![]() "We are in a tough business," says Naderi. ![]() But even if you have done the best engineering possible, you still don't know what Mars has in store for you on the day your arrive. Humans, even very smart humans, are fallible particularly when many thousands of parameters are involved. "That's why we check, double check, test and test again and then have independent eyes check everything again. "We do everything humanly possible and try to avoid human mistakes," says Naderi. "It has the potential to have been an abode of life." "Mars is the most Earth-like of the planets in our solar system," says Naderi. "The challenge after we land," says Rob Manning, manager of Mars Exploration Rovers entry, descent and landing operations, "is how to get the vehicle out of its cramped cocoon and into a vehicle roving in such a way as to please the scientists." No matter how hard it is, getting to Mars is just the beginning. (Explore the landing sites for Spirt and Opportunity) Unpredictable winds can also stir up further complications. Even the toughest airbag can be punctured if it hits a bad rock. The martian surface is full of obstacles-massive impact craters, cliffs, cracks and jagged boulders. Landing is complicated by difficult terrain. Mars doesn't exactly put out a welcome mat. So, the challenge of entry, descent and landing is how to get something that massive traveling at 19,300 kilometers per hour (12,000 miles per hour) slowed down in six minutes to have a chance of survival." "What's inside the airbag weighs 453 kilograms (half a ton). It bounces as high as a four-story building and continues to bounce afterward, perhaps 30 times all together. It hits the ground at 48 kilometers per hour (30 miles per hour) or 80 kilometers per hour (50 miles per hour) if it is windy. The spacecraft freefalls the rest of the way cocooned in airbags to cushion the blow. "Now, the retro rockets fire to bring the spacecraft down to zero velocity, and we're the height of a four-story building above the surface. A parachute opens to slow the spacecraft down to 'only' 321 kilometers per hour (200 miles per hour), but now we have only 6 seconds left and are only 91 meters (100 yards) off the ground. "However, at the end of this phase, we're still traveling at 1,600 kilometers per hour (1,000 miles per hour), but now we have only 100 seconds left and are at the altitude that a commercial airliner typically flies. "During the first four minutes into descent, we use friction with the atmosphere to slow us down considerably," says Naderi. Spirit and Opportunity will enter the martian space traveling 19,300 kilometers per hour (12,000 miles per hour). "One colleague describes the entry, descent and landing as 'six minutes of terror,'" says Naderi. If getting to Mars is hard, landing there is even harder. Nothing less than exceptional technology and planning is required. Even before the trip to Mars can begin, a craft must be built that not only can make the arduous trip but can complete its science mission once it arrives. The road to the launch pad is nearly as daunting as the journey to Mars. Firouz Naderi, NASA's Mars Program Office It has the potential to have been an abode of life." "Mars is the most Earth-like of the planets in our solar system. Hazards range from what engineers call "single event upsets," as when a stray particle of energy passes through a chip in the spacecraft's computer causing a glitch and possibly corrupting data, to massive solar flares, such as the ones that occurred this fall, that can damage or even destroy spacecraft electronics. Adjustments to their flight paths can be made along the way, but a small trajectory error can result in a big detour and or even missing the planet completely. To get there, Spirit and Opportunity, the two Mars Exploration Rovers launched this past June and July, will have to fly through about 483 million kilometers (300 million miles) of deep space and target a very precise spot to land. One reason for the failures is simple: getting to Mars is hard. The first time we landed on a planet it was Mars, and the first time we roved around the surface of a planet, it was Mars. The first time we orbited a planet, it was Mars. "The first time we flew by a planet, it was Mars. "We - the United States and former USSR - have been going to Mars for 40 years," says Naderi, manager of the Mars Program Office at the Jet Propulsion Laboratory. Firouz Naderi puts it -"Mars is a favorite target." Two out of three missions to the red planet have failed, a loss rate highlighted by the fact that - as NASA's Dr. Landing on Mars provides some difficult challenges
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