39 ms·

Spaceflight from Super-Earths is difficult

58 points by walkingolof 8y ago

lainga 8y ago
dang, could you please unshout the title
- dang 8y ago
  yes
soperj 8y ago
First I ever heard of this idea was on this site. Crazy to see a paper about it now.
- dogma1138 8y ago
  My own estimate was 1.5-2 earth masses it's so awesome that there is now research that proves something similar. https://news.ycombinator.com/item?id=12280432 https://news.ycombinator.com/item?id=12280432
antisthenes 8y ago
A bit disappointing. I was expecting them to elaborate on the nuclear propulsion that might be used to achieve escape velocity for a typical Super-Earth. Wouldn't such a spaceship still need to have materials that are able to withstand the heat/energy produced by nuclear propulsion?
- abecedarius 8y ago
  Start with https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
qrazhan 8y ago
Are there any harmful effects the increased surface gravity would have on the human body and if we were to live on these Super-Earths how would we mitigate them?
- headcanon 8y ago
  Humans raised on earth would find living there extremely unpleasant. The body would adapt by becoming stronger but it would be painful simply existing, and would wear out joints significantly. People with already poor health may be unable to survive, depending on how strong the gravity is. We obviously don't have any data on how humans raised in different gravities would react, but its likely that humans raised on a higher surface gravity would grow shorter, stocker, and more muscular. Humans on lower surface gravity would likely grow taller, wispier, and more elongated, and would by the same token find life on earth equally unpleasant. The Expanse series does a good job of highlighting these differences in a human way, since there are many people who grow up in asteroid colonies that cannot live on Earth easily.
- ThurmaUman 8y ago
  Imagine hanging a weight on every cell and fluid in your body. I don't think people would live very long. We already know there's damage (eyes) after months in space due to a reduction in gravitational effects.
alistproducer2 8y ago
Can someone elaborate on why escaping a planet's gravity is about velocity and not just attaining a certain height from the surface? More concretely, why isn't getting to space as easy as taking a balloon to a certain height?
- pradn 8y ago
  This is the simplest way to explain it, I think. https://www.youtube.com/watch?v=xfZHUwyh59k https://www.youtube.com/watch?v=xfZHUwyh59k
- baq 8y ago
  The absolutely best thing you can do to really internalize what achieving orbit make is to play a bit of Kerbal space program. No sarcasm, it's an eye opening experience the first time you make it.
- dredmorbius 8y ago
  Gravity + tyranny of the rocket equation. http://www.physlink.com/Education/AskExperts/ae158.cfm http://www.physlink.com/Education/AskExperts/ae158.cfm Escape velocity is the inverse of terminal velocity of an object falling from infinite height (discounting air resistance). https://youtube.com/watch?v=uWjdnvYok4I https://youtube.com/watch?v=uWjdnvYok4I
- pavel_lishin 8y ago
  It's because you need to not just get to space, you need to be in orbit. If you just take a magic balloon up to a certain height, once you're up there and let go fo the balloon - you just start falling back down. You need to have a lot of sideways velocity in order to actually get into orbit, to be revolving around whatever body you're trying to get off of. (It didn't used to make sense to me, either.)
  - ythn 8y ago
    Couldn't you theoretically escape a planet's gravity without going into orbit? I mean, gravity weakens by the square of distance, so it wouldn't be long before Earth didn't have much influence on you
pavel_lishin 8y ago
Scott Manley has a pretty accessible Kerbal Space Program video about this: https://www.youtube.com/watch?v=amjuJJwI3iM https://www.youtube.com/watch?v=amjuJJwI3iM
code51 8y ago
Imagine a higher culture formed in a super-earth, keeping peaceful with the earth and not leaving their home without a sufficiently eco-friendly technology being discovered. They are used to their gravity. It is hard to leave so they find value in sustainability earlier on. They only leave with super-advanced form of green technologies.
- everdev 8y ago
  We can send a person to space, but we can't colonize another planet yet, so our capabilities are virtually the same as in the premise you state.
- nickik 8y ago
