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In this scenario, humanity has managed to colonise some of the solar system, including Mars, some of the moons of Saturn and Jupiter and some of the larger asteroids of the belt. In most places they have been able to terraform the atmosphere so that it is breathable, so while perhaps not as dense as Earth's atmosphere, it is survivable. To save on energy consumption or to save polluting the atmosphere, humans tend to use human-powered vehicles to get about.

  1. What design features would have to be considered to build a working bicycle/human-powered vehicle to get about in these conditions?
  2. How would riding a bicycle/human-powered vehicle in low gravity/lower atmosphere density differ from riding one on Earth?
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  • $\begingroup$ All the worlds that you name in your question are in our solar system. The phrase "some of the galaxy" implies that humans have spread to other stars in the galaxy. Are humans confined to the solar system or spreading out into the galaxy in your scenario? $\endgroup$ – M. A. Golding Mar 2 at 18:55
  • $\begingroup$ In a scenario where Earth people have colonized and terraformed other worlds in the solar system it seems extremely probable that the main source of energy will be fusion. Therefore electric vehicles should be common. I suspect that stationary bicycles for exercise and also for additional electricity production may be far more common than bicycles for transportation outside of and between settlements on a world. $\endgroup$ – M. A. Golding Mar 2 at 19:00
  • $\begingroup$ Sorry I did indeed mean in the solar system, was having a bit of a brain melt - I will edit it ASAP! $\endgroup$ – L Mason Mar 2 at 19:17
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There wouldn't be much difference from here.

If the air is breathable, then it is at least as thin as in the highest peaks on Earth. There are people who are crazy enough to ski down from them; the difference in air friction is negligible.

Also, if you are keeping an atmosphere that is breathable, we are talking about at least martian gravity. No moon in our solar system is massive enough for that. Titan does manage to keep an atmosphere, but only because it is very cold. Heat it up, and it will lose its atmosphere in millenia. It will have global, violent winds the whole time.

To keep a breathable atmosphere on a moon like Io, Ganymede or some other large moon you'd have to keep a constant input of gas which would mean constant hurricanes - because the gradients in pressure would be extreme. That would render the moon inhabitable.

If you do manage to terraform, say, Mars, then using a regular bike on it is a no brainer. It will be almost exactly like biking on Earth, but you will be able to go faster since you will only have 37% of your Earthly weight there. Mountain biking would be easier, and due to your lower weight you will be able to fall from greater heights before you get hurt.

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  • $\begingroup$ Thanks for this - I was thinking it may be a possibility as they would be cheaper and easier to maintain than something with an engine, but was worried about issues such as traction, and whether they would be too bouncy. However, if they are also much faster - they definitely would be an advantage. $\endgroup$ – L Mason Mar 2 at 19:46
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The first problem with bicycles would be hitting a bump in the road. This would be likely, if not to send you into orbit, then at least to catapult you high above the ground with the possibility of landing on your head.

Secondly, traction relies on pressure on the ground so wheel skids would be common. It could be comical to see someone pedalling furiously without getting anywhere.

Therefore roads for wheeled vehicles would best be made straight and level. Rough terrain might be possible by skilled and healthy individuals who had grown up with these things.

Instead of wheeled vehicles I suggest making the best use of low gravity by jumping. A pogo stick would be ideal. It would also be great fun.

Highest Jump on a pogo stick - Meet the Record Breakers https://youtu.be/JQ-747DPTPc

enter image description here

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  • $\begingroup$ Thanks for this - great, and also entertaining answer to imagine! One question with this though - if you are likely to bounce off on a bike into orbit when you hit a bump in the road, surely there's the same risk with pogoing off into space!?! $\endgroup$ – L Mason Mar 2 at 19:19
  • $\begingroup$ You can't achieve orbit just from being launched from the surface. If you are able to terraform the poace to have a breathable atmosphere, gravity and air friction will be high enough that you won't go much more up than you would here. Finally, even if you do go much higher up, the fall won't be so bad due to you and your bike weigthing less than on Earth since the gravity is lower. $\endgroup$ – Renan Mar 2 at 19:27
  • $\begingroup$ I think you would start with a very low efficiency pogo. It would allow you to practise without danger. As you get more proficient you can start to increase the springiness. The problem would of course be landing. Trampolinists can take all of the spring out by bending their legs and practically stop dead. I haven't yet found a video of this. I think there could be a lever that converts the pogo's spring instantaneously to a shock-absorber making landings easy. Actually the springiness could be adjustable on the fly as you see where you are landing. $\endgroup$ – chasly from UK Mar 2 at 19:28
  • $\begingroup$ P.S. It is already possible to get adjustable shocks. "... Adjustable Hydraulic Series shock absorbers offer the most flexible solutions to energy absorption application requirements when input parameters vary or are not clearly defined. By simply turning an adjustment knob, the damping force can be changed to accommodate a wide range of conditions." enidine.com/en-US/Adjustable_Shock_Absorbers $\endgroup$ – chasly from UK Mar 2 at 19:34

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