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April 23, 2018 2:55 PM   Subscribe

 
Interesting article. I had never thought of space travel relative to the size of the planet it launched from before.
posted by 4ster at 3:06 PM on April 23, 2018


obligatory comment about Interstellar and how it should have ended 2/3rds of the way through.
posted by GuyZero at 3:08 PM on April 23, 2018 [5 favorites]


I have no idea why they thought going to that planet was a good idea. But it is a very silly film.
posted by Artw at 3:11 PM on April 23, 2018 [6 favorites]


It would also probably do things to their physiology. Would blood be harder to circulate? I think it would.
posted by thelonius at 3:11 PM on April 23, 2018


Wouldn't the extra gravity make them super strong though - and if you're super strong they could be super big and have huuuuuge rockets, and their planet is huge so loads of fuel to launch.
posted by zeoslap at 3:43 PM on April 23, 2018


I think the issue is that the thrust power of fuel increases linearly, while the energy required for escape velocity is geometric.
posted by tavella at 3:49 PM on April 23, 2018 [6 favorites]


So let's figure out interstellar travel and go make a fortune by building space elevators for planet-bound intelligent species.
posted by MrVisible at 3:56 PM on April 23, 2018 [14 favorites]


The trick is to have your giant exoplanet circling a Red Sun and then quickly switch it to a Yellow Sun and Super the hell out of things!

Take that, Science!
posted by GenjiandProust at 3:59 PM on April 23, 2018 [5 favorites]


obligatory comment about Interstellar and how it should have ended 2/3rds of the way through.

Funny how they needed a Saturn V rocket to leave Earth but were able to just zoom out of a time-dilating gravity well like the Robinson family. Sure, the whole thing was stupendously silly but come on... commit to your concept, k?

(I have to admit that doing that would have ruled out a lovely bit of sound design leading up to the launch.)
posted by sjswitzer at 4:26 PM on April 23, 2018 [5 favorites]


Funny how they needed a Saturn V rocket to leave Earth but were able to just zoom out of a time-dilating gravity well like the Robinson family.

YES, THIS. It's like as soon as they went through the wormhole they went into a completely different Sci-Fi movie. I guess it's because people are trained by pop culture to know that "Spaceship liftoff from Earth = Very hard, big thrusters, slow" and "Spaceship liftoff from alien planet = Easy, probably just float away."
posted by Mr.Encyclopedia at 4:34 PM on April 23, 2018 [7 favorites]


Don't think a heavy water world wouldn't necessitate "super strong" critters or have any outrageous circulatory system demands, because they'd likely be +/- neutral buoyant. We got stuff living a few miles down in the water on this planet and the pressure is pretty crazy. But they certainly aren't going to be fashioning metal or stone tools.
posted by seanmpuckett at 4:53 PM on April 23, 2018 [3 favorites]


“It might just mean that there are indeed [aliens who are] practically locked onto their worlds,” he told Gizmodo.
There may well be intelligences who pity us that we are stuck with four dimensions and thus will never contact them.
posted by ricochet biscuit at 4:58 PM on April 23, 2018 [7 favorites]


Intelligences vast and cool and extradimensional.
posted by The Tensor at 5:11 PM on April 23, 2018 [6 favorites]


Huh. Would the thicker atmosphere provide a tradeoff of allowing aircraft greater lift, perhaps allowing aerodynamic craft to get further away from the surface that way, maybe to a distance where direct upwards thrust to take over? I don't know any of the math or physics involved, but maybe it'd be entertaining for someone who does to think about it then come in and school us on the subject?
posted by JHarris at 5:52 PM on April 23, 2018




There is no escape anywhere.
posted by Burhanistan at 6:19 PM on April 23, 2018 [4 favorites]


Intense Gravity of Super-Earths Could Trap Aliens on Their Home Planet
I'm about to read the article because I'm fascinated, yet first must note that this is blatantly the title of a Mogwai tune yet to be written.
posted by I'm always feeling, Blue at 6:30 PM on April 23, 2018 [6 favorites]


So one issue is that carrying the extra fuel means you have to spend more time accelerating the heavy fuel that you're just going to throw away anyway. A lot of SF and/or drunk brainstorming by engineers already focuses on designs that avoid powering themselves with onboard fuel in this wasteful way.

