At one point in Gene Wolfe’s “Book of the New Sun,” a story set on a far-future Earth lapsed into a Dark Age, the narrator glimpses a “warrior of a dead world” in an enigmatic picture hanging in a dusty gallery. Clad in bulky white armor and a bubble-like helmet of polished gold, standing beside a stiff banner in a desolate gray wasteland, the “warrior” is actually an Apollo astronaut planting an American flag on the moon. For most of the inhabitants of Wolfe’s fallen world, the moon landings and the people who made them had become little more than a half-remembered fairy tale.

I recalled Wolfe’s scene while reading one of the final anecdotes in Jay Barbree’s admirably accessible new book, a biography of Neil Armstrong, who died at age 82 in 2012. At the conclusion of a global tour promoting space exploration, Armstrong, the first man on the moon, sits in a roadside diner with Gene Cernan, the last, chatting over coffee about when humans might at last return to the lunar surface, and how we might someday visit Mars. More than 40 years ago, their Apollo missions had captivated billions, but now Armstrong and Cernan were retired and relatively anonymous, pining for a future that had never fully arrived.

Like most people Armstrong and Cernan now encountered, the server refilling their cups had no idea that his customers were living bookends to what, even now, is our modern era’s most astounding adventure. Yet unlike in Wolfe’s tale, the moonwalkers’ fade to near-myth has happened not over countless millennia, but in less than a half-century. Somehow, as Apollo and its astronauts have aged, its legacy has been perversely twisted, with human interplanetary voyaging now routinely depicted as just an old-fashioned eccentricity of the Cold War rather than the existential imperative it truly is. Barbree’s well-crafted book is both a passionate defense of space travel’s importance for humanity’s long-term future and a personal remembrance of NASA’s most celebrated astronaut, though in both tasks it occasionally falters.

Much of Barbree’s writing has a “you are there” immediacy, because he was present for many of the book’s key events. During his more than a half-century as space correspondent for NBC News, Barbree witnessed and reported on each and every launch of the U.S. human space program. He is at his best when describing the visceral thrill of rocket flight, the lifeless majesty of the moon, and the visual splendor of Earth from space. These poetic passages are made all the more poignant by his close brush with becoming an astronaut, as a finalist in NASA’s failed-to-launch “Journalist in Space” program.

Over the course of his long career, many of the astronauts Barbree covered inevitably evolved from subjects to close friends. He knows and keeps their secrets, so that the stories he tells about them are often the same ones they love to tell about themselves: jovial, well-spun yarns scrubbed of inconvenient or unwholesome details through countless retellings at dinners and cocktail parties. Barbree’s story of Armstrong’s life is no exception — those hoping that his half-century of conversations with the first man on the moon will produce sensational bombshells or a work of exhaustive detail could be disappointed by the book’s streamlined, sanitized narrative.

‘Neil Armstrong: A Life of Flight’ by Jay Barbree (Thomas Dunne)

Barbree’s graceful portrait of Armstrong is a familiar tale of a stoic, somewhat reluctant hero, an adept aviator who always seemed destined to be among “the people who punched holes in the sky.” As a teenager in rural Ohio, he had recurring dreams of soaring in which he could stay aloft simply by holding his breath, and he performed his first solo flight before he could even legally drive. Throughout his eventual aerospace career, Armstrong’s hallmark was his unflappability in the face of potential disaster. Time after time, he escaped unscathed from deadly situations through quick wits and a cautious respect for the limits of humans and machines — see, for instance, Barbree’s pulse-pounding account of Armstrong’s near-death experience in 1968 on the “Flying Bedstead,” NASA’s finicky lunar-landing test vehicle. Armstrong’s legendary cool head, combined with his well-deserved reputation for humility, are often said to have been what propelled him to those first, fateful steps upon the Sea of Tranquility.

But, in one of the most touching new details Barbree reveals, the deciding factor in Armstrong’s eventual voyage to the moon may well have been the untimely death in 1962 of his 3-year-old daughter due to a brain tumor. The tragedy, according to Barbree, galvanized Armstrong and gave him “a new purpose” in volunteering for NASA’s astronaut corps. Barbree tastefully doesn’t dwell on his subject’s grief, but makes clear that it flowed as a dark undercurrent throughout the rest of Armstrong’s life, and even hints that the astronaut left a secret, unauthorized memorial to his departed daughter on the moon.

Somewhat like NASA’s human spaceflight program itself, after the pinnacle of the Apollo missions the book loses steam, compressing all the rest of Armstrong’s long life and all of post-Apollo space exploration into a few short chapters. In the remainder of the book, Barbree’s treatment of Armstrong verges on the hagiographic.

NASA, on the other hand, receives a proper flogging. Since the retirement of the space shuttle fleet in 2011, the agency has had no direct way to get humans into space, and America’s astronauts have been forced to rely on Russian rockets for rides into orbit. Like Armstrong himself, who spent his last years dismayed that, in Barbree’s words,“NASA was going nowhere fast,” Barbree has a low opinion of the institution today. Poor political stewardship and an institutional attitude of “arrogant complacency” have reduced the once-mighty agency to where it now “can’t send a live flea to the moon and bring the speck of life back still breathing.” The book lays the lion’s share of blame for this sorry state of affairs at the feet of every post-Apollo presidential administration. Strangely, Richard Nixon — the president who cancelled the Apollo program, scaled back NASA’s post-Apollo ambitions, and saddled the agency with a dangerously compromised space-shuttle design — entirely escapes Barbree’s wrath.

Armstrong’s preferred solution for NASA’s woes — and presumably Barbree’s, too — consisted of rekindling the glory days of Apollo, using colossal (and colossally expensive) rockets, built and operated by NASA, to go back to the moon and eventually on to Mars. Part of this plan is already underway: In the book, Armstrong expresses joy that NASA’s Space Launch System (SLS), which includes a rocket bigger than Apollo’s Saturn V, is now being developed. Detractors argue that the SLS will prove so expensive it will leave NASA with no funding to conduct missions properly utilizing the new hardware, but Barbree avoids mentioning these criticisms.

Indeed, the most glaring absence from this book about Armstrong is any deep reflection on the practical lessons to be learned in the aftermath of his greatest achievement. Why, after consuming so many billions of dollars, did Apollo’s momentum fizzle? Why, after investments of hundreds of billions more to build and operate space shuttles and a space station for decades, are the benefits from those projects still so elusively intangible? How can the extremely high costs of an ambitious human space program be sustainably managed, or, better yet, drastically reduced? Barbree writes that Armstrong believed the conquest of space was ultimately about becoming “masters of our own survival,” because Earth’s time in the sun won’t last forever, and sooner or later we will need new homes elsewhere. Though this fundamental truth makes finding answers to the foregoing tough questions all the more important, we do not encounter Armstrong’s thoughts on them here. Perhaps such matters are beyond the traditional purview of a biography, but facing them head-on would be the most fitting tribute possible for Armstrong and his fellow astronauts, those fading pioneers who first punched holes in the sky.

Lee Billings ’s first book, “Five Billion Years of Solitude: The Search for Life Among the Stars,” will appear in paperback later this year.