NASA Mars mission gets a helping hand from Europe, in pictures
Summary: The European Space Agency has given details of how it will track NASA's landing of the Curiosity rover on Mars, a mission that is seeking to gauge the habitability of the planet
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Curiosity rover
The Curiosity rover will carry laboratory instruments to analyse samples of rocks, soil and atmosphere. The 900kg machine is too heavy to make a gas-bag assisted landing, which is why it will be lowered by skycrane.
Image credit: NASA/JPL-Caltech
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8 Rockets are on the Skycrane
If you want the full story, check out: http://mars.jpl.nasa.gov/msl/
The caption skips right from atmospheric entry all the way to the Skycrane deployment. EDL officially begins with the ejection of the cruise-stage (the components that communicated to Earth and steered during the long interplanetary flight) from the aeroshell (capsule made of the backshell and heat-shield). The lion's share of the deceleration (5900 m/s to 400 m/s) is handled by the PICA heatshield, which is steered by shifting the center of mass and tiny pulse-jets. A lot of reporters are overlooking the fact that this is the first time we've ever attempted a precision that steers the MSL during entry to dial in what used to be a landing zone hundreds of kilometers long, to less than 20 (the difference between landing in Connecticut, to landing on Martha's Vineyard, for those of you back East).
Then, the aeroshell deploys parachutes that slow the vehicle to 80 m/s in the thin Martian atmosphere, jettisoning the shield along the way. Finally, the Curiosity rover and its Skycrane jetpack eject from the capsule and use the jetpack's "eight throttle-controllable rockets" to fly like a helicopter to a standstill 20 m off the ground.
The three tethers you mention are between Curiosity and the Skycrane, and are what allows it to lower the rover the last 20 meters to the surface while automatically steering to avoid boulders and correct for wind gusts that can reach 90 km/hr. Those gusts very nearly crashed one of Curiosity's little MER forefathers.
I think there is only one umbilical and no tethers from the "spacecraft" (capsule?) to Curiosity, which get severed when the rover and jetpack eject. Another umbilical goes to the heatshield, but I don't know if it is rigged to the rover or the capsule. The rover actually downloads a lot of telemetry being acquired by the rest of the spacecraft and sensors embedded in its heatshield during the decent and will (hopefully) upload all that information once Curiosity is safe, sound, and operational.