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posted by martyb on Wednesday November 14 2018, @10:33PM   Printer-friendly
from the with-an-oink-oink-here-and-a...oh,-wait dept.

Exoplanet discovered around neighbouring star

Astronomers have discovered a planet around one of the closest stars to our Sun.

Nearby planets like this are likely to be prime targets in the search for signatures of life, using the next generation of telescopes.

The planet's mass is thought to be more than three times that of our own, placing it in a category of world know as "super-Earths".

It orbits Barnard's star, which sits "just" six light-years away.

Writing in the journal Nature [DOI: 10.1038/s41586-018-0677-y] [DX], Guillem Anglada Escudé and colleagues say this newly discovered world has a mass 3.2 times bigger than the Earth's.

Barnard's Star.

Also at phys.org.


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  • (Score: 2) by Immerman on Friday November 16 2018, @02:21AM (4 children)

    by Immerman (3985) on Friday November 16 2018, @02:21AM (#762472)

    So where do you put the second fuel tank so that it's not destroyed when the first tank explodes? Not to mention, even if you can pull that off you almost certainly need ALL that fuel to make it home, so destroying one tank is just as deadly as destroying all of them.

    That would have to be a phenomenally large torus, as the exhaust plume expands rapidly thanks to being at higher pressure than the surrounding vacuum.

    The beauty of a skyhook is that you don't *need* to reach escape velocity (or more accurately, orbital velocity - once you're in orbit reaching escape velocity is relatively simple). Picture the cable as one pair of spokes describing a line through the center of a wheel. A wheel which is spinning at just the right speed so that the lowest point on the rim perfectly matches speed with the top of the atmosphere. Essentially you get a wheel rolling across the top of the atmosphere. And if you're in, say, a stationary hot air balloon directly beneath it you'll see a point on the rim come almost straight down above you, stop, and go back up again. Like this, only the wheel would be rolling around a circle, rather than along a flat plane: https://en.wikipedia.org/wiki/Cycloid [wikipedia.org]

    So, you're sitting in your hot air balloon (which does indeed work even better in the dense atmosphere likely on a Super-Earth), floating at the top of the atmosphere. And when that cable tip comes down and momentarily stops right above you - you grab it. You can then ride the "wheel" up to the top of the arc, at which point you'll be traveling at over twice orbital speed. For a skyhook in low Earth orbit (~8km/s) , it that means you'd be traveling at ~16km/s, about 5km/s faster than escape velocity from orbit (escape velocity from orbit is sqrt(2) times the circular orbital speed), more than fast enough to reach the orbits of Pluto or Mercury without any further propulsion. So probably you want to let go before you reach the top.

    That is to say - skyhooks can be *insanely* effective. Basically you're transfering angular momentum from the skyhook to the ship, but the skyhook's presumably much greater mass will keep it in orbit, where you can use ion thusters or other slow, high-efficiency propulsion to regain the lost momentum over a much longer time period. Or, you can rendevous incoming ships near the top of the wheel to slow them down and drop them gently into the atmosphere at negligible relative speed, in which case you transfer their angular momentum to the skyhook. A 100% efficient atmosphere-to-orbit momentum transfer bank with no moving parts.

    As for launching from super-Earths, the big problem is that the superlinear rocket equation gets worse much faster, to the point that you just can't carry enough chemical propellant to reach orbit with a "simple" rocket. Nuclear rockets would still do the job nicely, as might some of the more clever and efficient launch systems we've dreamed up. But it means a civilization that started out on the surface of a planet would have to develop powerful nuclear rockets before they could reach orbit. If you start in orbit though, where you can build orbital space elevators of various types, then you simplify things immensely (for sufficiently obtuse definitions of "simplify" - we were building nuclear rockets within decades of our first orbital chemical rockets - while we're still nowhere close to building a skyhook. Theoretically we have the basic materials and technology to do it easily, but the cost and details of attempting an orbital project of that scale have kept us from doing so.

