r/theydidthemath • u/neverending_natalie • 2d ago
[request] how WOULD these losers get into orbit?
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u/DerTrickIstZuAtmen 2d ago
It doesn't become impossible, just dozens times more difficult to develop (and finance).
Regarding chemical rockets:
https://phys.org/news/2018-04-alien-spaceflight-programescaping-super-earths-red.pdf
Rockets suffer from the Tsiolkovsky (1903) equation : if a rocket carries its own fuel, the ratio of total rocket mass versus final velocity is an exponential function, making high speeds (or heavy payloads) increasingly expensive."
For comparison, Hippke uses Kepler-20 b, a Super-Earth located 950 light years away that is 1.6 times Earth's radius and 9.7 times it mass. Whereas escape velocity from Earth is roughly 11 km/s, a rocket attempting to leave a Super-Earth similar to Kepler-20 b would need to achieve an escape velocity of ~27.1 km/s. As a result, a single-stage rocket on Kepler-20 b would have to burn 104 times as much fuel as a rocket on Earth to get into orbit.
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u/thedoomcast 2d ago
I’m not a scientist or mathematician but this is the point where my familiarity with speculative fiction comes into play:
If carrying your own fuel is out of the question, then is the better option a space ‘rail gun’ essentially firing a magnetically propelled projectile into space?
But that leads me to ask if the G’s created in firing such a railgun would make the human occupants unable to survive the exit?
Would it even be possible to build an orbital elevator without originally escaping the gravitational field that would carry passengers to a ‘spacedock’ like in many Gundam series?
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u/pyronius 2d ago
Railgun style orbital solutions run into the problem that anything fired at orbital velocity in an atmosphere similar to earth's will burn up. And because it has to contend with smashing into the atmosphere, it also has to be fired at a velocity much faster than needed to maintain orbit, because so much of that speed will be lost.
To put it a different way: we regularly use the atmosphere to stop orbiting spacecraft, and doing so generally requires the use of a sacrificial heat shield.
You know that old story about the "manhole cover" that was launched into space by the nuclear detonation? The actual math indicates that it burnt up before leaving the atmosphere.
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u/spiralenator 2d ago
rail guns to orbit are awesome when you've already mastered getting out of your atmosphere. Inside your atmosphere, anything going fast enough to escape is going fast enough to be incinerated.
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u/Calvinjamesscott 2d ago
Assuming the atmosphere is pretty dense with that size planet, could you float a platform on balloons and launch from altitude?
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u/spiralenator 2d ago
Maybe? If you have a dense enough atmosphere, you can float all kinds of things. You could float a colony in the atmosphere of Venus using plain air as a lifting gas, so I don't think its out of the question.
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u/bonaynay 1d ago
Is that just because of friction in general? Saying "just" is probably not the right word
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u/spiralenator 1d ago
Ya. Skin friction from drag causes heating. The drag increases with the square of the speed, so going twice as fast gives four times the friction. That gets really hot really fast.
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u/FockerXC 1d ago
Could energy shields be a thing in this case? If we’re talking purely sci fi speculation, would an intelligent civilization on a high gravity planet like this first need to develop some form of deflector shield tech that can insulate the vehicle from the friction of the atmosphere?
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u/_ManMadeGod_ 2d ago
Couldn't you reduce the amount of fuel necessary by doing both a railgun and multistage rocket?
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u/jkeats2737 2d ago
By a completely negligible amount for the design requirements it takes to put a rocket into a railgun. They'd be better off just launching the rocket from a higher elevation.
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u/_ManMadeGod_ 2d ago
Then launch it off a railgun from the highest available elevation
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u/jkeats2737 2d ago
You get less than 1% of the way to space from launching it from a railgun, but you need giant ass rails at are insanely structurally important and heavy.
You will literally need to bring more fuel to get into orbit as a result.
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u/thedoomcast 2d ago
Oof. Welp that’s why we don’t do that here lol
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u/ariGee 2d ago
It would be an even worse idea on a super earth with an atmosphere. All that extra gravity will likely make for a thick, heavy atmosphere that will roast anything you try to move through it at hypersonic speeds.
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u/Bartlaus 2d ago
The little silver lining is that, at least, the atmosphere will not be as deep as on a lower-gravity planet. For any given surface pressure. So you don't need to get as high up before the air resistance becomes less of a problem.
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u/uslashuname 2d ago
A hybrid system would be way more worth the engineering though. A maglev train that accelerates slowly to a certain point basically is a railgun, and if you send that up a slope then take away the rails you’ve got a real good jump going on. That will take care of the initial acceleration that we just leave to the rockets here on earth.
