Precautionary Investigation To Identify Source Of Unusual Voltage Changes

Science observations by NASA's Mars rover Curiosity have been suspended for a few days while engineers run tests to check possible causes of a voltage change detected on Nov. 17. "The vehicle is safe and stable, fully capable of operating in its present condition, but we are taking the precaution of investigating what may be a soft short," said Mars Science Laboratory Project Manager Jim Erickson at NASA's Jet Propulsion Laboratory, Pasadena, CA.

A "soft" short is a leak through something that's partially conductive of electricity, rather than a hard short such as one electrical wire contacting another.

The team detected a change in the voltage difference between the chassis and the 32-volt power bus that distributes electricity to systems throughout the rover. Data indicating the change were received on Sunday, during Curiosity's 456th Martian day. The level had been about 11 volts since landing day, and is now about 4 volts. The rover's electrical system is designed with the flexibility to work properly throughout that range and more -- a design feature called "floating bus."

A soft short can cause such a voltage change. Curiosity had already experienced one soft short on landing day in August 2012. That one was related to explosive-release devices used for deployments shortly before and after the landing. It lowered the bus-to-chassis voltage from about 16 volts to about 11 volts but has not affected subsequent rover operations.

Soft shorts reduce the level of robustness for tolerating other shorts in the future, and they can indicate a possible problem in whichever component is the site of the short. Operations planned for Curiosity for the next few days are designed to check some of the possible root causes for the voltage change. Analysis so far has determined that the change appeared intermittently three times during the hours before it became persistent.

The electrical issue did not cause the rover to enter a safe-mode status, in which most activities automatically cease pending further instructions, and there is no indication the issue is related to a computer reboot that triggered a “safe-mode” earlier this month.

NASA's Mars Science Laboratory Project is using Curiosity inside Gale Crater to assess ancient habitable environments and major changes in Martian environmental conditions.  JPL, a division of the California Institute of Technology in Pasadena, built the rover and manages the project for NASA's Science Mission Directorate in Washington.

(NASA image self-portrait of NASA's Mars rover Curiosity combines 66 exposures taken by the rover's Mars Hand Lens Imager "MAHLI")

www.nasa.gov/msl