Greg Redfern, wtop.com
Mars Science Laboratory (MSL), nicknamed Curiosity, is humanity's latest robotic emissary to the red planet Mars. As I write this, Curiosity is traveling over 8,0100 miles per hour and is 116,600 miles from touchdown inside the ancient 98-mile wide Gale Crater.
The $2.5 billion, one-ton nuclear powered rover has been flying towards Mars since launching from Earth last November. The 154 million mile journey to date has gone very smoothly but the most treacherous and dangerous part of the mission for Curiosity is yet to come in the last 7 minutes before scheduled touchdown.
Seven minutes of terror
To land on Mars safely Curiosity must successfully complete EDL - Entry, Descent, Landing. The spacecraft's heat shield will glow like the surface of the Sun and be heated to several thousand degrees. when it hits Mars's thin atmosphere at 13,000 mph.
When the entry phase is complete, the largest supersonic parachute ever used on another world will deploy and endure 65,000 pounds of force and 9 to 10 gs. The spacecraft will jettison the heat shield so the landing radar can see the surface and gain the necessary data for the upcoming landing. Curiosity is now traveling 200 mph, still way too fast for landing. The parachute has slowed Curiosity but now the Sky Crane must do its job.
In the first ever use of the Sky Crane concept, the parachute and backshell are jettisoned leaving Curiosity attached to the Sky Crane, which ignites rocket engines to begin powered descent. But first the Sky Crane must avoid the parachute and backshell by a tilt maneuver.
Curiosity is then lowered on tethers 60 feet long which keeps the rocket engines at a safe distance. The spacecraft has now slowed to about 1.5 mph. Curiosity is now coming in for landing in a vertical descent. Her 6 wheels have been deployed and when she touches down the tethers are separated and the Sky Crane flies away to crash at a safe distance.
Oh, did I mention that all of this is done by the spacecraft's on-board computers using 500,000 lines of code? There is no human intervention in this entire sequence since it takes 14 minutes for radio signals traveling at 186,000 miles per second - the speed of light - to complete one way transmission and reception.
These seven minutes of terror for Curiosity and the mission team at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. will come to an end with the spacecraft either alive and well or dead on the surface. It will take another 7 minutes before we know one way or another.
Touchdown in Gale Crater is scheduled for 1:31 a.m. EDT, Aug. 6, so we should know Curiosity's fate 7 minutes later. Winds affecting the parachute could alter the landing time but not by much. We should get our first low resolution pictures from Curiosity minutes after landing.
NASA will attempt to record Curiosity's landing using the Mars Reconnaissance Orbiter (MRO) as was done for the Mars Phoenix mission several years ago
MRO and another orbiting spacecraft, Mars Odyssey, will be used to relay radio signals between Earth and Curiosity during the scheduled two year mission. During the crucial landing phase, Australia's Canberra Deep Space Communication Complex will be used for communications.
What's on board
Curiosity is the most capable spacecraft that has been sent to the Martian surface to date. She is a small SUV size roving chemical laboratory that is powered by the heat of decaying non-weapons grade Plutonium 238 that will allow her to roam all year long and not be dependent on solar power as her predecessors were. The 10 instruments onboard are designed to identify any organic compounds that are discovered in rock and soil samples.
Curiosity has a laser beam that can ablate and then analyze samples of rocks to determine their composition. She can scoop up samples and heat them up to find out what they are made of. Curiosity can examine and photograph samples and vistas to an unprecedented level of detail. She has a top speed of 98 feet per hour.
All of this capability is at the core of Curiosity's mission - to determine whether Mars had or has the right conditions to support life. Gale Crater was chosen as the landing site after an exhaustive survey of candidate landing sites because of the presence of minerals that can only be formed with water. Curiosity's landing zone is located in an area at the base of three mile high Sharp Mountain and has sedimentary layers that are visible. It is these layers and the surrounding area that Curiosity will explore and sample to see if life could exist on Mars.