NASA Prepares For Solar Conjunction Blocking Mars to Earth Communications

NASA engineers are getting ready for the next Mars solar conjunction that will put two rovers and two Mars orbiting spacecraft beyond reach because all communications between Earth and Mars, with the sun in between, will be blocked for most of the month of April.

Every 26 months Earth, Sun and Mars align in one line, with the central star in between the two inner solar system planets, in what is called a Mars solar conjunction and which disrupts radio transmissions. The event is therefore a regular event for NASA or most of the spacecraft on and above Mars; only the Curiosity rover, which arrived last August, has not gone through a solar conjunction.

"This is our sixth conjunction for Odyssey," said Chris Potts, mission manager for Odyssey, which has been orbiting Mars since 2001. "We have plenty of useful experience dealing with them, though each conjunction is a little different."

Transmissions to the Curiosity will be suspended from April 4 to May 1; transmissions to the Opportunity rover and the orbiters Mars Odyssey and Mars Reconnaissance Orbiter will cease from April 9-26. These numbers also give a feeling for the enormous size of the sun, considering that our fast orbiting planet (about 107,000 km/h) will still need about 2 weeks to cross the 'shadow' in the line of sight to Mars, considering that the radial velocity of Earth is about twice as fast as that of Mars.

One thing to avoid is to let any of the spacecraft receive a disrupted, partial command because it could corrupt the computer systems, according to NASA's Jet Propulsion Laboratory (JPL).

The mission teams will thus set up command sequences and send them to the spacecraft before the conjunction begins so when communications get cut the rovers will still be able to conduct stationary science work and the orbiters will continue to receive data transmissions from the orbiters.

"We are doing extra science planning work this month to develop almost three weeks of activity sequences for Opportunity to execute throughout conjunction," Opportunity mission manager Alfonso Herrera of JPL said in a statement.

Once Mars emerges from behind the Sun, several weeks of backlogged data will be transmitted from the Red Planet.