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Why aren't orbital vehicles made of plastic? Some type of plastic have good characteristic such as airloys which have low thermal conductivity, good pressure resistance and very low density. Why don't we use those materials to build space vehicles?

Edit: Lets narrow down the question to airloys which I think it's considered a plastic material.

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    $\begingroup$ I am far from an expert on this, but I suspect that part of an answer would be that a lot, if not all, plastics degrade when exposed to the radiation of space. $\endgroup$
    – fibonatic
    Commented Mar 4, 2015 at 2:36
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    $\begingroup$ Linked: space.stackexchange.com/questions/3077/… $\endgroup$
    – Everyone
    Commented Mar 4, 2015 at 7:43
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    $\begingroup$ airloy = aerogel (a term people will be more familiar with, I expect). $\endgroup$
    – Hobbes
    Commented Mar 4, 2015 at 9:10
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    $\begingroup$ I'm not entirely sure if "very low density" is a good quality per se. it means you have a large volume for a given mass, and large volumes are hard to launch (aerodynamic drag). $\endgroup$
    – MSalters
    Commented Mar 4, 2015 at 12:47
  • $\begingroup$ Aerogels typically are great as thermal insulation. They're typically anything but great as structural material. $\endgroup$
    – David Hammen
    Commented Mar 5, 2015 at 12:23

2 Answers 2

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The reason is quite simple. Plastics have a lower specific strength (strength to weight ratio) than metal alloys, which in turn have a lower specific strength than various carbon composites. There are some other reasons too, such as resistance to temperature extremes, a spaceship is exposed both to high temperatures and extreme cold and metals will generally deal with this better than plastics. But just the strength to weight ratio is reason enough to prefer carbon composites or metal over plastic.

Moving onto airloy/aerogels. They are being used or developed by Nasa, as in here or here, including for use as inflatable heat shields. The extremely high insulative value of aerogels would make them ideal for such a purpose, if made out of an appropriate substance.

Also some plastics already have very high applicability for use in space. One example is Kevlar which has many excellent properties, Kevlar has a specific tensile strength 8x greater than steel and is moderately resistant to both heat and cold. Because of it's great tensile strength Kevlar is often used in whipple shields. Kevlar and other high-strength plastics are ideal materials to be used for future inflatable space habitats. Kevlar would also be ideal for tethers. The weakness of kevlar is very low compressive strength and it is moderately vulnerable to degradation from UV radiation. Plastics are also more permeable than metal due to the long molecular chains. Composite materials can exploit the best properties of different materials, and most composites have a plastic component.

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  • $\begingroup$ I'd also tack on to this that a lot of plastics have issues with out gassing, which makes then more difficult to get approved. Doable, but not necessarily worth it $\endgroup$
    – Diesel
    Commented Jan 26, 2020 at 0:48
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Why should they use plastic? It doesn't have tensile strength, It doesn't resist temperatures, it doesn't resist radiations, it is fragile. There is really no reason to use plastic.

At least you can use composite materials (and they are starting doing that), but it's not plastic.

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  • $\begingroup$ This is not a very well researched answer. Granted, plastics aren't used as massive structural elements for various reasons (funny, they're too heavy) but they are used in variety of systems, from thermal and electric insulators, adhesives, environmental protection coatings, to ablative heat shields. Spray-on foam insulator (SOFI) on Space Shuttle External Tank is essentially a polyiso plastic foam. So is Multi-Layer Insulation (MLI) as metal coated plastics, Phenols in ablative heat shields, PVC wire coating, anti-condensation PF coatings,... $\endgroup$
    – TildalWave
    Commented Mar 4, 2015 at 19:22
  • $\begingroup$ @TildalWave I should have put my answer as a comment, but it's not a well researched answer because it's not a well researched question. And the answer above mine list exactly the same point that I listed: no tensile strength, no temperature resistance and the use of composite materials. $\endgroup$
    – Gianni Alessandro
    Commented Mar 4, 2015 at 22:05
  • $\begingroup$ Well Kevlar is a plastic (poly-paraphenylene terephthalamide). So is Vectran (aromatic polyester). And many epoxy laminates have greater tensile, specific and yield strengths than steel. So I'm not really too fascinated by the other answer you're comparing yours now with either. But the other one at least shows some effort, adds some interesting links and answers the question about airloys. Anyway, I've added quite some information in the comments now (probably more than both the answers), so feel free to edit any in your answer at your own discretion. Oh, some propellants are plastics too. ;) $\endgroup$
    – TildalWave
    Commented Mar 4, 2015 at 23:08
  • $\begingroup$ Also, re airloy, here's an interesting video youtube.com/watch?v=k8OhJKR3AA4 It wouldn't be useful as a structural material for quite obvious reasons, displayed in the video $\endgroup$
    – TildalWave
    Commented Mar 4, 2015 at 23:11
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    $\begingroup$ @GianniAlessandro but your answer is also substantially wrong. Plastic can have excellent tensile strength - nylon is plastic, and kevlar is too. Also some epoxies are good to 500C, there are plastics suitable for cryogenic uses, and some plastics have excellent UV resistance. The problem really is getting a plastic which has all those qualities simultaneously while also being stronger than steel, making it suitable for use as a spaceship/satellite hull. $\endgroup$
    – Blake Walsh
    Commented Mar 5, 2015 at 6:45

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