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REFRACTIONS - By Henry Petroski

Landing on Mars

A triumph less of science than of engineering

Photo: HENRY PETROSKI - CERN’s collider, like NASA’s rover, depends on ingenious systems design.Last August, after an eight-month journey through space, the NASA rover Curiosity touched down safely on Mars. There was elation in the control room at the Jet Propulsion Laboratory over the flawless landing, which employed a daring new system to let the 1-ton vehicle down gently onto the Martian surface. The feat was widely reported in news media around the world.

Just one month earlier, science and technology news was dominated by an achievement of another kind and scale. At the European Laboratory for Nuclear Research, known as CERN, a team of physicists announced that they had found evidence of the existence of the elusive Higgs boson elementary particle. With its discovery, a key piece of the puzzle surrounding the nature of matter may be in hand.

In response to all the press that the JPL rover team was getting for its interplanetary achievement, the CERN Higgs-boson team initiated some presumably good-natured banter. According to a spokesman, the Mars landing “does not qualify as a significant scientific achievement and should not be getting so much of the public’s attention.”

Of course, the set-down on Mars of the rover was not an achievement of science; it was one of engineering. Landing anything on Mars is at least as difficult as landing it on the moon. The acceleration due to gravity on the red planet is about twice as great, and the rarefied Martian atmosphere provides little help from friction. In combination, these effects make it tough to slow down an object that makes entry at a speed in excess of 13,000 miles per hour.

The soft landing sequence employed with Curiosity is a model of engineering system design. Earlier rovers had effectively been wrapped in air bags and allowed to bounce to a stop after free falling from a safe speed. But the air-bag technique was not viable for use with the considerably larger and heavier Curiosity. Instead, a so-called sky crane operation was employed.

After a parachute and other means slowed the landing module to a target speed, retro rockets allowed the module to descend in a controlled manner toward the landing area. When close to the surface, the module effectively hovered then lowered the rover to the ground and put it down on its wheels. When this had been achieved, the powered module took itself a safe distance away before crash landing.

Ironically, the begrudging scientists at CERN owed at least as much to ingenious systems design for their detection of the Higgs boson. Their instrument of discovery, the Large Hadron Collider, is the world’s largest and most powerful particle accelerator, whose guts are contained in a circular tunnel of 17-mile circumference that straddles the Franco-Swiss border.

As are scientific instruments generally, the collider is obviously a product not of science but of engineering. Indeed, it is arguably the case that science depends more on engineering than engineering does on science. In its pursuit of knowledge and understanding, especially of things as elusive as elementary particles and as remote as rocks on the surface of Mars, science has great need for complex engineered systems.

It is thus unfortunate that NASA’s most recent highly visible space mission is named the Mars Science Laboratory and the collection of mobile robotic instruments is referred to as the Mars science rover. The mission was certainly motivated by scientific curiosity and the goal is certainly scientific discovery, but without creative and careful engineering, the rover could have neither gotten off the ground nor journeyed the 350 million miles from Earth to Mars and landed there softly.


Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University. His latest books are An Engineer’s Alphabet: Gleanings from the Softer Side of a Profession (2011) and To Forgive Design: Understanding Failure (2012).


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