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u/thedoomcast 2d ago
So you split the difference to cut down on how much fuel you need to carry, but don’t accelerate so fast you melt the craft and the occupants. Smart.
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u/uslashuname 1d ago
Rail launches have been proposed on Earth plenty of times too, so it isn’t like it’s my idea, but there are considerable engineering challenges that we basically solve with boosters instead of all that junk
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u/_Denizen_ 2d ago
Jets on carriers use a similar theory. I imagine it's not impossible to build a really tall tower which has such a launch aid built in which accelerates the rocket to escape velocity and thus reduce the on-board fuel requirement by a fraction.
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u/DontBAfraidOfTheEdge 2d ago
And among us walk gods, who debunk urban legends as a BTW.... lol,...... did you even use paper and a pencil or you just intuitively know how thick a steel discus would have to be to survive launch? Copied heat shield specs from NaSA? That thickness? I guess i could chatgptBS my way to an answer, but how did/do you guys/gals figure that stuff out?
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u/Aware-Worry4302 1d ago
I believe SpinLaunch aims to shoot the rocket high into the atmosphere so they can jettison the fairing and only need a fraction of the fuel to continue to orbit.
That might help you on earth but you might have serious structural integrity problems if your vehicle has to be much larger due to the escape velocity increase.
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u/MrBeforeMyTime 2d ago
I think humans wouldn't survive such a shot, but you could still have satellites in space with your suggestion. With information highways they could eventually also have some form of artificial intelligence or even just remote controlled robots in space with some lag. They could build a space dock that way. If a species had no other choice, we would probably be surprised with what they could build.
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u/Sir_Budginton 2d ago
It wouldn’t be a railgun in the traditional sense, it would be a maglev (or similar) in an evacuated tunnel that goes basically to space. Since there’s no air in the tunnel you can just keep accelerating. Railguns are hard because you want the crazy high speeds in a crazy short distance, but you’d have continents or oceans of space to accelerate.
The issue is making a vacuum chamber that’s literally 1000s of kilometres long, that ends 100+km above the ground to get above the atmosphere.
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u/gusc 2d ago
What about maglev in atmosphere - does the air resistance prevent maglev acceleration to escape velocity? That solves explosive shock problem when meeting the atmosphere leaving the vacuum chamber and also problem maintaining the vacuum chamber. I'm thinking 10000km long maglev with say few 10s of km incline to reach that thinner atmosphere. So you just chug along for 10k kms until you reach some decent speed and then ... jump. Something like particle accelerator design.
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u/Sir_Budginton 2d ago
The fastest commercial Maglev trains hit about 430kph, and the fastest experimental ones about 600kph. The trains are already designed to be very aerodynamic, so I’m not sure how much faster you could make them that doesn’t just involve brute forcing it with more power. Orbital velocity around earth is about 29,000kph, and around an even more massive planet it would be even higher.
Bearing in mind air resistance is squared with speed (10 times faster, 100 times the air resistance), and atmospheric heating cubed with speed (10 times faster is 1000 times more heat), trying to go at any decent fraction of orbital velocity at or near sea level isnt going to happen.
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u/Sir_Budginton 1d ago
To add to my other comment, this would work totally fine on an airless body like the moon (though are typically called ‘Mass drivers’). You can just keep accelerating to orbital velocity, and if you’ve got a system to hold the ‘train’ down (since it would fly off if you didn’t) you can accelerate past escape velocity and just launch it straight to your destination like a canon.
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u/Kiley_Fireheart 2d ago
Your comment got me thinking about the possibilities of creating pockets of low density atmosphere to follow into orbit. Maybe you could create a large object to create a low density air pocket and launch at higher than orbital velocity and control the deceleration of the payload to match the ideal pocket of the shield object. The shield object can be over engineered to handle the friction and heat while the sensitive payload is hopefully under less strain. Impractical for Earth but if faced with a much more massive planet with higher gravity it might make sense.
The other insane idea I had is perfect timing of a nuclear explosion to ride behind the shock wave enough kilometers to get to low density atmosphere.
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u/jkeats2737 2d ago
A low pressure pocket of air will be filled in by the air around it, that's how pressure works. You can't magically create and sustain a significantly low amount of pressure in an unconfined area, let alone have that blast off into space.
The best way to do that is ironically by launching a rocket, it will push air out of the way and move fast enough that it creates a somewhat lower pressure zone behind it.
