A lot to take into Consideration
Satellites and the rockets that encapsulate them are made of many combinations of materials to keep us safe and keep it and its contents safe, whilst getting the best science possible from a mission.
However, for the most part, space agencies like to focus on the safety of the machine and what’s in it, being complex, with satellites exposed to the noise, vibration and gravitational forces of takeoff. Then, there’s the dramatic changes in temperature from going into and out of the Sun’s reach, creating fast and large temperature changes, leading to “thermal stress, vibration and cracking” [1] (with the ISS orbiting once every 92 minutes, creating 15 to 16 sunrises daily [2], and Mercury, a planet with little atmosphere, having temperatures as hot as 472ºC in the Sun, and as cold as -180ºC when facing away [14]).
And then, there’s the constant bombardment of UV (Ultra-Violet) radiation (along with other ionising forms of radiation), leading to plastics and coatings cracking, and materials outgassing (which also leads to the new car smell), contaminating the surface of instruments [1].
This has then led to the creating of new combinations of materials that combat these problems, then making them space-ready. These include kevlar: the material featured in bullet proof vests back on Earth, but used on satellites in Space, for its resistance to temperature change and the constant threat of space debris impacting the satellite. Then, there’s aluminium: a light weight material that, when combined with others in an alloy, is strong, so much so that it’s used on the ISS’s shutters to protect windows from space debris impacts (which, incidentally, are made of twice the number of panes, all at greater thickness, than those used on Earth) [3].
Space Shuttle Endeavour's impact with space debris on radiator. Credit: NASA
Progress in Temperature Control
Satellites use a range of coatings and technologies to regulate their temperature, keeping both the equipment, and possibly people within, safe.
One such technology is an Optical Solar Reflector (OSR), glued to the outside of the satellite’s radiator panels (panels threaded with pipes containing ammonia, which changes from gas to liquid to release waste heat from the craft, before cycling around again [4]), rejecting solar radiation whilst dissipating excess heat from the satellite.
However, the OSRs, made of quartz, are heavy, fragile, and therefore expensive, whilst not having the ability to be applied to curved surfaces, with polymer foils having taking its place in such circumstances, while suffering from issues of longevity, lasting only 3-5 years.
Another technology came out in 2018 that greatly improved this technology, known as meta-OSR, designed around metal oxides, with the added benefits of being lighter in weight, durable, and taking the place of not just the OSR, but louvers (which are rather like Venetian window blinds, regulating how much heat is lost [5]) as well, through different combinations of these metal oxides [6].
The ISS's panels & radiators (white panels). Credit: NASA
Advances in Harvesting Solar Energy
Energy is another very important resource in Space, with most satellites getting it from the Sun (except the few that use technologies like nuclear power, such as Voyager 1 and 2 [7]), shown by spacecraft such as ESA’s Philae lander, which lost power to transmit data back to Earth, because it was in a place with only 1.5 hours of sunlight in 67P’s (the comet) 12 hour day [8].
However, what if you could use more efficient solar panels, getting more energy from the Sun so more data can be transferred, possibly helping the next big discovery to happen? One such technology is called perovskite: a crystal discovered 200 years ago, which is more efficient because of its wider use of the electromagnetic spectrum (made of light at different frequencies), with 27.3% efficiency instead of the 22% of typical silicon solar technology around now [9]. It is also flexible [10], allowing for easier and cheaper designs of solar arrays on satellites in the future.
Thin film perovskite solar cell. Credit: Jordi Sastre-Pellicer/EMPA, CC BY-NC 2.0
Environmental Impact
However, the technology for satellites is designed with the survival of the satellite and what’s inside it in mind; not who and what is left on Earth. The rockets that send those satellites up do have an affect on important parts of our atmosphere, like the Ozone Layer, located in the Stratosphere. Particles emitted by the rocket’s engines act as a nucleus, or starting point, for ice to form, leading to ozone being depleted. Moreover, some rockets emit chlorine gas, which acts like the CFCs (Chlorofluorocarbons) banned worldwide for their affect of creating a hole in the Ozone Layer [11].
And then, there’s the space debris problem, where, upon reentry of a satellite, small particles of alumina (synthetic aluminium oxide), which, as Takao Doi (professor at Kyoto University and a Japanese astronaut) put it, “will float in the upper atmosphere for many years” [12], also contributing to the problem of loss of ozone when released in the Stratosphere.
The Ozone Hole from 1984 to 1997. Credit: NASA Earth Observatory
Wood: the Newish Super-Material
The answer could lie in the new proposal (published on 24th December 2020) by Sumitomo Forestry (a Japanese forestry company) and Kyoto University (based north east of Osaka in Japan, south west of Tokyo), in which wood is the material of choice for a satellite, to be finished in 2023 [13]. Wood, unlike traditional aluminium alloys, would burn up in the atmosphere upon reentry, releasing no harmful substances and releasing no debris to interact with the Ozone Layer or become space debris [12].
Moreover, wood doesn’t stop electromagnetic radiation (light) or magnetic fields, meaning that devices like antennas (for transmission of information) and attitude control mechanisms (controlling the orientation of the satellite), leading to simpler, more cost effective satellite designs. However, the materials used will also be resistance to temperature change and harmful solar radiation described earlier [13].
These new discoveries and inventions are just scratching the surface of what developments await in the future, making space technology more sustainable and good for our planet, whilst revealing more secrets of our universe.
Artist impression of the world's first wooden satellites. Credit: Sumitomo Forestry
By George Abraham, ADAS member
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References
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"Perovskites: The future of solar?". BBC Sounds. Archived from the original on 4th January 2021.
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