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With a planet this large, visiting it would be a one way trip due to the "The Tyranny of the Rocket Equation" [0]. I'm looking forward to the day we start find

With a planet this large, visiting it would be a one way trip due to the "The Tyranny of the Rocket Equation" [0]. I'm looking forward to the day we start finding exo-planets that are closer to Earth in size and which could potentially have space-faring races (and which we could leave if we were ever to visit them). [0] - https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html https://www.nasa.gov/mission_pages/station/expeditions/exped...

JumpCrisscross 7y ago
> With a planet this large, visiting it would be a one way trip Assuming chemical propulsion and no refuelling at the destination.
- Supermancho 7y ago
  If it's chemical propulsion, you're dead when you get there. If there's no refuelling (and you need refuelling) with some other travel mechanism, you can't get back. So we have an "or" assumption, not "and", with an additional and assumption about refuelling. That's how I read it.
- dogma1138 7y ago
  I think what the GP refers to is that there isn’t enough energy in chemical rockets to overcome its gravity, even flight might not be even possible albeit that’s also dependent on the density of the atmosphere to some extent.
  - sandworm101 7y ago
    Flight would actually be easier on such a planet. The advantage of increased atmospheric density is greater than the downside of the increased gravity.
    - soulofmischief 7y ago
      So... if one made a very aerodynamic craft, and launched at a more extreme lateral angle, do you think it would supplement the chemical rockets enough that escape would be possible?
      - dogma1138 7y ago
        not really going to orbit is about velocity not altitude the gravity at low earth orbit is pretty much the same as at sea level. The savings you get when launching from say an aircraft at 40,000 feet mainly come from not having to go through max-q at sea level the relative amount of propellant you’ll need to get to orbit is the same you can just use a smaller rocket but it doesn’t help to overcome the rocket equation trap.
        sandworm101 7y ago
        But at altitude you do get higher ISP, which is a greater limiting factor than drag/max-Q. The Saturn-V would not even get off the pad in an even slightly denser atmosphere. But lift it up to where the air is thinner, where its engines can generate more thrust, and it might have enough DeltaV to get something into an orbit.
    - dogma1138 7y ago
      That is of the atmospheric density is higher, we don’t know the composition and temperature don’t forget that at higher pressures the boiling point of water is higher so it might not actually have water vapor in the atmosphere. The atmosphere can also be much more shallow than earth. Also I was more referring to winged flight than balloons balloons might be a problem of their own if the pressure at ground level is too high for them to inflate normally. Between earth and Venus there are a lot of options so if the atmosphere is similar to earths sans the water vapor I’m not entirely sure flight would be actually easier I can probably do some napkin maths over the weekend for this.
- allannienhuis 7y ago
  The amount of fuel at the destination doesn't change the rocket equation for being able to get into orbit from the planet. From the provided link: "If the radius of our planet were larger, there could be a point at which an Earth escaping rocket could not be built. <snip> That radius would be about 9680 kilometers (Earth is 6670 km). If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport."
archgoon 7y ago
It's 111 light years away. For all intents and purposes, that's a one way trip right there; irregardless of the rocket equation. Even at relativistic speeds, you can't come home anymore.
- ajconway 7y ago
  Theoretically, you can. At 0.99c 111 light years take about 15 years of ship time to travel.
  - archgoon 7y ago
    You can make the trip arbitrarily small from your perspective (in theory at least :) ). The issue is that by the time you've made it back home, it's 222 years later. Hence "you can't go home anymore". :)
    - stickfigure 7y ago
      If you put some money in an interest-bearing account you could at least buy a new home when you got back.
      - repiret 7y ago
        You know where I can find one of these interest-bearing accounts that can outpace housing cost inflation?
        fujiters 7y ago
        While not an interest bearing account, investing in an index fund of global stocks should outpace housing. Investing in a REIT should roughly keep pace with housing costs.
      - RandomBacon 7y ago
        Better do it in different countries and in different currencies and hope none of them get confiscated or have hyperinflation.
kadoban 7y ago
So that's purely for a chemical rocket, right? Is there any combination of tricks that can realistically push the envelope there? For example can we use a space elevator to start higher/faster (or, I don't know, balloons? a catapult or railgun or something?), laser power delivery from the ground, so we don't have to carry all the fuel, and an orbiting way-station for refueling, etc.?
- Miner49er 7y ago
  Solar sails might be able to beat it. https://en.wikipedia.org/wiki/Solar_sail https://en.wikipedia.org/wiki/Solar_sail
  - AgentME 7y ago
    Aren't solar sails just for propelling yourself once you're in space? I can't imagine how you could launch off the surface of a planet with a solar sail.
    - 0xffff2 7y ago
      Yes, and even then they're incredibly low thrust devices. A light sail (whether solar or laser powered) may well be viable for sending a tiny unmanned probe to another star system (see [0]). It's really unlikely that it will ever scale up enough to take an average communication satellite the same distance, much less a manned craft. [0] https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot
