For the silver foxes among us, we may remember where we were when JFK died or when Challenger breathed her last in the skies above the Kennedy Space Center (KSC). But for NASA’s Curiosity rover—which alighted on Mars, inside the yawning bowl of Gale Crater, five years ago, today—its recollection is forever imprinted. “Five years ago tonight,” the mission tweeted Saturday, “I was rappelling out of a jetpack onto the surface of #Mars. Where were you?”
Sixty months ago, the world watched and waited for the moment of truth, as many years of planning and preparation yielded to the “Seven Minutes of Terror”. High above the plains of Mars, the incoming Curiosity rover was about to become the United States’ fourth successfully operator rover to land and traverse the surface of the Red Planet. However, unlike its predecessors—Sojourner, Spirit and Opportunity—the large size and mass of Curiosity meant that an airbag-cushioned touchdown was out of the question.
Instead, the 1,980-pound (900 kg) rover depended upon a complex arrangement of parachutes, retrorockets and a never-before-tried “Sky Crane” to guide it to a pinpoint landing within the 96-mile-wide (154 km) Gale Crater. In an event which proved as much of a miracle as a technological triumph, it succeeded, and Curiosity’s first five years have revolutionized our understanding of Mars, so much so that in December 2012 its mission was extended indefinitely.
Since then, the plucky rover has traveled more than ten miles (15 km), acquired over 200,000 images and yielded tantalizing clues of a warmer, wetter past for Mars. It has drilled 15 rock samples and its list of discoveries includes confirmation that lakes once flowed in Gale Crater, that the planet itself had an oxygen-rich atmosphere and offered exciting evidence of ancient organics and the possibility of microbial life.
Curiosity’s journey to Mars began from Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Fla., in November 2011, atop a United Launch Alliance (ULA) Atlas V booster. A little over eight months later, on the night of 5/6 August 2012, it was readied for the perilous, seven-minute-long Entry, Descent and Landing (EDL) maneuver, which placed it within a “landing ellipse” of just 12 x 4.3 miles (19.3 x 6.9 km), far narrower than anything attempted by any previous mission. Throughout the process, Curiosity operated autonomously, according to pre-loaded software parameters, and was watched “live” by an estimated 3.2 million people on NASA TV, cable networks and online.
Folded within an “aeroshell” for the bulk of its voyage to Mars, Curiosity separated from its cruise stage about ten minutes ahead of atmospheric entry. Shortly thereafter, thrusters on the aeroshell were fired to cancel out the spacecraft’s slow rotation and the process of entering Mars’ atmosphere began. Protected by a 15-foot-wide (4.6-meter) heat shield of phenolic impregnated carbon ablator, the cocooned rover survived peak temperatures of 2,090 degrees Celsius (3,790 degrees Fahrenheit) and a maximum deceleration of around 15 G. Ejectable ballast mass weights were deployed at several key stages during entry, and reaction control thrusters were fired to provide the aeroshell with sufficient “lift” during this highly dynamic phase.
Within minutes, the incoming spacecraft had slowed to Mach 1.7, and at an altitude of about 6.2 miles above the surface, a 52-foot-diameter (16-meter) parachute was deployed, after which the heat shield separated. NASA’s Mars Reconnaissance Orbiter (MRO), orbiting high above the planet, photographed the parachute deployment. Falling further into the atmosphere, the rover and its descent stage separated from the aeroshell at a velocity of 220 mph (354 km/h) and an altitude of 1.1 miles (1.7 km).
The descent stage consisted of a platform above Curiosity, armed with eight hydrazine engines, which provided 90-700 pounds (40-320 kg) of variable thrust to slow the descent, after which the Sky Crane lowered the rover with a 25-foot-long (7.6-meter) tether to a soft, wheels-down landing on the red-hued surface. After detecting and confirming “Weight on Wheels”, a series of pyrotechnic charges cut cables to free Curiosity from the descent stage, which then flew away to a crash landing about four miles (6.4 km) away.
Simply reading that description of Curiosity’s arrival on Mars makes it all the more remarkable that it was pulled off at all, let alone that it was pulled off entirely without incident, although not without a certain amount of nail-biting tension on the part of the mission control team and space enthusiasts around the world. Curiosity achieved Weight on Wheels on the Martian surface at 10:17 p.m. PDT on 5 August (1:17 a.m. EDT on 6 August 2012) and touched down less than 1.5 miles (2.4 km) from its target…after a 350-million-mile (563-million-kilometer) journey. Firm confirmation of its successful landing reached the ears of an exuberant flight control team about 14 minutes later.
Its landing site was Gale Crater, an enormous impact basin, estimated at somewhere between 3.5 and 3.8 billion years old. Within the crater lies the forbidding 18,000-foot (5,500-meter) peak of Aeolis Mons (“Mount Sharp”). And here, for the last five Earth-years, Curiosity has conducted a truly astounding program of scientific observation and discovery which the whole world has had the opportunity to share and experience.
“We now know Mars offered favorable conditions for microbial life, billions of years ago,” said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena, Calif. “It has been gratifying to succeed, but that has also whetted our appetites to learn more. We hope those enticing layers at Mount Sharp will preserve a broad diversity of other environmental conditions that could have affected habitability.”