I have an idea for a futuristic way to travel for my Story. People get into a capsule, and it launches itself extremely fast in the air. What would be needed to make this happen for real and what complications would exist?


The people can't die.

The people must be able to be comfortable inside

It has to be somewhat reusable

It has to be FAST. Faster than airplanes now.

It has to be accurate. Landing in an airport like place.

My Ideas:

I thought a stabilizer inside would be important, so the capsule can spin, but the cabin itself can feel like it's staying upright

Any Ideas?

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    $\begingroup$ This is basically what a plane is, but without the safety precautions like flight controls, landing gear, breathing apparatus, etc. $\endgroup$ – Frostfyre Jul 30 '19 at 20:54
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    $\begingroup$ This is not going to fly as described, sorry. We can't be accurate with unguided projectiles in atmosphere, which means capsules should have their own engines. $\endgroup$ – Alexander Jul 30 '19 at 20:56
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    $\begingroup$ Could it have directional guidance only? Say it has air stream equipment and directional control, could it stay on a reliable path? $\endgroup$ – Jwrecker Jul 30 '19 at 20:57
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    $\begingroup$ @Jwrecker atmospheric drag will throttle the initial speed very shortly. Passengers are not going to survive if initial acceleration is too high. You may launch a capsule equipped with fins and parachute for a distance of a few miles, but that's about it. $\endgroup$ – Alexander Jul 30 '19 at 21:02
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    $\begingroup$ Ah, you mean Elbonian Airlines! $\endgroup$ – Spitemaster Jul 30 '19 at 21:14

Catapults have two problems:

  1. You have only until the arm releases the capsule to accelerate the vessel. That means you have a fraction of a second to reach cruise speed. Such acceleration would turn your victims' insides into paste.

  2. Friction would quickly deccelerate the capsule, so it wouldn't go very far. Supposing the capsule is as aerodynamic and heavy as a Cessna 172 as it reaches the highest point in its trajectory at the Cessna's cruise speed (226km/h, or 140mph), it will behave exactly the same as a Cessna 172 with its engines off.

A plane at cruise speed with its engines off does not drop as a stone. Rather, it behaves as a glider. It just so happens that planes that are not designed as proper gliders epically suck at gliding. You can play with Microsoft Flight Simulator or Kerbal Space Program for an approximated idea - just reach cruise speed and altitude with any self-powered aircraft, shut the engines down and try to land. It's actually possible to land a Cessna without too much damage, but if I ever had to go through that as a passenger in real life I would never fly again.

There is a way to solve 1 and reduce problem 2 if you are flexible. You wanted to use catapults, so we have been meddling in the realm of wacky engineering from the start. Let's up the ante and replace the the catapult assembly with guns.

Someone once asked Randall Munroe (a honorary god to worldbuilders) whether it would be possible to assemble a machine gun jetpack. Mr. Munroe always researches and answers scientifically, and his conclusion was that a jetpack would be unfeasible - but a machine gun powered plane would be a no brainer.

The A-10 Warthog has a machine gun (the GAU-8 Avenger) that produces 62.5% of the thrust of its twin engines, so it runs the risk of stalling when firing straight forward.

A-10 Warthog

If you replaced the two engines with two other GAU-8 machine guns, it would be able to accelerate and fly faster!

But we can improve it further. Mr. Munroe says:

As good as this gun would be as a rocket pack engine, the Russians built one that would work even better. The Gryazev-Shipunov GSh-6-30 weighs half as much as the GAU-8 and has an even higher fire rate. Its thrust-to-weight ratio approaches 40, which means if you pointed one at the ground and fired, not only would it take off in a rapidly expanding spray of deadly metal fragments, but you would experience 40 gees of acceleration.


But if you somehow braced the human rider, made the craft strong enough to survive the acceleration, wrapped it in an aerodynamic shell, and made sure it was adequately cooled ...

a pilot leaves an area very quickly by shooting it a lot and then flies over a mountain.

… with a GSH-6-30, you could jump mountains.

Since your goal seems like giving your passengers a slightly worse experience than nowadays current airline flights, machine gun engines will at least make it survivable.

