The 6 wheeled rover Opportunity is currently roaming Mars and that has been doing so since 2004. It´s equipped with a solar array making it almost exclusively solar powered. The solar array on this mobile robot is built of germanium substrates.

spirit opportunity mars rover digital image germanium

A digital image of the mars rover Opportunity its solar array showing off as wings
Credit: NASA/JPL

Opportunity began its journey in 2004 together with a sibling robot named Spirit and now 9 years later as the year is 2013 it is still going strong. The initial mission was for the robot to be functioning for 3 earth months but Opportunity surpassed all our expectations, today she has driven further than any other NASA vehicle. A big reason the rover has been able to continue functioning during this long time is because it’s powered by a renewable and never ending energy source, more exactly the sun. The high quality solar panels propelling NASAs little rover forward are made by a company named Umicore.

Harsh surroundings require extreme technology

On Mars the climate is such that it is crucial that the robot has available power at all times. This is because the temperatures on mars can drop down to a chilling −153 °C and therefore Opportunity needs artificial heating built in to its core to avoid important parts of the machinery to freeze and brake down. The rover can only function when its temperature is maintained from −40 to +40 °C. To be able to keep the heat up the rover is isolated with silica aerogel and a layer of thin gold film. The heating is provided from radioisotope heaters and if needed the rover turns on its electrical heaters as well to avoid freezing. To be able to run itself and all the necessary heating Opportunity gathers power with its solar arrays during the day. The energy is then stored in lithium ion batteries so the rover will be able to draw power from them and keep functioning later at night.

Because of the month long blinding sandstorms on the surface of Mars, the light reaching Opportunity’s solar arrays can at times be very scarce and therefore it presents a challenge to accumulate as much energy that is needed to keep Opportunity alive. That is why it is of outmost importance that the solar cells in the rover’s panels are capable to absorb and transform as much as possible of the light that hits them.

 

The rovers solar array is made of germanium

The germanium solar array the rover uses are of the highest quality and are capable of producing approximately 140w per hour, with is twice as much than if one would try to use a normal silicon solar array of the same size to do the job.
 

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building mars rover opportunity in lab

Photo: public domain NASA

Germanium is a lustrous hard grey metalloid witch means it has properties in between a metal and a nonmetal. Chemically its properties are very much alike the ones of silicon. Silicon as you may already know is also used as a base in solar panels, but these are not used in space. Germanium solar cells have an advantage over silicon solar cells because they have more then on p-n junction. They are so called multijunction photovoltaic cells. This basically means that they have more points in them where light can hit and be converted into usable electric power. In turn this means that they are much more efficient then the solar cells that only have one junction. The rover on Mars has a solar array with triple junctions.

Because Germaniums lattice constant is very similar to gallium arsenide it may be utilized in the making of gallium arsenide solar arrays. The germanium form the base of the solar cells and then scientist make other materials grow on the top of that. The other materials are then responsible of harvesting different wavelength of light each

International Space Station solar array

This is a picture is of the Germanium solar array on the international space station taken by the expedition 17 crew
Photo: public domain NASA

When you are in space you need to find a solar array that is as efficient as possible for their size. This is because to get stuff into space you have to launch it there. This is done in very expensive space rockets and space craft’s that unfortunately don’t have unlimited storage space. Everything needs to be kept as small as possible.

Germanium solar panels are so good at their job that they are not only used on Mars but also on many of the satellites currently circulating in space.

 

Vanguard 1 showing of solar array

A picture of the very classic looking Vanguard 1 satellite with its matching tiny solar array.
Photo: public domain NASA

First solar array in space

The first solar panels ever used in space were placed on the American satellite Vanguard 1 in 1958. After that day solarpower has been the main power source for distant satellites like the Mars Observer, Juno, Mars Global Surveyor and Magellan.  And the list can be prolonged with close range satellites orbiting the earth witch are The Rosetta space probe and the Hubble Telescope.

If you liked this article then our next one, that continues on with the solar panels in space theme will surely amaze you. We will take a closer look on the future for solar panels in space

 

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