Proxima Centauri Has a Terrestrial Planet
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28-08-2016, 06:37 AM
RE: Proxima Centauri Has a Terrestrial Planet
(28-08-2016 12:07 AM)true scotsman Wrote:  
(24-08-2016 12:20 PM)Popeyes Pappy Wrote:  Only about a thousand years from here using currently available technology. Who's up for a road trip.

We could send a ship now which we could overtake with a newer ship and then a newer ship. It might not take that long. Think about it. With time dilation, assuming we could get a ship up to a sizable fraction of the speed of light, they might only be a couple weeks into the journey when something like the star ship enterprise pulls up and beams them all aboard for the 2 day trip at warp 2. Wink

Wait, the early ship's going fast enough for significant time dilation? .... so how do we beat the rocket equation? And then how do we stop?
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28-08-2016, 06:50 AM
RE: Proxima Centauri Has a Terrestrial Planet
(28-08-2016 06:37 AM)Reltzik Wrote:  
(28-08-2016 12:07 AM)true scotsman Wrote:  We could send a ship now which we could overtake with a newer ship and then a newer ship. It might not take that long. Think about it. With time dilation, assuming we could get a ship up to a sizable fraction of the speed of light, they might only be a couple weeks into the journey when something like the star ship enterprise pulls up and beams them all aboard for the 2 day trip at warp 2. Wink

Wait, the early ship's going fast enough for significant time dilation? .... so how do we beat the rocket equation? And then how do we stop?

I am terrible at understanding time dilation. I am always struggling with the frame of reference. As for stopping? That's a good question. Do we stop or just do a Pluto-style flyby? Maybe visit other systems. Space might be very empty outside star systems.

We have to remember that what we observe is not nature herself, but nature exposed to our method of questioning ~ Werner Heisenberg
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28-08-2016, 06:55 AM
RE: Proxima Centauri Has a Terrestrial Planet
(25-08-2016 10:20 PM)Chas Wrote:  
(25-08-2016 03:14 PM)unsapien Wrote:  No it isn't, at best it's an intersolar planet.

Astronomers use the terms "terrestrial planet" and "gas giant" (or "Jovian planet") to identify the two broad classes of planets.

And to non-astronomers it's misleading. They think "Hey, they've found Pandora!" (Doubling down on the errors.)
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28-08-2016, 08:36 AM
RE: Proxima Centauri Has a Terrestrial Planet
Some quick caveats:
- The planet has a very small fast orbit around its star, so it likely to be tidally locked. That makes habitability more dicey
- Red dwarves have very active early lives so there is good reason to think it would be sterile currently
- Starshot could get there in forty years but would be travelling at .1c when it arrived with no way to slow down. The result being one hell of a brief flyby.

Give me your argument in the form of a published paper, and then we can start to talk.
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28-08-2016, 08:42 AM
RE: Proxima Centauri Has a Terrestrial Planet
click click click and gone Smile
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28-08-2016, 08:50 AM
RE: Proxima Centauri Has a Terrestrial Planet
(28-08-2016 08:36 AM)Hafnof Wrote:  Some quick caveats:
...
- Starshot could get there in forty years but would be travelling at .1c when it arrived with no way to slow down. The result being one hell of a brief flyby.
That means it would take 80 minutes to go from Earth to the Sun.
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28-08-2016, 06:12 PM
RE: Proxima Centauri Has a Terrestrial Planet
Yeah, and consider that we would like to take close up non blurry pictures of proxima b. The craft would travel 300km in the duration of a 1/1000s exposure. It would be able to remain within 100,000 km of a given object for a third of a second.

Give me your argument in the form of a published paper, and then we can start to talk.
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28-08-2016, 06:29 PM
RE: Proxima Centauri Has a Terrestrial Planet
(28-08-2016 06:12 PM)Hafnof Wrote:  Yeah, and consider that we would like to take close up non blurry pictures of proxima b. The craft would travel 300km in the duration of a 1/1000s exposure. It would be able to remain within 100,000 km of a given object for a third of a second.

My Mamiya would have taken 333 pictures in that time frame.
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29-08-2016, 12:19 AM
RE: Proxima Centauri Has a Terrestrial Planet
(28-08-2016 06:50 AM)tomilay Wrote:  
(28-08-2016 06:37 AM)Reltzik Wrote:  Wait, the early ship's going fast enough for significant time dilation? .... so how do we beat the rocket equation? And then how do we stop?

I am terrible at understanding time dilation. I am always struggling with the frame of reference. As for stopping? That's a good question. Do we stop or just do a Pluto-style flyby? Maybe visit other systems. Space might be very empty outside star systems.

RS explained the principle behind the math to me at once point, but I still don't get it. The practical affect, however, is this:

High velocities or being inside heavy gravity wells makes how time FROM DIFFERENT REFERENCE POINTS is experienced. In other words, for any given person, time will always seem to proceed normally. However, if we're looking at another person (ship, clock, whatever) in a different reference point -- some frame of reference that is traveling at high speed or in a big gravity well -- time may seem, from the outside, to be going slower for them.

So if we imagine looking at Big Ben, and then a fast-traveling spaceship through a telescope that has its own clock mounted on its exterior (absurd, but bear with me), Big Ben will seem to be keeping time accurately, and the spaceship clock will seem to be running slow. However, an astronaut tethered to that ship looking at its clock will see it running at the right speed, and Big Ben running slow.

That's not the problem. It's wacky and insanely counter-intuitive, but it's not the problem. If leveraged properly, it might be hugely advantageous, like making a trip to a distant planet seem like years when it's actually centuries.

