Rover designs evolve

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A new phrase entered the JPL lexicon in the early 1990s: the Mars Science Microrover. The Rocky family slowly grew and by 1992, Rocky 4 was incorporating a rock chipper, seismometer and sensors, and displaying even better mobility. The next generation microrover, quite possibly the flight rover, would have to be solar powered, generating only a few watts of power. Thus, each electrical component would have to consume as little power as possible. The rover would also need to have a brain, and JPL selected the trusted Intel 80C85 microprocessor that had been reliably used on its space probes for years. It was slow, having only 6,500 transistors, but it could withstand the rigors of space radiation and could perform all the tasks required for this first Martian rover.

In the JPL world of space hardware design, however, everything is always subject to change. The design of the microrover was really in a state of flux, whether it involved the rover suspension and wheel design, thermal control, telecommunications design, power generation, or other systems. This was entirely new ground for the engineers at JPL, because it was one thing to design terrestrial rovers with little regard to either size or weight, but an entirely different thing to downsize the rover and all that entailed in order to fit on a lander that would take it to the surface of Mars. There were routine peer reviews of the rover design as it evolved and during the 1993 to 1994 timeframe, it became clear that the rover would have to have sufficient ground clearance during its short traverses, while at the same time being as compact as possible in order to fit on the folded lander. How could this be accomplished?

The solution was quite clever. The rocker-bogie suspension system was designed to be collapsible in relation to the rover body. Months of work went into this vital aspect of the microrover and when refined, it succeed in reducing the stowed height of the vehicle to only eighteen centimeters. Aside from this, an on-going debate continued as to whether the rover should operate with an electrical tether running to the lander, or whether the it should operate wirelessly. There were strong cases for and against each approach. The primary case for a tether was that it ensured uninterrupted communication and power from the lander to the rover. Against it was the very distinct possibility of the tether deployment spool somehow becoming jammed or the tether becoming snagged by a rock. In the end, the rover team succeeded in winning the vote for wireless communications. The rover would have onboard battery power, but they would not be rechargeable as this would add prohibitive weight to the vehicle. Instead, solar power would be the rover's primary electrical power source. By 1994, the flight rover program was given the name Microrover Flight Experiment (MFEX).

The rover and the lander were meant to be technology demonstrators. The mission to Mars was designed to prove capability through all aspects of the mission,

Robotic rover development at JPL began in earnest with the design of the rocker-bogie suspension system, resulting in the Rocky family of technology demonstration prototype rovers during the 1990s. Rocky III included a robotic sampling arm. (NASA/JPL-Caltech)

from launch, to entry into Mars' thin atmosphere, descent to its surface and deployment of the spacecraft once there. Any science would take a back seat. That did not sit too well with the scientific community, however, which saw this mission as a prime opportunity to gain new knowledge about Mars, something they had not been able to do for almost twenty years. However, MESUR Pathfinder was still regarded as a means to an end, a technology demonstrator that would prove many vital mission aspects that would be employed on future rover missions. Any scientific instruments on either the lander or the rover that jeopardized the fixed mission funding cap would be dispensed with.

"Pathfinder from beginning to end was a technology demonstration mission,'' Andrew Mishkin told this author in a 2006 interview. Mishkin was a Senior Systems Engineer on the program and would later work on the Mars Exploration Rover (MER) program. "It never became a science-driven mission. It was a cost-capped mission and was given the option of reduced capability in order to stay within that cost cap. That is one of the differences from a science-driven mission, where other things would have to be rearranged to ensure that the original science objectives were met. This mission could be adapted and various capabilities altered in order to ensure that demonstration of the low-cost landing system could be achieved.'' [Mishkin's1997 book, Sojourner: An Insider's View of the Mars Pathfinder Mission, is listed in the Bibliography.]

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Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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