  - hinkley 7y ago
    M2P2 was going to test out magnetic sails, but Wikipedia is telling me they generate less thrust per kilowatt hour than ion thrusters. Explains why I haven't heard anything further about it. https://en.wikipedia.org/wiki/Magnetic_sail https://en.wikipedia.org/wiki/Magnetic_sail
  - civilian 7y ago
    Solar sails are good for inter-planetary travel, but they aren't going to move the needle for launching off of a planet with 2g gravity! You need something that is compact and would give you a big impulse. As a KSP engineer would say, it "needs more boosters" https://i.redd.it/zuymxc5bb7s21.jpg https://i.redd.it/zuymxc5bb7s21.jpg
SJSque 7y ago
There's also the Wait Calculation to consider: https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calculation https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calcu...
- PorterDuff 7y ago
  Hey, I like that idea. Maybe it implies that every interstellar mission is just an in-flight rescue mission.
- 0xffff2 7y ago
  That's interesting in theory, but as far as I know our interstellar propulsion technology hasn't advanced significantly at all in the last 50+ years. You can't do theory in a vacuum forever. I'd argue that unless we launch an interstellar something, we're never going to see any technological advances in the field.
- ryacko 7y ago
  The wait calculation implies that the returns from economic growth will eventually be converted into rocket fuel. A fun equation, but economics doesn’t translate well on time scales where depreciation of capital is 100% and becomes another expense.
hinkley 7y ago
I made it well into this decade before I was made aware of this fact. It's kind of a shock, still. At some point your planet is massive enough that you can't get into orbit with chemical rockets (even, I think, by flying them up like Burt Rutan?). The implications for the Drake equation are pretty big. Rockets without any promise of ever being able to break orbit are good for what, war? Would you keep developing them? Would you give up dreams of the stars? Would you look for intelligent life you couldn't ever possibly meet?
- jerf 7y ago
  "At some point your planet is massive enough that you can't get into orbit with chemical rockets (even, I think, by flying them up like Burt Rutan?)." Nuclear rockets don't seem to be very hard. They're somewhat dangerous if they explode, but they aren't very hard. Fairly solid prototypes were built decades ago and there's little to suggest they couldn't have been made production-grade [1]. We'd have them now if we didn't find the risk/reward to be too highly slanted to the "risk". Other species and other ecosystems may come to different conclusions, e.g., an ecosystem already more exposed to radiation and evolved to deal with much higher levels of it may judge it much less "risk" for some radionuclides to be scattered across the landscape in case of failure. What can be more of a problem is being in a place where you have no obvious access to technology at all. However smart our cetacean buddies may be, it is not clear even at this point in the 21st century what path to technology they could possibly have from their starting point. "The literature", a.k.a. "science fiction" has hypothesized breeding programs to develop various tools, but it's still not entirely clear how they'd get from "breeding useful jellyfish" to, well, anything like technology as we know it. It's possible we're just not solving this problem because we don't have to, maybe there's some easy path with the right development path, but it's still not clear what that would be. [1]: One of my markers for "the space age is truly here" is when we lift a nuclear rocket into space, sans fuel, and fuel it with space-sourced radionuclides. Earth-bound citizens will still complain, because "NUCLEAR BAD!", but their complaints will be ignorable at that point.
  - hinkley 7y ago
    Do solids settle out of air on a high gravity environment faster? The air would be thicker. Does gravity or buoyancy win than tug of war? I spent a day once trying to figure out what the Bronze Age would be like for marine creatures. Oxidation is less of a problem but galvanic action is huge. Fire pretty much doesn't work, which blocks a whole bunch of precursors like ceramics.
TheOtherHobbes 7y ago
Surface gravity will be around 2g, so even if it has a rocky surface it's not going to be a very comfortable home from home.
- dsfyu404ed 7y ago
  So a 150lb person will weigh 300lb. Sure that's gonna suck on day one but there's plenty of people who weigh that much who get by. Without all the health complications from high body fat it wouldn't be that bad. You'd probably die young but I don't think that would bother people.
  - sky_rw 7y ago
    Not sure the two are comparable. 300lb obese person's bone structure weighs the same, their heart and lungs weigh the same. I suspect 2x the weight on every organ is going to be seriously detrimental for sustained periods.
    - partiallypro 7y ago
      Not to mention you'd go from years and years of near 0G gravity to twice the gravity of earth. You wouldn't even be able to walk.
      - ben_w 7y ago
        Compare to the difficulty of getting there in the first place, getting spin gravity to work right isn’t a big problem.
      - rhinoceraptor 7y ago
        I would assume if we can figure out accelerating to near the speed of light, we'd also be able to make a viable rotating spacecraft to use centripetal force to solve that problem.
      - thenickdude 7y ago
        If you're making this trip in any reasonable amount of time, you're probably accelerating during the journey at least half a G anyway.
yellowapple 7y ago
I wonder if we could work around the stronger gravity by using a spaceship as the anchor for a space elevator or skyhook? Both of those technologies are pretty far off, but so is getting humans to another star system.
- hinkley 7y ago
