14 DAY TRIAL // NASA's Mars Reconnaissance Orbiter should start looping Mars on March 10. It should reach its planned low-altitude orbit after another seven months. But it first has to pass a critical stage called aerobraking.
"We're getting into the dangerous portion of the mission," said James Graf, the project's manager. "It's going to be difficult to get it into orbit," said Doug McCuistion, the head of NASA's Mars Exploration Program. "Mars is hard, Mars can be unpredictable, but we've got a good team here."
Compared to over the 80 percent chance of successfully landing a craft on Mars, NASA has only a 65 percent success rate in getting space probes orbiting the planet. The spacecraft has to be slowed down enough to be captured by the gravitational field of Mars. Getting it precisely right is difficult.
The initial capture by Mars' gravity should put the spacecraft into a very elongated, 35-hour orbit. The final orbit would be an almost circular two-hour loop. The spacecraft would not brake using solely its engines - this would have been much too fuel costly and would have left too little room for the science instruments. Aerobraking involves using hundreds of carefully calculated dips into the upper atmosphere - deep enough to slow the spacecraft by atmospheric drag, but not deep enough to overheat and crash down the orbiter.
"Aerobraking is like a high-wire act in open air," Graf said. "Mars' atmosphere can swell rapidly, so we need to monitor it closely to keep the orbiter at an altitude that is effective but safe." Current orbiters at Mars will make the job a little easier by providing a daily watch of the lower atmosphere.
"This mission will greatly expand our scientific understanding of Mars, pave the way for our next robotic missions later in this decade, and help us prepare for sending humans to Mars," said McCuistion. "Not only will Mars Science Laboratory's landing and research areas be determined by the Mars Reconnaissance Orbiter, but the first boots on Mars will probably get dusty at one of the many potential landing sites this orbiter will inspect all over the planet."
The orbiter has six instruments on board that will enable the studying of every level of Mars from underground layers to the top of the atmosphere. Its instruments include: - the most powerful telescopic camera ever sent to a foreign planet (which is capable of observing rocks around 2 meters in size) - an advanced mineral-mapper able to identify water-related deposits - a radar for probing after buried ice and water - a weather camera for monitoring the entire planet daily - an infrared sounder for monitoring atmospheric temperatures and the movement of water vapor.
The probe has a 3 meters antenna that will allow it to send the data back to Earth at a rate ten times higher than any previous Mars mission. "This spacecraft will return more data than all previous Mars missions combined," said Graf.
"We're especially interested in water, whether it's ice, liquid or vapor," said Dr. Richard Zurek, project scientist for the orbiter from the Jet Propulsion Laboratory. "Learning more about where the water is today and where it was in the past will also guide future studies about whether Mars has ever supported life."
During its planned five year mission the satellite will also support future land missions on Mars such as the Phoenix Mars Scout, which is being built to land on icy soils near the northern polar ice cap in 2008, and the Mars Science Laboratory, an advanced rover which is due to be launched in 2009.
-- Images: 1. The Mars Reconnaissance Orbiter in its aerobraking stage. 2. The spacecraft using its Shallow Radar (SHARAD) to "look" for liquid or frozen water up to a kilometer under the surface.
Credits: NASA/JPL
