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Video grab taken from the Chilean TV shows the Fenix capsule beginning the ascent during the rescue operation at the San Jose mine, near the city of Copiapo, Chile.

HO/AFP/Getty Images

Sitting atop a concrete pad in the moonscape of the Atacama Desert, the slender capsule designed to rescue 33 trapped Chilean miners bears a striking resemblance to a comic book rocket ship. So it's only fitting that the steel cage was engineered with great precision using advice from NASA scientists.

The problem: How to pull men up a narrow shaft more than 600 metres long, punctuated by mine passages that could snag a rescue capsule.

The solution: the "Fenix," a four-metre-tall, half-metre-wide steel cage.

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Three weeks after the mine collapsed, Clint Cragg, a top NASA engineer, went to Chile with some of the space agency's health-care experts to lend a hand. After speaking with engineers in the Chilean navy, he suggested that he could help them design a rescue capsule.

After returning to the United States, Mr. Cragg assembled a group of 20 NASA engineers and began working on the problem.

"Over the course of three days we hammered out a 12- to 13-page list of requirements for the capsule and sent that to the Chilean Minister of Health," Mr. Cragg said in a statement as the rescue proceeded.

The suggestions included everything from outfitting the device with an oxygen tank to advising that the contraption be built so it wouldn't scrape against the walls of the drilled rescue shaft.

The engineers also had a precedent to look at: the "Dahlbusch Bomb," built in 1955 to rescue three men trapped in the Dahlbusch coal mine in the Rurh region of western Germany. It was used on several other occasions, most famously to pull 11 miners from the flooded Lengede-Broistedt mine in November of 1963, after they had been trapped underground for 14 days.

Slightly shorter and stubbier than the Fenix, it is about 2.5 metres tall and 38.5 centimetres wide.

Using NASA's list, the Chilean navy ultimately came up with the design for the 400-kilogram Fenix. The interior of the capsule is just wide enough for a man's shoulders and about two metres tall. It is fitted with a harness to hold the miner in place and equipped with a microphone and an oxygen supply.

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To ensure it rolled smoothly against the rock walls and steel reinforcement in the shaft, it was equipped with spring-loaded retractable wheels.

The slim design was necessary to fit into the narrow shaft connecting the underground chamber to the surface. The length was needed to ensure the capsule remained within the shaft at all times and didn't inadvertently swing into a mine passage on the way up.

To be especially careful, engineers designed three nearly identical capsules. The first was used during tests, while the second has been used during the rescue operation.

"We have used the Fenix One for many tests and training of the rescuers, so it has been moved a lot and hit. So the Fenix Two is in better condition," Chilean Mining Minister Laurence Golborne told reporters ahead of the rescue.

Painted the red, white and blue of Chile's flag, the device has functioned almost flawlessly, quickly and safely pulling miners up the long, narrow shaft. It had a door that stuck occasionally, and its wheels needed lubricating at least once, but it worked exactly as planned.

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