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The
Orbiter has now successfully extended the long-armed antenna of its
radar, preparing the instrument to begin probing for underground layers
of Mars. The Shallow Subsurface Radar, provided by the Italian
Space Agency, will search to depths of about one kilometer (six-tenths
of a mile) to find and map layers of ice, rock and, if present, liquid
water. The
radar's antenna had remained safely folded and tucked away throughout
the flight to Mars from Aug. 12, 2005, to March 10, 2006, and while the
orbiter used the friction of dipping into the top of Mars' atmosphere
426 times in the past six months to shrink the size of its orbit.
Latches on the restraints were popped open on Sept. 16, and the
spring-loaded twin arms of the antenna unfolded themselves. Subsequent
information from the spacecraft indicates that each arm properly
extended to its 5 meter (16.4 feet) length.
The
radar received its first radio echo from the Martian surface during a
test on Sept.18, providing a preliminary indication that the entire
instrument is working properly. Researchers will use the
instrument for more test observations at the end of this month.
Communication with all spacecraft at Mars will be intermittent during
most of October while that planet is behind the sun from Earth's
perspective. The two-year-long main science phase of the Mars
Reconnaissance Orbiter mission will begin in November. The Shallow
Radar will be used to map buried channels, study the internal structure
of ice caps and see boundaries between layers of different
materials. This will provide useful information from just under
the Martian surface, where ices might reside that would be accessible
for future explorers.
The
radar instrument on the Mars Reconnaissance Orbiter will complement a
similar instrument that went into use last year on the European Space
Agency's Mars Express orbiter, the Mars Advanced Radar for Subsurface
and Ionospheric Sounding. The two instruments use different radar
frequencies. The one on Mars Reconnaissance Orbiter can
discriminate between thinner layers, but cannot penetrate as deep
underground, compared with the one on Mars Express. Both result from
Italian and American partnership in using radar for planetary probes. |
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The
spacecraft has now (September 2006) completed the challenging half-year
task of shaping its orbit to the nearly circular, low-altitude pattern
from which it will scrutinize the planet. It fired its six
intermediate-size thrusters for 12.5 minutes Monday afternoon, Sept. 11,
shifting the low point of its orbit to stay near the Martian south pole
and the
high point
to stay near the north pole. The altitude of the orbit ranges from
250 kilometers (155 miles) to 316 kilometers (196 miles) above the
surface. This is effectively the "science orbit" from
which all the work will be done. Challenging activities remain
ahead this month, such as deploying an antenna 10 meters (33 feet) long
and removing a lens cap from a crucial instrument. The main
science investigations will begin in November.
The
flight team for the Mars Reconnaissance Orbiter sent the bus-sized
spacecraft through the upper fringe of Mars' atmosphere 426 times
between early April and Aug. 30. This "aero-braking"
technique used friction with the Martian atmosphere to gradually
decrease the highest-altitude point of the elliptical orbit from 45,000
kilometers (28,000 miles) to 486 kilometers (302 miles). The
lowest-altitude point during aero-braking ranged from 98 to 105
kilometers (61 to 65 miles). It was carefully managed with input
from researchers at JPL; Lockheed Martin Space Systems,
Denver
;
NASA
Langley
Research
Center
,
Hampton
,
Va.
, and elsewhere, based on spacecraft data and atmospheric
fluctuations.
During the first three weeks after it arrived at Mars on March 10, the
spacecraft took more than 35 hours to fly each very elongated orbit.
During the final weeks of aero-braking, it was flying more than 10
orbits each day.
The
latest manoeuvre was the mission's biggest burn since the 27-minute
firing to slow the spacecraft enough for Mars' gravity to snare it into
orbit on March 10th. The benefit of aero-braking is to avoid
hauling unnecessary fuel to Mars for thrusters. Compared with
relying solely on thruster firings to shrink and shape the orbit, this
cut the mission's fuel needs by about 600 kilograms (about 1,300
pounds).
One
key remaining preparation for the mission is deployment of the antenna
for the Shallow Subsurface Radar, an instrument provided by the Italian
Space Agency. The antenna, developed by Northrop Grumman Space
Technology Astro Aerospace,
Carpinteria
,
Calif.
, remained safely stowed during aero-braking. Later this month it
will be released to unfold itself and extend 5 meters (16.4 feet) on
either side of the spacecraft. After this ground-penetrating radar
has been checked and calibrated, it has the potential to detect buried
channels, buried craters and ice layers.
A
series of trial observations by all the instruments will complete the
spacecraft checkouts at the end of the month, including tests of all
observing modes. In addition to data acquisition by the radar and
spectrometer, images will be taken by the High Resolution Imaging
Science Experiment and the Context Imager. The Mars Colour Imager
and Mars Climate Sounder will also begin monitoring Mars' atmosphere.
During the next four years, these instruments will examine Mars to learn
about processes that have affected it and to inspect potential landing
sites for future missions. The spacecraft will also serve as a
communications relay for Mars surface missions. |
