Washington, Dec 7 (IANS): NASA said its Curiosity Mars rover is not currently using its arm for science as it has detected an issue with a motor that moves the rover's drill.

Curiosity is at a site on lower Mount Sharp selected for what would be the mission's seventh sample collection drilling of 2016.

The rover team learned this week that Curiosity did not complete the commands for drilling. The rover detected a fault in an early step in which the "drill feed" mechanism did not extend the drill to touch the rock target with the bit, NASA said in a statement on Tuesday.

Curiosity's drill, as used at all 15 of the rock targets drilled so far, combines hammering action and rotating-bit action to penetrate the targets and collect sample material.

"We are in the process of defining a set of diagnostic tests to carefully assess the drill feed mechanism. We are using our test rover here on Earth to try out these tests before we run them on Mars," said Steven Lee, Curiosity Deputy Project Manager at NASA's Jet Propulsion Laboratory in Pasadena, California.

"To be cautious, until we run the tests on Curiosity, we want to restrict any dynamic changes that could affect the diagnosis. That means not moving the arm and not driving, which could shake it," Lee explained.

Two among the set of possible causes being assessed are that a brake on the drill feed mechanism did not disengage fully or that an electronic encoder for the mechanism's motor did not function as expected.

Lee said that workarounds may exist for both of those scenarios, but the first step is to identify why the motor did not operate properly last week.

The drill feed mechanism pushes the front of the drill outward from the turret of tools at the end of Curiosity's robotic arm.

The drill collects powdered rock that is analysed by laboratory instruments inside the rover.

While arm movements and driving are on hold, the rover is using cameras and a spectrometer on its mast, and a suite of environmental monitoring capabilities.