"Crossing the Threshold is a carefully considered, insightful narrative that should interest anyone and everyone who cares about the future of spaceflight."

- Homer Hickam, author of Rocket Boys/October Sky

"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."

- Henry Petroski, Professor of Civil Engineering and Professor of History, Duke University, author of The Essential Engineer: Why Science Alone Will Not Solve Our Global Problems

"Crossing the Threshold is very impressive for the range of ideas and technical specifics."

- Felix Godwin, author of The Exploration of the Solar System

"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."

- Norm Augustine, author of Augustines Laws, former president of the American Institute of Aeronautics and Astronautics, former CEO of Lockheed Martin Corporation

"[Wieland] is proposing ... vaulting a discontinuity in space utilization."

- Jeff Foust, TheSpaceReview.com,