NASA is taking an enforced holiday of sorts in April as it suspends Mars exploration missions for 17 to 21 days. This isn't due to budget cuts, but rather because Mars will be in conjunction with the Sun during April, which will make direct communications with the probes difficult, if not impossible. During this time, mission control will place NASA’s unmanned Mars spacecraft on low activity and will not send any new command signals.
In April, Mars and the Earth will be on opposite sides of the Sun. Because of the different orbital speeds of the two planets, this occurs every 26 months and because Mars is so close to the powerful radiation of the Sun, this can disrupt communications with spacecraft orbiting the Red Planet or on its surface. This is especially true this year because Mars will pass at an angle of only 0.4 degrees away from the Sun’s disk on April 17.
What is worse, this is during at the peak of the Sun’s active phase of its 22-year cycle. Though the Sun isn't as turbulent as it normally is during the cycle, it is still enough to blot out or seriously compromise communications. When this happens, there is not only the problem of data from the spacecraft being corrupted and needing retransmission later, but it can also harm command signals coming from Earth, which could damage the probes. To prevent this from happening, mission control at the Jet Propulsion Laboratory (JPL) in Pasadena, California is going to concentrate on Earthside jobs or taking some time off.
Transmissions to the orbiting Mars Reconnaissance Orbiter (MRO) and Mars Odyssey will be suspended from April 9 to 26, though the Odyssey will continue observations and send signals back to Earth. However, engineers expect that Odyssey data will need to be retransmitted later. Meanwhile the MRO will go on record-only mode and collect 60 gigabits of data from its instruments and uploading another 12 gigabits from the Curiosity rover on the surface for transmission in May. During the blackout, Curiosity will send status signals back to Earth to reassure mission control of its readiness.
“We will maintain visibility of (Curiosity) rover status two ways," said Torsten Zorn of JPL, conjunction planning leader for the mission's engineering operations team. "First, Curiosity will be sending daily beeps directly to Earth. Our second line of visibility is in the Odyssey relays."
Also on the surface, the Mars Exploration Rover Opportunity is scheduled to continue operations based on pre-sent instructions. "We are doing extra science planning work this month to develop almost three weeks of activity sequences for Opportunity to execute throughout conjunction," said Opportunity Mission Manager Alfonso Herrera of JPL.
Presumably, ESA’s Mars Express would also be affected, though the European agency has not yet made a statement.
The video below explains how NASA handles the Mars solar conjunction.