The book tells the (fictional) story of a more perilous alternative to the Apollo mission, evolved from the fear that the Russians would beat the US to the moon.
I was surprised just how enjoyable it was to read. First published in 1964, when the Apollo project was in its infancy (before any flights had actually been made), it was certainly convincing enough as an alternate history, and believable. The story deals as much with the politics of spaceflight and family issues as the mission itself.
All in all, it was a jolly good read. If anyone wants to borrow it, drop me a line.