In June 2015, Mars will swing almost directly behind the sun from Earth’s perspective, and this celestial geometry will lead to diminished communications with spacecraft at Mars.
The arrangement of the sun between Earth and Mars is called Mars solar conjunction. It occurs about every 26 months as the two planets travel in their sun-centered orbits. The sun disrupts radio communications between the planets during the conjunction period. To prevent spacecraft at Mars from receiving garbled commands that could be misinterpreted or even harmful, the operators of Mars orbiters and rovers temporarily stop sending any commands.