Mars Reconnaissance Orbiter Preparing for Years Ahead

NASA’s Mars Reconnaissance Orbiter (MRO) has begun extra
stargazing to help the space agency accomplish advances in Mars
exploration
over the next decade.

The spacecraft already has worked more than double its
planned
mission life since launch in 2005. NASA plans to keep using it
past the
mid-2020s. Increased reliance on a star tracker, and
less on aging gyroscopes,
is one way the mission is adapting
to extend its longevity. Another step is wringing
more useful
life from batteries. The mission’s extended service provides
data
relay from assets on Mars’ surface and observations with
its science
instruments, despite some degradation in
capabilities.

“We know we’re a critical element for the Mars Program
to
support other missions for the long haul, so we’re finding ways
to extend
the spacecraft’s life,” said MRO Project Manager Dan
Johnston of NASA’s
Jet Propulsion Laboratory, Pasadena,
California. “In flight operations, our
emphasis is on
minimizing risk to the spacecraft while carrying out an
ambitious scientific and programmatic plan.” JPL partners with
Lockheed
Martin Space, Denver, in operating the spacecraft.

In early February, MRO completed its final full-swapover
test
using only stellar navigation to sense and maintain the
spacecraft’s orientation,
without gyroscopes or
accelerometers. The project is evaluating the recent test
and
planning to shift indefinitely to this “all-stellar” mode in
March.

From MRO’s 2005 launch until the “all-stellar”
capability was
uploaded as a software patch last year, the spacecraft always
used
an inertial measurement unit — containing gyros and
accelerometers — for
attitude control. At Mars, the orbiter’s
attitude changes almost continuously,
with relation to the Sun
and other stars, as it rotates once per orbit to keep
its
science instruments pointed downward at Mars.

The spacecraft carries a spare inertial measurement unit.
The
mission switched from the primary unit to the spare after about
58,000
hours of use, when the primary began showing signs of
limited life several
years ago. The spare shows normal life
progression after 52,000 hours, but now needs
to be conserved
for when it will be most needed, while the star tracker
handles
attitude determination for routine operations.

The star tracker, which also has a backup on board, uses a
camera to image the sky and pattern-recognition software to
discern which
bright stars are in the field of view. This
allows the system to identify the spacecraft’s
orientation at
that moment. Repeating the observations up to several times
per
second very accurately provides the rate and direction of
attitude change.

“In all-stellar mode, we can do normal science and
normal
relay,” Johnston said. “The inertial measurement unit powers
back on only when it’s needed, such as during safe mode,
orbital trim
maneuvers, or communications coverage during
critical events around a Mars
landing.” Safe mode is a
precautionary status the spacecraft enters when
it senses
unexpected conditions. Precise attitude control is then
essential for
maintaining communications with Earth and
keeping the solar array facing the Sun
for power.

To prolong battery life, the project is conditioning the two
batteries to hold more charge, reducing demand on the
batteries, and is planning
to reduce the time the orbiter
spends in Mars’ shadow, when sunlight can’t
reach the solar
arrays. The spacecraft uses its batteries only when it is in
shadow, currently for about 40 minutes of every two-hour orbit.

The batteries are recharged by the orbiter’s two large solar
arrays. The mission now charges the batteries higher than
before, to increase
their capacity and lifespan. It has
reduced the draw on them, in part by adjusting
heater
temperatures before the spacecraft enters shadow. The
adjustment preheats
vital parts while solar power is available
so the heaters’ drain on the
batteries, while in shadow, can
be reduced.

The near-circle of MRO’s orbit stays at nearly the same
angle
to the Sun, as Mars orbits the Sun and rotates beneath the
spacecraft. By
design, as the orbiter passes over the sunlit
side of the planet during each
orbit, the ground beneath it is
about halfway between noon and sunset. By
shifting the orbit
to later in the afternoon, mission managers could reduce the
amount of time the spacecraft spends in Mars’ shadow each
orbit. NASA’s Mars
Odyssey spacecraft, older than MRO,
successfully did this a few years ago. This
option to extend
battery life would not be used until after MRO has supported
new
Mars mission landings in 2018 and 2021 by receiving
transmissions during the
landers’ critical arrival events.

“We are counting on Mars Reconnaissance Orbiter
remaining in
service for many more years,” said Michael Meyer, lead
scientist of NASA’s Mars Exploration Program at the agency’s
Washington
headquarters. “It’s not just the communications
relay that MRO provides,
as important as that is. It’s also
the science-instrument observations. Those
help us understand
potential landing sites before they are visited, and
interpret
how the findings on the surface relate to the planet as a
whole.”

MRO continues to investigate Mars with all six of the
orbiter’s science instruments, a decade after what was
initially planned as a
two-year science mission to be followed
by a two-year relay mission. More than
1,200 scientific
publications have been based on MRO observations. Teams
operating the two instruments named most often in research
papers — the High
Resolution Imaging Science Experiment
(HiRISE) camera and the Compact
Reconnaissance Imaging
Spectrometer for Mars (CRISM) mineral-mapper — are
dealing
with challenges but are ready to continue providing valuable
observations.

For example, some HiRISE images taken in 2017 and early 2018
show slight blurring not seen earlier in the mission. The cause
is under
investigation. The percentage of full-resolution
images with blurring peaked at
70 percent last October, at
about the time when Mars was at the point in its
orbit
farthest from the Sun. The percentage has since declined to
less than 20
percent. Even before the first blurred images
were seen, observations with
HiRISE commonly used a technique
that covers more ground area at half the resolution.
This
still provides higher resolution than any other camera orbiting
Mars —
about 2 feet (60 centimeters) per pixel — and little
blurring has appeared in
the resulting images.

Using two spectrometers, CRISM can detect a wide range of
minerals on Mars. The longer-wavelength spectrometer requires
cooling to detect
signatures of many minerals, including some
associated with water, such as
carbonates. To do this during
the two-year prime science mission, CRISM used
three
cryocoolers, one at a time, to keep detectors at minus 235
Fahrenheit
(minus 148 Celsius) or colder. A decade later, two
of the cryocoolers no longer
work. The last has become
unreliable, but is still under evaluation after
34,000 hours
of operation. Without a cryocooler, CRISM can still observe
some
near-infrared light at wavelengths valuable for detecting
iron oxide and
sulfate minerals that indicate past wet
environments on Mars.

The Context Camera (CTX) continues as it has throughout the
mission, adding to near-global coverage and searching for
changes on the
surface. The Shallow Radar (SHARAD) continues
to probe the subsurface of Mars,
looking for layering and ice.
Two instruments for studying the atmosphere —
the Mars Color
Imager (MARCI) and Mars Climate Sounder (MCS) — continue to
build on nearly six Mars years (about 12 Earth years) of
recording weather and
climate.

The University of Arizona operates HiRISE, which was built
by
Ball Aerospace & Technologies Corp., Boulder, Colorado. The
Johns
Hopkins University Applied Physics Laboratory, Laurel,
Maryland, leads MRO’s
CRISM investigation. The Italian Space
Agency provided SHARAD. Malin Space
Science Systems, San
Diego, built and operates CTX and MARCI. JPL, a division
of
Caltech in Pasadena, California, manages the MRO Project for
the NASA
Science Mission Directorate in Washington and leads
the MCS investigation.
Lockheed Martin Space built the
spacecract.

News Media Contact

Guy Webster / Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278 / 818-393-2433
guy.webster@jpl.nasa.gov / andrew.c.good@jpl.nasa.gov

Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
laura.l.cantillo@nasa.gov / dwayne.c.brown@nasa.gov

2018-028