The problem in this context is actually a mix of two problems. The first is that you have to be traveling really, really fast for time dilation to be noticeable and significant for anything but insanely fast and persnickety computers. At the EXTREMELY FAST .1c that Hafnof described (which, by the way, is not something you want to do if you're going to run into even one speck of interstellar dust), the time dilation effect is a mere one half of one percent. That means that if we experience 40 years here on Earth, the astronauts would experience roughly 39.8 years. While nifty, that's not enough to produce major savings on life support or rations for astronauts. You still have to pack a lifetime supply of both. To get to the years to centuries level -- that is, one year aboard is one century to the rest of the universe -- your ship would have to be flying at 99.995% of the speed of light.

(Oh, and the dust particle thing is a real problem. At .1c, it's like being hit by a sand-blaster where every grain of sand is traveling fast enough on its own to punch through titanium armor and still emit a sonic boom... in sound waves traveling through the armor itself. If you don't want to run into a speck of interstellar dust at .1c, you REALLY REALLY REALLY don't want to hit one at .99995c. That's like a sandblaster where every grain of sand hitting your spacecraft results in a nuclear explosion. I mean a literal fusion bomb.)

The OTHER big problem is the rocket equation. There's an ugly-looking formula for it, and it gets even uglier when we factor in relativity, so I'll try to put it in simple terms instead.

We've got a few different ways for accelerating (which includes decelerating and turning) a spacecraft. The most flexible and potent ones involve basically throwing gas out of a nozzle. Imagine that scene from Wall-E with the fire extinguisher. Possibly we heat it up first, or perhaps we shoot a bunch of BBs instead of spraying out gas, but the basic idea is the same: We push mass away from us in one direction, and we get pushed in the other direction in an equal and opposite reaction. The mass that we throw away from us is called "reaction mass" for this reason. The problem is, when we push that mass away from us, we've lost it, and can't use it again in the future. The fire extinguisher eventually empties out. What's more, the mass that we have yet to push away from us, that we're going to use in the future, ALSO needs to be accelerated with the ship... increasing the amount of mass that we need for the initial stages of acceleration.

Greatly oversimplifying, let's say we do a series of "burns" like this, and each burn requires us to expel reaction mass equal to the mass of the rest of the craft, and doing so accelerates us by .01c. To get to .1c, we'd have to do this 10 times. That would mean that we'd need to bring reaction mass equal to 2^10 times the mass of the rest of our ship to get up to .1c, because we have to burn half of what we've got to get to .1c, and then half of what's left after that to get to .2c, and half of what's left to get to .3c, and so on, and after halving 10 times we'd still need to have our entire ship, just with empty tanks. To then DECELERATE would require us to reverse the process again, so we'd now need 2^20 times the mass of the rest of the ship in reaction mass. And if we also want to make a return trip, we'd have to reaccelerate back to .1c from Proxima Centauri, and then decellerate once more once we got to the Solar system. That would require 2^40 times as much reaction mass as the rest of the ship. The contents of our thrusters' tanks would have to mass over a TRILLION TIMES what the rest of the ship (including the empty tanks and the thruster assemblies) did. That's... not theoretically impossible, but it's absurdly, absurdly impractical. (Note that I've greatly oversimplified things for this illustration.)

Now there's some shortcuts and tricks we can pull to improve on this. First, we can throw the mass out the back at relativistic speeds. Because of the black magic of relativity, this means that the mass "counts" as being much larger than it actually is for purposes of how much it accelerates the ship. This is what cutting-edge ion engines do. This doesn't get rid of the problem... at all... but it does cut down on how much of a problem it is. Think "billion times" the craft's mass instead of "trillion times"... and again, oversimplifying for illustration.

Other solutions include picking up more reaction mass in flight with a ramscoop.... which is basically a big funnel in front of the spacecraft that works a bit like a jet turbine. This is entirely theoretical and there aren't any practical designs for it, and it might slow you down picking up the mass just as much as it helped you speed up, but in theory it would allow you to "refuel" as you go. Or you can use a solar sail, which uses light pressure (and solar winds) rather than reaction mass. While this gets you away from the rocket equation, you're stuck using the solar sail only in the directions and strengths of the sunlight that's available. You'd have almost no flexibility at all. Solar sails are even more cutting-edge than ion drives. You can also use gravitational assists with close passes by various planets, essentially stealing some of their momentum to increase your own momentum. (Don't worry, they have a LOT to spare.) This is called a slingshot and is what Hafnof is talking about. The problem is that the planets LITERALLY have to be in alignment to get you where you're going at the speeds you want. Expect a good alignment to pop up every few years or decades, and you have to time your trip to hit that window with only an hour or so to spare on either side. You'd also have to pinball between various planets a few times, doing this trick each time, before you were ready to leave the solar system, and the initial back-and-forth maneuvers would take months. This also requires rockets at each slingshot, albeit very efficient uses of the rockets.

Put these two together. You've got the rocket equation, which makes it very hard to accelerate to high speeds... and then doubles the problem if you want to slow down again. You've got relativity, which doesn't provide the promised time-dilation benefits unless you get to suicidally high speeds. And I'm not talking "never tell me the odds" suicidal, I'm talking "let's literally turn our ship into a fusion bomb" suicidal. And then you've got the fact to reach those speeds, using rockets, is doubly impossible due to the rocket equation.
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29-08-2016, 01:36 AM
RE: Proxima Centauri Has a Terrestrial Planet
(24-08-2016 12:20 PM)Popeyes Pappy Wrote:  Only about a thousand years from here using currently available technology. Who's up for a road trip.



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