An atmospheric envelope for ground-based telescopes.

The original idea was to use the tube to lauch spacecraft. It therefore was already intended to be highly directional. You direct the orientation of the tube to follow that of the telescope. If you use pressurized gas rather than liquid the pressure does not have to be especially strong. In fact for gases since pressure changes exponentially with altitude you can choose the gas and temperature so that the pressure is nearly constant over its length (long scale length.) Then inputting say 5000 psi pressure at the bottom will result in close to that at the top. There are light-weight carbon fiber tanks that already operate at these pressures.

Bob Clark

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Pressurized gas would almost certainly be better than liquid. This is because they are lighter so the pressure that would need to be input at the bottom would not need to be as great in order to get suffient pressure out at the top. Since the pressure changes exponentially for a gas, by making the scale height sufficiently long the pressure could even change just by a few percent over kilometer lengths by using low molecular weight gas at high temperature.

Bob Clark

I suggest you calculate the thrust you would get. My experience suggests it will be much too low to lift the pipe any useful distance but I will be delighted if you prove me wrong. This time though, make sure you use the nozzle exit pressure and area, not the pipe pressure.

George

temperature

There is not an *upward* force from the sides of this tapered tube but there is a downward force. Once I include that in my calculation I conclude that there is no dependence on cross-section as you said. So tapering the container alone can not change the pressure profile.

So if this idea for a telescope shroud is to work you would need to cover the top with a thin cover. Since the pressure at this altitude is so low, it could probably be thin enough so as not to affect seeing.

Bob Clark

"Pressurized gas would almost certainly be better than liquid. This is because they are lighter so the pressure that would need to be input at

the bottom would not need to be as great in order to get suffient pressure out at the top."

Have you ever worked with a vacuum? The apparatus must be very strong or an implosion will destroy it . The amount of vacuum needed to help with atmospheric impairment for a telescope would need a strong rigid design. I am not even going to attempt to calculate the pressure needed in a flexible tube to hold a vacuum. I don't think it is possible because of material strength.

Bernouilli DOES NOT assume that the fluid is incompressible - you can apply it to a gas stream just as well as a liquid one. But you need to take into account that the density of the fluid is a variable rather than a constant - and if you are talking about major changes in elevation, "g" also becomes a variable with altitude.