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 SPACE.com.
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 SPACE.com.
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."
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