Living on Mars?

[Bohandas]

While we're on the topic of superconstruction pipe-dreams, what if we generated power by building a massive coil around a rapidly spinning magnetar (turning it into a gigantic dynamo) and running a long wire of superconducting YBCO from it back to our own solar system. Once the decades required for the electricity to travel the lightyears of distance had passed we would have a nearly unlimited supply of power.

Also what if we launched a bakery into orbit so we could have actual pie in the sky

EDIT:

What kind of engine do you need to put a castle in the air?

[halfeye]

Assuming the Kuiper Belt has a total mass between 0.04 to 30 Earth masses

Where the fritz did you get that lower bound? There are Pluto, Eris, Sedna, Haumea and many others, surely the combination of just those named takes it above that?

[factotum]

Where the fritz did you get that lower bound? There are Pluto, Eris, Sedna, Haumea and many others, surely the combination of just those named takes it above that?

Those bodies are not very massive--they're mostly made of lighter materials like ice and are quite small. Eris is the most massive known Kuiper belt object at 0.0028x Earth mass, Pluto is a touch lighter, Haumea is less than 1/1000th Earth mass and I don't think Sedna's mass has been measured--so even if all four bodies were as massive as Eris (which they're not) the total would only be 0.0112 Earth masses, quite a bit less than WhatThePhysics' lower limit.

[WhatThePhysics]

The problem you have is energy, again. Changing the orbits of Kuiper belt material to bring it down into the inner Solar System wouldn't be too hard because they're not travelling very fast when they're out there, but pulling them into a useful orbit when they're actually *in* the inner Solar System and travelling at ridiculous velocities (something like 1.4x Venus' orbital velocity when they're at the same orbital distance, I think) would be an incredibly difficult thing to do.

Nudge them into eccentric orbits that bring them close to the Sun, then use the contained gases that'll form to insert the comets into Venusian, Terran, or Martian L4/L5 Points. Depending on the efficiency of the local fuel processing systems, they might need to loop around Sol a few times to get enough fuel. Once this is done, redirect them into the cyclical Hohmann transfer orbits, and you're good to go.

The Kuiper belt is also mind-bogglingly huge. Detecting useful matter in this region is a staggering challenge which we'd need to overcome before putting it to use. Distances are between 30AU and 50AU from the sun, compared to a bit more than 3AU for the asteroid belt past Mars (which is at 1.5AU from Sol, or 0.5AU from Earth's orbital path).

A simple, 2D comparison of the Kuiper belt to the rest of the solar system suggests you'd need to survey a region nearly twice as large as the rest of the system. Matter in the Kuiper belt would be far more diffuse and poorly-lit than it is closer to the sun. It may well be that there is a lot of stuff out there worth putting to use, but the challenge of doing so is an order of magnitude harder compared to using other sources.

Mass produce probes, and have some of them be statites with collapsible solar sails. The latter group's sensory capabilities should be maximized due to the sails blocking solar radiation, and the units remaining stationary relative to obscurable stars.

Where the fritz did you get that lower bound? There are Pluto, Eris, Sedna, Haumea and many others, surely the combination of just those named takes it above that?

The Structure of the Kuiper Belt: Size Distribution and Radial Extent.

[Lacuna Caster]

Also what if we launched a bakery into orbit so we could have actual pie in the sky

Have the crew of the ISS not done this yet? It sounds like a neat photo-op.

'Mannequin Skywalker'. Heh.

[factotum]

Have the crew of the ISS not done this yet? It sounds like a neat photo-op.

I can see a couple of problems trying to cook a pie on the ISS. First is that you'll get bits of pastry, flour and who knows what else floating around in the microgravity and potentially causing issues. Secondly, I don't think conventional ovens work well in microgravity because there's no convection, so hot air tends to cluster around the heating elements--I suppose you could fix that one by using a fan-assisted oven, though.

[Rockphed]

I can see a couple of problems trying to cook a pie on the ISS. First is that you'll get bits of pastry, flour and who knows what else floating around in the microgravity and potentially causing issues. Secondly, I don't think conventional ovens work well in microgravity because there's no convection, so hot air tends to cluster around the heating elements--I suppose you could fix that one by using a fan-assisted oven, though.

I thought conventional ovens cooked things via radiation. Or maybe there is an oven temperature when the primary heating method changes from convection to radiation.

[LordEntrails]

Who said you had to cook the pie on the ISS? Just ship it up there...

[georgie_leech]

I thought conventional ovens cooked things via radiation. Or maybe there is an oven temperature when the primary heating method changes from convection to radiation.

They heat the air in the oven, which transfers heat to the food through conduction. Microwave ovens use resonant frequencies to increase the effectiveness of the energy delivered to specific parts of the food based on position, which is why they tend to do things like be frozen on the outside until you bite a piece of molten cheese. Neither is really radiative heat transfer the way it works outside of the atmosphere.

[factotum]

A grill cooks things through radiation. Ovens do it via transferring heat from the heating elements (or the gas flame, if you have a gas cooker) to the air inside the oven, and thence to the food, as georgie_leech said. That's why fan ovens exist--they're more efficient at transferring the heat.

[WhatThePhysics]

All this talk of pies, shipping, and fan ovens makes me wonder how much it'd cost to add a spin gravity module to the International Space Station.

[Rakaydos]

All this talk of pies, shipping, and fan ovens makes me wonder how much it'd cost to add a spin gravity module to the International Space Station.