  As gravity increases the tensile strength necessary for the elevator increases. We haven't even figured out how to mass produce materials that would suffice for an elevator on earth yet.
  - yellowapple 7y ago
    I mean, we're already talking about getting humans to another star 111 lightyears away; I'd assume by the time we're ready to do that we'll have figured out how to mass-produced nanotubes or something.
- scrumbledober 7y ago
  currently we have no known materials that would actually be strong enough to support their own weight at the length of a space elevator on earth. double the gravity and the length will also at least double (possibly quadruple? not sure on the math here) so it may also be impossible to build a space elevator on one of these planets, at least without the use of active suspension (possible? theoretically.)
  - 0xffff2 7y ago
    Currently we have no known materials that would actually survive a 111 light year trip to another solar system, so that fact that we can't actually build the space elevator when we get there seems irrelevant. They're both roughly the same order of magnitude of impossible with our current technology.
    - fwip 7y ago
      Sure we do. Chuck a rock in the right direction, it'll still be a rock 111 light years later.
cthalupa 7y ago
I mean, as far as I am aware, that problem is due to the propulsion method. Would a nuclear based rocket not be able to solve this issue? My understanding is that it would.
- perl4ever 7y ago
  A nuclear rocket still needs propellant, doesn't it?
  - cthalupa 7y ago
    Yes, but significantly less of it by weight. You get significantly more energy per kg of nuclear fuel than you do traditional chemical propellant.
    - perl4ever 7y ago
      Perhaps, but my intuition is it wouldn't make a whole lot of difference, because the reason you can't get off a heavy planet is because of an exponential runaway effect.
      - cthalupa 7y ago
        https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html https://www.nasa.gov/mission_pages/station/expeditions/exped... An experimental nuclear rocket from the 70s nearly doubled our "payment energy". It should greatly reduce the initial and total mass portions of the rocket equation as well. I don't have all of the numbers to punch into the rocket equation to figure out things exactly, but the exhaust velocity and initial/total mass make up significant portions of the equation, and increasing the former while decreasing the latter will make significant impact on the ability to leave a more massive planet.
pierre_d528 7y ago
Or we could shift to an other side of the universe by "inverting" the mass of the ship where the speed of light is much higher[1]. Cosmology is so cool... too bad we do not have time for that: we cannot even cure the common cold! [1]: https://januscosmologicalmodel.com/pdf/2014-ModPhysLettA.pdf https://januscosmologicalmodel.com/pdf/2014-ModPhysLettA.pdf Cosmological bimetric model with interacting positive andnegative masses and two different speeds of light,in agreement with the observed acceleration of the Universe
- atonalfreerider 7y ago
  > Special Relativity can be summed up in the sentence: “We live in a spacetime which is an M4 manifold with a hyperbolic Lorentz metric of signature (+−−−)”. General Relativity can be stated accordingly: “The Universe is an M4 manifold with a Riemannian metric of signature (+−−−)” which is a solution of the Einstein equation:Rμν−12Rgμν+Λgμν=χTμν. It sounds like you get anti-gravity for free along the way to getting superluminal travel.
  - pierre_d528 7y ago
    No because no "run away" effect. "inverted" mass means that the mass goes on the other side... gravity works the same there.
spullara 7y ago
I couldn't find anything with its approximate radius (it mentions about-earth sized and 8x the mass but that could mean anything) to make an evaluation of the likely gravitational force at the surface in order to make the evaluation of whether you could get off the planet cheaply.
nothis 7y ago
> I'm looking forward to the day we start finding exo-planets that are closer to Earth in size and which could potentially have space-faring races (and which we could leave if we were ever to visit them). I just realized I have no real concept of how many stars there even are within, say, a 100 light year radius of our sun (I guess that's a more realistic thing to find out than the number of planets). A quick search provided some estimates and they're kinda... disappointingly low, at around 20000 stars. That's a number where some "1% of 1% of 1%" kinda filter quickly ends up in a scenario where a planet fitting all our criteria might simply never be in reach. For something more "realistic" (I know, heh!) like 20 light years, there are only 150 solar systems. I've seen different numbers and have no idea how they're calculated but for the usual astronomic scales which quickly go into "billions" territory, it seems we're kinda stuck with a comparably small list of candidates.
- tejtm 7y ago
  It might cheer you up to to think we have yet to prove there is a star with no planets.
- flukus 7y ago
  On the plus side there are more moons than planets and many of them may be habitable. We've barely started looking at extra solar Jupiter like planets because of the much longer orbital periods.
- newsbinator 7y ago
  > That's a number where some "1% of 1% of 1%" kinda filter quickly ends up in a scenario where a planet fitting all our criteria might simply never be in reach. It might cheer you up to think that's the only reason the human race happens to be the one in our neighborhood that made it into space, without being stepped on by an Old One.
- deleted 7y ago
  [deleted]
- perl4ever 7y ago
  I think people are beginning to realize, that just as there are more asteroids than planets, and more space junk than large asteroids, there are a lot more free floating planets than stars. It could well be the universe is filled with life, but the dominant mode is underground chemo/radiotrophic microbes on planets without stars.

