[meteorite-list] During Solar Conjunction, Mars Spacecraft Will Be on Autopilot

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Oct 23 14:18:48 2006
Message-ID: <200610231818.LAA10389_at_zagami.jpl.nasa.gov>

http://marsrovers.jpl.nasa.gov/spotlight/20061020.html

During Solar Conjunction, Mars Spacecraft Will Be on Autopilot
Jet Propulsion Laboratory
October 20, 2006

Every day for the past decade, the U.S. has had a presence at Mars,
using spacecraft to understand this extreme world and its potential as a
past or present habitat for life.

During that time, all spacecraft have become virtually incommunicado for
about two weeks every two years. The reason is solar conjunction, which
occurs again from October 18-29, 2006. Solar conjunction is the period
when Earth and Mars, in their eternal march around the Sun, are obscured
from each other by the fiery orb of the Sun itself. Like dancers on
either side of a huge bonfire, the two planets are temporarily invisible
to each other.

Mission controllers at NASA's Jet Propulsion Laboratory respond in a
variety of ways. They turn off some instruments. They collect data from
others and store it. In some cases, they continue sending data to Earth,
knowing that some data will be lost. Whether they get a break from
everyday operations depends on what mission they're supporting.

No one attempts to send new instructions to Mars during solar
conjunction. It's impossible to predict what information might be lost
due to interference from charged particles from the Sun, and that lost
information could potentially endanger the spacecraft. Instead, prior to
solar conjunction, engineers send two weeks worth of instructions and wait.

While that may seem risky, automatic pilot has come a long way.
Engineers have become skilled at letting spacecraft be on their own.
Like parents who raise youngsters to be responsible and let them go on a
short vacation with their friends, they've done all they can to ensure
the voyagers will be healthy and safe.

The Question: To Rest ...

"We worry a little bit because it's always possible that something
unexpected could happen," said Jake Matijevic, engineering team chief
for NASA's Mars Exploration Rovers. "But, the rovers have made it
through solar conjunction before and we think they'll be OK."

Mission planners have already sent detailed schedules of activities to
the rovers. Spirit and Opportunity will scan the Martian sky for clouds,
measure atmospheric dust, conduct chemical analysis of dust, rocks, and
soils, and take pictures. Opportunity will join Spirit in staying put
temporarily. Both rovers will store the data and transmit it to Earth
later.

Solar conjunction might even be an opportune time for some team members
to take a few, well-deserved vacation days.

... Or Not to Rest?

In contrast, it's hard for the Mars Reconnaissance Orbiter team to stay
away. The newest mission to arrive at Mars, the orbiter recently began
operating all of its instruments for the first time. The team is lining
up to see some of the most detailed images of Mars ever returned, as
well as new data that will likely rewrite our current understanding of
the Martian environment. Though scientists will turn off the
high-resolution camera during solar conjunction, some other instruments
may still collect data.

"The spacecraft is getting a break, but everyone on the ground is still
working just as hard," said engineer Robert Sharrow, a system engineer
at NASA's Jet Propulsion Laboratory.

That's true for the Mars Odyssey team too, who may be busier than usual
in coming weeks.

"Solar conjunction is not typically looked at as time off," said Odyssey
Science Office Manager Gaylon McSmith. "One of the things we'll be doing
is getting ready to increase our global mapping coverage of Mars, using
a technique known as off-nadir pointing."

Starting in December, instead of keeping the spacecraft pointed straight
down at the surface of Mars (nadir), navigators will rotate the
spacecraft to collect stereo images -- slightly offset images of the
same terrain. Like a pair of human eyes, the stereo views will enable
Odyssey's thermal camera to perceive depth and the relative position of
surface features.

Odyssey will continue sending its own data to Earth and relaying data
from NASA's two Mars rovers. Based on experience, Mars explorers know
they will lose some data while Mars is behind the sun with respect to
Earth. "After solar conjunction, we'll have a big cleanup job telling
the rovers what information to re-transmit," said Matijevic.

Some Things Get Better with Age

These activities pose no problems for the pros. Mars Global Surveyor,
the granddaddy of all spacecraft at Mars, has continously mapped Mars
since 1999. Team members have solar conjunction down pat, and rest
easier than in prior solar conjunctions, when an antenna problem caused
some worries.

For a long time, explained Project Manager Tom Thorpe, an obstruction
limited the range of motion of the dish antenna that sends data to
Earth. To get around the problem, navigators flip-flopped the
spacecraft's high-gain antenna in a fairly complex procedure called a
"Beta Supplement <http://mars.jpl.nasa.gov/mgs/technology/>," which
enabled them to point the dish at Earth. They had to be careful to keep
the dish from hitting the boom that supports it.

Suddenly, last year, the obstruction disappeared. Engineers concluded
that the problem likely resulted from a kink in the cabling rather than,
as some had originally thought, a loose screw that wiggled loose during
launch.

"This is our fifth solar conjunction and we've pretty much got it down
to a science," Thorpe said. "We're in our 5th Mars year of sensing --
one Mars year is equal to almost 2 Earth years -- and we're still making
new discoveries all the time."
Received on Mon 23 Oct 2006 02:18:45 PM PDT