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The future of Mars exploration is, at least in the short term, riding, pardon the pun, quite literally on a two thousand pound car sized rover called Curiosity.

The weight of the two and a half billion dollar mission, called the Mars Science Lab, is not lost on the scientists and engineers at NASA’s Jet Propulsion Laboratory in California who built Curiosity. Mission Chief Engineer Rob Manning doesn’t sugar coat it. “If it does fail is that the end of exploration? Well, it may be the end for awhile. It may require a stop and regroup. Certainly it will.”

Engineer Adam Steltzner is in charge of EDL, that’s the Entry, Descent and Landing phase of the mission. “Full nights of sleep have eluded me for a couple of years now,” says Steltzner.

Why the anxiety? NASA has a good track record landing vehicles on Mars. What is so different this time around? Well, other than the planet, just about everything is different. In fact, the landing method has never been tried before. It is so unique and complicated the Space Agency has dubbed it, “Seven minutes of terror.” From the time Curiosity touches the top of the Martian atmosphere to the time it lands is seven minutes.

In the past, NASA has used either legged landers or has tucked its rovers inside giant airbags that would bounce along the Martian surface. But Curiosity is too big to be stuffed inside an airbag cocoon. And, where it is going requires a far more precision landing than every attempted before. Steltzner says, “We’re going to a place on Mars called Gale Crater and we’re landing quite literally between a rock and a hard place.”

Nestled inside a protective shell, Curiosity will hit the Martian atmosphere at thirteen thousand miles per hour shedding energy as it falls. But unlike in the past Steltzner says, “This time we’re steering as we fly through the upper atmosphere of Mars and using that steering to shrink our landing uncertainty.”

The next step is to deploy a parachute to further slow the spacecraft. But that only reduces the speed down to two hundred miles per hour. So, the spacecraft is equipped with a kind of jetpack.

“At about two kilometers above the surface, a little less,” says Steltzner, “she lets go of her parachute, turns on the rockets and flies until she’s just twenty meters above the surface. Then twenty meters above the surface the rover is lowered below the jetpack and the two together descend their way to the Martian surface.”

The scientists and engineers determined this was the only feasible landing method to get them to the Gale Crater site inside of which sits a mountain. Steltzer says, “At the end of the day we feel that the net result is a very reliable system. This architecture although it looks challenging really in the end results in a higher reliability, safer way of getting a rover of this size onto the surface of Mars.”

It’s a tight fit, says Manning, “To get there safely though we need to be able to land on the one big flat spot that sits right at the foot of that mountain inside the walls of the crater. Now, if we fly outside of those walls and hit the mountain or the walls of the crater, we’re not in good shape.”

Of course, if it all works, the payoff could be historic. Curiosity is designed to detect the building blocks of life. Scientists think water, a primary ingredient, might at one time have flowed inside the Gale crater. If this Sherlock Holmes of rovers finds that life could have existed on Mars or perhaps still does that could spark a new wave of Mars exploration fever.

With limited exploration dollars in the NASA budget, failure, on the other hand, would but a damper on or perhaps end future robotic exploration of Mars.

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.