The Martian landscape is otherworldly. The ground is twisted into ropelike coils, rippling waves and jagged spikes; sulfurous gases billow from vents in the ground, bits of volcanic glass glitter in faint sunlight that filters through the undulating fog.

Two astronauts clamber across the tortured terrain, encumbered by the heavy scientific instruments they carry on their backs and in their hands. They are looking for rocks that could tell us whether life ever existed on Mars.

At makeshift mission control inside a converted conference room several miles away, Darlene Lim surveys video from the scene. The NASA geobiologist has been planning this mission for months. She listens attentively to the chatter between the roving astronauts and their counterparts at "base camp" and watches as one of the scientists in the field points a handheld spectrometer at a rock and scans it, Star Trek-style. Data on the rock's composition starts streaming onto Lim's computer screen.

"This is super awesome," Lim murmurs under her breath. Remembering a reporter is listening over the phone, she laughs at herself. "It is!"

This landscape, of course, is not actually Mars, and the people exploring it aren't really astronauts. But the expedition to the Mauna Ulu volcano on the Big Island of Hawaii is a dry run for the distant day when NASA intends to send a real crewed mission to the Red Planet.

Though NASA has spent billions of dollars and countless hours trying to get people into space, what they actually do up there can be an afterthought. Lim wants to change that.

"You're trying to keep people alive and trying to get them beyond low Earth orbit … there are experiments that are done, but the science isn't really baked in," Lim said. "But when we head out to somewhere like Mars, and we're going to be there for a while … we're going to have to look at designing these missions with an inherent component to science."

With the exception of space suits - and the thin, oxygen-less atmosphere that necessitates them - it is as high-fidelity a mission to Mars as Lim can muster. The Hawaiian mountainside is similar to the landscape scientists think existed on Mars billions of years ago, when the atmosphere was thicker and the planet seethed with volcanic activity. The "astronauts" tasked with collecting rock samples use instruments that are being developed for real space missions; one heavy backpack contains a spectrometer that is destined to fly to the moon. Their time in the field is limited to the length of an average astronaut excursion outside the spacecraft: about four hours per day. Their communications to "mission control" (the conference room where Lim and her colleagues are set up) are subject to a five- to 15-minute delay that mimics the actual signal latency between Earth and Mars.

And the science is real. Unlike many other NASA analog missions, which test gear and operations design on safe, familiar terrain, Lim and her team are exploring a site they have never seen. They are collecting rocks not for practice, but for research - the samples will be studied to understand the relationship between rock types and the microbes that live in them. Some day, the scientists hope their findings will help guide the search for past or present Martian life.

NASA has been trudging toward its goal of launching a human Mars mission in the 2030s - though at the program's current pace, it's unlikely to meet that deadline. And about six weeks before the mission's trip to Hawaii, SpaceX founder Elon Musk announced his conceptual plans for a powerful rocket and spacecraft that would help humans colonize the Red Planet. Discussing the news at NASA's Ames Research Center in Moffett Field, Calif., engineer Amanda Cook shook her head.

"The rocket's the easy part," she said. "It's people who really throw a monkey wrench into things."

This is the guiding principle for the Hawaiian mission, called BASALT, which stands for Biologic Analog Science Associated with Lava Terrains and is also the name of a kind of volcanic rock. Robots, satellites and space telescopes have produced pioneering, Nobel Prize-winning science - and they don't require food, oxygen or a return trip home. If NASA is going to put humans on Mars, it needs to be certain the discoveries made are worth the expense and risk of sending them there.

During the Apollo program, science goals were secondary to the sheer technical challenge of getting people to the moon, and most astronauts had backgrounds in the military rather than research. Though the astronauts got some training in geology, and landing sites were selected according to pre-mission surveys of the moon's surface, the collection of rock samples was relatively haphazard. Subsequent research on board the International Space Station has yielded mostly minor discoveries, and it is conducted in the relative security of low Earth orbit, where every detail can be monitored by principal investigators on Earth.

On Mars the risks are more immense, and help from home is dependent on weak and sometimes erratic connection with mission control. That's why BASALT takes place in an environment known to the researchers mostly through satellite images. Lim wants to make sure that the mission leaves room for the unknown.

"NASA has a lot of legacy of automation," she explained. The space agency understandably prefers to minimize the potential for the unpredictable, given that lives are on the line. "But we're trying to figure out how to not stamp the humanity from human exploration."

With that goal in mind, Lim has recruited experts from a wide range of fields to help with her Mars analog mission. Engineers such as Cook are building instruments that astronauts can carry on their backs and in their hands. Computer programmers develop communications software that can inform astronauts without overwhelming them. Geologists establish protocols for quickly analyzing rock types and prioritizing which ones to sample. The team even includes an ethnographer whose job is to analyze members' interactions and figure out better ways for them to collaborate - a necessity for future Mars astronauts, who will have spent months in cramped, inescapable quarters.

It's the "unsexy" side of mission planning, planetary scientist Rick Elphic admitted during that meeting at Ames. "But if you don't do it, you'll design a mission that doesn't work."

A month and a half later, Elphic and his colleague Kara Beaton are standing on the side of the Hawaiian volcano, in the middle of finding out whether all that preparation paid off. Already, there have been hiccups, which is helpful. Better to find out now that a communication tool doesn't work or a schedule needs to be rearranged. It's the eighth day of the expedition and the second day at this particular site. The "astronauts" asked to return to the rugged expanse of black and red rock after not having sufficient time to explore it the day before - field work almost always takes longer than expected - and geologists at mission control acceded to their judgment.

The fog that cloaked the mountain at the beginning of the expedition has burned off, revealing the treacherous terrain. Most of the BASALT team has scraped palms and scratched knees from collisions with the craggy rock, and the scientists are wary of concealed lava tubes, whose thin crusts could crack under a person's weight, dropping them into caverns below. Beaton spends several minutes trying to maneuver toward an intriguing rock formation before deciding it's not safe. With little more than half the time left in their expedition, she and Elphic need to wrap in the pre-sampling phase, in which they measure rocks against the criteria drawn up for them by geologist colleagues to decide which are most worth bringing home.

They are looking for examples of alteration, volcanic rocks whose composition has been changed by water and weather. The samples they collect will be analyzed by colleagues such as Allyson Brady, an organic geochemist at McMaster University in Canada. Brady will be looking for biosignatures, traces left by organisms that once inhabited the rock. Ideally, these biosignatures will correspond with qualities that can be seen from satellites; then researchers studying data from Mars orbiters can look for the same features in the Martian landscape and identify spots of interest to the future explorers.

"Sitting back watching these video feeds coming back from people actually out in the field and trying to see what's around them … it's different, that's for sure," Brady said. Researchers like her are used to doing their own field work, spending days searching for the right samples. It's disconcerting to put those decisions in someone else's hands.

"Oh, we absolutely could just apply to a grant to go check out basalts in Hawaii," she acknowledged. But that's not the point.

"You can do the science separately and the exploration separately. But that doesn't really tell you very much about whether, from science perspective, the exploration concept you're testing has actually done a good job. … I want to make sure that when someone does go to Mars, they have tested all the things that are going to give them the best possible science."