Undergrad Can a Tube Launch System Harness Atmospheric Energy to Reach Space?

[nasu]

, accelerating the projectile to high speed.

High speed? What makes you say that? The force exerted by atmospheric pressure on the bottom of the projectile may be less than the weight of the projectile. In which case the velocity will be zero. All this to obtain a pressure on the bottom of one atmosphere? Vacuum does not have some magic power. It does not create large forces on objects. At the most it can allow the atmospheric pressure to act unbalanced.

 

[Captnq]

Well, wait a minute... So, what if we built a giant Funnel? This funnel is transparent. We make the base about a mile wide and coat the ground beneath it with Fanta Black. That is going to generate a great deal of heat when the sun hits it. The hot air will rise, getting trapped in the funnel. This will create a constant upward thrust. Depending on how high we could get the funnel, a great deal of air will be rushing up it. If your spacecraft is carried up by a balloon it'll be forced out the top with a considerable amount of force. I bet you could get quite high up into the upper atmosphere with this set up by late afternoon, especially if you set it up in an area with extreme temperature swings and no clouds. Once the balloon passes the end of the tube, your craft cuts loose, activates thrusters, and takes the rest of the way into low orbit.

 

[sophiecentaur]

@Captnq just do a few sums about the energy required to lift an object to a great height. The thermal Power from the Sun, warming a piece of ground is limited to about 1kW per metre square. You are actually proposing what, in general terms, is called a Heat Engine. They are not a very efficient way of using heat, when the temperature difference is small so you would get a small fraction of that thermal energy that arrives at the ground.
What is being proposed is an Engineering Project and, in Engineering, the numbers really do count, I'm afraid. Solar energy is certainly handy but it needs to be 'concentrated' into a fuel or some other form before it's able to provide any serious amount of intense mechanical work. Take a look at the 'special cases' of solar driven aeroplanes and boats to get an idea of its limitations.

 

[Ibix]

The basic principle of the device to which you refer, captnq, is called a "solar chimney" if you want to look it up.

 

[sophiecentaur]

The basic principle is called a "solar chimney"

It's the sort of effect that drives the weather; massive amounts of energy involved but not particularly usefully directed when the energy turns up in a small space. (Hurricanes and other bad weather examples). Wind turbines and sailing ships use it but don't have much effect on (even) the local weather.