# Travelling through Flexible Material?

If a tube was built between two planets that stretched and moved as they did (don't worry about how it connects to the planets) and if a set of rails was on the inside, could a rail based vehicle move through it without being crushed and have its passengers survive?

• Rather than a tube, consider just a set of rails with a car attached externally. You've just described a variation on the space elevator (for which there are loads of articles) – John Feltz Dec 18 '16 at 21:42
• @JohnFeltz But would it would it work interplanetary with the material stretching. – Mendeleev Dec 18 '16 at 21:44
• Most practical space elevator designs include some amount of flexibility to deal with passing satellites, etc. But without handwavium, there's no material you can use for either an elevator or a tunnel that will stretch over orders of magnitude of length. – John Feltz Dec 18 '16 at 21:46
• @JohnFeltz But if we had a theoretical substance capable of this would it allow the car to travel along it fine. – Mendeleev Dec 18 '16 at 21:49
• Why not? You are putting rails inside a tube I am just suggesting that you put rails outside the tube. What does the tube gain you? – John Feltz Dec 18 '16 at 21:50

Yes. With the amount of handwavium required to create a tube like that, permitting travel within it would be a cakewalk. The material properties of such an stretchable material are far more difficult to achieve than those required for travel. A similar question might be "If a society could construct a space station like the ISS and keep six astronauts alive year after year without mishaps, would they be able to make toast up there?"

Depending on what your definition of "rail" is, you may need to invest heavily in expansion joints:

We use these on rail lines to handle the natural expansion and contraction of the metal rails due to temperature.

• Thank you, I was slightly worried that it would not work due to stretching in such away it would stop the vehicle from moving, would that not be a problem? – Mendeleev Dec 18 '16 at 21:46
• @Mendeleev It depends mightily on the vehicles. A maglev train may not care at all about the tracks stretching underneath it. Personally, I'd be more concerned with how the tube attaches to the planets. It strikes me that there's more engineering challenges there. – Cort Ammon Dec 18 '16 at 21:51
• I have the connection covered as several solutions were proposed here, worldbuilding.stackexchange.com/questions/64926/…. – Mendeleev Dec 18 '16 at 21:54

Possibly, but rail travel isn't a very good way of going between planets. If we say that ~1,000km/h is a reasonable speed for a high-speed train in a vacuum, then to go from Earth to Mars would take between six and seven years.

Much better - once in space - to use a rocket and take advantage of the friction-less environment.

# Sure

Assuming your material has sufficiently high elasticity and strength at strain (which is a measure of the elongation of a material under pressure).

However, do consider that two planets, even those near each other can vary widely in distance. Consider that Venus can be anywhere from 38 to 261 million kilometers. The thickness of your rail will be significantly reduced when you stretch it. If the rail stretches by a factor of ~7 as the bridge to Venus would, then the rail itself will decrease in cross-section by the square root of that factor, or about 2.6. So you would need an engineering solution to ensure your 'vehicle' fits your tracks as they change size.

• That is what I was worried about, the vehicle being crushed but if we have the length without stretching long enough for the furthest distance could we have it work without crushing the vehicle. – Mendeleev Dec 18 '16 at 21:52

Why risk wrapping the rails around the sun by going to mars? Let's go to Alpha Centauri so the orbits of the planets are trivial when compared to the distance between.

Now stretching is a non issue. Just have that pesky speed of light to deal with

• Most people are using our Solar system as the planets I am referring to I am not however, I assume that at some point you will need a way around a star. – Mendeleev Dec 19 '16 at 16:06