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Rolling on Red

by Josh Zeisel

While the world was thoroughly entranced by the 30th Summer Olympiad in London, England, something that can be considered an Olympic feat was accomplished early Monday morning. The Mars Curiosity rover, NASA’s newest automated robot, made its dangerous approach and difficult, but elegant, landing on the surface of Mars.

Curiosity is the latest rover to land on the surface of Mars. The history of Martian exploration began in 1976 with the Viking 1 lander. Unlike the more recent rovers, Viking 1 did not have wheels to roam the planet. Instead, its landing zone was carefully selected so it could perform experiments on the soil. Viking 1 contained sensors to perform experiments during its descent through the atmosphere to its landing spot.

On November 26, 2011, Curiosity was launched from Earth on its 352 million mile journey to Mars. Curiosity was built to perform tests that would help better understand if Mars was once able to sustain life. The rover has the most wide range of instruments and sensors than any other rover NASA has sent to Mars before.

The autonomy of the rover is also quite impressive, especially compared to its older brethren. The operator back on Earth in NASA’s Jet Propulsion laboratory in California can make a task list for the rover, pick out spots the rover should travel to, and select the experiments it will perform once it gets to the chosen spot. This information is sent out to the rover and while the operator gets lunch or goes home for the night, the rover will continue with its work. If Curiosity runs into an obstacle on the planet, like a large boulder in its path, it is smart enough to know to change its course all without the need for the operator to tell it what to do.

The most impressive aspect of this mission may not even be the experiments the rover performs, but as discussed before, the approach and landing or “The Seven Minutes of Terror,” as it has come to be known, might also be the most impressive piece of engineering and planning humanity has ever developed. The landing gets its name because while the entire sequence takes about seven minutes, the signals the spacecraft sends back to earth takes 14 minutes to travel. You can tell that the reaction of those involved was well-earned.

The rover, a machine about the size of an SUV, starts the landing from the orbiter inside a capsule. The capsule has a heat shield on one side that is directed into the path of travel when it enters the atmosphere. Even though the density of the Martian atmosphere is 0.02 kg/m3 (Earth is 1.2 kg/m3), it will still heat up the spacecraft to about 1600 degrees Fahrenheit.

Unlike Earth, Mars’ thin atmosphere does not slow the spacecraft down enough. A supersonic parachute is used to decelerate the spacecraft from 1000 miles per hour to about 200 miles per hour. The parachute is said to be the largest supersonic parachute in the world, but it is just the largest supersonic parachute on Mars. The parachute weighs only about 100 pounds, but can withstand supersonic drag forces close to 65,000 pounds.

Two hundred miles per hour is very fast and not slow enough for the rover to land, so the parachute is cut from the capsule. Inside the capsule, which is eventually blown away, is the rover and sky crane. The sky crane contains retrorockets, which continue to slow the spacecraft from 200 miles per hour to zero miles per hour 25 feet above the surface of Mars. At 25 feet from the surface, the sky crane hovers while gently lowering the rover to the ground. The sky crane stops at this height due to the exhaust from the retrorockets. At this height the exhaust does not blow dust onto the rover, but away from the rover. When the rover tells the sky crane that it is safely on the surface it flies away to crash without damaging the rover.

After the sequence is completed and the rover is safe, it lets us know back on Earth by taking a picture. At each step of the sequence a signal is sent back to Earth so the scientists know that step has started. Each signal sent back to Earth means we know the rover is one step closer to surviving the landing. A lack of a signal would have been a huge disappointment and most likely an assurance that the rover is no longer operational.

Previous rovers did not land so elegantly. The rovers Spirit and Opportunity landed on Mars in giant inflatable balls. These balls bounced along cushioning the rover inside. They were a kind of forced landing technique, unlike the grace of Viking 1 and Curiosity.

While watching the landing at 1:30 AM EDT Monday morning, it was exciting to hear that each step had started. It was great to watch these people’s reactions to these messages. You were not so much watching a landing (we could not actually see any of it), but the culmination of people’s lives over the last few years. This is truly a team effort and a win for the people at NASA’s Jet Propulsion Laboratory, the United States of America, and humanity in general. It proves we can accomplish the toughest of feats. It is said that landing a spacecraft on another planet within a few miles of a chosen spot is like shooting an apple off of Newton’s head with a arrow from a mile away. (I said that because it is THAT impressive.)

Image courtesy of MRO's HiRiSE Camera, via @MarsCuriosity

 

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Josh Zeisel is a professional mechanical engineer and graduate of Boston University. His favorite meal is a chicken parm sub and an orange soda. On clear sunny days you might look up and find him flying something. Strike up a conversation with Josh at josh.zeisel[at]theinclusive.net