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    $\begingroup$ Eh, shells and braces are for people who are scared of the gym. Just grab that machine gun tight and keep the barrel down. Long bandoliers welcome. $\endgroup$ – Willk Jul 31 '19 at 0:13
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    $\begingroup$ I would like to point out that this vehicle would go through about 30kg of "fuel" per second and "thuster". Assuming two guns and 6t of "fuel" capacity, that's 100s of thrust, total. So, while it wouldn't look like a catapult, its flight trajectory would fit the profile. $\endgroup$ – Ruther Rendommeleigh Jul 31 '19 at 9:27
  • $\begingroup$ @Willk depending on the grip, effects could range from just losing the grip, to losing your fingers, mangled shoulders or (if you were smart enough to put the stock against your chest) major damage to your internal organs, fractured ribs, one really bad bruise and maybe even some external bleeding. This guy got knocked out with major bruises by 55g - and he was sitting in an ergonomic chair rather than leaning against the back end of a machine gun. And if you think sitting is any better - it's worse. $\endgroup$ – John Dvorak Jul 31 '19 at 11:21
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    $\begingroup$ Your catapult projectile is not going to behave like a Cessna 172 with the ENGINE (yes, a 172 only has one engine) off, unless it also has the wings of a 172, Except that the wings of a 172 would be torn off by the stresses of launch. It's also quite possible to land a 172 or other light aircraft with engine off, if you have a handy runway (or field, dry lake bed, &c). In fact, you normally do land with the engine at idle. $\endgroup$ – jamesqf Jul 31 '19 at 18:06
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    $\begingroup$ @bukwyrm: Forget the Gimli Glider (or the other airliner that glided to a landing in IIRC the Canary Islands due to a fuel leak). If you want something with an abyssmal glide ratio that lands without power, consider the Space Shuttle :-) $\endgroup$ – jamesqf Aug 1 '19 at 17:43

This is a "catapult" less like the medieval siege engine and more like the device of the same name used to launch jets from aircraft carriers.

  1. Acceleration happens over a long period so as not to squash passengers with G forces. This would be a long tube, possibly evacuated of air to reduce air resistance during launch. It could be built up the side of a mountain.
    This idea from the Halfbakery is close. https://www.halfbakery.com/idea/Steam_20Space_20Launch_20Facility#1128447586

Or you could use a railgun but just not maximize the acceleration this method could produce. You don't need to because you have a tunnel several km long.

  1. Cabin on gimbals. This would allow the outer portion to spin very fast, stabilizing the vehicle gyroscopically. https://en.wikipedia.org/wiki/Gimbal

A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of the rotation of its support (e.g. vertical in the first animation). For example, on a ship, the gyroscopes, shipboard compasses, stoves, and even drink holders typically use gimbals to keep them upright with respect to the horizon despite the ship's pitching and rolling

  1. Vehicle takes a ballistic trajectory. This is essentially a mini-ICBM. https://en.wikipedia.org/wiki/Ballistic_missile. Its path is calculated with Newtonian physics. Most of its travel is in the distant reaches of the upper atmosphere where wind resistance is both more predictable and weaker.

  2. Parachute brakes. Like an Apollo spacecraft. Nice and easy.

  3. Better on the moon. Atmospheric vagaries make this less accurate than would be the case with no atmosphere, although ICBMs are still accurate enough to hit their targets a continent away.


  • $\begingroup$ ICBMs have guidance systems, the earliest ones allowed accuracy within mile or two from the target. $\endgroup$ – Alexander Jul 30 '19 at 23:07
  • $\begingroup$ @Alexander - even on the way down? I thought they were guided some on the way up but after the rocket burned out that was that. Or do they have flaps or something like a glider? $\endgroup$ – Willk Jul 31 '19 at 0:10
  • $\begingroup$ Yes, MARV & MIRV systems are doing just that. Even without maneuvering warheads, ballistic missiles are still controlling their trajectory during boost phase (which results in so-so accuracy). $\endgroup$ – Alexander Jul 31 '19 at 7:45
  • $\begingroup$ You make some valid points, but the question asks for transporting people faster than aircraft would, which this answer doesn't really address (I assume because it can't be done in earth conditions, but it'd be good to be explicit about that). $\endgroup$ – Ruther Rendommeleigh Jul 31 '19 at 9:35

