NASA's Mars rover heading toward '7 minutes of terror'

Engineers will use rockets, a supersonic parachute and a sky crane to land robotic rover (see video)

When NASA's newest and largest robotic rover lands on Mars early Monday morning, it will use a supersonic parachute, a tether and rockets to safely alight 350 million miles from home.

Seven minutes will elapse between the time the spacecraft enters the Martian atmosphere and the time it touches down on the planet's surface. NASA engineers say this will be the seven scariest minutes of the mission.

"Entry, descent and landing is referred to as the 'seven minutes of terror' because we've got literally seven minutes to get from the top of the atmosphere to the surface of Mars, going from 13,000 miles an hour to zero in perfect sequence, perfect choreography and perfect timing, and the computer has to do it all by itself with no help from the ground," said Adam Steltzner, a NASA engineer, in a video interview. "If any one thing doesn't work just right, it's game-over."

After a journey of more than eight months, NASA's SUV-sized robotic rover -- the Mars Science Laboratory, also known as Curiosity -- is set to land at 1:31 a.m. Eastern time on Monday in a 96-mile-wide crater.

The $2.5 billion, nuclear-powered rover will start a two-year mission to help scientists learn if the area has, or ever had, conditions that could support life.

Equipped with 10 scientific instruments, Curiosity has the most advanced payload of scientific gear ever used on the surface of Mars, including chemistry instruments, environmental sensors and radiation monitors. The payload is more than 10 times as massive as those of earlier Mars rovers.

However, before work can begin, Curiosity has to safely make it to the ground. And that is a huge job.

NASA engineers explained that when the spacecraft hits the Martian atmosphere, it will be traveling at 13,000 miles an hour. The atmosphere will slow the craft a bit, but not enough for a safe landing.

That's why it will release a parachute when it hits 1,000 miles per hour.

"The parachute is the largest and strongest supersonic parachute that we've ever built," said Anita Sengupta, a NASA engineer who has worked on the rover's landing capabilities. "It has to be able to withstand 65,000 lbs. of force even though the parachute itself only weighs about 100 lbs."

At that point, the heat shield is jettisoned because it's blocking the craft's radar. "The radar has to take just the right altitude and velocity measurements at just the right time or the rest of the landing sequence won't work," said Steve Lee, another NASA engineer.

The parachute is expected to slow the craft down to about 200 mph, but that's still not slow enough to land.

NASA engineer Tom Rivellini said that at about a mile above the surface, the parachute is cut off and the rover fires up rockets that will further slow its descent. Using the rockets, along with radar to calculate where it's headed, the rover will head straight down to the bottom of a crater.

However, before it can land, it needs one more piece of equipment.

"We can't get those rocket engines too close to the ground," said Sengupta. "Because if we were to descend propulsively with our engines all the way to the ground, we would create this massive dust cloud, and that dust cloud could go and land on the rover and it could damage mechanisms and it could damage instruments."

To deal with that, when the spacecraft is about 65 feet above the ground, it will lower the rover on a 21-foot-long tether, also known as a sky crane. When the rover's wheels touch the ground, the tether will be cut and the spacecraft that carried the rover will fly off to land a safe distance away.

Upon landing, Curiosity is expected to be not just inside a crater but beside a mountain that's three miles high.

NASA announced last week that engineers have maneuvered its Mars Odyssey robotic spacecraft, which has been orbiting Mars since 2001, into position so it can relay information back to Earth from the rover during its descent and after its landing.

Team members at NASA's Jet Propulsion Laboratory share the challenges of the Curiosity Mars rover's final minutes to landing on the surface of Mars.

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin or on Google+, or subscribe to Sharon's RSS feed . Her email address is

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