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BATTERIES THAT ARE OUT OF THIS WORLD
A group of engineers and technicians work on the rover's warm electronics box that houses the avionics, or “brains,” which are crucial electronics that control rover movement and instrument deployment. This box-like feature is located in the center of the rover.
Throughout the years, the National Aeronautics and Space Administration (NASA's) long-term program of robotic exploration of Mars has depended on the use of batteries to power its robots. The scientists working on this application have come across numerous obstacles along the way.
Most batteries, as other components used in the Mars mission, initially were not designed to survive the extremely cold Martian nights. The batteries needed to be kept above -4 degrees Fahrenheit (-20 degrees Celsius) for when they are supplying power and above 32 F (0 C) when they are being recharged. The solution was putting the batteries inside a warm electronics box that uses a combination of heater units. The heat given off by other components and also houses systems key to the rover's operation. Another problem occurred when using solar panels to charge the batteries. The Mars Exploration Rovers carried two 8-amp-hour lithium batteries. During the rovers' prime missions, their solar arrays were able to produce about 900 watt-hours of energy per Martian day, or sol. Well into the extended mission, efforts to drive the robots through and toward solar-rich areas provided up to 410 watt-hours per Martian sol. The power systems also provided energy when the sun was not shining, especially at night. Unfortunately over time, the batteries gradually degraded and were not be able to recharge to full capacity. With the next few explorations, NASA explored other options. One rover carried a 40-amp-hour lithium battery. And a nuclear battery enabled another unit to operate year-round and farther from the equator than would be possible with only solar power. For more information on this and other aspects of Mars exploration, visit http://mars.jpl.nasa.gov. This image is a bird's eye view of a group of engineers and technicians who are working on placing solar cells on the Spirit rover's “wings” in JPL's spacecraft assembly facility.
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AVIATION AFTERMARKET DEFENSE | WINTER 2016/17
about one quarter of the weight of a leadacid battery of the same capacity, making them an attractive choice for aircraft applications. Because safety is paramount, these batteries use a microprocessor-based Battery Monitoring System (BMS) that tracks individual cell activity and protects the battery from abnormal conditions, such as excessive electrical current during charging or discharging, over/under voltage, and extreme operating temperatures. The BMS on some batteries controls battery heating for operation in cold environments, or the system may provide cooling if battery's internal temperature becomes too high. In addition, the system balances the battery's cells to maximize usable capacity and monitors overall battery health. It also can interface with both digital and analog output controls for chargers and other external devices. USE OF LITHIUM-ION BATTERIES IN AIRCRAFT Lithium-ion batteries generally work well in laptops, cell phones, portable power tools, and such. Though there have been notable exceptions, including the recent issues with Samsung's Galaxy Note S7's battery meltdown and subsequent worldwide recall. There also have been problems with larger applications, particularly in aircraft. For instance, Boeing's new 787 Dreamliner had issues with lithium-ion batteries catching on fire, and aircraft were grounded in January 2013 following two LIB incidents. Battery fire containment solutions and other safeguards were put into place in April of that year, and the planes were returned to service. Another issue is that the service life of lithium-ion batteries installed in aircraft has not yet been established. Many battery manufacturers project a service life of 5 years or more, but these projections are based on laboratory data and not field experience. Lithium-ion batteries for consumer products typically last around 2 to 3 years, but aircraft applications operate in more extreme environments, so battery service life may be significantly less. The cost for lithium-ion batteries also can be three to six times that of a lead-acid battery. Given the possibility of a shorter service life, it may be difficult to justify the WWW.ABDONLINE.COM