Every 26 months Mars ends up behind the sun when seen from the perspective of Earth. That means that while the Red Planet is behind the Sun, communications between the spacecraft on and orbiting the planet will be diminished. The phenomenon is known as the Mars solar conjunction and leads to disrupted radio communications between the planets. To prevent any garbled communications between Earth and Mars from causing potential harm to spacecraft, communications are stopped temporarily.
NASA teams running the three active Mars orbiters and two Mars rovers will stop sending commands to their spacecraft from about June 7 through June 21. For that period of time the sun will be within two degrees of Mars in the Earth’s sky.
The teams operating the spacecraft and rovers will also put restrictions on commanding such as reduced data rates or will communicate with the spacecraft only in emergency situations during days before and after that time frame. The spacecraft will continue to make scientific observations during the Mars solar conjunction, but rovers will receive no driving or arm movement commands.
This will be the first solar conjunction for MAVEN, which arrived in Mars orbit last September. Mars Odyssey and Mars Reconnaissance Orbiter will continue to transmit data, but the data may not be received on Earth. The data will also be stored locally inside the spacecraft for retrieval at a later date.