MarsRover - http/catless.ncl.ac.uk/Risks/19.49.html What...

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http://catless.ncl.ac.uk/Risks/19.49.html What really happened on Mars Rover Pathfinder Mike Jones <[email protected]> Sunday, December 07, 1997 6:47 PM The Mars Pathfinder mission was widely proclaimed as "flawless" in the early days after its July 4th, 1997 landing on the Martian surface. Successes included its unconventional "landing" -- bouncing onto the Martian surface surrounded by airbags, deploying the Sojourner rover, and gathering and transmitting voluminous data back to Earth, including the panoramic pictures that were such a hit on the Web. But a few days into the mission, not long after Pathfinder started gathering meteorological data, the spacecraft began experiencing total system resets, each resulting in losses of data. The press reported these failures in terms such as "software glitches" and "the computer was trying to do too many things at once". This week at the IEEE Real-Time Systems Symposium I heard a fascinating keynote address by David Wilner, Chief Technical Officer of Wind River Systems. Wind River makes VxWorks, the real-time embedded systems kernel that was used in the Mars Pathfinder mission. In his talk, he explained in detail the actual software problems that caused the total system resets of the Pathfinder spacecraft, how they were diagnosed, and how they were solved. I wanted to share his story with each of you. VxWorks provides preemptive priority scheduling of threads. Tasks on the Pathfinder spacecraft were executed as threads with priorities that were assigned in the usual manner reflecting the relative urgency of these tasks. Pathfinder contained an "information bus", which you can think of as a shared memory area used for passing information between different components of the spacecraft. A bus management task ran frequently with high priority to move certain kinds of data in and out of the information bus. Access to the bus was synchronized with mutual exclusion locks (mutexes). The meteorological data gathering task ran as an infrequent, low
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This document was uploaded on 10/27/2011 for the course CSE 321 at SUNY Buffalo.

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MarsRover - http/catless.ncl.ac.uk/Risks/19.49.html What...

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