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For Moratorium on Sending Commands to Mars, Blame the Sun
Jet Propulsion Laboratory
July 14, 2017

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:

http://mars.nasa.gov/allaboutmars/nightsky/solar-conjunction

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:

https://mars.jpl.nasa.gov

https://www.nasa.gov/mars

News Media Contact
Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster@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

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