Anyone who thinks astronauts ply a glamorous trade would do well to read Mary Roach’s “Packing for Mars.” The book is an often hilarious, sometimes queasy-making catalog of the strange stuff devised to permit people to survive in an environment for which their bodies are stupendously unsuited. Roach eases us into the story, with an anecdote that reveals the cultural differences among spacefaring nations. In Japan, psychologists evaluate astronaut candidates by, among other things, their ability to fold origami cranes swiftly under stress.

Soon, however, Roach has left all decorum behind. With an unflinching eye for repellent details, she launches readers into the thick of spaceflight’s grossest engineering challenges: disposing of human waste, controlling body odor without washing, and containing nausea — or, if containment fails, surviving a spacewalk with a helmet full of perilously acidic ­upchuck.

In a wry account, Roach herself braves motion sickness on NASA’s “Vomit Comet,” a C-9 transport plane modified to fly in parabolas — the only means of experiencing weightlessness outside of orbit. Its cabin is padded, and on its upward path, passengers are pressed against the floor with a force of roughly twice their body weight. But over the parabola’s crest and during the half-minute journey downward, fliers “rise up off the floor like spooks from a grave.” Having taken Scop-Dex, NASA’s anti-motion-sickness drug, Roach is euphoric. Other passengers — NASA regulars call them “kills” — are not so fortunate. Violently ill, they have had to be belted into their seats. “It’s like the Rapture in here every 30 seconds,” Roach declares. “Weightlessness is like heroin, or how I imagine heroin must be.”

The heroin imagery, I suspect, has as much to do with the motion-sickness meds as with the microgravity. They are a potent combination of scopolamine (an anti-emetic sedative) and dextroamphetamine (a stimulant).

Quoting the astronaut Jim Lovell, Roach exposes NASA’s untold sanitation woes. The Gemini 7 mission, he says, was “like spending two weeks in a latrine.” Roach appears to have combed every mission transcript from the 1960s and ’70s for scatological references. The astronauts in “Packing for Mars” don’t say prim things like “Houston, we have a problem.” While on the moon, sitting inside the Apollo 16 lunar module with the astronaut Charlie Duke, John Young blurts: “I got the farts again. I got ’em again, Charlie. I don’t know what the hell gives them to me.” Roach devotes careful attention to the design of Apollo’s “fecal bag,” a clumsy receptacle into which germicide had to be manually massaged. In contrast, she portrays the space shuttle’s suction toilet as a technological triumph, although docking with its tiny aperture can be a challenge — requiring ground-based practice on a “Positional Trainer.”

Admirers of “Stiff,” Roach’s droll report on the ways that science has used cadavers, will be pleased that “Packing for Mars” also contains post-mortem high jinks. The engineering team for the Orion spacecraft (a project scaled back by President Obama) couldn’t gather adequate collision data from mere crash dummies, so the team used dead people. In a wonderfully slapstick scene, Roach describes the engineers’ efforts to insert a freshly thawed cadaver into a spacecraft mock-up: “Think of wrestling a comatose drunk into a taxicab.”

Likewise, fans of “Bonk,” her look at the science of sex, will enjoy her relentless inquiry into off-planet mating. When it comes to graphic details, Roach elicits amazing confidences. NASA, she learns, doesn’t expect a celibate Mars crew, but one that will “mix and match or what­ever.” Roach persuades a Russian astronaut to explain ground control’s reason for nixing his request for a blowup sex doll: “We would need to put it in your schedule for the day.” And a bone-loss-study participant, forced to lie in bed for three months to simulate the effect of weightlessness on his skeleton, divulges where and how study participants conduct their auto­erotic lives.

Just when I thought there was no question Roach wouldn’t ask, and no subject she wouldn’t broach, one appeared: emotion. Or, more specifically, grief. While camping on Devon Island, a remote outpost in the High Arctic of Canada, Roach interviews Jon Clark, a flight surgeon who helped investigate the 2003 Columbia space shuttle disaster. He details for Roach how bodies break apart at high speeds. Then she realizes: he is the widower of the astronaut Laurel Clark, who died on Columbia. Roach — and the reader — want desperately to know how he coped with the loss, and how he continued to do this grisly work. But she refuses to find out: “It seemed insensitive to ask.”

Happily, Roach does not dwell on Lisa Nowak, the astronaut who drove from Texas to Florida, allegedly in diapers, to confront her ex-boyfriend’s new girlfriend. She does, however, point out that male astronauts have a diaper alternative that fits directly onto their anatomy. In the way of Starbucks, where a small is termed a “tall,” the men’s devices come only in L, XL and XXL.

On a long-duration Mars trip, urine would have to be recycled, which is not as vile as it sounds. “I will tell you sincerely and without exaggeration that the best part of lunch today at the NASA Ames cafeteria is the urine,” Roach writes, adding that after purification and desalination, it tastes like Karo syrup. Her husband, however, doesn’t share her keenness and protests when she stores her urine in their refrigerator.

The strongest parts of “Packing for Mars” chart the American space effort during the cold war. Roach deals less knowingly with the situation today, when space is, as the private entrepreneurs say, a place, not a program. While investigating zero-gravity sex, she mentions that Robert Bigelow, the founder of Budget Suites America, plans to build an orbiting hotel. But she doesn’t convey that NASA itself has begun spurning Big Aerospace boondoggles (like Orion) in favor of shoestring alternatives (a contract with tiny, upstart SpaceX for cargo flights to the International Space Station).

Just as Roach refuses to grapple with grief, she also plays down spaceflight’s greatest danger: radiation, for which no cost-efficient shielding has yet been engineered. Linked to brain damage and rapid-onset leukemia, it could quickly devastate a Mars crew. In contrast to excrement and sex, which have dedicated chapters, radiation surfaces in a scattershot, piecemeal fashion. Roach states that astronauts are classified as “radiation workers” because they receive such high doses. She tells us that cosmic rays — high-energy heavy ions from outside our solar system — can be damaging to cells, and that hydrogen compounds (not metal spacecraft hulls) are required for shielding. But she never directly addresses the radiation from solar flares, and makes a joke about a brilliant idea that, in my view, deserves a chapter of its own: on a Mars mission, the astronauts’ solid waste (rich in hydrocarbons) could be wrapped around the crew quarters to protect against cosmic rays.

At the book’s end, after more than 300 pages of debunking the romance of spaceflight, Roach herself buys into that idea, making a misguided, emotional pitch for a $500 billion human Mars mission — at the expense of cheap, reliable, robotic missions. I am not impervious to sentimentality. I felt a surge of tenderness when Roach described the “unlikely heroics” of a patch of moss on Devon Island: “something so delicate surviving in a place so stingy and hard.”

Yet compared with the irradiated void of space, a frozen rock in the High Arctic is as cozy as a baby’s crib. Packing for Mars, Roach has shown, can be entertaining here on Earth. But no way are humans ready to make the actual trip.