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Oumuamua may be a hydrogen iceberg
- monadic2 6y agoMakes me wonder if you could slingshot around the sun towards relativistic speeds with thermal power. At the very least it could save fuel on the egress, if not the second half. Can you aerobrake around a star?
- sq_ 6y ago> Can you aerobrake around a star? Not a physicist, but it seems like you should be able to do something similar to aerobraking (not one-to-one since the Sun's "atmosphere" is different from a planet's). Maybe using a solar sail of some sort directed at the right angle?
- idreyn 6y agoI went on a wiki-binge on this topic a few days ago and so I recognize this as a magsail[0]. It would be an attractive addition to an interstellar craft since it obviates the need to carry propellant for deceleration. [0] https://en.wikipedia.org/wiki/Magnetic_sail https://en.wikipedia.org/wiki/Magnetic_sail
- sq_ 6y agoThat's really cool. Definitely helpful in order to drop deceleration fuel requirements if we ever manage to put together a relativistic interstellar spacecraft.
- phkahler 6y agoIn a bit over 1M years another star is expected to pass around 1000 AU from the sun. Chemical rockets should be able to get there in a decade or two. It's a huge stretch, but we have a million years to prepare.
- sq_ 6y agoOh wow. Had never heard about that. Wouldn't that pass within the range of the Oort Cloud? Seems like we might have some issues from the gravitational effects if so (although that's assuming humans manage to keep ourselves going for another million years).
- Koshkin 6y agoSomething makes me doubt that humans will still be around at that time.
- sq_ 6y agoWith the way we’re going, maybe not. But maybe we’ll shape up and some version of humanity will make it.
- theandrewbailey 6y agoGilese 710? https://en.wikipedia.org/wiki/Gliese_710 https://en.wikipedia.org/wiki/Gliese_710
- tectonic 6y agoSee also e-sail: https://orbitalindex.com/archive/2019-04-09-archive-Issue-7/ https://orbitalindex.com/archive/2019-04-09-archive-Issue-7/
- troymc 6y agoBrown dwarf stars can be relatively cool and can have atmospheres, so you could aerobrake around those.
- isoprophlex 6y agoMagneto-braking maybe?
- mhh__ 6y agoCan't do the maths at the moment but you'd probably need a lead spacecraft to get close enough. Getting close to the sun also means you'll be going ridiculously fast e.g. Parker Solar Probe will hit something like 200km/s and it's still millions of kilometres from the sun
- ddxxdd 6y agoThermal power requires a reservoir of cold temperature; your car's engine would do nothing if the incoming air was just as hot as the post-ignited air.
- dmurray 6y agoI'm sure this is true in practice, but I can't wrap my head round why it's correct in theory. Let's say I hook up my exhaust to my intake, I can still squirt some gasoline into the engine, make it explode and expand and thereby drive a piston, at the cost of having even hotter air the next time round. If I repeat this long enough, my engine will melt, but that's a minor matter of materials science. Maybe I can win my drag race before it melts. Is that the limiting factor or is there some other reason I'm missing that we need a heat gradient?
- marcosdumay 6y agoIf you heat it more each time, yeah, the old air can act as a cold reservoir and make things run. If you do draw it with enough detail, you'll notice that if you do not heat it more at each turn, you won't be able to get any pressure difference at your "explosion".
- monadic2 6y agoYes, I was envisioning solid hydrogen fuel powering by outgassing as envisioned in the article.
- TeMPOraL 6y ago> Can you aerobrake around a star? If you can keep your cool, why not? Matter is matter. What's better, you could technically radiation-brake around a star. I don't know how big of a solar sail you'd have to present to get a meaningful force from it.
- DarmokJalad1701 6y ago> slingshot around the sun You can only slingshot around the sun if you were already in a hyperbolic orbit w.r.t the sun. An object in a closed helio centric orbit cannot gain any momentum by "slingshotting" around the sun.
- monadic2 6y agoIt can if it loses mass, correct? Energy conservation would result in increased momentum.
- fennecfoxen 6y agoYes. Your mass in low Sol orbit has a much higher specific orbital energy, so thrusting a rocket or ejecting mass while at or near perihelion makes more of a difference than doing so in deep space.