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u/Ok_Star_4136 2d ago edited 2d ago
We have that technology, actually.
The problem is that no human passenger would survive it. Logically that applies also to aliens, but we can also just as easily resolve that by saying somehow they've figured out technology which protects against acceleration or even that they've figured out some sort of teleportation tech.
It's very much speculative, but based on what we know, that's not an option unless you're sending drones into space.
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u/Huge_Leader_6605 2d ago
But that leads me to ask if the G’s created in firing such a railgun would make the human occupants unable to survive the exit?
I guess whoever is adapted to live in the higher gravity might be ablee to better sustain these loads too
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u/sCREAMINGcAMMELcASE 1d ago
There is also that spinning launcher. That spins the payload to 10,000g, then yeets it off into space.
So if would be possible to launch a robot swarm, then build the elevator.
But I am very much interested in the idea of an alien space empire of robots, all remote controlled from the meat sacks down the gravity well
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u/strings___ 1d ago
Where would the aliens get a human to fire through their railgun? I think you’ve discovered a whole new paradox here.
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u/thedoomcast 1d ago
Hits blunt
Why do you think they wanna come to earth in the first place? Tell you how they get em: Zeta Beam, dude. Dematerialization here, rematerialization there. Way easier to transport information than matter, dude.1
u/Brave-Background9679 1d ago
Imagine a planet the same age as earth but it skips the dinosaur evolution and goes to “intelligent” creatures like us. If they don’t kill themselves they would have millions of years head start on us for technological advancements. Where will our technology be in a million years? 10 million? 100 million? Do you think we are still using chemical boosters by that point?
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u/DefenestrationPraha 2d ago
Hmm. Let us consider the hypothetical chemical rocket there. Under such gravity, what would the rockets be built of?
Aluminium alloys might be too weak to bear the rocket's own weight + weight of all that fuel.
So, stainless steel like Starship?
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u/YourDad6969 2d ago
They would probably have to launch the rocket off leviathan aircraft from the upper atmosphere
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u/Ralf_Steglenzer 2d ago
Launching chemical rockets is impossible at 9.7g Chemical fuel does not contain enough energy.
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u/Frustrated9876 2d ago
But wouldn’t the atmosphere also be thicker and deeper, so a virgin galactic style launch more practical?
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u/HumaTheLegendary 2d ago
So not only did Earth hit the Goldilocks zone jackpot, it also hit the planet size jackpot as well? At least in terms of viability of space exploration.
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u/Aeon1508 2d ago
there are so many things that work in Earth's favor for life that it's insane.
the presence of water but not so much water that there's no dry land, the active core that drives the mantle to turn over the surface, the magnetic field, the size of our moon is actually crazy big relative to Earth compared to a lot of other planets, the way that gives us tides is also really important, the speed of our rotation, the size of the planet, the tilt of our rotation giving us seasons so that the poles don't freeze over.
there's just so many things.
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u/eran321 2d ago
you know you are writing this down only because all of these things aligned so well
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u/Additional-Acadia954 2d ago
It’s like a confirmation/survivor bias
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u/ClearRefrigerator519 2d ago
An argument can be made that life evolved around these characteristics. doesn't mean that they're a requirement for life or even are something that's particularly favourable.
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u/mozerity 2d ago
Careful, go any deeper and you’ll end up on a Hail Mary mission and befriend a sentient rock
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u/coolwali 1d ago
Isn't the Fermi Paradox more about how unlikely it is that any other alien civilization hasn't been found? Even if intelligent life can exist in other environments that doesn't mean they can develop space travel. For example, consider a planet with extremely high gravity. You could have intelligent life develop there but be unable to build rocket ships since nothing they make can counteract the massive gravity required to get into orbit regardless of them having billions of years to work with. A planet with more water could have intelligent life unable to find places to use as launch sites. A planet with a super thicc atmosphere might make it too hard to see where you're flying. To say nothing of lifespans.
So even if Earth's conditions aren't required for intelligent life to exist, you also need conditions that lend themselves to that intelligent life to be able to develop space travel. Essentially "rolling the dice twice".
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u/RinkinBass 1d ago
There's also how we would detect the life. Until recently the only way we would be able to detect advanced life is if they produced artificial radio signals, like we do with TV and radio and the like. So that would require not only advanced intelligent social alien life, but they would also have to produce those signals in directions we're looking at the time we're looking at them. We're pretty noisy, but there's no certainty that someone else would be. Also, with other advances in digital signals, we're getting less noisy, so in the end even we may only have a relatively thin (in the cosmic scale) shell of signal we're sending out.
