Solar-powered spaceship overhead next Wednesday |

Solar-powered spaceship overhead next Wednesday

Each of the space station's double-paneled solar arrays is 112 feet long; total area is over a half-acre.
Courtesy of NASA |

Put the date on your calendar: Wednesday, Aug. 9, 9:46 p.m.

Here on Earth, life is easy.

That two pounds of oxygen your body used today? No problem — green things on the land and in the water replace it as fast as it’s used.

The clean water you drank and turned into pee? Soil bacteria turn urea into plant food, making the water clean again.

Leave Earth, though, and we leave this give-and-take behind.

Traveling through space, we need more than sunscreen to avoid roasting, more than sweaters to avoid freezing.

We need to pull from the air the carbon dioxide we exhaled, replace the oxygen we inhaled.

We need to make potable (POE-tuh-bul) water from our dishwater, sweat and pee.

All this recycling takes energy.

Having completed its interplanetary mission — sending to Earth phenomenal images and measurements of Jupiter and Saturn — Voyager 1 (launched 1977) recently began its interstellar mission. No humans live aboard the spacecraft, but it still requires energy to run its instruments, keep itself warm, radio its observations back to Earth.

Nearly thirteen billion miles out from the sun, our star appears only about as bright as the full moon. Even with nearly all the spacecraft’s instruments and cameras shut down (including, most recently, its heater), attempting to generate the Voyager’s electricity with solar would require a humongous array.

Having discovered radium at the very end of the nineteenth century, Marie and Pierre Curie found this element always warmer than its surroundings ­— it was giving off energy.

Too far to use solar panels, Voyager 1 makes electricity from the continual warmth of plutonium, supplying the dozens of watts the Voyager needs to maintain contact with Earth.

The International Space Station, orbiting Earth for twenty years now, always has humans aboard — a rotating crew of six.

Fortunately, at Earth’s distance, our star shines brightly enough to make solar power realistic. But to keep the station alive, run its experiments, charge its batteries, and perform all the recycling needed by life, takes, plus-or-minus, a hundred thousand watts. That much power in turn requires a solar array that is, in a word, humongous — better than a half-acre of solar cells.

The station absorbs a lot of sunlight, turning some into (useless) heat (just as a sun-lit wall grows warm), turning some into electricity. But the glass-surface cells also reflect a fair amount of sunlight — enough sunlight to make the space station the brightest satellite in orbit. (Other satellites, when they catch the sun just right, can be as bright, or brighter, but only for a second or so; the space station shines continuously).

Next Wednesday, at 9:46, the International Space Station (ISS) will rise in the northwest and arc toward the northeast. Between its rise and set, the ultra-bright spacecraft will pass directly over Nevada City, Grass Valley and San Juan Ridge.

Al Stahler enjoys sharing nature with students of all ages. His science stories can be heard on radio station KVMR (89.5 FM), and he may be reached at

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