Reconnaissance Orbiter Steps Closer to Mars
(From the May/June
2006 issue of StarDate magazine)
Mars Reconnaissance Orbiter (MRO), which entered orbit around Mars on March
10, is designed to search for evidence of water on or below the planet's surface.
Before it can hunt for the wet stuff, though, it first must dip its toe into
the fringes of the planet's atmosphere — a six-month process that will
shape its final orbit.
"In theory, it saves money by cutting down on the fuel you have to carry,
and if you're successful, it probably does," says James Murphy, head of
the astronomy program at New Mexico State University and one of three leaders
of a team that is advising MRO's flight controllers on conditions in the Martian
atmosphere.
MRO’s first images show plains, impact craters,
and gullies. Above: The first high-resolution image (of the area shown
in box at right) shows details as small as 25 feet in diameter. Images
from its final mapping orbit will show features as small as a coffee table.
MRO entered a highly elliptical orbit, ranging from about 250 to 27,500 miles
(400-44,000 km) above Mars. To achieve its science objectives, however, it
must reach a near-circular orbit of less than 200 miles. To lower its orbit,
the craft dips a little deeper into the atmosphere on each pass around Mars
in a process called aerobraking. Two current Mars orbiters used the technique
to shape their own orbits.
Controllers must carefully target MRO's altitude, though, so that MRO passes
through a layer of atmosphere that is the correct density. "If it's too
dense, you can generate too much heat from friction and damage the spacecraft," says
Murphy. "If it's not dense enough, then you're not getting enough drag
to shape the orbit."
The density of the atmosphere can vary quite a bit by time of day and location
over the planet, however, particularly when large dust storms swirl into action.
The advisory team convenes daily to evaluate readings from the orbiting Mars
Global Surveyor and other data, then predict what conditions will be like over
the next several days.
When it begins its science observations late this year, MRO will snap some
of the most detailed pictures of Mars to date. Its instruments will map water-related
minerals in patches as small as a baseball infield and peek below the surface
for layers of rock and water. And another instrument will chart the temperature,
water vapor, and dust in the sky — long after MRO has finished "dipping
its toes" in the Martian atmosphere. -- Damond Benningfield
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