November 26, 2013
Curiosity Returns To Normal Voltage Levels, Resumes Regular Duties
Lee Rannals for redOrbit.com - Your Universe OnlineNASA said the decision to resume scientific activities resulted from successful work by engineers in diagnosing the likely cause of the Nov. 17 change in voltage Curiosity experienced. The space agency maintained that the voltage issue caused no damage to the rover’s safety or health.
Curiosity’s electrical system features a “floating bus” design that enables it to tolerate a range of voltage differences between the vehicle’s chassis and the 32-volt power lines that deliver electricity throughout. When the “soft short” occurred last week, the level of volts dropped down to about four, compared to the 11 volts the rover's electrical system had on landing day.
"We made a list of potential causes, and then determined which we could cross off the list, one by one," rover electrical engineer Rob Zimmerman of NASA's Jet Propulsion Laboratory, Pasadena, California, said in a statement.
NASA said the likely cause is an internal short in the Multi-Mission Radioisotope Thermoelectric Generator, which is Curiosity’s power source. NASA’s Cassini spacecraft, which is in orbit around Saturn, has also experienced shorts in a similar generator.
Rover engineers discovered on Saturday that the rover had on its own returned to pre-November 17 voltage levels. NASA said this discovery helped to confirm their diagnosis of an internal short in the generator.
The issue did not cause the rover to enter a safe-mode status, during which the activities would have automatically ceased pending further instructions. NASA halted Curiosity’s operations only as a precautionary measure.
“The analysis work to determine the cause of the voltage change gained an advantage from an automated response by the rover's onboard software when it detected the voltage change on Nov. 17,” NASA said. “The rover stepped up the rate at which it recorded electrical variables, to eight times per second from the usual once per minute, and transmitted that engineering data in its next communication with Earth.”
After activities resumed, Curiosity’s arm delivered portions of powdered rock to a laboratory inside the rover. The powder has been stored in the arm since the rover collected it by drilling into the Martian rock “Cumberland” six months ago. Although several portions of the soil had already been analyzed by Curiosity, the rover’s on board laboratory has several ways to examine samples.