Mars is as seductive to space explorers as the sirens were to ancient mariners. The U.S., Russia, Japan and Europe have sent 40 spacecraft to explore the fourth planet from the sun since the space age began. Twenty-six have failed, yet Earthlings keep trying.
Mars Curiosity is NASA's latest and boldest attempt yet to go where robots -- but no man -- have gone before. Today it was on final approach, with touchdown scheduled for 1:31 a.m. EDT Monday. If it works.
This intrepid chemistry set on wheels, packed with cameras and gadgets galore, was designed to look for signs that life once existed on Mars. Not Marvin the Martian, but signs that Mars could once have had the chemical resources needed to support microbial life. This could mean potential sources of water, food and energy that could someday support visiting humans from Earth.
The landing has been dubbed "Seven Minutes of Terror" by the engineers who figured out the best way to land. Adam Steltzner, team leader for the entry, descent and landing of Curiosity, said that as the ship was in the planning, he found himself waking up in the middle of the night thinking about the sequence of events that would have to go perfectly.
"The big trick is you are going 13,000 miles an hour," he said. "You slam into the Martian atmosphere and you want to gracefully get the spacecraft down sitting quietly on the surface on her wheels, and all of that takes different changes in the configuration of the vehicle, 79 events that must occur."
For decades, presidents have grandly proposed to send astronauts to Mars. All words, little funding or follow-through. As road trips go, Earth to Mars would only be for the truly hardy. The list of obstacles is daunting. Radiation exposure, psychological stress, reduced muscle mass because of the lack of gravity -- even the human eyeball changes shape, damaging astronauts' eyesight. How would you support a crew on what would be a three-year round trip? What about propulsion? Getting a spacecraft large enough to carry a crew and their supplies to Mars and back requires tremendous energy. Would plasma fusion be best? Nuclear power?
No, a human expedition to Mars would mostly run on funding, and there's the rub. If it cost $100 billion to construct the International Space Station over 12 years, what would a mission to Mars cost? The consensus is that no one nation could pocket those costs, but in these tough economic times, an international consortium like the one that built the ISS could be a hard sell.
Curiosity was set to land when Mars was 154 million miles from Earth. It weighed 5,293 pounds on Earth -- the size of a small car and much, much bigger than the rovers Spirit and Opportunity, which were cushioned by airbags when they landed in 2004. Engineers quickly figured out that airbags would burst if they were tried on Curiosity. So they designed it to be lowered to the Martian surface by a heat shield, then a parachute, then retro-rockets, and finally a sky crane -- something that had never tried before -- and that's what made this so scary for them. Just one slip would mean $2.5 billion down the drain.
How long will it take for us to know if the landing is a success? Almost 14 minutes. That's how long it currently takes a radio signal to reach Earth from Mars.
Curiosity launched on Thanksgiving weekend 2011 and traveled 354 million miles in eight months. Its target: Gale Crater on Mars.
The landing was set to happen in an area that would be facing away from Earth as the planet turned. The spacecraft was equipped with an X-band transmitter that will let the rover communicate directly with Earth, but its first attempt to phone home would be relayed by an older U.S. probe in orbit around Mars. Controllers cautioned that Curiosity could make a perfectly good landing -- but hours or even days could pass before confirmation reached Mission Control at the Jet Propulsion Lab here in Pasadena.
How long was Curiosity designed to roam the planet? One Martian year, which is 22 months for Earthlings. Spirit and Opportunity -- NASA deliberately played down expectations -- were only expected to run for 90 Martian "sols," or days, but Spirit kept on going until 2010 and Opportunity is still puttering around on Mars.
The U.S. has had its share of failures getting to Mars, but it has done better than other countries. Russia has the most dismal record: it launched 19 missions and 19 failed. You have to give them credit for trying. Phobos Grunt, a mission to return a small soil sample from one of Mars' tiny moons, ended in spectacular fashion last fall, unable even to leave Earth orbit. India just announced it would fund its first mission to Mars to launch next year.
Why do this? Aswin Vasavada, a project scientist for Mars Curiosity, said there is an elemental drive in humans.
"We are humans, we want to explore," he said. "We see a mountain, and we want to climb it. As scientists we want to answer the big questions."