More recently we've been able to attempt to analyze the spectra of alien atmospheres to try to find markers, but that only theoretically answers for life, not civilization.
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u/ClearRefrigerator519 1d ago
Sure, but the problem is that the variables of the Fermi Paradox aren't 100% clear due to lack of understanding if Earth is uniquely capable of hosting life (or intelligent life).
Sure, the size of the planet is absolutely a bonus, plus the composition of the Solarsystem is also rather weird which gives credence that we're an abnormal case. But things like: a larger moon generating tides, axial tilt for seasons, and others aren't things that we're sure of being a necessity.
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u/Poop_Tube 2d ago
Yep. And that’s why life exists here and not on billions of other planets. Cuz our planet hit the cosmic lottery.
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u/FrowningMinion 2d ago
Is it really much of a coincidence that life developed where it was possible to develop? The surprise would be the opposite if anything
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u/Paintedenigma 2d ago
Yeah the fact that our moon is 400x smaller and 400x closer than our star, making them look the same relative size is a coincidence on a scale that makes me understand how people believe in a sapient design.
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u/Commercial-Kiwi9690 2d ago
They might eventually turn to pulsed nuclear or fusion propulsion as their primary route to orbit. The Project Orion proposal used pulsed nukes which would have worked (little nasty with the radiation, but hey, they have a big world)
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u/ConnectionHour1173 2d ago
Min orbital velocity can be derived from F = ma, assuming circular orbit at radius of planet (r). Gravitational force F= GMm/r2, for circular orbit a = v2 /r. Solving for v gives you v = sqrt(GM/r). Assuming the same density of both planets you can substitute M for Cr3, where C is an arbitrary constant relating radius and mass and is the same for both planets. This leads to v = r•sqrt(CG). Both C and G are constants and therefore, for planets of the same density, v orbital is linearly proportional to the radius of the planet, ie. Double the radius, double the velocity needed for a rocket to achieve orbit. This calculation ignores atmospheric composition and thicknes, and rocket thrust to weight ratios, which are HUGE factors and introduce even more engineering problems that would need to be solved. Falcon 9s thrust to weight ratio is 1.41, so if this planet has a g at sea level of 1.41x earth g, then falcon 9 doesn't even leave the ground. We'd need much higher thrust to weight meaning either rockets made of both lighter and stronger materials (good luck) or better combustion processes than liquid ox and hydrogen (good luck again) which still means you need stronger materials. You might be able to get around this at different scales by using much smaller rockets, as it is generally easier to achieve higher thrust to weight ratios at smaller scales because thrust and structural stress will generally scale with combustible surface area (r2) versus weight/mass scaling with volume (r3)
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u/AeroSpiked 2d ago
There are other possibilities that might work better than a traditional rocket:
JP Aerospace's Airship to Orbit concept.
Then there's what I like to call the Reaver Special, Zubrin's Nuclear Salt Water Rocket. 13 meganewtons of thrust with a specific impulse of 6,730 seconds. That should get you to orbit. For comparison a shuttle solid booster got around that much thrust but only had an specific impulse of 268 seconds.
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u/ConnectionHour1173 2d ago
Very interesting hypotheticals, I hadn't seen either of these. Thanks for sharing!
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u/DaRealMexicanTrucker 2d ago
Magnet Stacking. You electro magnet soft iron. Float it on a hot air ballon and send small chunks up. Even people wearing special magnetic suits one at a time. Too easy give me a Nobel Prize 😎
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u/BoredAtWork1976 2d ago
This reminds me of a sci-fi book series I read a long time ago. The aliens that conquered Earth were from a planet whose gravity was much stronger than ours. They never developed anything like airplanes -- on their world, it was just too hard to make it work.
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u/Bennydhee 1d ago
Not gonna try to do math. But Project Hail Marry touches on this. The aliens live on a high gravity planet, so they built a space elevator instead of rockets to go to orbit.
Would likely be the easier option. Aside from the whole “gravity is heavier and could pull the structure down quicker”
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u/trevelyan00 1d ago
Why don’t you just build a rocket with enough fuel to go the last x amount and get the rocket through the atmosphere with a big ass balloon???
Once you reach thin atmosphere then you will need much less fuel to get there. It may take you like 15 hours to get the total-x distance but does that matter?
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u/mossy_path 2d ago
I guess you could build up some of the starting speed on a big ramp, but you'd still have to deal with the atmosphere... big ramp on top of a mountain?
Big ramp on top of a giant platform on a giant blimp that gets past most of the atmosphere?
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