JumpCrisscross 7y ago

> With a planet this large, visiting it would be a one way trip Assuming chemical propulsion and no refuelling at the destination.

Supermancho 7y ago
If it's chemical propulsion, you're dead when you get there. If there's no refuelling (and you need refuelling) with some other travel mechanism, you can't get back. So we have an "or" assumption, not "and", with an additional and assumption about refuelling. That's how I read it.
dogma1138 7y ago
I think what the GP refers to is that there isn’t enough energy in chemical rockets to overcome its gravity, even flight might not be even possible albeit that’s also dependent on the density of the atmosphere to some extent.
- sandworm101 7y ago
  Flight would actually be easier on such a planet. The advantage of increased atmospheric density is greater than the downside of the increased gravity.
  - soulofmischief 7y ago
    So... if one made a very aerodynamic craft, and launched at a more extreme lateral angle, do you think it would supplement the chemical rockets enough that escape would be possible?
    - dogma1138 7y ago
      not really going to orbit is about velocity not altitude the gravity at low earth orbit is pretty much the same as at sea level. The savings you get when launching from say an aircraft at 40,000 feet mainly come from not having to go through max-q at sea level the relative amount of propellant you’ll need to get to orbit is the same you can just use a smaller rocket but it doesn’t help to overcome the rocket equation trap.
      - sandworm101 7y ago
        But at altitude you do get higher ISP, which is a greater limiting factor than drag/max-Q. The Saturn-V would not even get off the pad in an even slightly denser atmosphere. But lift it up to where the air is thinner, where its engines can generate more thrust, and it might have enough DeltaV to get something into an orbit.
  - dogma1138 7y ago
    That is of the atmospheric density is higher, we don’t know the composition and temperature don’t forget that at higher pressures the boiling point of water is higher so it might not actually have water vapor in the atmosphere. The atmosphere can also be much more shallow than earth. Also I was more referring to winged flight than balloons balloons might be a problem of their own if the pressure at ground level is too high for them to inflate normally. Between earth and Venus there are a lot of options so if the atmosphere is similar to earths sans the water vapor I’m not entirely sure flight would be actually easier I can probably do some napkin maths over the weekend for this.
allannienhuis 7y ago
The amount of fuel at the destination doesn't change the rocket equation for being able to get into orbit from the planet. From the provided link: "If the radius of our planet were larger, there could be a point at which an Earth escaping rocket could not be built. <snip> That radius would be about 9680 kilometers (Earth is 6670 km). If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport."

