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What you need to know for 07/23/2017

Star Talk: Curiosity takes NASA back to Mars

Star Talk: Curiosity takes NASA back to Mars

Supersize it! That’s how we might describe Curiosity, the next Mars rover, which is just one week fr

Supersize it! That’s how we might describe Curiosity, the next Mars rover, which is just one week from reaching the Red Planet.

Curiosity dwarfs the previous Mars Exploration Rovers, Opportunity and Spirit, which are barely half its size, and its science goals are the most ambitious yet for a rover investigating the surface of Mars.

Curiosity is the central component of the Mars Science Laboratory mission and a key element in NASA’s Mars Exploration Program, a long-term effort to explore the Red Planet with mobile robots. Although this newest rover is not designed to detect life directly, it has the instrumentation to assess whether Mars once had an environment to support simple life forms such as microbes. In NASA parlance, this mission is to determine the “habitability” of Mars.

Curiosity is a science laboratory on wheels. Within its frame are both a biology and a geology mini-lab. Rocks and soil samples will be tested in these miniature laboratories for evidence of minerals that formed in the presence of water.

Curiosity will also catalog such organic compounds as carbon, hydrogen, nitrogen and oxygen, which are the chemical building blocks of life. In addition, the rover will search for features that could have resulted from various biological processes.

Largest rover yet

Launch of the Mars Science Laboratory took place on Nov. 26. A Boeing Atlas-V rocket lifted the spacecraft into the sky over Cape Canaveral, Fla., and into Earth orbit. The rocket’s upper stage then ignited and pushed the spacecraft out of orbit and onto its 352-million-mile journey to the Red Planet. Thus far, the spacecraft’s systems have all been functioning normally and the robot rover is “healthy.”

This latest Mars rover is about the size of a subcompact car and literally weighs a ton. Its large size and mass result from its two internal laboratories, making Curiosity about two times longer and five times heavier than either Spirit or Opportunity.

As the rover moves, it will image its surroundings with color cameras atop its mast and remotely identify rocks with a rock-zapping laser. When it finds an interesting sample, the rover will drive to it so that it is within reach of its robotic arm. At the end of its arm are a digital magnifying glass, X-ray analyzer and a drill to pulverize the rocks for sampling. Curiosity’s “hand” is almost the size of the 1997 Mars Pathfinder rover!

And none of the bat-winged-shaped solar panels on the Mars Exploration Rovers are used to generate power for this mechanized giant. To meet its need for power, Curiosity uses a nuclear power source that provides energy from the radioactive decay of plutonium. In principle, this source could supply power for more than a dozen years, although Curiosity’s nominal mission is for one Martian year (about two Earth years).

Seven minutes of terror

The size and mass of the Curiosity rover mean that it cannot come crashing onto the surface of Mars protected in an enclosure of air bags as the Opportunity, Spirit and the Pathfinder rovers did. Its weight would puncture the airbags.

Consequently, an involved landing procedure never attempted before will be used. The Jet Propulsion Laboratory engineers on the landing team call the time it takes Curiosity to go from the top of Mars’ atmosphere to the time it reaches the surface the “seven minutes of terror.”

Mars has an atmosphere 100 times thinner than the air surrounding Earth, and it is not dense enough to slow the Mars Laboratory to a safe landing speed. However, it is enough atmosphere so that it has to be dealt with, particularly because the spacecraft will be slamming into it at more than 13,000 miles per hour.

The mission’s entry phase starts 10 minutes before the spacecraft enters the atmosphere when the rover’s capsule sheds its cruise stage that carried it from the Earth to Mars. Nine minutes before entry, the space capsule is reoriented so that its heat shield is tilted at the correct angle to enter the atmosphere.

At a time count of zero, the capsule enters the Martian atmosphere at an altitude of 81 miles above the surface. This will not be a passive entry. Small thrusters on the back shell of the capsule slightly adjust the angle and direction of its tilt, generating lift so the spacecraft can steer out any unpredictable variations in the atmosphere on the day of landing.

During this time, the vehicle is slowing down violently as it wrangles against aerodynamic drag, causing its heat shield to glow at almost 4,000 degrees. Four minutes and 15 seconds after entry, at seven miles above the surface, the craft is still going at 900 miles per hour when the largest parachute ever to land a space vehicle on the surface of another world is deployed.

Twenty-four seconds later and five miles above the surface, with the spacecraft slowed to 300 miles per hour, the heat shield is jettisoned. With the heat shield out of the way, video is taken of the ground to compare with the programmed database of the landing site.

At six minutes, 50 seconds after atmospheric entry and one mile above the surface, the back shell of the space capsule is separated, carrying the parachute with it. Vehicle speed is now 200 miles per hour.

Power descent

Ten seconds later, an eight-rocket backpack surrounding the still-folded rover ignites and starts the powered descent phase of the landing. Twelve seconds before touchdown, at a height of 66 feet when the vehicle has been decelerated to under 2 miles per hour, four of its rockets shut down. The remaining rockets maintain the downward velocity as the rover is lowered to the surface on a nylon bridle. This is called the “sky crane” maneuver.

The rover extends its wheels and suspension system just before touchdown to act as its landing gear. When the rocket pack senses touchdown, the connecting cords are cut and the backpack flies away. Curiosity switches from landing mode to surface mode and begins its autonomous activities on the surface of Mars.

It will be 3 p.m. local time on Mars when Curiosity is set down in Gale Crater next to its three-mile high central peak, a place where satellite images indicate there was water on Mars in the distant past.

There is essentially zero margin of error during the descent and landing of this $2.5-billion mission. We’ll know the results on Aug. 6 at 1:31 a.m. EDT, the expected landing time of Curiosity.

Richard Monda is an astronomer living in the Capital Region.

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