The most famous is the railgun-style electromagnetic launcher. Your power comes from generators that don't move so all you launch is the payload. If you imagine our aliens can withstand six of their gravities (15G for us) during launch, a 2000 km launch tube will get them to escape velocity in about 3 minutes. 2000 km is pretty long but it is a flatter planet with 5 times our surface area, they should be able to find a spot for it.

There are a ton of over novel designs most of which I've forgotten most of the details of. I recall using lasers being popular too--not (as in outer space) using the photons themselves but using the laser energy to heat up something else that pushes the spaceship. (There's a nifty cyclic accelerator design out their too but my back-of-the-envelope their makes it seem like you'd need a 1000+ km radius circle so that seems a step too far)

I guess since it's a paper having made up aliens facing challenges for their imaginary rockets is about the limit of non-existent stuff. They don't want to talk about speculative solutions with imagined technology as well.

(I was trying to sketch out an SF story that could highlight this stuff and a novel solution. I'm really bad at creativity so my version has human scientists, observing inhabitants from orbit on a planet like this. The scientists are all bros and they spend a lot of time getting drunk, making "your momma" jokes and emptying their toilets on the world below, confident that the aliens will never be able to retaliate from their rocky prison. Until one day . . . )
posted by mark k at 6:40 PM on April 23, 2018 [3 favorites]


My McGuffins for easy-peasy interstellar travel, when I once dabbled with being creative, were:

1. Some kind of magical space rock that was basically a geode but its inner surface crystals all had a refraction rating (I forget) of -1, so that light passed through them actually sped up, and because all the crystals were surprisingly perfectly aligned due to Space Mystery, if you put light into the rock it quickly went supernova and somehow we harnessed the energy for our spaceship engines? I called them LNC (Law of Non-Contradiction) Drives and basically because of metaphysics or whatever, since it is impossible for the same identical thing to be in two places at once, you could use the accelerated light geode that powered the LNC to simply tell the ship, via your Mac laptop, that the ship was in the place you wanted it to be, and it just happened, because the Law of Non-Contradiction says that if it's in that place (your destination) then it's not possible for it to be in the other place (your starting point);

2. This one was easy, since the world was basically a video game version of our world. As in, not in a video game, but the physics and rules worked the same, and all the characters were ripoffs of video game characters (one of the protagonists was Tex Wrexum, based on Duke Nukem, and can I just say, I came up with this before Wreck-It Ralph), and if you've ever played any kind of video game ever, you know that weird shit sometimes happens, so the way you do interstellar travel in that universe is you just glitch them to where they need to be. Tex was mad though because he went on a mission once and glitched through the bottom of the map, where he was trapped for ten years. Also the main boss guy was based on Ted Maul, from Brasseye, so not a video game character, but fun to write! This was when I was dealing with pretty significant depression and the moral of the story was meant to be "sometimes you just glitch through the bottom of the map".

So that's part of the story of why I never quite tapped into any market ever.
posted by turbid dahlia at 7:13 PM on April 23, 2018 [4 favorites]


Interestingly, Earth gravity has managed to keep me basically on my home planet (some air travel might be an exception) for my entire life!
posted by hippybear at 7:42 PM on April 23, 2018 [9 favorites]


I remember reading a similar paper last year, which made the same argument from a slightly different angle. That one made a similar calculation about the payload/fuel ratio, but talked about the engineering challenges of making a rocket weigh so little. E.g. when your fuel needs to be 99.99% of the mass, that doesn't leave a lot of materials for the rocket. And I believe that argument is the same if you use chemical or nuclear - someone correct me if I'm wrong, but it's not the energy that's the limiting factor (though of course it's important), but rockets need to push mass out the back.
posted by Horselover Fat at 8:16 PM on April 23, 2018


Funny how they needed a Saturn V rocket to leave Earth but were able to just zoom out of a time-dilating gravity well like the Robinson family. Sure, the whole thing was stupendously silly but come on... commit to your concept, k?