  Going to space and living their forces the devlopment of advanced technology that can make the world eco-friendly. Water recycling, factory farming, resistant plants, nuclear power innovation, advanced solar power, syntetic fuel production, fuel cells and so on. The attitude that we should never do anything because its not green enough is just naive. Would you have been sitting around in 1800 and tried to stop people from explointing coal? > They only leave with super-advanced form of green technologies. We have that technology. We could use nuclear energy as Nuclear Thermal rockets, we can use it as a space battery, we can use it as a nuclear reactor to drive ion enignes, we can use it on mars to make rocket fuel and so. Ironoically envoirmentalist are partly responable that we almost use no nuclear technology anymore. They advocated for 40 years against all use of nuclear energy, and the most harmful effect is widespread misunderstanding of risks. The political deadlock about all issues nuclear make it a nightmare to deal with, and that's threw your supply chain. A Nuclear Thermal rocket was planned to be a major part of Mars exploration when von Braun thought about it in the 60s. Robert Zubrin who planned 'Mars Direct' in the early 90s, want to use a nuclear reactor to make fuel on mars and he was strongly avocating for NTRs in the second generation. Elon Musk has said that he would want nuclear reactors on mars and NTRs in later generations. That's exactly the advanced green technology you are looking for. After our first steps we should have moved onto that next level. Sadly it has not happened and it will take a while longer. It is currently practically impossible to devlop such a technology, unless you have direct support from NASA and other governments agencies. They themselfs have little interest in doing much in this space. So, I think space people are happy to do it as greenly as you like, but then a whole set of regulations have to change.
scj 8y ago
I've always been interested in the other case: What advances in spaceflight would be made by a technologically similar civilization if they had much lower gravity?
- pronoiac 8y ago
  I read some musings by Warren Ellis [1] which brushed up against easier space travel, very briefly: "The Olympus Mons mountain on Mars is so tall and yet so gently sloped that, were you suited and supplied correctly, ascending it would allow you to walk most of the way to space. Mars has a big, puffy atmosphere, taller than ours, but there’s barely anything to it at that level. 30 Pascals of pressure, which is what we get in an industrial vacuum furnace here on Earth. You may as well be in space. Imagine that. Imagine a world where you could quite literally walk to space." It's mostly not about your question, but I liked this part. [1] http://www.warrenellis.com/?p=14314 http://www.warrenellis.com/?p=14314
  - LeifCarrotson 8y ago
    Walking to the altitude of space and standing on something is very, very different than accelerating to the velocity necessary to stay in space. But that is an interesting point. On a super-Earth, with super-sized mountains or super-thick atmosphere, it might be more useful to start from an extremely high place so that you don't have as much atmosphere to deal with.
    - alonmower 8y ago
      Definitely, though being able to walk to the edge of the atmosphere could let you do things like use rail guns to get payloads up close to orbital speeds
    - kd5bjo 8y ago
      The next logical step after this is a space elevator. Because the structure is mechanically linked to the rotation of the planet below, you can achieve orbital velocity simply by climbing up to geostationary altitude and pushing off. I'm almost certain that there are physical limits that prevent such a thing from forming naturally, but I don't know how close to it something like a mountain can get without collapsing under its own weight.
njarboe 8y ago
Spaceflight from super-Earths might be easier (for a civilization to accomplish) than from smaller planets as the difficulty of not using nuclear power will cause nuclear tech to be developed. Development of this tech could make spaceflight easier than the chemical rockets we have on Earth.
- azernik 8y ago
  Why would non-nuclear power on such a planet be more difficult?
  - cfadvan 8y ago
    I think the idea is that non-nuclear power would be insufficient given the rocket equation, so the only way they could have rocketry is if it was nuclear powered.
hinkley 8y ago
This came up a couple weeks ago and blew my mind. Doesn’t this mean the Drake equation needs to include the rocket equation?
- inteleng 8y ago
  Would love to see your formulation of it!
hinkley 8y ago
On a planet with high gravity and a thick atmosphere, doesn’t the Space Ship One launch protocol become much more cost effective than launching from sea level? And similarly don’t launches from the equator become more critical to success, due to delta-v increasing faster than v due to rotation?
- deleted 8y ago
  [deleted]

