NASA's
newest mission to the red planet--the Mars Reconnaissance Orbiter (MRO)--is
working well as it shaves off altitude in order to swing into active
science-gathering duties later this year.
The initial capture by Mars' gravity put
the spacecraft into a very elongated, 35-hour orbit.
Now
underway is the delicate art of "aerobraking"--using hundreds of cautiously
calculated dips into the upper atmosphere of Mars. The process uses
brief burns from MRO's thrusters. Those dips have to be deep enough to slow
the spacecraft by atmospheric drag ... but not deep enough to overheat or damage the
orbiter.
At
aerobraking's end, MRO's orbit around Mars will be approximately two hours. At that point,
from the spacecraft's nearly circular orbit, the mission's
science observations are to begin in earnest.
The
multi-tasking Mars Reconnaissance Orbiter will study the history of water
on the red planet. In addition, it will become the first link in a
communications bridge back to Earth--an "interplanetary Internet" that can be
used by spacecraft in coming years.
Furthermore,
MRO's ultra-powerful camera system can guide future spacecraft missions--such as
NASA's Phoenix lander and the Mars Science Laboratory--to precise and safe landings
on that faraway world. Data gleaned by MRO can also help plot the touch down
zones for human explorers too.
Half-empty, half-full
Making aerobraking all the more risky is
that Mars' atmosphere can swell rapidly. It must be monitored closely to keep
MRO at an altitude that is effective but safe. In this regard, other orbiters
at Mars are providing a daily watch of atmospheric conditions at Mars.
Jim Graf, project
manager for MRO at the Jet Propulsion Laboratory (JPL) in Pasadena, California has likened aerobraking to "a high-wire act in open air".
Right now, for MRO, "the glass is either half full or half empty depending on
how you want to look at it," Graf said. "The spacecraft is presently well on
its way through its aerobraking phase having completed approximately five out
of 24 weeks of activity--or around 20 percent--relative to the calendar," he told
SPACE.com.
The
orbit duration of MRO has decreased from the original 35 hours to 25 hours,
Graf said. MRO's apoapsis--the point in its orbit which is farthest from that Mars--has
decreased from 27,340 miles (44,000 kilometers) down to 21,748 (35,000
kilometers).
"That
sounds like a lot of progress...and it is," Graf added. "The team has worked very
hard to get MRO to this point. But looking at the glass half empty, he continued,
"we have completed only 26 of the planned 547 orbits...so we have a long way to
go."
Mars milestone
MRO
handlers here on Earth expect to reach the 24-hour orbit around Mars milestone
on May 14.
As
MRO's orbit period gets smaller, the rate of reduction is increased and the
process is more demanding. In August, the period should be down to about 4
hours and the team will be very busy monitoring the individual drag passes,
Graf explained.
"The
spacecraft is performing superbly with no anomalies being worked at this time,"
Graf said, and temperature readings on the MRO during the drag passes are
matching computer model results.
Performing
the dainty maneuvers is a combined team located both in Denver at a Lockheed
Martin control center and at JPL in Pasadena.
"Periodically,
they perform small maneuvers to push the spacecraft lower into the atmosphere
to keep the proper level of drag per pass through the atmosphere," Graf said.
For
example, MRO's thrusters were fired again May 10 lowering the spacecraft's
periapsis altitude--the point in an orbit when MRO and Mars are closest together--down
to roughly 65 miles (104 kilometers), Graf said.
Instrument deployments
Another
step toward full-commission of MRO is set for September.
The
team is preparing for this transition phase--the final MRO instrument
deployments.
The
Shallow Subsurface Radar (SHARAD) and the Compact Reconnaissance Imaging
Spectrometers for Mars (CRISM) will be operated for the first time in their
science modes, Graf said.
SHARAD will seek liquid or
frozen water in the first few hundreds of feet (up to one kilometer) of Mars'
crust. The radar wave return, which is captured by the radar's antenna, is
sensitive to changes in the electrical reflection characteristics of the rock,
sand, and any water present in the surface and subsurface. SHARAD is an
instrument supplied by the Italian Space Agency (ASI).
CRISM will search for the
residue of minerals that form in the presence of water and might have been left
by hot springs, thermal vents, lakes, or ponds on Mars far back in its history
when water may have been present on the surface. CRISM will read the hundreds
of "colors" in reflected sunlight to detect patterns that indicate certain
minerals on the surface, including the signature traces of past water. This
device has been provided by the Applied Physics Laboratory at Johns Hopkins University.
Eagle-eye vision,
Last
March, MRO's powerful High Resolution Imaging Experiment (HiRISE), the Context
Camera (CTX), a Mars Color Imager (MARCI), and a Mars Climate Sounder (MCS)
received their first checkouts.
Thanks to MRO's eagle-eye
vision, the orbiter can hone in on objects just a few feet across. With that
capability, the most promising locales for scientific study can be spotted. In
addition, the spacecraft's zoom lens gear can help pick future sites for
expeditionary crews to boot across.
MRO was launched on August
1, 2005 from Cape Canaveral Air Force Station, Florida, slipping across the interplanetary
void to arrive at Mars on March 10 of this year.
The $720 million MRO mission is
managed by JPL, a division of the California Institute of Technology, Pasadena, for the NASA Science Mission Directorate in Washington, D.C. Lockheed Martin
Space Systems, Denver, is the prime contractor for the project and built the
spacecraft.
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