A test double for the Mars rover Sojourner at Jet Propulsion Laboratory's… (Cheryl A. Guerrero / Staff…)
Two weeks before the rover Curiosity's scheduled landing on Mars, NASA engineers stood on a hill overlooking the Jet Propulsion Laboratory campus, punching commands on their iPhones to test model rovers' ability to navigate over bulky red rocks.
They were working on JPL's Mars Yard, a carefully constructed fake Martian surface. Just like the Red Planet itself, everything at JPL's Mars Yard is a dusty red color — as long as you ignore the deer-crossing sign and occasional weed popping up through the soil.
The testing surface, made from a blend of beach sand, decomposed granite, brick dust and volcanic ash, has undergone several transformations since it was built for the Pathfinder and Sojourner missions in the 1990s.
The first yard, which stood where JPL's fire station is today, was about 80 feet by 60 feet. As the rovers grew, so did the Mars Yard. The second Martian landscape was created in 1998 at the corner of Pioneer and Loki roads, and it dwarfed its predecessor at 216 feet by 118 feet.
In 2007, when JPL began working on the Mars Scientific Laboratory, nicknamed Curiosity, workers expanded the yard again.
“It was clear we needed a larger space,” said Issa Nesnas, a JPL robotic software systems supervisor. “For imaging purposes, we wanted to look further out than 10 to 15 meters.”
Nesnas, who helped plan the second- and third-generation Mars Yard, said designers included slopes this time around so engineers could test the rover's ability to traverse hills.
Curiosity is slated to land Sunday night in Mars' Gale Crater, at the foot of a steep mountain, so the installation of a slope was key. “It turned out to be a very important feature in the Mars Yard,” Nesnas said.
A building adjacent to the yard has offices for researchers and doubles as a garage for retired rovers. Last year, Mars program veterans came together to watch Marie Curie, the test double for Sojourner, roll out of its box and join its successors in the yard.
Many of the volcanic rocks in the Mars Yard are hand-me-downs from previous testing sites, collected from the Mojave Desert. Engineers and scientists use lightweight landscaping rocks to create new scenes without bringing in bulldozers.
“Visually, they look like normal rocks,” said JPL Mobility and Robotic Systems Manger Richard Volpe. “But they're less dense than the ones on Mars.”
If it sounds like a movie set, well, they've tried that, too. Workers once used hollow set rocks, but JPL generally stopped using them because they deteriorate quickly, Volpe said.
Joseph Giri, a Long Beach artist, designed custom murals for the first and second yards that depicted JPL rovers exploring the Red Planet. Today, hills and rocks of various sizes and colors fill the space and give it a more three-dimensional feel.
JPL scientists made sure the color of the soil in the Mars Yard matches that on Mars, and not just for aesthetic reasons. The primary engineering cameras on Curiosity are black and white, and scientists wanted the spectral colors on the fake planet to be the same as on the real one.
During missions, the yard is altered based on what terrain the rover is driving over. Flat rocks were added after Spirit and Opportunity experienced slips. Volpe said JPL will likely rearrange the yard again after Curiosity lands.
“I expect that as we get into Gale Crater and need to do tests, we will modify the Mars Yard to mimic it,” he said.
The Mars Yard is fairly low maintenance, Volpe said. The decomposed granite, smooth and dry like the surface of Mars when first laid out, can become hard after a rainstorm. JPL workers till the soil in the springtime to soften it. Occasionally, they have to pull a weed that pokes through the surface.
“When plants pop up, it doesn't look like Mars anymore,” Volpe said.
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