58 points by walkingolof 8y ago

lainga 8y ago

dang, could you please unshout the title

dang 8y ago
yes

soperj 8y ago

First I ever heard of this idea was on this site. Crazy to see a paper about it now.

dogma1138 8y ago
My own estimate was 1.5-2 earth masses it's so awesome that there is now research that proves something similar. https://news.ycombinator.com/item?id=12280432 https://news.ycombinator.com/item?id=12280432

antisthenes 8y ago

A bit disappointing. I was expecting them to elaborate on the nuclear propulsion that might be used to achieve escape velocity for a typical Super-Earth. Wouldn't such a spaceship still need to have materials that are able to withstand the heat/energy produced by nuclear propulsion?

abecedarius 8y ago
Start with https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

qrazhan 8y ago

Are there any harmful effects the increased surface gravity would have on the human body and if we were to live on these Super-Earths how would we mitigate them?

headcanon 8y ago
Humans raised on earth would find living there extremely unpleasant. The body would adapt by becoming stronger but it would be painful simply existing, and would wear out joints significantly. People with already poor health may be unable to survive, depending on how strong the gravity is. We obviously don't have any data on how humans raised in different gravities would react, but its likely that humans raised on a higher surface gravity would grow shorter, stocker, and more muscular. Humans on lower surface gravity would likely grow taller, wispier, and more elongated, and would by the same token find life on earth equally unpleasant. The Expanse series does a good job of highlighting these differences in a human way, since there are many people who grow up in asteroid colonies that cannot live on Earth easily.
ThurmaUman 8y ago
Imagine hanging a weight on every cell and fluid in your body. I don't think people would live very long. We already know there's damage (eyes) after months in space due to a reduction in gravitational effects.

alistproducer2 8y ago

Can someone elaborate on why escaping a planet's gravity is about velocity and not just attaining a certain height from the surface? More concretely, why isn't getting to space as easy as taking a balloon to a certain height?

pradn 8y ago
This is the simplest way to explain it, I think. https://www.youtube.com/watch?v=xfZHUwyh59k https://www.youtube.com/watch?v=xfZHUwyh59k
baq 8y ago
The absolutely best thing you can do to really internalize what achieving orbit make is to play a bit of Kerbal space program. No sarcasm, it's an eye opening experience the first time you make it.
dredmorbius 8y ago
Gravity + tyranny of the rocket equation. http://www.physlink.com/Education/AskExperts/ae158.cfm http://www.physlink.com/Education/AskExperts/ae158.cfm Escape velocity is the inverse of terminal velocity of an object falling from infinite height (discounting air resistance). https://youtube.com/watch?v=uWjdnvYok4I https://youtube.com/watch?v=uWjdnvYok4I
pavel_lishin 8y ago
It's because you need to not just get to space, you need to be in orbit. If you just take a magic balloon up to a certain height, once you're up there and let go fo the balloon - you just start falling back down. You need to have a lot of sideways velocity in order to actually get into orbit, to be revolving around whatever body you're trying to get off of. (It didn't used to make sense to me, either.)
- ythn 8y ago
  Couldn't you theoretically escape a planet's gravity without going into orbit? I mean, gravity weakens by the square of distance, so it wouldn't be long before Earth didn't have much influence on you

pavel_lishin 8y ago

Scott Manley has a pretty accessible Kerbal Space Program video about this: https://www.youtube.com/watch?v=amjuJJwI3iM https://www.youtube.com/watch?v=amjuJJwI3iM

code51 8y ago

Imagine a higher culture formed in a super-earth, keeping peaceful with the earth and not leaving their home without a sufficiently eco-friendly technology being discovered. They are used to their gravity. It is hard to leave so they find value in sustainability earlier on. They only leave with super-advanced form of green technologies.

