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What limitations are keeping this from reality?...
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You are currently reading a thread in /n/ - Transportation

Thread replies: 29
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What limitations are keeping this from reality? This being a personal craft capable of independent vertical liftoff, and able to travel out of earth's orbit and back
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physics, economy, technology, etc.
And of we some day find a solution they will come up with clever laws and governmental regulations to prevent this.
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>>908877
The moon is pretty close. That's worth visiting. additionally, being able to leave orbit would let you travel across the planet much faster
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In a nutshell, the problem is propulsion.

You have to carry a lot of consumables (fuel and/or reaction mass) to get to orbit. So if you want to get 10 tons of people, armor and guns into orbit, you'll need several hundred tons of rocket to do so.

This is the case not because of some momentary technological deficiency, but because of fundamental physics - you can't speed up without pushing against something, and in space there's nothing to push against.
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>>908877
FWIW, Cowboy bebop takes place within the Solar System. Earth is fucked, and people have colonized several moons and asteroids to supplement it.

>>908884
For intra-planetary travel, you don't even have to reach orbit. It's enough to get high enough to lose most of the drag. This is actually achievable today - you could stuff the required engines in a body that could conceivably fit in a modern airport.
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>>908893
>Ganymede
Yep.

CB is pretty nice. It's more of a space western than legit sci-fi, but it's one of those rare cases where the sci-fi setting is not so soft as to offend a hard sci-fi fan.
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>>908872
If you could work out the propulsion and power problems, maybe by figuring out how to fuel a scramjet in a vaccum, then you'd run into the problem of your wings and those dumb cannon thingys snapping off from the sheer velocity, and hot air getting trapped in nooks and crannies and burning through the hull on reentry. Most SSTO concept vehicles are either rockets or look like this
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What limitations are keeping this from reality?
This being a public transportation network capable of supplacing the car, and able to serve all the residents of the city by getting them from their home to their destination and back
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>>908940

no cheap, safe and reliable way to keep things floating in the air.
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>>908940
no spending on public transportation or infrastructure...
because --> "socialism"
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>>908926
Well, if we assume that thereĀ“s no shortage of fuel or reaction mass you could always do your braking before entering the atmosphere. With the engines, and not by atmospheric friction, removing the need for a heat shield.

Now that leads to the question why we never see spaceships with their engines pointing back, like they should if the craft is slowing down or making a turn. But hey, that would look weird, right? Lets just pretend some wings and a big ass rocket engine is all you need for cool dogfights in vacuum.
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>>908963
errm, i wanted to say "why we never see spaceships with their engines pointing anywhere else than back"
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>>908940
But it already is reality in a few places.
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Also, keep in mind rockets are controlled explosions. You need a lot of explosion, pointed directionally. You need enough thrust to get you into orbit without blowing you up. It's a difficult problem. Challenger blew up. So did a bunch of early US, Russian and German test rockets.

More recently, a failed strut obliterated a Space X rocket; their first launch failure, but still a major setback.

Getting into space is not easy. It's expensive and every engineer's work has to be checked multiple times. Things have to be built way beyond spec. It's all specialized unlike the airplane industry; which has expended to general parts because of the growing market. Rocket fuel ... and rockets ... are still prohibitively expensive to make them a standard transport mechanism.
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>>908889
Actually, there is a technological deficiency side to it. With more powerful engines, you can achieve the same delta-V with much less reaction mass. However, for a spacecraft to reach orbit with fuel making up less than 50% of its takeoff weight would require a specific impulse of over 1,000 seconds. And we have no engine that can do that AND produce enough thrust to actually take off. Solid-core nuclear rockets are just below this margin - they might be able to make it to orbit with extreme luck. Liquid core nuclear engines might provide the needed performance, but I think we have yet to produce a working prototype, let alone one that's safe to use commercially. And even then we're talking spacecraft with half their takeoff weight being reaction mass. For spacecraft like you see in science fiction, with very small fuel tanks, would require a near 100% efficient fusion drive or something.
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>>908926
>snapping off from the sheer velocity
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>>908940
>Paris
>not already having a grand public transit system that goes everywhere
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>>909083
I think he meant from aerodynamic stresses from entering the atmosphere at 5 miles a second
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>>908872

Know how you make a small fortune?
Take a very, very large fortune into space.
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>>908922
Jupiter isn't that large in any of the Galilean skies. It's only like 20 times the width of a full moon on Io, the closest.
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>>908872
Traveling to orbit single stage in something the size of fighter plane without the benefit of a lifting body or auxiliary rockets would require fusion that works without all the heavy shielding or equipment needed for ignition. It would take a miracle.
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This thread has more accurate, concise and relevant info than most /sci/ threads for laymen.
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>>911090
We do not know what camera took the picture. If it was highly zoomed in, Jupiter should look unnaturally large. If it had a very short focal length, or wide feild of view, it could be very small.

>>908963
Or you could do a couple controlled passes through the atmosphere before actually committing to landing, loosing velocity so that you do not generate so much heat on landing (and so you do not get to the surface at, like mach 3, after ripping all your parachutes off).

>>908965
In Science fiction? I think I recall a few examples. The newer Battle Star Galactica had some very nice scenes with fighters manuvering in zero G. Most of the time people make spacecraft look like airplanes because the real way they should fly would look very alien and be difficult to explain to the audience, I guess.
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>>908963
>>908965
>why we never see spaceships with their engines pointing back

It would be a pointless depiction, because your POV would have to select an arbitrary fixed position in newtonian space, which would require the spacecraft zooming past too fast for the framerate and field of view at orbital velocities. So to fix that you'd have to match the POV's velocity to something closer to, but not the same as the spacecraft, but that wouldn't be right either because you lose a proper sense of how fast the spacecraft is moving relative to "fixed" and it seems comically wrong somehow. So ultimately then, the only solution to make for a coherent camera shot is for the velocity of the POV to be basically the same as the spacecraft, at which point, by definition, the engines are always pointed "back".

Remember, newtonian spacetime was abandoned nearly 100 years ago, so it's time we accepted that "slowing" is the same as "speeding up" from the engine's perspective. Depicting perfectly accurate orbital mechanics in a way that make intuitive sense to a casual viewer without breaking narrative flow is a ridiculous expectation and you are being ridiculous. It would be better to complain about phaser noises in space.
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>>908965
But I do see that, all the time. Cowboy Bebop, again, is one example.

You can see several ways to do it, even in fiction:
>varying power to several main engines
>swiveling the main engine exhausts a bit
>turning the engines themselves around
>using slats to redirect engine exhaust gas
>firing small thrusters installed in fixed directions
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>>911091
the majority of the rocket stages are wasted just getting through the atmosphere. If you had a high flying jet like the SR-71, it could release a fighter sized aircraft that could go into orbit
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i dreamed, that Elon mad the touchdowon.,
,, of course that cant, be true?, whiskeys like that.
,,, seemso True,, the legs Snap down and balance?,, nextit will walk!
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>>908872
the energy to escape earth's gravity is too much.
60 MJoule / kg
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>>911212
I would imagine they could depict it as the ship flying "backwards" while approaching a planet.
Thread replies: 29
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Thread DB ID: 422159



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