I assume calculations start with the payload weight. A massive foundation would be needed lots of concrete and rebar meters thick. Also a harmonically sealed tunnel a thousand miles long filled with helium at a low pressure,very expensive. Steam or a linear motor powerful enough to achieve the crazy speeds needed to hurl such a huge object in to low orbit and a heat shield. I envision the spaceship a mile long and pointy like a big dart filled with 400 astronauts.

  • $\begingroup$ Welcome on the Space SE! I suggest, please try to formulate your post as a question. So you will get useful answers. $\endgroup$ – peterh - Reinstate Monica Apr 6 '19 at 17:59
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    $\begingroup$ Harmonically sealed? Music free? $\endgroup$ – Organic Marble Apr 7 '19 at 0:34

Yes, you start with the payload weight and the acceleration. That gives you an amount of energy you need to transfer, which tells you how many power stations you need to build.

Then you need to consider what happens when your ship leaves the gun barrel: it slams into the atmosphere at 10 km/s. This has 2 consequences:

  • the ship will start to decelerate at a high rate. This rate is important, you need to have 8 km/s left when you're outside the atmosphere. And you need this rate to be survivable (so less than 5G or so), which will dictate the aerodynamics of your ship.
  • the friction will heat the ship rapidly. This means you need a heat shield, which you have to add to the payload weight, and you need to start the calculation again.

there's a load of related questions, some of which have lots of calculations to inform your design.

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    $\begingroup$ One more thing to add: To accelerate to 10 km/s at 50 m/s^2, you need 200 seconds. Moving 200 seconds at an average speed of 50 km/s, you traverse 1000 km. For comparison, Earth's radius is 6378 km. This is an awfully long tube... (which also means that by the time you clear the cannon mouth, there won't be that much atmosphere to worry about - if you start out horizontal, you'll already be 78 km above Earth's surface. Not quite enough to be a threat to the ISS, but it's well enough to become an engineering nightmare to even build, not to mention withstand the launches... $\endgroup$ – John Dvorak Apr 6 '19 at 19:04
  • $\begingroup$ I'd also recommend adding a second cannon facing the opposite direction. The catching system will be fun to design, but if you manage that, you could use it to decelerate incoming crafts and not need that much heat shield. $\endgroup$ – John Dvorak Apr 6 '19 at 19:07
  • $\begingroup$ +1 for answering the unanswerable $\endgroup$ – Muze Apr 6 '19 at 19:11

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