How does one potty in zero gravity?

When Mary Roach describes her writing process, she is nothing if not self-deprecating.

“I always know that there will be three or four months of utter confusion and no sense of what the book will be,” she says. “Usually there’s a period of low-grade panic, of sad flailing.”

The 51-year old author started her writing career as a copy editor and publicist before penning her first freelance column for the San Francisco Examiner. With her 2003 debut book “Stiff: The Curious Lives of Human Cadavers,” she launched a bestselling series of hybrid humor/science books that includes “Spook: Science Tackles the Afterlife” and “Bonk: The Curious Coupling of Science and Sex.”

Speaking via phone from her home in Oakland, she recounts her expectations for “Stiff”: “I thought it was a one-off for sure. I thought no one will (a) buy this book, (b) read it and (c) like it.”

She adds that she’s not trying to sound full of humility.

“It’s actually true,” she says. “It’s hard for me to envision a scenario where people walk into a bookstore and say, ‘Oh, a book about cadavers! That’s what I’m going to read next.’ ”

But Roach’s tale of dead bodies -- or “mounds of tissue” as she puts it -- piqued the public interest and garnered her a rabid fan base. After following up with volumes delving into the paranormal and human sexuality, her new book is “Packing for Mars: The Curious Science of Life in the Void” (W.W. Norton & Company).

Other aerospace volumes on the market may detail historical timelines of missions to Mir or attempt to elucidate the physics of antigravity, but Roach approached the topic with a witty candor that’s her trademark -- along with a level of curiosity that would mortify most casual investigators.

Though “Packing for Mars” opens by describing the physiological screening of Japan’s aspiring astronauts, it later gets to the good stuff: zero gravity bathroom practicalities, liquor cabinets in space, vomiting in helmets and intercourse in orbit. Roach says that she set out to humanize aerospace, a topic that tends to maintain a sense of steely nobility.

“Space: what could be more strange and hostile than that?” she asks. “What happens when you put someone up there and there’s nothing green and they can’t eat fresh food and they miss their family and they can’t have sex?”

With chapters titled “Houston, We Have a Fungus” and “Eating Your Pants: Is Mars Worth It?”, Roach employs the morbid inquisitiveness that’s won over readers who prefer their science peppered with humor. Like her other books, “Packing for Mars” has plenty of first-person anecdotes and hilarious footnotes, such as explanations of “maximum absorbent garments” which are, essentially, space diapers. Her prose remains delightfully wry, with statements such as “Gravitation is the lust of the cosmos,” and passages that proclaim “a space station is a rangy monstrosity, a giant erector set built by a madman.”

Two years in the making, “Packing for Mars” necessitated visits to aerospace institutions in various countries, as well as the sipping of her own recycled urine. For research.

Asked if it was difficult to get NASA’s American astronauts to confess about vomiting or mid-orbit existential crises, she simply says: “Why do you think I went all the way to Russia?” During her Russian trip, it should be noted, she toured a museum dedicated to Soviet rocketry, discussed head lice and took shots of whiskey with retired cosmonauts. All by 11 a.m., Moscow time.

Roach has a lifelong obsession with travel; she graduated with a degree in psychology from Wesleyan University because it was the major most accepting of credits from studying abroad. Her travels -- which involve encounters with eccentric experts and sage taxi drivers -- bleed freely into her writing. First person has been fundamental to her style from her very first published pieces.

“It’s the easiest journalism to do, in a way. As you mature, you move away from first-person journalism,” she says, before adding, “I guess I never matured.”

One question Roach is often asked is why her latest book doesn’t follow the tradition of her previous books with a monosyllabic title, like “Stiff” and “Spook.” The answer is less meaningful than many readers might assume: She and her publishers simply couldn’t think of one that they liked. “Zoom” and “Blast” were vetoed, as was “Orbit” because Roach thought it sounded too much like a chewing gum. Collaborating, they settled on “Packing for Mars.”

“Writing is something you don’t do in vacuum, to use the space analogy,” she says.

For someone who asserts that she never envisioned herself as a writer, Roach is still surprised that her career has landed her on bestseller lists.

“I didn’t really realize that writing ... would be fun and people would pay you to do it,” she says. “Being an astronaut is a glory profession, and so is writing in a way.”

Glory, of course, is as subjective as it is elusive. As an author who’s had sexual intercourse in an MRI machine for “Bonk” and tested a space toilet for “Packing for Mars,” Roach herself remains a vital character in each of her books. Her interactions with experts lend the gritty scientific details a sense of addictive levity.

None of her experiences are embellished, though she does say she “strips away the stuff that’s not interesting or funny,” leaving “moments [in which] I feel bewildered, shocked and disgusted. The more entertaining moments.” Quickly returning to self-deprecation, she adds, “Day by day I’m kind of a bore.” Hard to believe.

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alie.ward@latimes.com

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