I am no sciencer, but if the time-dilating gravity well doesn't contain any physical obstructions and gravity exerts the same force on both sides, wouldn't traveling into and then out of it be sort of like the gravity assist maneuvers we do with our IRL space probes? When you pass through the inflection point you'd already be moving faster than escape velocity because gravity would have accelerated you on the way in.
posted by XMLicious at 8:28 PM on April 23, 2018


Would the thicker atmosphere provide a tradeoff of allowing aircraft greater lift, perhaps allowing aerodynamic craft to get further away from the surface that way, maybe to a distance where direct upwards thrust to take over?

I think increased lift is cancelled out by increased drag, at least for a glider (the density term cancels out when you calculate lift-to-drag ratio). I'm guessing things get more complicated when you throw an engine in the mix.

A thicker atmosphere would, however, provide more lift for a balloon.
posted by dephlogisticated at 9:11 PM on April 23, 2018 [1 favorite]


A thicker, denser atmosphere works better for internal combustion engines, too. More power.
posted by bz at 9:19 PM on April 23, 2018 [1 favorite]


We got stuff living a few miles down in the water on this planet and the pressure is pretty crazy. But they certainly aren't going to be fashioning metal or stone tools.

That's what they want you to think, sure.
posted by flabdablet at 9:48 PM on April 23, 2018 [7 favorites]


Ya know, there does exist Kerbal Space Program. I wonder if it could be modded to make Kerbin heavier and with a denser atmosphere, as a test case. Both the balloon and engine power (for jet engines, which don't carry their own oxygen) cases sound interesting. Especially the balloon, which effectively leverages the planet's gravity against it. It'd take a pretty big balloon to get a sizable craft up where gravity is significantly lessened though, and I'd think the balloons wouldn't be easily recoverable afterwards.

On the plus side, thick atmosphere means reentry parachutes should be very effective!
posted by JHarris at 6:17 AM on April 24, 2018 [1 favorite]



Wouldn't the extra gravity make them super strong though - and if you're super strong they could be super big and have huuuuuge rockets, and their planet is huge so loads of fuel to launch.


This is true, there's a long-running documentary series about them.
posted by curious nu at 6:43 AM on April 24, 2018 [1 favorite]


An interesting corollary of this is that intelligence on a planet with lower gravity would have a much easier time setting up orbital industry/habitation.
posted by Thalience at 10:11 AM on April 24, 2018 [2 favorites]


If you have sufficient Isp and enough thrust to keep gravity loss to a reasonable amount, the rocket equation looks a lot less daunting. Basically, if you figure out fission, you can get off the surface of anything that qualifies as a rocky planet.

On Earth it (would, if we were willing to do it) lets us launch something the size of a skyscraper into orbit with around a megaton of total yield. With 10 times the gravity you just build bigger bombs and a bigger pusher plate and maybe have less available payload depending on the exact scaling law involved in how much energy you can capture.

IIRC, the various Orionish proposals floated over the years have included some that used relatively few large bombs, so one ought to be able to get at least ten times the thrust of the design chosen back in the 60s. A Saturn V sized craft is at least an order of magnitude lower in mass than the ship (exclusive of the propulsion system) was supposed to be, so I'm fairly certain a nuclear impulse rocket could be made to work on any terrestrial planet, assuming the proper resources were available, of course.
posted by wierdo at 11:03 AM on April 24, 2018


We got stuff living a few miles down in the water on this planet and the pressure is pretty crazy. But they certainly aren't going to be fashioning metal or stone tools.

Definitely no Cyclopean tomb-cities, that's for sure.
posted by FatherDagon at 1:05 PM on April 24, 2018 [5 favorites]


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