Credit: NASA/JPL/CALTECH
It will last all of seven minutes, but as engineers say, it’s all a “gulp moment”.
NASA’s Mars Science Laboratory’s (MSL) entry, descent and landing (EDL) – will determine the fate of the mission. And MSL’s aeroshell is absolutely vital to getting the Mars Curiosity Rover safely down on the sands of Mars.
Built by Lockheed Martin, the aeroshell comprises a back shell and a heat shield.
“This aeroshell at nearly 15 feet across is the largest capsule we’ve ever flown and the design had to address the large size and weight of the rover along with the requirement for landing at a more-precise point on Mars, said Rich Hund, aeroshell program manager for Lockheed Martin Space Systems Company’s support of the NASA mission.
Peak heating
The back shell protects the Curiosity rover during cruise and descent, and provides structural support for the parachute and the unique descent stage, a system that will lower the rover to a soft landing on the surface of Mars.
According to a Lockheed Martin press statement, the biconic-shaped back shell is covered with a thermal protection system composed of the cork/silicone super light ablator (SLA) 561V that originated with the Mars Viking landers of the 1970s.
Because of the extreme heat the unique entry trajectory through the atmosphere will create, the heat shield uses a tiled Phenolic Impregnated Carbon Ablator (PICA) thermal protection system.
This will be the first time PICA has flown on a Mars mission.
Peak heating occurs about 75 seconds after atmospheric entry, when the heat shield temperature will reach about 3,800 degrees F. Peak deceleration occurs about 10 seconds later, with maximum deceleration forces possibly reaching as high as 15 Gs.
Guided entry
After MSL finishes its guided entry maneuvers — at an altitude of about seven miles and a velocity of about 900 miles per hour, the parachute – 51 feet in diameter – deploys about 254 seconds after entry.
Twenty-four seconds later, the heat shield separates and drops away with the spacecraft at an altitude of about five miles and traveling at a velocity of about 280 miles per hour.
Just a mile above the ground, and falling at 180 miles an hour, eight throttleable retrorockets on the descent stage begin firing.
Sky crane maneuver
Decelerating abruptly to 1.7 miles per hour, nylon cords begin to spool out to lower the rover from the descent stage in the “sky crane” maneuver. The rover’s wheels and suspension system, doubling as landing gear, rotate into place just before touchdown. When Curiosity senses touchdown, the connecting cords are severed and the descent stage flies out of the way, coming to the surface at least 492 feet from the rover’s position.
Soon after landing, Curiosity’s computer switches from EDL mode to surface mode. This initiates autonomous activities for the first Martian day on the surface of Mars, Sol 0.
The time of day at the landing site will be mid-afternoon — about 3 p.m. local mean solar time at the destination: Gale Crater.
NOTE:
The folks at Lockheed Martin have issued an interesting and informative video about MSL’s sky dive to Mars – “Protecting Curiosity”
Check it out at:
http://www.youtube.com/watch?v=OYsezwD_AIs
By Leonard David