For Moratorium on Sending Commands to Mars, Blame the Sun

This month, movements of the planets will put Mars almost
directly behind the sun, from Earth’s perspective, causing
curtailed communications between Earth and Mars.

NASA will refrain from sending commands to America’s three Mars
orbiters and two Mars rovers during the period from July 22 to
Aug. 1.

“Out of caution, we won’t talk to our Mars assets during that
period because we expect significant degradation in the
communication link, and we don’t want to take a chance that one
of our spacecraft would act on a corrupted command,” said Chad
Edwards, manager of the Mars Relay Network Office at NASA’s Jet
Propulsion Laboratory, Pasadena, California.

Data will keep coming from Mars to Earth, although loss or
corruption of some bits is anticipated and the data will be
retransmitted later. “We will continue to receive telemetry, so
we will have information every day about the status of the
vehicles,” Edwards said.

As seen from Earth, Mars periodically passes near the sun about
every 26 months, an arrangement called “Mars solar
conjunction.” During most solar conjunctions, including this
year’s, Mars does not go directly behind the sun.

Viewers using proper eye protection to watch the total solar
eclipse on Aug. 21 will gain a visible lesson in why Mars
doesn’t need to be directly behind the sun for communications
between Earth and Mars to be degraded. The sun’s corona, which
always extends far from the surface of the sun, becomes visible
during total eclipses. It consists of hot, ionized gas, which
can interfere with radio waves that pass through it.

To prevent the possibility of the ionized gas near the sun
corrupting a command radioed to a spacecraft at Mars, NASA
avoids transmitting for a period including several days before
and after Mars gets closest to passing behind the sun.

Teams that operate Mars orbiters and rovers have been preparing
for weeks in anticipation of the moratorium that will begin on
July 22.

“The vehicles will stay active, carrying out commands sent in
advance,” said Mars Program Chief Engineer Hoppy Price, of JPL.
“Orbiters will be making their science observations and
transmitting data. The rovers won’t be driving, but
observations and measurements will continue.”

The rover teams are determining the most useful sites for the
rovers Curiosity and Opportunity to remain productive during
the solar-conjunction period.

All of NASA’s active Mars missions have experience from at
least one previous solar conjunction. This will be the eighth
solar conjunction period for the Mars Odyssey orbiter, the
seventh for the Opportunity rover, the sixth for the Mars
Reconnaissance Orbiter, the third for the Curiosity rover and
the second for the MAVEN orbiter.

Edwards said, “All of these spacecraft are now veterans of
conjunction. We know what to expect.”

A video showing Mars solar conjunction geometry is at:

NASA’s five current Mars missions, plus Mars missions scheduled
for launches in 2018 and 2020, are part of ambitious robotic
exploration to understand Mars, helping to lead the way for
sending humans to Mars in the 2030s.

NASA’s Goddard Space Flight Center manages the MAVEN project
for the principal investigator at the University of Colorado,
Boulder, and for the NASA Science Mission Directorate,
Washington. JPL, a division of Caltech in Pasadena, manages the
Odyssey, Opportunity, Reconnaissance Orbiter, and Curiosity
projects, and NASA’s Mars Exploration Program, for the Science
Mission Directorate. Lockheed Martin Space Systems, Denver,
built all three NASA Mars orbiters. For more about NASA’s Mars
Exploration Program, visit:

News Media Contact

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.

Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726 /