archgoon 7y ago

It's 111 light years away. For all intents and purposes, that's a one way trip right there; irregardless of the rocket equation. Even at relativistic speeds, you can't come home anymore.

ajconway 7y ago
Theoretically, you can. At 0.99c 111 light years take about 15 years of ship time to travel.
- archgoon 7y ago
  You can make the trip arbitrarily small from your perspective (in theory at least :) ). The issue is that by the time you've made it back home, it's 222 years later. Hence "you can't go home anymore". :)
  - stickfigure 7y ago
    If you put some money in an interest-bearing account you could at least buy a new home when you got back.
    - repiret 7y ago
      You know where I can find one of these interest-bearing accounts that can outpace housing cost inflation?
      - fujiters 7y ago
        While not an interest bearing account, investing in an index fund of global stocks should outpace housing. Investing in a REIT should roughly keep pace with housing costs.
    - RandomBacon 7y ago
      Better do it in different countries and in different currencies and hope none of them get confiscated or have hyperinflation.

kadoban 7y ago

So that's purely for a chemical rocket, right? Is there any combination of tricks that can realistically push the envelope there? For example can we use a space elevator to start higher/faster (or, I don't know, balloons? a catapult or railgun or something?), laser power delivery from the ground, so we don't have to carry all the fuel, and an orbiting way-station for refueling, etc.?

Miner49er 7y ago
Solar sails might be able to beat it. https://en.wikipedia.org/wiki/Solar_sail https://en.wikipedia.org/wiki/Solar_sail
- AgentME 7y ago
  Aren't solar sails just for propelling yourself once you're in space? I can't imagine how you could launch off the surface of a planet with a solar sail.
  - 0xffff2 7y ago
    Yes, and even then they're incredibly low thrust devices. A light sail (whether solar or laser powered) may well be viable for sending a tiny unmanned probe to another star system (see [0]). It's really unlikely that it will ever scale up enough to take an average communication satellite the same distance, much less a manned craft. [0] https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot
- hinkley 7y ago
  M2P2 was going to test out magnetic sails, but Wikipedia is telling me they generate less thrust per kilowatt hour than ion thrusters. Explains why I haven't heard anything further about it. https://en.wikipedia.org/wiki/Magnetic_sail https://en.wikipedia.org/wiki/Magnetic_sail
- civilian 7y ago
  Solar sails are good for inter-planetary travel, but they aren't going to move the needle for launching off of a planet with 2g gravity! You need something that is compact and would give you a big impulse. As a KSP engineer would say, it "needs more boosters" https://i.redd.it/zuymxc5bb7s21.jpg https://i.redd.it/zuymxc5bb7s21.jpg

SJSque 7y ago

There's also the Wait Calculation to consider: https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calculation https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calcu...

PorterDuff 7y ago
Hey, I like that idea. Maybe it implies that every interstellar mission is just an in-flight rescue mission.
0xffff2 7y ago
That's interesting in theory, but as far as I know our interstellar propulsion technology hasn't advanced significantly at all in the last 50+ years. You can't do theory in a vacuum forever. I'd argue that unless we launch an interstellar something, we're never going to see any technological advances in the field.
ryacko 7y ago
The wait calculation implies that the returns from economic growth will eventually be converted into rocket fuel. A fun equation, but economics doesn’t translate well on time scales where depreciation of capital is 100% and becomes another expense.

