A Boeing Delta 2 rocket carrying the first MER spacecraft, named Spirit, lifts off from Cape Canaveral in Florida on June 10, 2003. Click on image for full size (31K :JPEG) Image courtesy NASA.

Both Mars Exploration Rovers (MER) were launched from Cape Canaveral, Florida, during the summer of 2003. The first, Spirit, blasted off on June 10. The second, Opportunity, was launched on July 7. After leaving Earth, each spacecraft spent slightly more than six months in its "cruise phase" on the journey to Mars, with just a few minor mid-course corrections of its trajectory along the way.

January 2004 is when the tedium of the long, uneventful outbound journey ended and the pace of events for the missions started to really heat up (literally!). Spirit landed in Gusev Crater on January 3, 2004, and Opportunity touched down on Meridiani Planum on January 24, 2004. The entry, descent, and landing sequence for each vehicle began when the rover, sheltered inside its protective aeroshell, first encountered the Martian atmosphere while traveling at a speed of 19,000 km per hour (12,000 mph). As the craft's heat shield warmed to a toasty 5,000 to 6,000° C (9,000 to 10,800° F), the vehicle rapidly decelerated to 1,600 km per hour (1,000 mph) in about one minute, subjecting the vehicle to 10 G's of force. A parachute opened at an altitude of 10 km (6 miles), further slowing the vehicle from 400 meters per second (1000 mph) down to about 85 m/s (nearly 200 mph). As the lander approached the Martian surface, it inflated a cocoon of airbags (four airbags that each have six "lobes") around itself to cushion the landing. Next, the vehicle fired three small solid rocket motors for four seconds at an altitude of 80 to 100 meters (260 to 330 feet), which brought the downward motion of the craft to a halt at a height of 10 to 15 meters (33 to 48 feet) above the ground. A cable cutter (a small pyrotechnic guillotine) severed the tether attaching the airbag-enshrouded rover to its parachutes and retro-rockets, allowing the airbag bundle to drop to the ground. The bundle eventually bounced to a halt.

Once settled on the surface, the lander retracted the airbags and unfolded itself. The rover spread out its solar panels and unfolded its wheels and camera mast, then drove off the lander system onto the Martian surface. The landers are designed to spend the 90 days exploring the surface of Mars, roaming during the day as their solar panels soak up sunlight and hibernating through the cold Martian nights. The rovers are expected to traverse about one kilometer (0.6 miles) of the Martian surface during that time. The rovers' lifetimes will be dictated by how long their electrical energy supplies hold out. Mars' orbit carries it slightly further from the Sun during the course of the MER's surface operations, it will be autumn in Mars' southern hemisphere where the MERs landed so the days will be growing shorter, and dust from the Martian atmosphere is gradually collecting on the rovers' solar panels. All of these factors will gradually reduce the ability of MER's solar panels to power the rovers. Eventually, the vehicles will "run out of gas" and stop working.

A Boeing Delta 2 rocket carrying Spirit blasts off from Cape Canaveral in Florida on June 10, 2003. Click on image for full size (31K :JPEG) Image courtesy NASA.

Both Mars Exploration Rovers (MER) were launched from Cape Canaveral, Florida, during the summer of 2003. The first, Spirit, blasted off on June 10. The second, Opportunity, was launched on July 7. After leaving Earth, each spacecraft spent slightly more than six months in its "cruise phase" on the journey to Mars. During that trip, each spacecraft had a few minor mid-course corrections of its path along the way.

In January 2004 Spirit and Opportunity made it safely to Mars. Spirit landed in Gusev Crater on January 3, 2004. Opportunity touched down on Meridiani Planum on January 24, 2004.

Each spacecraft first had to enter the Martian atmosphere while traveling at a speed of 19,000 km per hour (12,000 mph)! Their heat shields kept them from burning up. When they had gotten within 10 km (6 miles) above the surface of Mars and had slowed to about 400 meters per second (1000 mph) their parachutes opened. Next, the landers inflated airbags around themselves to help cushion their landings. Retrorockets that fired just above the surface slowed the landers even more. Finally, the vehicles cut the lines connecting them to their parachutes and dropped 10 to 15 meters (33 to 48 feet) to the Martian surface. Each bounced more than twenty times before stopping.

After each lander was settled on the surface of Mars, it let the air out of its airbags and pulled the bags in to itself. Then each lander unfolded itself. Next, each rover spread out its solar panels and unfolded its wheels and camera mast. After engineers tested each rover's systems to make sure they were OK, each rover drove onto the surface of Mars. We think the rovers can last about 90 days on Mars. They are exploring during the daytime and "resting" at night. After a while the solar panels will stop making enough electricity to keep the rovers going. Hopefully we will learn a lot from them before that happens!

A rocket carrying Spirit blasts off from Florida on June 10, 2003. Click on image for full size (31K :JPEG) Image courtesy NASA.

Both Mars Exploration Rovers (MER) were launched from Florida in the summer of 2003. The first, Spirit, blasted off on June 10. The second, Opportunity, blasted off on July 7. Each spacecraft spent about six months in space on the way to Mars.

Spirit and Opportunity made it safely to Mars in January 2004. Spirit landed in Gusev Crater on January 3, 2004. Opportunity landed on Meridiani Planum on January 24, 2004.

The spacecraft were going very fast, about 19,000 km per hour (12,000 mph), when they got to Mars! They slowed down very quickly when they went into the atmosphere of Mars. Their heat shields kept them from burning up. They had parachutes that slowed them down some more. They also had airbags around them to make their landings softer. They bounced more than 20 times when they landed!

After they stopped bouncing they let the air out of their airbags. Then they unfolded themselves. Each rover spread out its solar panels and unfolded its wheels. Engineers on Earth tested each rover to make sure they were OK. Then the rovers drove onto the surface of Mars. We think the rovers can last about 90 days on Mars. They are exploring during the daytime and "resting" at night. After a while the solar panels will stop making enough electricity to keep the rovers going. We hope to learn a lot from them before that happens!