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Curiosity’s recent bad month on Mars – Science operations halted again by electrical issue

The Curiosity rover has paused operations on Mars, after a recent electrical issue that resulted in a voltage drop. Image credit: NASA/JPL-Caltech/MSSS

This past month has turned out not to be a very good one for the Mars Science Laboratory rover Curiosity on Mars. After experiencing a software reboot that put the rover into a “safe mode” for a couple of days starting on November 7, and not long after science operations had resumed afterward – Curiosity’s activities have to be put on hold once more. NASA announced Nov. 20 that it has paused Curiosity’s science and roving operations, to investigate an electrical issue that occurred on Nov. 17, when engineers on the ground detected a drop in voltage between the rover’s chassis and its 32-volt power bus.

The power bus is responsible for distributing electric power between the rover’s different instruments and components, and the chassis is the rover’s ‘main body’ that stores inside all of Curiosity’s computer hardware and other vital equipment like the Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments. Engineers received data from the rover on Nov. 17, indicating that the bus-to-chassis voltage had decreased from 11 to 4 Volts.

A map showing the distance Curiosity has traveled since landing through Sol 455 (Nov. 16, 2013). Image credit: NASA/JPL-Caltech/Univ. of Arizona

A map showing the distance Curiosity has traveled since landing through Sol 455 (Nov. 16, 2013).
Image credit: NASA/JPL-Caltech/Univ. of Arizona

Interplanetary probes and rovers like Curiosity, are designed with redundancies in place, so as to continue operating normally in case of emergencies or other malfunctions. And Curiosity’s electrical distribution system was designed with that in mind, being able to continue providing electricity even in the case of such voltage losses , due to a design feature called a ‘floating bus’.

This design has more than proved its worth, since this isn’t the first time that Curiosity has been in this situation. During the rover’s dramatic Entry, Descent and Landing known as ‘EDL’ (or more commonly as the ‘seven minutes of terror) phase on August 5 2012, the rover experienced a similar drop to its bus-to-chassis voltage from 16 to 11 volts. It is believed that this was caused by the explosive releases of various parts of its entry capsule during approach and landing on Mars. The rover has been operating with that voltage ever since.

After the recent drop, every rover operation was halted as a precautionary measure, in order to understand why the issue had occurred. The best possible explanation is that it was caused by a ‘soft short’.

“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.” says MSL Project Manager Jim Erickson, working at NASA’s Jet Propulsion Laboratory located in Pasadena, California.

Curiosity launched in November 2011 atop a United Launch Alliance Atlas V rocket. Photo Credit: USAF

Curiosity launched in November 2011 atop a United Launch Alliance Atlas V rocket. Photo Credit: USAF

As opposed to a ‘hard short’, which happens when two conductive materials like two exposed wires touch creating a short-circuit, a soft short happens when electricity leaks from a more conductive material to a less conductive one, resulting in a power loss. But although soft shorts may be relatively harmless, every time they happen, they make the rover less robust in tolerating with similar events in the future. And a soft short may be a sign of a more serious issue in the electrical system, potentially causing it to develop in a hard short, that could fry sensitive equipment and instruments on the rover.

Engineers want to assess the situation, to help prevent such events in the future that could undermine the mission. Analysis of the situation so far, has shown that this latest voltage drop was preceded by three more intermittent ones, but it doesn’t seem to be related to the Curiosity’s computers’ soft reboot incident that occurred a few weeks earlier.

Curiosity is currently in the middle of its 8-km trek towards Mount Sharp, where it will investigate the mountain’s many different geologic layers, which may shed some light to the Red Planet’s geologic past hundreds of millions of years ago, when conditions are believed to have been favorable for the existence of life.

This is the primary mission of the one-ton, rover – to discover if Mars ever supported a habitat conducive to life. Curiosity was also dispatched to study the Martian climate and geology. it touched down, via a “jetpack” known as the sky crane. This device allowed Curiosity to hover above the terrain before being lowered via cables. Upon safely touching down on the planet’s surface, the cables were cut and the sky crane maneuvered a safe distance away where it impacted. Curiosity cost about $2.5 billion and has a planned primary mission of about two years.


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