hinkley 7y ago

I made it well into this decade before I was made aware of this fact. It's kind of a shock, still. At some point your planet is massive enough that you can't get into orbit with chemical rockets (even, I think, by flying them up like Burt Rutan?). The implications for the Drake equation are pretty big. Rockets without any promise of ever being able to break orbit are good for what, war? Would you keep developing them? Would you give up dreams of the stars? Would you look for intelligent life you couldn't ever possibly meet?

jerf 7y ago
"At some point your planet is massive enough that you can't get into orbit with chemical rockets (even, I think, by flying them up like Burt Rutan?)." Nuclear rockets don't seem to be very hard. They're somewhat dangerous if they explode, but they aren't very hard. Fairly solid prototypes were built decades ago and there's little to suggest they couldn't have been made production-grade [1]. We'd have them now if we didn't find the risk/reward to be too highly slanted to the "risk". Other species and other ecosystems may come to different conclusions, e.g., an ecosystem already more exposed to radiation and evolved to deal with much higher levels of it may judge it much less "risk" for some radionuclides to be scattered across the landscape in case of failure. What can be more of a problem is being in a place where you have no obvious access to technology at all. However smart our cetacean buddies may be, it is not clear even at this point in the 21st century what path to technology they could possibly have from their starting point. "The literature", a.k.a. "science fiction" has hypothesized breeding programs to develop various tools, but it's still not entirely clear how they'd get from "breeding useful jellyfish" to, well, anything like technology as we know it. It's possible we're just not solving this problem because we don't have to, maybe there's some easy path with the right development path, but it's still not clear what that would be. [1]: One of my markers for "the space age is truly here" is when we lift a nuclear rocket into space, sans fuel, and fuel it with space-sourced radionuclides. Earth-bound citizens will still complain, because "NUCLEAR BAD!", but their complaints will be ignorable at that point.
- hinkley 7y ago
  Do solids settle out of air on a high gravity environment faster? The air would be thicker. Does gravity or buoyancy win than tug of war? I spent a day once trying to figure out what the Bronze Age would be like for marine creatures. Oxidation is less of a problem but galvanic action is huge. Fire pretty much doesn't work, which blocks a whole bunch of precursors like ceramics.

TheOtherHobbes 7y ago

Surface gravity will be around 2g, so even if it has a rocky surface it's not going to be a very comfortable home from home.

dsfyu404ed 7y ago
So a 150lb person will weigh 300lb. Sure that's gonna suck on day one but there's plenty of people who weigh that much who get by. Without all the health complications from high body fat it wouldn't be that bad. You'd probably die young but I don't think that would bother people.
- sky_rw 7y ago
  Not sure the two are comparable. 300lb obese person's bone structure weighs the same, their heart and lungs weigh the same. I suspect 2x the weight on every organ is going to be seriously detrimental for sustained periods.
  - partiallypro 7y ago
    Not to mention you'd go from years and years of near 0G gravity to twice the gravity of earth. You wouldn't even be able to walk.
    - ben_w 7y ago
      Compare to the difficulty of getting there in the first place, getting spin gravity to work right isn’t a big problem.
    - rhinoceraptor 7y ago
      I would assume if we can figure out accelerating to near the speed of light, we'd also be able to make a viable rotating spacecraft to use centripetal force to solve that problem.
    - thenickdude 7y ago
      If you're making this trip in any reasonable amount of time, you're probably accelerating during the journey at least half a G anyway.

yellowapple 7y ago

I wonder if we could work around the stronger gravity by using a spaceship as the anchor for a space elevator or skyhook? Both of those technologies are pretty far off, but so is getting humans to another star system.

hinkley 7y ago
As gravity increases the tensile strength necessary for the elevator increases. We haven't even figured out how to mass produce materials that would suffice for an elevator on earth yet.
- yellowapple 7y ago
  I mean, we're already talking about getting humans to another star 111 lightyears away; I'd assume by the time we're ready to do that we'll have figured out how to mass-produced nanotubes or something.
scrumbledober 7y ago
currently we have no known materials that would actually be strong enough to support their own weight at the length of a space elevator on earth. double the gravity and the length will also at least double (possibly quadruple? not sure on the math here) so it may also be impossible to build a space elevator on one of these planets, at least without the use of active suspension (possible? theoretically.)
- 0xffff2 7y ago
  Currently we have no known materials that would actually survive a 111 light year trip to another solar system, so that fact that we can't actually build the space elevator when we get there seems irrelevant. They're both roughly the same order of magnitude of impossible with our current technology.
  - fwip 7y ago
    Sure we do. Chuck a rock in the right direction, it'll still be a rock 111 light years later.

