Solar Sunday Photo of the Day – March 18, 2018

Watch this slide show of how the International Space Station’s (ISS’s) 262,400 solar cells were taken up in stages to the station’s 400-kilometres-above-the-earth orbit. They now encompass an area of about 10 tennis courts – 27,000 square feet (2,500 square meters). Each solar array (the collection of solar cells) is 10 metres longer than a Boeing 747’s total wing span (73m compared to 65m) and the station’s entire electrical system is connected by 12.9 km (8 miles) of wire. Altogether they generate 84 to 120 kilowatts of electricity — enough for about 40 homes.

So how DO you get those panels up there?

The arrays were mounted on “blankets” folded like an accordion. Once a blanket is in orbit, ground controllers send commands to unfold the blankets to full size.  The final blankets/arrays were taken up the STS-119 space shuttle crew and installed and deployed In March 2009.

Repairs and replacements sometimes needed

It didn’t all go smoothly. In the NASA photo that is today’s Solar Sunday Photo of the Day astronaut Scott Parazynski cuts a snagged wire and installs homemade stabilizers designed to strengthen a damaged solar array’s structure and stability. The 7-hour, 19-minute spacewalk, operation took place November 3, 2007. Once the repair was complete, flight controllers on the ground successfully completed the deployment of the array.

The arrays and systems are actually different on the Russian and USOS parts of the station. (USOS stands for US Orbital Segment, constructed and operated by the U.S., Canada, Europe, and Japan). The Russian side uses uses 28 volt direct current and The USOS uses 130–180 V DC.  The two station segments share power with converters.

The arrays are attached to the ISS with two sets of gimbals that rotate them to face the sun at all times and maximize power generation. One set of gimbals follows the sun as the station moves around the earth and the other adjusts the panels for the ecliptic orbital variations throughout the year. They even have different tracking modes for the arrays called “Night Glider” and “Sun Slicer”.

Of course, when the earth is between the station and the sun, no power is generated. It takes the station about an hour and a half to orbit the earth (think about that for a second) and it is in the ‘eclipse’ part of the journey for about 35 minutes. The station had nickel-hydrogen batteries installed originally, which were replaced in January of 2017 with lighter and more efficient lithium-ion units.

Watch ISIS being built from 2002-2009

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