Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Gentlefish]

True, it'd be slow, but not all space travel would be interstellar, and a solar sail would be very useful in terms of interplanetary, and a whole heck of a lot cheaper, if used to travel to an intermediary satellite or space elevator.

[Osmosis Jones]

True, it'd be slow, but not all space travel would be interstellar, and a solar sail would be very useful in terms of interplanetary, and a whole heck of a lot cheaper, if used to travel to an intermediary satellite or space elevator.

¿por qué no los dos?

[10ebbor10]

There are several problems with solar sails, but the most noteworthy is that it's very weight inefficient (Hence slow and expensive), requires quite a lot of maintenance, and can only be used at certain angles from the sun (Making manoevring hard and limiting your launch opportunities seriously).

[Jopax]

Graphene turns out to be an awesome capacitor of sorts, GO SCIENCE!

[Another]

The energy of a conventional battery is stored in chemical reaction*. The energy of a capacitor is in its internal electric field. The total energy of a capacitor is 1/2ɛ*E^2*V where permittivity ɛ is not very far from 1 for all no-conducting materials, E is the electric field strength in Volts/meter and V is the total internal volume of the capacitor.

The most important material for any capacitor is not one from which its conducting parts are made but one which divides them and prevents internal discharge. It is unlikely that what was found was some kind of graphene superinsulator. Without better insulators capacitors are still less volume (and mass) efficient energy storage solution than chemical based ones.

Marketing almost instantly charging batteries for phones is all right if you can make 1 charge to last for a full day. Charging a car worth of energy in a few seconds would require massive currents though and associated problems like melting wires, huge magnetic fields and need for impulse Gigawatt generating capacities on demand.

*Chemical reactions can be thought of as inter-atomic electromagnetic fields rearranging themselves into more energy favorable configurations. And atomic electromagnetic field strengths are really large.

P.S. Cooking graphene on a blue-ray or DVD disk is the best part of that video. Add a 3D printer and something like modern consumer 3D printers but for [UV laser?] cutting thin films to 100 nm precision and you would be able to make a processor from doped carbon layers at home. Basic technology is already here.

[Scoops Novel]

We need a Wild Mass Guessing thread for the fermi paradox.

[Virex]

It is unlikely that what was found was some kind of graphene superinsulator.

The graphene would be used for electrochemical capacitors, which do not rely on a solid dielectric, but rather on a solid or liquid electrolyte, in which a Helmholz layer provides the actual capacitance.

Graphene turns out to be an awesome capacitor of sorts, GO SCIENCE!

If you're going to link to an awesome discovery, at least provide a peer-reviewed reference as well (Paywalled, you can message me for a copy)

[Starver]

Something tells me that they wouldn't work very well while traveling towards a star, which means that it wouldn't be terribly useful for interplanetary travel or whatever.

By the time you're going towards the star.... you're of course looking to slow down from whatever heady excesses of velocity (*ahem*) that the solar sail got you up to while departing your original system...

Still, we're talking about generation ships with decreasing acceleration as you leave your home system (with or without a projected laser-assist from your home port), so there's an awful lot of coasting or near-coasting before you finally get the opportunity to achieve increasing deceleration at the other end (make sure you know how relatively active the solar pressure is from, of course)....

Maintenance?  Well, from debris strikes (large area)...  I suppose having an 'accident' on the way down through the destination's Oort Cloud could quite ruin your day, or at least mean you're now on a bit of a high-speed fly-by.


I was going to say that solar-sailing wouldn't actually be that good for half of interplanetary travel (i.e. inwards-going orbital transfers), but while in orbit around your planet of origin you could use it to judiciously make your orbit so your final escape from that orbit was essentially inwards... or, in other terms (or from an insignificantly attractive launch body), you're aiming back retrograde (i.e. less prograde than your orbital body).  Which even with a significant component of outward force (I'm imagining a 45-degree angle away from the sight-line to the sun, but I'm sure other angles work) means you'll find yourself in an increasingly elliptical orbit (a higher aphelion, but your perihelion does lower and you're heading there first).


(All this reminds me of a children's ("young adult"'s probably being the term these days) SF book I read back when I was young, where the people on a certain watery-planet used "solar sails" to move their boats around the surface.  Not only were they apparently good enough to move boats around, and somehow not be affected by (or make use of) the wind or even stationary atmosphere, but with this planet having multiple suns (at least three, but memory tells me it was something like seven...  oh yeah, one for the astromechanics to argue over with that little detail...) they had multiple sails, one for each sun...  So they could (with skill, of course, it wasn't just a walk in the park) go any direction they wanted, using the appropriate sails for the appropriate suns to aid in them going on their chosen heading...  Almost one for the "nitpicks" thread, that one. )

[Virex]

Of course you can just fold in a solar sail to prevent it from pushing you off course while in interstellar space.

[Another]

It is unlikely that what was found was some kind of graphene superinsulator.

The graphene would be used for electrochemical capacitors, which do not rely on a solid dielectric, but rather on a solid or liquid electrolyte, in which a Helmholz layer provides the actual capacitance.

Graphene turns out to be an awesome capacitor of sorts, GO SCIENCE!

If you're going to link to an awesome discovery, at least provide a peer-reviewed reference as well (Paywalled, you can message me for a copy)

Since the abstract does not cite any number for energy density - can you just tell if it is bigger than common lithium-ion capacitors or not?

[olemars]

Since the abstract does not cite any number for energy density - can you just tell if it is bigger than common lithium-ion capacitors or not?

This article about the same experiment has a graph (LSG being the LaserScribed Graphene).

[Another]

About 1-2 W*hour/L. Can be useful for regenerative brakes or gauss cannon I suppose. Not something to power a car or a phone as was implied in the promo video.

[Scoops Novel]

http://www.sciencedaily.com/releases/2013/02/130218132355.htm

There's some contradictory evidence to the theory that the moon formed from a collision between earth and another planetoid. Specifically, water in what is thought to represent the original crust and couldn't have survived the impact.

[Pnx]

I thought the water was supposed to come from ice meteors?

EDIT: Er, or maybe I should shut up, read the article, and not post so much in thinky threads when tired.

[Gentlefish]

It could be that the moon is just younger than we thought and there was vast amounts of water that helped super-cool the moon into the cold, dense geoid we know now.