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Old 31st March 2021, 08:52 AM   #121
RecoveringYuppy
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Originally Posted by 3point14 View Post
You'd get better returns from the Kuiper belt (about 10% of earth's mass).
No, that would be far worse returns. You waste far more material that could be used more productively some other way. And you still don't get a second Earth.
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Old 31st March 2021, 08:54 AM   #122
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Originally Posted by RecoveringYuppy View Post
No, that would be far worse returns. You waste far more material that could be used more productively some other way. And you still don't get a second Earth.

I wasn't really thinking about alternate uses, just other sources of matter.

I'm pretty convinced mushing Venus into Mars is the best and most practical solution. Not sure how much reaction mass you'd need. And it would be important to miss the Earth on the way past...
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Old 31st March 2021, 08:57 AM   #123
RecoveringYuppy
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Originally Posted by 3point14 View Post
I wasn't really thinking about alternate uses, just other sources of matter.

I'm pretty convinced mushing Venus into Mars is the best and most practical solution. Not sure how much reaction mass you'd need. And it would be important to miss the Earth on the way past...
Not sure if serious, but...


If you can do that you can do far better things with the mass of both Mars and Venus.
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Old 31st March 2021, 09:18 AM   #124
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Yeah, I'm totally serious about slinging a mass driver onto a planet and crashing it into another planet that's, I don't know, one AU or so? (totally guessing) away at closest approach...

Of course, you'd only be able to fire up the mass driver for a small portion of any given day, but, on the plus side, if you got the inial 'burn' right, then it'd just lithobrake at journey's end, so you wouldn't need to slow it down...

ETA:
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Old 31st March 2021, 03:52 PM   #125
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Originally Posted by RecoveringYuppy View Post
No, that would be far worse returns. You waste far more material that could be used more productively some other way. And you still don't get a second Earth.
And why would you want one anyway? The one we have is vastly more habitable already (so much so that one might almost think it was made for us - or us for it), and keeping it that way is a piece of cake compared to terraforming Mars.

This has to be the ultimate "grass is always greener' fallacy. Mars is a lifeless hunk of red rock that will never be any use to us. The sooner we accept that the sooner we can get back to making our own planet more habitable.
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Old 31st March 2021, 03:58 PM   #126
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Hopefully someone with actual knowledge will chime in, but I believe it would take less effort to get from Earth to Mars than move around between objects in the Asteroid belt.

Pretty much all science fiction relies on magical drives that don't need fuel.
(And spanning distances without taking any time to do so.)

Distances and relative velocities in space are really nasty barriers to be overcome.
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Old 31st March 2021, 03:59 PM   #127
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Originally Posted by novaphile View Post
Distances and relative velocities in space are really nasty barriers to be overcome.
Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space...
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Old 31st March 2021, 04:09 PM   #128
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Originally Posted by novaphile View Post
Hopefully someone with actual knowledge will chime in, but I believe it would take less effort to get from Earth to Mars than move around between objects in the Asteroid belt.

Pretty much all science fiction relies on magical drives that don't need fuel.
(And spanning distances without taking any time to do so.)

Distances and relative velocities in space are really nasty barriers to be overcome.
Moving from Earth to Asteroid belt would take more fuel than to Mars of course.
Moving around the belt is cheap. Even getting from one side to another just means taking a bit higher orbit, and wait. It can be months of waiting, but you'll get there.
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Old 31st March 2021, 04:09 PM   #129
RecoveringYuppy
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Originally Posted by novaphile View Post
Hopefully someone with actual knowledge will chime in, but I believe it would take less effort to get from Earth to Mars than move around between objects in the Asteroid belt..
No. Why do you think that? Asteroids are in very similar orbits to each other and all have lower, even much lower, gravity wells than Mars.

I'll see if I can find a great link I've had for this in the past.

ETA:

https://www.reddit.com/r/space/comme...ystem_updated/

note that asteroids are energetically in between the intercept points for Mars and Jupiter. Also note what it takes to get to the surface of Mars, or any planet, in terms of delta-v.

Last edited by RecoveringYuppy; 31st March 2021 at 05:26 PM. Reason: Fix link
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Old 31st March 2021, 05:02 PM   #130
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Distance is just time.
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Old 31st March 2021, 05:18 PM   #131
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Originally Posted by theprestige View Post
Distance is just time.
Not really. No amount of waiting will get you to Mars. You have to go against the slope of Sun's gravity well.
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Old 31st March 2021, 05:38 PM   #132
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Originally Posted by Dr.Sid View Post
Not really. No amount of waiting will get you to Mars. You have to go against the slope of Sun's gravity well.
Sure. But once you make that throw, you just have to wait until you get there. Throw harder, or keep running, and you get there faster.

Or you just hibernate for however much time it takes to get there on a cheap throw. One more way that robots are better than humans.
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Old 31st March 2021, 06:32 PM   #133
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Originally Posted by theprestige View Post
Sure. But once you make that throw, you just have to wait until you get there. Throw harder, or keep running, and you get there faster.

Or you just hibernate for however much time it takes to get there on a cheap throw. One more way that robots are better than humans.
Cheap throw won't get you there. You can save something by some resonant orbit, or at least go around Venus .. which both would increase travel time several times .. but if you want to go direct, both manned and unmanned missions use what's pretty close to cheapest and slowest. Anything less and you won't get there, ever.
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Old 1st April 2021, 08:14 AM   #134
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Originally Posted by Dr.Sid View Post
Cheap throw won't get you there. You can save something by some resonant orbit, or at least go around Venus .. which both would increase travel time several times .. but if you want to go direct, both manned and unmanned missions use what's pretty close to cheapest and slowest. Anything less and you won't get there, ever.
It's weird to misunderstand my "cheap" as "too cheap to succeed". Pretty much all of our space travel is done by getting a mass to escape velocity, and then relying on inertia to do the rest. Fuel-wise, that's about as cheap as it gets. You could get to Mars with constant acceleration, which would be a lot faster, but the fuel cost is impossibly high.

Simply put, space travel is about making the cheapest possible throw that produces the necessary inertia, and then waiting. Or even more simply: Distance is time.
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