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  • (Score: 2) by edIII on Friday November 16 2018, @05:48AM (3 children)

    by edIII (791) on Friday November 16 2018, @05:48AM (#762559)

    You really got me thinking about the viability of this. Fun to think about.

    So where do you put the second fuel tank so that it's not destroyed when the first tank explodes? Not to mention, even if you can pull that off you almost certainly need ALL that fuel to make it home, so destroying one tank is just as deadly as destroying all of them.

    Think of an engine as a module that contains a thruster, antimatter storage pod, and then whatever matter we are mixing with (Deuterium?). The modules are separated. I do imagine the module can split in half with smaller thrusters to allow it to come apart and navigate back to the rear of the ship keeping maximum distance while rotating backwards, being dragged in half at the rear. Antimatter on one side, Deuterium on another.

    That would have to be a phenomenally large torus, as the exhaust plume expands rapidly thanks to being at higher pressure than the surrounding vacuum.

    You got me there. It would need to turn into a super structure at 100k feet behind if the plume expands that rapidly. Although, that also makes me wonder just how much heat is actually experienced along the surface area of the torus? The ineffiency you mentioned of being directly behind was blocking some of it right? A torus, or series of them, should allow most of it to pass right around them. Which brings up an interesting idea depending on the level of heat, and that is directly feeding off it for greenhouses and other needs. You would have backups, but imagine the steam baths.

    I do imagine the torus would be as large as possible. Resources are difficult to get in the middle of nowhere, so I was assuming a ship that was more of a biodome. I would imagine several miles in diameter, and as many as we could reasonably tow while still being nimble enough to get around safely. The inside of the torus could be hundreds of feet in diameter. I'm thinking a generational ship since nobody mentioned we were escaping the speed of light, just using thrusters with a lot of energy. Even at a reasonable fraction of C, it would be several generations to get to this star and back.

    The skyhook on a cycloid sounds pretty damn neat too. It would be one hell of an interesting ship if it could be built.

    --
    Technically, lunchtime is at any moment. It's just a wave function.
    • (Score: 2) by Immerman on Friday November 16 2018, @03:23PM (2 children)

      by Immerman (3985) on Friday November 16 2018, @03:23PM (#762713)

      I think keeping your antimatter and hydrogen (no benefit to deutrium outside of fusion, and it's a lot rarer) separate is fairly pointless. After all, the antimatter containment system, engine, ship, etc. is after all made entirely out of matter that will react just as strongly as the hydrogen would. In fact, a dense liquid or powder would likely be a much better choice than hydrogen since it's only the mass that matters, and the denser it is, the easier it is to store the same amount of mass.

      As for the temperature of the exhaust - it's going to be high - ridiculously high. You'll probably be using the antimatter annihilation to power an ion drive since the matter-antimatter reaction will leave you with only massless photons, mostly gamma radiation, and photon drives suck. (Also, you *really* don't want to stand in an exhaust stream composed primarily of gamma radiation) When you get right down to it temperature is a measure of average molecular speed - and the entire point of an antimatter powered drive is that it can expel the reaction mass at a much higher speed than is possible with chemical propellant. The faster (hotter) the exhaust when it leaves the rocket, the more momentum it has, and thus the more it causes your ship to accelerate for the same amount of reaction mass. For reference, the exhaust temperature of a Merlin engine is apparently 1500C, or 3km/s - and you probably want the ion drive exhaust to be at least 10-100x higher than that. The VASMIR ion drive in comparison has an exhaust speed of about 50km/s. Not sure how that translates to temperature - it's not a straightforward conversion, and depends on the mass of the molecules involved.

      • (Score: 2) by edIII on Friday November 16 2018, @10:50PM (1 child)

        by edIII (791) on Friday November 16 2018, @10:50PM (#762880)

        Thanks for explaining all of this, btw. I'm not very strong in physics at all.

        --
        Technically, lunchtime is at any moment. It's just a wave function.
        • (Score: 2) by Immerman on Saturday November 17 2018, @02:12AM

          by Immerman (3985) on Saturday November 17 2018, @02:12AM (#762922)

          My pleasure.