cthalupa 7y ago

I mean, as far as I am aware, that problem is due to the propulsion method. Would a nuclear based rocket not be able to solve this issue? My understanding is that it would.

perl4ever 7y ago
A nuclear rocket still needs propellant, doesn't it?
- cthalupa 7y ago
  Yes, but significantly less of it by weight. You get significantly more energy per kg of nuclear fuel than you do traditional chemical propellant.
  - perl4ever 7y ago
    Perhaps, but my intuition is it wouldn't make a whole lot of difference, because the reason you can't get off a heavy planet is because of an exponential runaway effect.
    - cthalupa 7y ago
      https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html https://www.nasa.gov/mission_pages/station/expeditions/exped... An experimental nuclear rocket from the 70s nearly doubled our "payment energy". It should greatly reduce the initial and total mass portions of the rocket equation as well. I don't have all of the numbers to punch into the rocket equation to figure out things exactly, but the exhaust velocity and initial/total mass make up significant portions of the equation, and increasing the former while decreasing the latter will make significant impact on the ability to leave a more massive planet.

pierre_d528 7y ago

Or we could shift to an other side of the universe by "inverting" the mass of the ship where the speed of light is much higher[1]. Cosmology is so cool... too bad we do not have time for that: we cannot even cure the common cold! [1]: https://januscosmologicalmodel.com/pdf/2014-ModPhysLettA.pdf https://januscosmologicalmodel.com/pdf/2014-ModPhysLettA.pdf Cosmological bimetric model with interacting positive andnegative masses and two different speeds of light,in agreement with the observed acceleration of the Universe

atonalfreerider 7y ago
> Special Relativity can be summed up in the sentence: “We live in a spacetime which is an M4 manifold with a hyperbolic Lorentz metric of signature (+−−−)”. General Relativity can be stated accordingly: “The Universe is an M4 manifold with a Riemannian metric of signature (+−−−)” which is a solution of the Einstein equation:Rμν−12Rgμν+Λgμν=χTμν. It sounds like you get anti-gravity for free along the way to getting superluminal travel.
- pierre_d528 7y ago
  No because no "run away" effect. "inverted" mass means that the mass goes on the other side... gravity works the same there.

spullara 7y ago

I couldn't find anything with its approximate radius (it mentions about-earth sized and 8x the mass but that could mean anything) to make an evaluation of the likely gravitational force at the surface in order to make the evaluation of whether you could get off the planet cheaply.

nothis 7y ago

> I'm looking forward to the day we start finding exo-planets that are closer to Earth in size and which could potentially have space-faring races (and which we could leave if we were ever to visit them). I just realized I have no real concept of how many stars there even are within, say, a 100 light year radius of our sun (I guess that's a more realistic thing to find out than the number of planets). A quick search provided some estimates and they're kinda... disappointingly low, at around 20000 stars. That's a number where some "1% of 1% of 1%" kinda filter quickly ends up in a scenario where a planet fitting all our criteria might simply never be in reach. For something more "realistic" (I know, heh!) like 20 light years, there are only 150 solar systems. I've seen different numbers and have no idea how they're calculated but for the usual astronomic scales which quickly go into "billions" territory, it seems we're kinda stuck with a comparably small list of candidates.

tejtm 7y ago
It might cheer you up to to think we have yet to prove there is a star with no planets.
flukus 7y ago
On the plus side there are more moons than planets and many of them may be habitable. We've barely started looking at extra solar Jupiter like planets because of the much longer orbital periods.
newsbinator 7y ago
> That's a number where some "1% of 1% of 1%" kinda filter quickly ends up in a scenario where a planet fitting all our criteria might simply never be in reach. It might cheer you up to think that's the only reason the human race happens to be the one in our neighborhood that made it into space, without being stepped on by an Old One.
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perl4ever 7y ago
I think people are beginning to realize, that just as there are more asteroids than planets, and more space junk than large asteroids, there are a lot more free floating planets than stars. It could well be the universe is filled with life, but the dominant mode is underground chemo/radiotrophic microbes on planets without stars.