing the Threshold is a NASA veteran's thoughtful and considered look at the value of space travel and exploration, not only for satisfying humanity's seemingly unquenchable thirst for adventure and knowledge but also for preparing and positioning us technically to begin to solve some of the greatest problems facing us on Earth."
"Crossing the Threshold is very impressive for the range of ideas and technical specifics."
"Paul Wieland knows space from the bottom-up…and offers a fresh and valuable perspective. I intended only to skim the book but became so interested I soon found myself deeply involved in reading it."
"[Wieland] is proposing ... vaulting a discontinuity in space utilization."