NASA Probe Set for First Dip Through Martian Atmosphere
NASA's Mars Reconnaissance Orbiter (MRO) will use 556 aerobraking passes to gradually shave its orbit into a circular shape that reaches an altitude of about 160 miles (255 kilometers) at its closest point later this year.
Credit: NASA/JPL/Caltech.

NASA's Mars Reconnaissance Orbiter (MRO) will get its first taste of the Martian atmosphere late Tuesday, dipping through the planet's wispy outer fringe in the first of hundreds of maneuvers to circularize its orbit.

MRO is due to fly through the outer edge of the Martian atmosphere at about 8:00 p.m. EST (0000 April 5 GMT) in the first of about 556 aerobraking maneuvers, which use atmospheric drag to slow and shape a spacecraft's orbit, mission managers told

The probe is expected search for signs of subsurface water on Mars, scrutinize the planet's surface and atmosphere, and hunt for potential landing sites for future red planet explorers. But first MRO must reach its target orbit of about 160 miles (255 kilometers) above Mars, hence six months of aerobraking maneuvers. MRO arrived in Mars orbit on March 10.

"We don't expect to find really much atmosphere there, but it will be the first time the vehicle gets into the aerobraking environment," said Dan Johnston, deputy mission manager for MRO at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, in a Tuesday telephone interview. "This is just barely touching the atmosphere."

At about 3:00 a.m. EST (0700 GMT) today, MRO fired its main engines at its furthest distance from Mars to send it hurtling through the planet's outer atmosphere - about 91 miles (147 kilometers) above the Martian surface - at a speed of 10,289 miles per hour (or about 4.6 kilometers per second), mission managers said.

"There's a great deal of experience with it," Dan Kubitschek, MRO's deputy aerobraking phase lead at JPL, told

First tested by NASA during the agency's Magellan mission to Venus, aerobraking has become a rather dependable way to place planetary orbiters into their final science-conducting positions while saving on vital fuel. In 1997, NASA's Mars Global Surveyor used the method to shape its orbit around the red planet, followed by the Odyssey spacecraft's maneuvers that concluded in January 2002.

"It just takes time," Kubitschek said, adding that MRO will spend about six months of aerobraking before reaching its target orbit. "If we go too deep in the atmosphere, we can accomplish that braking faster but then of course you risk overheating the spacecraft."

MRO mission managers and flight controllers said they have taken proper precautions to ensure the health of their spacecraft.

Kubitschek said the probe's primary instruments and large solar arrays - which together provide about 265 square feet (20 square meters) of solar cells - will face aft of MRO to prevent damage. Image and infrared data from MGS and Odyssey also provide daily updates on Mars' atmospheric conditions, which MRO handlers can use to adjust their aerobraking passes.

"We monitor that on daily basis, though as of now, everything is looking clear," Johnston said.

Johnston added that the initial heating rate build-up on MRO due to the atmosphere is expected to reach 0.001 watts per square centimeter. At the most intense phase of aerobraking, that rate is expected to climb to about 0.15 watts per square centimeter, he added.

"That's really tiny," Johnston said of the initial heating rate MRO will experience.

While most of MRO's science program must wait until after the probe completes the aerobraking process, though researchers do plan to watch the spacecraft's accelerometers to determine the Martian atmosphere's density from its drag effect on the spacecraft.

"We'll actually feed that back into our aerobraking process, so that it becomes another data point for our planning," Johnston said.

As MRO heads into the Martian atmosphere, the spacecraft is in good health and functioning properly, mission managers added.

"Everything is very ideal, right now," Johnston said. "I'm starting to feel pretty excited that we're going to get this underway."