I think these are the key elements your story would need to touch on for this mode of transportation to be understandable by your audience: 1) Power Source that drives this system is too large to fit in a capsule for 2-4 people 2) A capsule can store energy to power control surfaces, navigation, etc but nothing exists that can store propulsive power required for travel range

1+2 mean all the required velocity has to be imparted by ‘catapult’

3) automated control surfaces use increased drag and spinning vanes to accurately guide capsule to destination anti-catapult or counter-catapult where the capsule is caught and slowed to a stop at a tolerable acceleration or is accelerate again and thrown at a new destination. hop-skip-jump mode of travel

4) mishaps happen, people died, corruption and incompetence uncovered, people fixed problems, safest way to travel.

5) other answers involving gimbled compartments and spinning shell are totally on point. And, same for acceleration, it needs to be long and tolerable.

6) low friction material or techniques like plasma induced low drag methods were important tech break through that made this mode of travel possible. Same for very and powerful power source

After that you can use whatever form of catapult you want — maglev, induction, artificial gravity, crazy technology harnessing weak force in inconceivable ways — other than traditional medieval siege weapon like a trebuchet or scorpion


Security around the catapult is going to need to be pretty severe. Anything valuable within range of the catapult is vulnerable to insane people, people intent on "suicide by cop," sabotage, terrorism, what have you.

People trusted to work on, operate, and maintain any part of this system will need to be very carefully screened. No unstable people allowed. Nobody with huge gambling debts or a drug problem. Nobody with whacky political ideas who might be tempted to pull something.

There will need to be ways to remotely shut down the catapult so that any supposed "trouble makers" can't launch capsule after capsule into populated areas. That could be as simple as shutting off electricity to the launch site. Though that means that you also lose all other electrical devices, such as security cameras, smoke detectors, what have you. Maybe you need some clever method to be able to shut down the catapult, and be confident it can't be turned on again, but leave the other stuff working. Maybe the power circuits for all that other stuff have to be physically widely separated from the catapult. So any possible terrorists might need to bring kilometers of thick power cables with them to be able to re-power the catapult.

Maybe a capsule is less of a draw for putting dangerous stuff on board. Not much chance of a hijacking from inside the capsule since it's going where the catapult sends it, with only the smallest of variations. So maybe there is less need for passenger screening.


Don't go for huge distances for the throw: Atmospheric drag dictates insane initial speeds, and thus unsurvivable (and uncomfortable ... i love that you specified it be both comfortable AND survivable - dodged the answers where you comfortably die) acceleration.

Go for serial lobbing - The lobbing stations are close to each other, minimising the error introduced by unforeseen winds. Capsules are caught and re-lobbed without slowing them, reintroducing the energy lost since the last lob.

Buildings close to lobbing station's receiving end (stations are one way) have to be built with aesthetically pleasing and extra-crumbly roofs, for emergency landing.

The lobs get increasingly fast, the angle of launch thus flattening. Reverse for approaching the destination.


You could do it while in space, for example when on orbit, to transfer between space stations. Your passengers climb aboard, suffer a high-g manouver for a moment as they get fired into a different orbit.

If you're willing to replace the catapult arms with electromagnetic railgun style launcher, this would be an effective way to travel and ship cargo around an airless, low gravity environment, such as a large asteroid or the moon. The lack of air makes ballistic trajectory energy efficient and accurate, requiring only very minor course corrections before landing in a specially designed capture location (maybe more rails, a big net, a runway, etc).

The only real drawback to this in an airless environment is the g-forces on launch and landing. It'd be ideal for chucking raw material around, and with a long enough wind up it'd be ok for human transport.

If you are prepared to do some scifi magic tech, you could have a forcefield around the capsule occupants, protecting them from high-g's. Then you can use a very powerful catapult to lob them long distances.


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