#1307: Orbitube

Last week I was asked by someone about weightlessness and it sparked a curious train of thought. A body travelling around the Earth will be in orbit if its velocity is given by v^2 = rg. What if this occurred not in space, but at sea level? A velocity of sqrt(6.4E6 *9.81) = 8km per sec (Mach 24) would be hard to achieve due to air resistance.

Today’s invention is therefore a pipeline joining cities which are far apart. This is in the shape of a perfectly circular arc bolted to the ground and made of sections of pipe which are sealed so that the whole pipeline can be evacuated.

Airlocks allow a capsule to be inserted and a series of external railguns accelerates this to huge velocity (and brakes it again at the far end).

During transit, the capsule will experience microgravity (possibly useful for in-transit materials processing). This arrangement would allow a small payload of cargo to get from New York to Melbourne in 35 minutes.

(Suddenly opening the downstream end would provide a way to inject satellites into a higher, conventional orbit).


  1. How do you prevent the capsule from rubbing the wall of the tube? At mach 24 that would cause almost instant destruction. Wheels would not survive either. Mag lev over that distance would be difficult to manage and maintain.

  2. I guess I was thinking of using maglev at the start and end sections only. The pipe need not be anything like a tight fit, so that some variation in orbital radius would not result in contact with the wall.

  3. No need for rail guns. Just fill the space behind the capsule with 0xygen and add fire. Bang!

  4. Many years ago (?1962?) there was an article in Scientific American which involved evacuated tubes that formed arcs below the surface; a capsule would be released and gravity would pull it down. Once it reached its low point, momentum would carry it up nearly all the way back to the surface – allowing for friction. A minor amount of propulsion would bring it up to the destination station. The whole trip would be much faster if the capsule was given an initial boost at the original station.

    • I knew about the gravity tunnels but not that they were evacuated or curved. I guess they didn’t involve achieving orbital velocity?

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