everdev 8y ago
We can send a person to space, but we can't colonize another planet yet, so our capabilities are virtually the same as in the premise you state.
nickik 8y ago
Going to space and living their forces the devlopment of advanced technology that can make the world eco-friendly. Water recycling, factory farming, resistant plants, nuclear power innovation, advanced solar power, syntetic fuel production, fuel cells and so on. The attitude that we should never do anything because its not green enough is just naive. Would you have been sitting around in 1800 and tried to stop people from explointing coal? > They only leave with super-advanced form of green technologies. We have that technology. We could use nuclear energy as Nuclear Thermal rockets, we can use it as a space battery, we can use it as a nuclear reactor to drive ion enignes, we can use it on mars to make rocket fuel and so. Ironoically envoirmentalist are partly responable that we almost use no nuclear technology anymore. They advocated for 40 years against all use of nuclear energy, and the most harmful effect is widespread misunderstanding of risks. The political deadlock about all issues nuclear make it a nightmare to deal with, and that's threw your supply chain. A Nuclear Thermal rocket was planned to be a major part of Mars exploration when von Braun thought about it in the 60s. Robert Zubrin who planned 'Mars Direct' in the early 90s, want to use a nuclear reactor to make fuel on mars and he was strongly avocating for NTRs in the second generation. Elon Musk has said that he would want nuclear reactors on mars and NTRs in later generations. That's exactly the advanced green technology you are looking for. After our first steps we should have moved onto that next level. Sadly it has not happened and it will take a while longer. It is currently practically impossible to devlop such a technology, unless you have direct support from NASA and other governments agencies. They themselfs have little interest in doing much in this space. So, I think space people are happy to do it as greenly as you like, but then a whole set of regulations have to change.

scj 8y ago

I've always been interested in the other case: What advances in spaceflight would be made by a technologically similar civilization if they had much lower gravity?

pronoiac 8y ago
I read some musings by Warren Ellis [1] which brushed up against easier space travel, very briefly: "The Olympus Mons mountain on Mars is so tall and yet so gently sloped that, were you suited and supplied correctly, ascending it would allow you to walk most of the way to space. Mars has a big, puffy atmosphere, taller than ours, but there’s barely anything to it at that level. 30 Pascals of pressure, which is what we get in an industrial vacuum furnace here on Earth. You may as well be in space. Imagine that. Imagine a world where you could quite literally walk to space." It's mostly not about your question, but I liked this part. [1] http://www.warrenellis.com/?p=14314 http://www.warrenellis.com/?p=14314
- LeifCarrotson 8y ago
  Walking to the altitude of space and standing on something is very, very different than accelerating to the velocity necessary to stay in space. But that is an interesting point. On a super-Earth, with super-sized mountains or super-thick atmosphere, it might be more useful to start from an extremely high place so that you don't have as much atmosphere to deal with.
  - alonmower 8y ago
    Definitely, though being able to walk to the edge of the atmosphere could let you do things like use rail guns to get payloads up close to orbital speeds
  - kd5bjo 8y ago
    The next logical step after this is a space elevator. Because the structure is mechanically linked to the rotation of the planet below, you can achieve orbital velocity simply by climbing up to geostationary altitude and pushing off. I'm almost certain that there are physical limits that prevent such a thing from forming naturally, but I don't know how close to it something like a mountain can get without collapsing under its own weight.

njarboe 8y ago

Spaceflight from super-Earths might be easier (for a civilization to accomplish) than from smaller planets as the difficulty of not using nuclear power will cause nuclear tech to be developed. Development of this tech could make spaceflight easier than the chemical rockets we have on Earth.

azernik 8y ago
Why would non-nuclear power on such a planet be more difficult?
- cfadvan 8y ago
  I think the idea is that non-nuclear power would be insufficient given the rocket equation, so the only way they could have rocketry is if it was nuclear powered.

hinkley 8y ago

This came up a couple weeks ago and blew my mind. Doesn’t this mean the Drake equation needs to include the rocket equation?

inteleng 8y ago
Would love to see your formulation of it!

hinkley 8y ago

On a planet with high gravity and a thick atmosphere, doesn’t the Space Ship One launch protocol become much more cost effective than launching from sea level? And similarly don’t launches from the equator become more critical to success, due to delta-v increasing faster than v due to rotation?

deleted 8y ago
[deleted]