A McKendree cylinder is a rotating space station that is 920 km (580 miles) in diameter, and 4600 km (2900 miles) in length.

This version would orbit the sun at 1 AU (at the same distance as earth). It would be oriented transversely ("sideways") relative to the sun, as seen in the diagram, with large mirrors used to reflect light through transparent windows at each end. (Assume windows are approximately 50% of the diameter of the cylinder itself.)

Diagram of orbital orientation of McKendree Cylinder

Is it possible to calculate how far light in the visible portion of the spectrum would penetrate into the cylinder? Would it be dim in the center? Or is it too difficult to tell due to the large number of variables? I'm trying to understand if a setup such as this would run into any issues with lighting the interior.

I should maybe point out that the atmosphere inside the cylinder hugs the walls, so that the axial center is nearly a vacuum. That should help light penetration because there is no air attenuation there.

  • $\begingroup$ Wouldn't this be better for Physics SE? $\endgroup$ – NL628 Mar 19 '18 at 5:55
  • $\begingroup$ Maybe a question for Space Exploration SE. $\endgroup$ – StephenG Mar 19 '18 at 11:26
  • $\begingroup$ @Lakey - As someone who is prone to getting skin cancer, I ask why do you want natural light that contains ultraviolet light? To me it always seems safer to collect sunlight to provide electrical power to power artificial lights calibrated to only emit visible light to illuminate the habitat. If the process is highly inefficient, just build vast but light weight solar panels or mirrors to get more sunlight for power. Transparent areas of hull are likely to weaker than opaque hull areas. $\endgroup$ – M. A. Golding Mar 19 '18 at 19:49
  • $\begingroup$ @M.A.Golding The idea would be that the mirrors would primarily reflect visible light frequencies into the station. Thermal management would be an issue with this station, so you'd want to filter out all the unnecessary frequencies anyway. $\endgroup$ – Lakey Mar 19 '18 at 20:04

/ I should maybe point out that the atmosphere inside the cylinder hugs the walls, so that the axial center is nearly a vacuum. That should help light penetration because there is no air attenuation there./

That would help the light penetrate. But what would then illuminate your walls / atmosphere / inhabited regions? How does the sunlight move laterally? Why would the light not pass through the vacuum and out the other side?

You might want something in the center that can scatter the light and so indirectly light your peripheral regions. Could particulate matter hang in the zero-gravity center? Maybe you could spray water up there. It would scatter the light, and gradually fall back to the exterior as a gentle rain. It would be like living in Portland, OR.

Or maybe one glob of shimmering water in the very center. The sunlight from either direction would hit the water and be refracted / reflected away. You would have a water-sun.
sun on pond


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    $\begingroup$ I like the idea of a water sun. It's very interesting. Yes, the water should theoretically stay in the center, although it would probably drift. However, I was under the impression that the sunlight would naturally spread out and strike the inner walls of the cylinder, since it's not columnar like a laser. The reflecting mirrors could possibly even contain a slight deflection that causes the light to spread out in a cone. $\endgroup$ – Lakey Mar 19 '18 at 20:23

The problem of illumination inside a McKendree cylinder was dealt in its original proposal. This does mean this question can be set aside. Rather than place windows at either end and be concerned about the penetration of light, build them as they were originally intended.

As originally proposed, the McKendree cylinder is simply a scaled-up version of the O'Neill cylinder. Like the O'Neill cylinder, McKendree proposed dedicating half of the surface of the colony to windows, allowing direct illumination of the interior.1 The habitat would be composed of a pair of counter-rotating cylinders which would function like momentum wheels to control the habitat's orientation.

Source: McKendree cylinder

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  • $\begingroup$ I know that the typical example of an O'Neill cylinder has large strips of windows running lengthwise. However, they are unsightly, and that configuration is not the only conceived design for such stations. There are many designs with windows in the end caps. There are also designs that have no windows, but which are artificially lit. The question is specifically regarding the version with transparent end caps. The purpose of this question is to simply determine how realistic that design is. $\endgroup$ – Lakey Mar 19 '18 at 20:12

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