Entry Decent and Landing to the Letter
NASA’s Mars Science Laboratory Curiosity rover is the biggest, most expensive, and most technologically advanced planetary expedition ever attempted. At the same time, Curiosity’s entry, descent, and landing (EDL) was, without a doubt, the most ambitious.
The EDL phase started when the spacecraft reached the Martian atmosphere, at a distance of roughly 125 kilometers or 78 miles above the surface, and ended with the Curiosity rover on the surface of Mars (10:32 p.m. PDT, 5 Aug. 2012).
This geek considers Curiosity’s EDL a major feat of ingenuity, imagination, and technology. After all, an unmanned spacecraft moving at approximately 13,000 miles per hour (mph) landed gently, upright, and on target with the help of rockets, a parachute, and a sky crane, in addition to engineers seated 352 million miles away.
Here’s what transpired during the EDL stage:
Cruise Stage Separation – The cruise stage ejects from the aeroshell and heatshield and is left to burn up as it descends through the Martian atmosphere.
Separation Cruise Balance Mass Devices (CBMD) – Curiosity drops two 165-pound, tungsten weights, roughly the size of laptops, to shift the vehicle’s center of mass. The vehicle generates lift using small thrusters to maneuver through the decent, increasing the accuracy of the landing (from hundreds of miles to within just 12 miles).
Entry Interface – Eighty miles above Mars, this stage sheds is marked by the vehicle shedding a large amount of its velocity and the official start of the “7 minutes of terror.”
Peak Heating – Curiosity has now been in entry for 80 seconds and collision with the Martian sky raises the temperature of the heatshield to a balmy 3,800 degrees Fahrenheit. The rover, housed safe inside a cozy aeroshell behind the heatshield, maintains a chilly temperature of between 32 and 77 degrees Fahrenheit.
Peak Deceleration – Starting at the Entry Interface the vehicle slows from 13,200 mph to just 1,000 mph as the thrusters guide the vehicle though a series of “S-shaped” curves to slow itself down as it cuts through the atmosphere.
Hypersonic Aero-maneuvering – Curiosity is still traveling at hypersonic velocities, over Mach 5! The vehicle is constantly analyzing its decent, making small adjustments to “fly” to its destination.
Parachute Deploy – At nearly 255 seconds into the decent and 7 miles from the Martian surface, the parachute deploys while still the mass is traveling at over 900 mph (Mach 2). The scientists and engineers copied the designs of previous Mars lander parachutes, but had to make Curiosity’s twice as large due to its immense size and weight.
Heatshield Separation – At the five-mile mark, the heatshield is shed. Curiosity is now traveling at Mach .7 or roughly 310 mph. Curiosity can use its “eyes” to record its first images of the Martian surface.
Backshell Separation and Powered Decent – Curiosity ejects the backshell, which includes the parachute; for about 80 seconds, the Rover and decent stage freefalls at 180 mph from a mile up in the atmosphere. This is where engineers hold their breath for the “leap of faith” in which the vehicle is engaged.
Rover Separation and Mobility Deploy – Now comes this geek’s favorite part of the decent, the sky crane. The rover slows its decent to 1.7 mph by firing eight retrorockets. Four of the retrorockets shut down and the attached rover is detached from the sky crane and lowered down on about 25 feet of nylon rope and an “umbilical cord.” The rover is about 66 feet from the surface of Mars. Curiosity will be on the ground in approximately 12 seconds.
Touchdown – The sky crane sets Curiosity down whilst blowing Martian dust up as the rockets fire. The rover lands on its wheels on virgin Martian soil directly on target in Gale Crater.
Fun Fact: Gale Crater is named after its discoverer Walter Frederick Gale, an amateur astronomer from Sydney, Australia, from the late 19th century.
Flyaway – In this stage, pyrotechnic charges separate the rover and the umbilical to the sky crane. The decent stage, now “brainless,” flies away from the landing site some estimated 492 feet away from Curiosity.
Curiosity arrived on Mars as scheduled without incident. This geek watched it all live via NASA TV, while taking in tweets from multiple sources. It was an exciting time, and Curiosity’s landing was a remarkable feat of science and engineering—one humans should be proud of as we begin to explore in detail a little slice of the galaxy.
Look for upcoming blogs about the mission and the scientific devices aboard Mars newest inhabitant, Curiosity.
Posted September 29th, 2012, by J VanDomelen
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