The general idea is to make rocket launches far more economical than they currently are... maybe even within eventual affordable range for the general populace! The goal of a tube is to significantly reduce the energy needed for the rocket to deliver its payload into orbit, as constraining the rocket's exhaust should return a lot of energy back to the rocket itself. At a glance, this seems to be a more feasible (and potentially economical) alternative to other extreme solutions, such as space elevators, spin launchers, space tethers, etc., which do not seem to even be achievable with current material sciences (to say nothing of budgets).
Consider what the optimal choice of these options must be (assuming state-of-the-art solutions applied to each of their implementations):
- Design a long launch tube such that the most energy-intensive part of the launch is accommodated, which is probably about the first quarter of the launch journey, at most. After that point, further needed thrust can be managed with more conventional rocket technology, but now in a slimmer form. The tube can have a curved shape, as needed.
- Building such a tube would be an engineering wonder if it were just a stand-alone structure. Maybe divide the structure between a large, unsophisticated earthen mound, and a 'tall tower' built atop said mound. Erect both of these structures to the highest extent that is feasible and economical for the goal at hand.
- Alternatively, bore a hole into a tall mountain, or maybe just any other place best suited for such a hole. I don't know what the ideal elevation amount would be to terminate the length of the tube at, and maybe just a 'rather deep hole' would suffice (regardless of elevation). It would certainly be cheaper than a 'tall tube tower', though may be subject to geological factors. Maybe a middle ground option would be ideal?
- To solve the problem of launch exhaust damaging the tube, make the initial launch point have a cavity for the exhaust to harmlessly expand. The further the rocket goes, the higher it's velocity, and the less duration/amount of its exhaust is exposed to any given area of the tube. Therefore, the tube could "tighten up", further along its length.
- Furthermore, if the tube is built into (reinforced) solid earth, the force alone from the exhaust shouldn't easily be able to destroy the tube structure. The tube lining, however, will need special accommodation against the heat and blast force. Besides heat-resistant lining materials, venting, cooling, or even necessitated repairs might come into play.
- To solve the problem of rocket friction against the tube, the rocket could be enclosed in a sabot, or possibly constrained to a track (or both). Friction upon these components could be further reduced with either (or both) a form of maglev technology, or an air cushion effect (akin to a hovercraft).
- To solve the problem of rocket exhaust damaging the rocket, the aforementioned sabot could be designed to shield the rocket. The sabot could even feature something to the effect of deteriorating materials or a cooling system, if needed.
- To solve the problem of air friction in front of the rocket, mechanical pumps and a gating system can be used to maintain a vacuum state inside the tube. Alternatively (or in addition?), an explosive gas can pumped into the tube and ignited to reduce its pressure by way of directional vents, which redirect the displaced gasses. These vents may also be used to take some of the edge off the rocket's exhaust, if needed.
So my question is: With all of these solutions in mind, are rockets still simply "too violent" for a launch tube to be feasible? Also, would this tube fail to make their launches economical enough to justify its cost?
