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Emcore Primes Cells For NASA And Beyond

Having celebrated more than a megawatt of power in space and a fistful of space contracts last year, Emcore looks set to serve up more of the same in 2014




Artist's concept of InSight Lander on Mars: Emcore will provide its third generation triple junction cells to power the spacecraft. [NASA]

Having celebrated more than a megawatt of power in space and a fistful of space contracts last year, Emcore looks set to serve up more of the same in 2014.

Already the US compound semiconductor-based product manufacturer has snared two major contracts, with US aerospace heavyweights ATK and Sierra Nevada to manufacture solar panels for NASA missions. And as vice president of business development, Navid Fatemi puts it: "Emcore provides solar panels to the vast majority of NASA missions, many more than our competitors. For example we've been working ATK for more than a decade and had more than a dozen successful missions."

Both contracts will see Emcore populating solar panels with its third generation triple-junction (ZTJ) InGaP/InGaAs/Ge solar cells, but for very different applications; Mars and low Earth orbiting satellites.

For ATK, Emcore will design and manufacture solar panels to power NASA's InSight spacecraft that will leave for Mars on March 2016, landing some six months later to study the planet's deep interior. Right now Emcore is manufacturing its ZTJ solar cells for integration to ATK's lightweight 'UltraFlex' fanfold solar array system, ready for final configuration on the spacecraft.

Meanwhile, Emcore will also design and manufacture ZTJ cells and panels for Sierra Nevada that will be integrated to NASA's Cyclone Global Navigation Satellite System (CYGNSS) by the Southwest Research Institute. Launching in October 2016, CYGNSS comprises eight low Earth orbiting satellites that will measure ocean surface winds and predict hurricanes.

From Earth to Mars, the ZTJ cells will be subject to extreme, but very different environments. Earth orbiting satellites, for example, experience relentless radiation. Here, protons and electrons generated by solar wind trapped by the Earth's magnetic field impinge onto the craft, and its solar cells constantly. At the same time, satellites experience very wide and extreme temperature cycling; from an incredible -180°C to around 100°C depending on orbit.

In contrast, on Mars, there may be little radiation, besides ultraviolet radiation, but the rocky planet has atmosphere with wind and, again, significant temperature cycling.

Still, as Fatemi highlights, Emcore's solar cells serve all purposes and will survive all flight conditions. "The solar cells we have designed and are planning for Insight are the same solar cells that have been space-qualified for Earth orbiting satellites," he says. "There's no difference in construction and the very same cells are currently navigating the asteroid belt between Mars and Jupiter as part of the NASA Dawn mission."

But while Emcore busies itself with its latest ATK and Sierra Nevada contracts for triple junction ZTJ cells, whatever happened to its much-awaited inverted metamorphic (IMM) solar cell? Excitingly, this could be unleashed sooner rather than later.

A 33% efficient, novel architecture GaAs-based cell was first slated for delivery, by Emcore, back in 2010. Four years later, industry still waits but hopeful signs are emerging.

In recent years Emcore has shifted its research focus from a three-junction IMM to four-junction IMM device in a bid to boost efficiency to 34%. Papers have been presented at conferences and now on its website, ATK claims: "UltraFlex is compatible with... IMM cells. anticipated to be ready for flight within the near future."

Fatemi won't commit to an absolute release date but is confident NASA would be a customer. "We've noticed that every time we introduce a new generation of solar cell with higher performance, NASA is one of the first organisations to use it," he says. "NASA spacecraft designers can always use more power within a limited area; this is something they will always take advantage of."

Space qualification awaits. While the individual junctions within the IMM structure are already used in Emcore's ZTJ cells, the entire cell is not yet qualified. Still Fatemi reckons 'a space qualification campaign' could start in the next year or two.

"The packaging of IMM is a little more challenging than that of your conventional triple junction solar cells; IMM is only a few microns thick and so is flexible yet very fragile," says Fatemi. "We're working on this, and once completed to our satisfaction that it will serve the needs of all customers, then space qualification will start."

Space and beyond

But while Emcore makes great strides on ZTJ cell manufacturing and IMM development, is NASA alone enough to ensure the space-based arm of the III-V systems developer thrives? Speaking last year to Compound Semiconductor insert link , Fatemi outlined the slow but steady decline of the terrestrial CPV market.

Having spent several years developing and manufacturing CPV modules based on its multi-junction solar cell for this sector, Emcore decided to step back and focus on space. But given NASA's very same slow but steady decline, surely Emcore is eyeing other space-based avenues?

Of course. According to Fatemi, commercial space markets - predominantly geosynchronous satellite missions for telecommunications - offer future promise.

As he highlights, these missions typically involve large satellites, which of course demand more power. And of course, more power means many more solar cells, than your average NASA mission.

"This market was not so healthy in 2013, but the indications are it will recover back to more than twenty orders, which is the norm. Last year the total order number was around seventeen," he says. "There's this potential to supply much larger panels, which is so important to the health of suppliers such as ourselves."



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