ISS: Power, Propulsion and Communications
The ISS is basically a large spacecraft. As such, it must be able to move about in space, its crew must maintain communications with controllers on the ground and it needs power to accomplish all of this.
We take for granted having electrical power to operate our homes. For example, to use your coffee maker, you simply plug it into the wall without a second thought. Like in your home, all of the onboard systems of the ISS require electrical power. Eight large solar arrays provide electrical power from the sun. Each array is 240 feet (73 meter) long and — cumulatively-speaking — they cover an area of around 27,000 square feet (2,500 square meters) [source: NASA].
On each array are two blankets of solar cells. Each blanket is on one side of a telescoping mast that can extend and retract to fold or form the array. The mast turns on a gimbal so that it can keep the solar cells facing the sunlight [source: NASA].
Like a grid on Earth, the arrays generate primary power — approximately 84 to 120 kilowatts of electricity, enough to keep the lights on at over 40 homes. NASA reports that while the ISS absorbs sunlight, around 60 percent of the electricity produced in this process goes to recharging batteries aboard the station [source: NASA].
Originally, the ISS was fitted with nickel-hydrogen batteries. But in 2017, after 18 years of service, those were swapped out for two dozen lithium-ion replacements. On top of being cheaper, these upgraded batteries are smaller and more efficient [source: Nield].
At the station's orbiting altitudes, Earth's atmosphere is extremely thin, but still thick enough to drag on the ISS and slow it down. Therefore, the ISS must be boosted every so often, lest it veer off-course and lose altitude by decelerating.
The Russian Zvezda service module has engines that can be used to boost the ISS. However, it's the Progress supply ships that do most of the reboosting. Each reboosting event requires rocket engine burns [sources: Pappalardo and NASA].
These same technologies could also be used to steer the vessel away from floating space debris (which is fairly common these days). Besides, it's sometimes necessary to adjust the station's orientation so it can link up with supply vessels.
Not only does the ISS crew need to know their precise whereabouts, but they've also got to locate other objects — and figure out how to get from Point A to Point B, especially during reboosts.
To discern its speed and location, the ISS uses Russian and U.S. global positioning systems (GPS). Also, there are multiple spinning gyroscopes that help the station maintain its desired orientation. Additionally, the ISS monitors the whereabouts of various stars, satellites and ground stations — as well as the sun — in order to navigate [source: NASA].
Now that you know how the ISS stays in space, let's see what it's like to live and work there.