A Mars visit via the Fitzgerald Theater
June 3, 2013
by Mark Ollig

Recently, yours truly attended the Mission to Mars presentation at the Fitzgerald Theater in St. Paul.

John Grotzinger, chief scientist of NASA’s Mars Curiosity mission, spoke for a couple of hours before a capacity crowd.

The event was moderated by Tom Weber of Minnesota Public Radio.

Curiosity is the latest NASA rover traversing the surface of Mars after its highly complex landing last August nicknamed, “Seven Minutes of Terror.”

It takes seven minutes for the rover (attached to the descent stage inside of a protective back shell capsule), to go from the top of the Martian atmosphere to its surface.

Unlike the Mars landings of rovers Opportunity and Spirit, each cushioned inside with inflated airbags to protect them when they landed and bounced along the surface until they stopped, the Curiosity landing was precisely controlled.

The capsule containing the Curiosity rover detached from the rocket which brought it from Earth, as it begins to enter the Martian upper atmosphere.

The attached aeroshell heat shield is subjected to temperatures of up to 3,800 degrees Fahrenheit as it enters the atmosphere; however, inside the capsule, it is a cool 50 degrees.

At approximately 13 miles above the surface, the friction from Mars atmosphere dramatically slows the capsule from 13,200 to 1,000 miles per hour.

At the seven-mile point in its descent, a parachute opens.

This parachute is the largest and strongest super-sonic parachute ever made.

Although it only weighs 100 pounds, the parachute needs to withstand 65,000 pounds of force.

The capsule’s heat shield drops off when it’s about five miles from the surface.

Five seconds go by and the capsule’s radar system activates. This determines its speed and altitude, which is needed in order to calculate when to begin a rocket-powered descent.

One minute and 20 seconds from when the heat shield drops off, the capsule and its connected parachute disconnect from the descent stage, and drift away.

This leaves the descent stage and its precious connected cargo, Curiosity, in a free fall, traveling towards the planet.

It’s a mile above the surface, and descending at a speed of 170 miles per hour.

At 4,224 feet above the surface, eight retrorockets, attached to the descent stage, fire. They maneuver the descent stage away from the falling empty capsule and attached parachute in order to avoid any chance of collision.

Here is where it gets complicated in the course of the landing.

NASA calls this next sequence the Sky Crane maneuver.

John Grotzinger jokingly called it, “Rover on a rope.”

Imagine a huge sky crane lowering a steel beam from a skyscraper to the ground. The steel beam in this example is the 2,000-pound Curiosity, being lowered by the descent stage as it travels at only 1.7 miles per hour towards the Martian surface, which is now roughly 490 feet away.

At approximately 45 feet from the surface, four of the eight descent stage’s retrorockets shut themselves off, as three 21-foot nylon ropes (supporting the rover); along with an information-relaying “umbilical cord,” immediately spool out from the descent stage, which is still connected to the rover vehicle.

At 25 feet from the surface, these nylon ropes slowly lower the Curiosity rover, towards the surface of Mars.

Approximately 16 feet from the surface, and traveling at 1.3 miles per hour, Curiosity’s six wheels and suspension system are lowered (like a commercial aircraft’s landing gear prior to landing).

With the nylon cables fully spooled out, the rover gently touches down onto the surface of Mars while the four retrorockets are still firing.

The descent stage sensors know the rover is now on the ground, because the weight on the nylon cables has been drastically reduced.

The nylon ropes, along with the umbilical cords disconnect from the rover.

The ropes and umbilical are still connected to the descent stage, as it quickly flies away and crashes (as planned) about 500 feet from the rover.

The seven minutes of terror are over.

The rover had safely landed on the surface of Mars, inside the 96-mile wide Gale crater, which was formed during a meteor impact about 3.5 billion years ago. This crater is thought to have held significant amounts of water in its past.

The time here in Minnesota was 12:32 a.m. Aug. 6, 2012, and yes, I was watching this event as it happened on NASA TV.

I learned that over 500,000 lines of computer programming code were used during this complicated landing.

According to Adam Steltzner, an engineer at NASA’s Jet Propulsion Laboratory (JPL), the successful landing was also “the result of reasoned engineering and thought.”

“Once upon a time, Mars and Earth were very similar,” Grotzinger said during his talk at the Fitzgerald Theater.

During a press conference held March 12, NASA announced Curiosity had discovered proof of past water on Mars.

“We have found a habitable environment that is so benign and supportive of life, that probably if this water was around, and you had been on the planet, you would have been able to drink it,” Grotzinger said.

For many of us in the Fitzgerald Theater, the big question we were waiting to have answered was whether Curiosity could prove if there was actual life on Mars during its past.

Be sure to read next week’s Bits & Bytes for the conclusion of this column.

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