- deleted 6y ago[deleted]
- perihelions 6y ago"if you could slingshot around the sun towards relativistic speeds with thermal power" Unfortunately, no. The boost you can steal from a powered flyby is only of the same order as the escape velocity of the massive object. For the sun, this is 617 km/s at its surface, or 0.002 c. The term you're interested in is "Oberth effect". To get relativistic speeds on the table, you'd need exotic, compact objects whose escape velocities are relativistic. I.e. white dwarfs, neutron stars & black holes. No one asked, but: Freeman Dyson pointed out [0] some astounding properties of a short-period white dwarf binary. (Particularly: there are two stars; both are extremely dense; and they are orbiting around each other at an extremely high relative velocity). If you could perform a close slingshot maneuver around one of these stars, you would be accelerated to relativistic speeds in mere seconds. What's more, this would be an entirely unpowered, propellantless manuevuer (stealing orbital momentum from the binary system). And finally, as an incredible example of the equivalence principle, human passengers wouldn't even notice the insane ~10^4 g's of acceleration: it's equivalent to free-fall. [0] This is a PDF https://www.ifa.hawaii.edu/~barnes/ast242_s14/Dyson_Machines.pdf https://www.ifa.hawaii.edu/~barnes/ast242_s14/Dyson_Machines... (1963)
- fenwick67 6y agoThis is great sci-fi fodder, imagine if you could land a tiny craft on that thing and then use the hydrogen as fuel without having to haul all that fuel into deep space (very unlikely to be practical but the idea is exciting).
- diroussel 6y agoThen the problem becomes getting oxygen. As a hydrogen won't burn in a vacuum.
- ISL 6y agoUnless you can fuse it into helium.
- throwaway2048 6y agoIf you have the tech to fuse hydrogen the amount of fuel you would need for a nearly unlimited amount of energy is tiny, you would save very little by harvesting it off a comet/asteroid.
- jandrese 6y agoDepends on how much energy you need. If you are talking about turning it into an interstellar spacecraft by hooking up some kind of fusion powered thruster (probably using H2 as the reaction mass) to the back you may need all of its mass. This is of course well beyond our current capabilities, but it's not something that's impossible to consider in the medium-distant future. Plus, even if you expend a colossal amount of energy accelerating you're still talking about thousands of years for the journey where you'll need to keep those reactors running for the entire trip (there is no useful solar collection in deep space) having a literal mountain of fuel to start with is important.
- Sharlin 6y agoYou still need propellant mass. Energy in itself doesn't get you anywhere. But in practice you'd probably be better off electrolyzing water ice which is ubiquitous in the outer Solar System.
- crimsonalucard1 6y agoIs there an element or compound in the universe that will remain a gas at 0K? Does everything become solid at that temp?
- eganist 6y agoIntuitively I would think so since 0K is a motionless state. By definition everything would be solid because nothing would be capable of e.g. filling a given volume, or for that matter, doing any action at all. But this isn't my field of expertise.
- dmitrygr 6y agoComplete lack of motion would violate Heisenberg uncertainty principle ("no motion" == "I know both momentum and location with zero uncertainty" and that's not allowed)
- whatshisface 6y agoNo, you can have zero momentum. However it comes along with having a position wavefunction that fills the whole universe.
- rrmm 6y agoHey let's probe the boundary conditions of the universe.
- NikolaeVarius 6y agoThe boundary condition is that at some arbitrary point god smacks you and tells you to knock it off
- rrmm 6y agoSorry God!
- bovermyer 6y agoI like the idea that these things could be potential star-seeds. It would be an interesting way for new solar systems to form.
- jamestimmins 6y ago"It has now passed beyond Saturn’s orbit and will travel another 10,000 years before exiting the system". How big is our solar system? I always assumed it referred to everything between the sun and Pluto, but 10,000 years suggests it's far larger.
- saberdancer 6y agoI'm not sure of what definition they used here, but one that is common is heliosphere, or in other words sphere around the Sun where solar wind is dominant. This is about 120 AU.
- Voloskaya 6y agoBut it would still take way less than 10000 years to cross the heliopshere boundary (it took 40 years for the Voyagers probes). It is probably referring to the gravitational sphere of influence of the solar system (marked by the Oort cloud) 1 to 2 light years away.
- wahern 6y ago‘Oumuamua's incoming and outgoing speed is ~5AU/year. In 10,000 years that's 50,000AU, which is approximately the distance to the outer most region of the Oort Cloud: https://en.wikipedia.org/wiki/Oort_cloud https://en.wikipedia.org/wiki/Oort_cloud
- lgl 6y agoI always thought the Oort cloud was a scientifically proven thing but apparently it's "a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2,000 to 200,000 au (0.03 to 3.2 light-years)"
- messe 6y agoToo faint to be proven with our current instruments.
- 6y ago