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| Fig. 1: International Space Shuttle and its Solar Arrays. [1] (Courtesy of NASA) |
On Earth, we have many different sources for electricity and power, and most people have at least a vague idea of how this energy is generated. However, in space, specifically in the International Space Shuttle, it it hard to guess how power is generated.
There is a common energy source that is available on Earth, but more readily available in space - Sun. International Space Shuttle generates electricity using solar energy. In order to collect solar energy, ISS uses solar arrays in a form of a "blanket." (Fig. 1) Solar panels attached to these "blankets" are foldable, allowing the panels to go up to the space in a compact form, and then to open up to full size once in space to gather sunlight. These solar arrays also rotate in the direction of the sunlight to get maximum solar power. Each wing has 32,800 solar cells, and according to NASA, the total of four sets of solar arrays can gather 84 to 112 kilowatts of power. [1]
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| Fig. 2: Modules containing three nickel-hydrogen batteries. (Courtesy of NASA) |
ISS does not face the direct sunlight every time. For 35 minutes in every 90 minute orbit, ISS needs to store the energy in order to provide constant electricity, as without electricity, everything on board can go wrong. To do so, ISS initially used rechargeable nickel-hydrogen batteries to store energy (see Fig. 2). [1] These batteries have design life of 6.5 years, and can endure 38,000 charge-discharge cycles. In 2017, nickel-hydrogen batteries were replaced by lithium-ion batteries. [2] Although the nickel-hydrogen batteries have been very sturdy for a long time, they have the drawback of being susceptible to "battery memory." This means that the battery can lose a portion of its capacity if it is not fully charged and discharged each cycle. While nickel-hydrogen batteries work by pressurizing hydrogen gas, lithium-ion batteries work via lithium ions moving between electrodes during the charging. For this reason, lithium-ion batteries are much lighter and smaller. A single lithium-ion battery was able to replace two nickel-hydrogen batteries. [2] And of course, lithium-ion batteries are not susceptible to "battery memory." However, lithium-ion batteries are much more sensitive to overcharging and have shorter design lifetime than nickel-hydrogen batteries. However, because the current lithium-ion batteries were designed to last 10 years longer than the ISS plans on being around, the lifetime of the lithium-ion batteries does not seem like a problem. [2]
© KiJung Park. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Reference Guide to the International Space Station," U.S. National Aeronautics and Space Administration, NP-2010-09-682-HQ, November 2010.
[2] D. Grossman, "Sometimes Even the International Space Station Needs New Batteries," Popular Mechanics, 30 Dec 16.