golden, Colo. — As NASA’s Mars Reconnaissance Orbiter (MRO) neared a record-breaking production milestone, problems with two instruments forced the agency to cut back on imaging operations.

The spacecraft carries six instruments designed to take gather data about Mars’ atmosphere, surface and subsurface. Two of those instruments the High Resolution Imaging Science Experiment (HiRISE) and the Mars Climate Sounder — have been experiencing problems, the Jet Propulsion Laboratory announced Feb. 7.

In late November the HiRISE team noticed a significant increase in noise, such as bad pixels, in one of the instrument’s 14 electronic detector s. Another detector that developed the same problem soon after MRO’s launch in August 2005 has worsened. Images from the spacecraft camera in January showed the first signs of this problem in five other detectors.

While the current impact on image quality is small, according to a JPL statement, there is concern as to whether the problem will continue to worsen. They are, however, still using the camera, which continues to return images of the martian landscape.

“For now we are using a slightly extended warm-up period before each image,” said Alfred McEwen, Director of the Planetary Image Research Lab at the University of Arizona in Tucson, Arizona and the HiRISE principal investigator.

“When we have evaluated whether or not the extended warm-up has potential long-term detrimental effects, then we can decide to extend this warm-up period in the future if the problem continues to worsen,” McEwen said.

Meanwhile, the Mars Climate Sounder, which is designed to map the temperature, ice clouds and dust distribution in Mars’ atmosphere, appears to have been skipping steps in its normal routine since December, which left its field of view slightly out of position. Following the uplink of new scan tables to the instrument, the position errors stopped and the instrument operated nominally, JPL officials said.

In mid-January, however, the position errors reappeared and became more frequent. As a result the sounder has been temporarily stowed while the science team investigates the root cause of the trouble.

While engineers wrestle with the anomalies, JPL officials noted that sometime in February the Mars Reconnaissance Orbiter still will eclipse the record for the “most science data” returned by any Mars spacecraft to date.

The rate of data return is projected to increase over the coming months as the relative motions of Earth and Mars in their orbits around the Sun shrink the distance between the planets. That Mars-Earth positioning means MRO should relay more than 30 terabits of science data — equal to more than 5,000 information-packed CD-ROMs.

MRO observations are an essential element of on-going studies of potential exploration sites for future missions such as the Phoenix Mars lander, which is scheduled to launch in August.

While HiRISE is acting up, Zurek observed that the instrument’s three months of science gathering to date has yielded roughly 1,000 images — more than 1.5 terabits (1,500 gigabits) of image data.

As part of that output, for example, HiRISE has redirected the landing site for the Phoenix Mars mission to a safer, boulder-free area, Zurek said, “and it has shown us Mars at a level of detail as good or better than you could see from a low-flying plane.”

“Our expectation is that HiRISE will continue to [operate] for a long time once we understand the noise problem better and craft our operations procedures accordingly,” Zurek said .