NASA's Mars rovers continued to be plagued by a global dust storm Saturday, but both of the golf cart-sized craft produced more power than they consumed this week, according to the mission's chief scientist.

"Both rovers are comfortably power positive, which means that they're generating significantly more power than they consume," said Steve Squyres, the rovers' principal investigator.

Opportunity, which is perched on the rim of a half-mile wide crater, continues to be hit hardest by the dust storm. Electricity output from Opportunity's solar panels dropped by as much as 80 percent in the last month, NASA said in a news release.

"Spirit is definitely producing more power than Opportunity," Squyres said. "Of course you never know what Mars is going to do next at either site."

Opportunity used more power than it produced for much of last week, causing officials to worry that the robotic explorer could exhaust the electricity stored in its batteries.

Opportunity and Spirit, which is stationed on the opposite side of the planet, have weathered the storm for several weeks. Both rovers showed slight improvement for most of this week.

"I wouldn't call either position precarious at the moment," Squyres said.

Controllers at the Jet Propulsion Laboratory in Pasadena, Calif., contacted Opportunity twice this week, Squyres said.

Opportunity had been ordered to curtail communication sessions with Earth due to fears of draining the rover's battery. The ground team also suspended driving and most science operations for both rovers.

"We're not collecting enough data to require daily [communication] windows, so it makes sense to save the power and delete some of them," Squyres told Spaceflight Now.

Data from both sessions indicated power levels were hovering slightly above 200 watt-hours of electricity – enough to run a 100 watt light bulb for two hours.

Sensors aboard the rovers also gauge the level of dust in the Martian atmosphere. The opacity is measured in units of tau, with higher numbers meaning more dust and cloudiness.

Squyres said this is the most serious storm encountered by the mission since the rovers landed in January 2004.

"There's no comparison," Squyres said. "This is far worse. It's a totally different experience."

This month's dust storm sent the rovers' tau values above two for the first time, according to Squyres.

Opportunity's tau value was slightly above four for much of this week, while measurements by Spirit yielded similar results.

But Spirit encountered a spike to a tau value of about 4.7 late this week, indicating the craft was receiving less sunlight to charge its batteries.

"We're still waiting out the storms, and we don't know how long they will last or how bad they will get," said John Callas, the mission's project manager.

The highest tau value experienced so far was measured by Opportunity, when tau readings reached above five last week.

Fresh dust also settled on Opportunity's solar panels late this week, putting additional stresses on the rover's power production system.

"Given how much dust there is in the atmosphere now, it would be reasonable to expect that we'll see enhanced dust accumulation on the arrays as the storm subsides," Squyres said. "We can't predict how severe it might be."

Opportunity is positioned at the edge of Victoria Crater, the largest Martian feature ever visited by a lander. The rover will enter Victoria in search of more evidence of ancient water on the Red Planet.

Because of the low power levels, the risky excursion in the crater will have to wait until the dust storm subsides.

"As soon as we have enough power to go in, we're planning to go in," Squyres said.