There was a proposal, but apparently there was problmes isolating the vibrations of the bearings from delicate zero-g expiriments elswhere on the station.

[factotum]

I would have thought the bigger problem would be preventing friction in the bearings transferring the rotation of the centrifuge to the main body of the station.

[Lacuna Caster]

I would have thought the bigger problem would be preventing friction in the bearings transferring the rotation of the centrifuge to the main body of the station.

You could probably compensate with microthrusters, but I thought the standard solution was having a counterweight spinning in the other direction?

Dunno how to fix the vibration problem, though. Could you just install some kind of floor-ventilation system to suck out all the flour and debris and create a crude proxy-gravity? There's a Nature paper in the making here, I just know it.

[Leewei]

Mass produce probes, and have some of them be statites with collapsible solar sails. The latter group's sensory capabilities should be maximized due to the sails blocking solar radiation, and the units remaining stationary relative to obscurable stars.

It'd take a heck of a lot of probes to survey a region with an inner diameter of around 200AU (2 x pi x R, where R is 30 AU). Can you somehow quantify what you'll need and speculate on where you'll get the material to build them?

[Ravens_cry]

It'd take a heck of a lot of probes to survey a region with an inner diameter of around 200AU (2 x pi x R, where R is 30 AU). Can you somehow quantify what you'll need and speculate on where you'll get the material to build them?

Asteroids and comets? For something building current tech probes, you need water*, carbon*, metals, and silica.
*For fuel and plastics

[Leewei]

Asteroids and comets? For something building current tech probes, you need water*, carbon*, metals, and silica.
*For fuel and plastics

There's some context here. The survey is being done to find comets to use for terraforming worlds such as Venus or Mars. I'm wondering how reasonable it is to survey, since it may well be you'd use up more than you got from the Kuiper belt.

[georgie_leech]

There's some context here. The survey is being done to find comets to use for terraforming worlds such as Venus or Mars. I'm wondering how reasonable it is to survey, since it may well be you'd use up more than you got from the Kuiper belt.

Specifically Venus, as supposedly the temperature will help offset the energy input by the comet slamming into the planet, which supposedly is being done to correct the direction of rotation? Because... I can't actually follow why that's supposed to be necessary, so because reasons?

[WhatThePhysics]

There was a proposal, but apparently there was problmes isolating the vibrations of the bearings from delicate zero-g expiriments elswhere on the station.

Darn, I guess we'll just need an ISS 2, then.

There's some context here. The survey is being done to find comets to use for terraforming worlds such as Venus or Mars. I'm wondering how reasonable it is to survey, since it may well be you'd use up more than you got from the Kuiper belt.

Ravens_cry has the right idea, though the probes don't need to be massive or large to be useful, which would make the initial comets capable of providing more than enough resources. If each probe has a mass of 1 megagram, something like Halley's Comet could possibly be converted into 220 billion probes. If the Kuiper Belt is a torus with a 50 AU major radius and 30 AU minor radius, its volume is about 400,000 cubic AU. If each probe's effective sensor field is a hemisphere with a 1 AU radius, and you ignore hemisphere packing issues, the Kuiper Belt could constantly be monitored by a minimum of roughly 200,000 probes.

Specifically Venus, as supposedly the temperature will help offset the energy input by the comet slamming into the planet, which supposedly is being done to correct the direction of rotation? Because... I can't actually follow why that's supposed to be necessary, so because reasons?

You don't slam the comets into Venus. You place them into cyclical Hohmann transfer orbits between Venus and Mars to: alter Venus's atmospheric composition and rotation, provide Mars with an atmosphere and hydrosphere, and ship goods and people between the two planets.

[Bohandas]

They heat the air in the oven, which transfers heat to the food through conduction. Microwave ovens use resonant frequencies to increase the effectiveness of the energy delivered to specific parts of the food based on position, which is why they tend to do things like be frozen on the outside until you bite a piece of molten cheese. Neither is really radiative heat transfer the way it works outside of the atmosphere.

based on composition

[georgie_leech]

based on composition

Partly. But the reason why relatively weak radiation is able to heat food uses both resonant frequencies, and patterns of constructive interference. It's why most microwaves rotate meals; certain areas within the microwave will be warmed faster than others, so rotating the food should ensure a more even cook. In theory at least. In practice, pockets of molten cheese continue to sit beside Frozen bits in our hot pockets

[factotum]

In practice, pockets of molten cheese continue to sit beside Frozen bits in our hot pockets

There's another reason for that behaviour--microwaves basically work by heating the water in the food, but they're not very good at heating ice. Since the heating is also uneven, as you say, and the clumps of ice are of differing sizes, you will tend to get bits that melt first and then heat very quickly while the other bits are still frozen and not absorbing microwaves very well. This is why you're supposed to stir frozen things partway through cooking, or else leave them to stand for a couple of minutes to allow the hot parts to melt the still-frozen bits.

[Rockphed]

There's another reason for that behaviour--microwaves basically work by heating the water in the food...

Microwaves also heat fats and some sugars, but mostly they heat the water.

[Bucky]

While we're on the topic of superconstruction pipe-dreams, what if we generated power by building a massive coil around a rapidly spinning magnetar (turning it into a gigantic dynamo) and running a long wire of superconducting YBCO from it back to our own solar system. Once the decades required for the electricity to travel the lightyears of distance had passed we would have a nearly unlimited supply of power.

The amount of current we can get through the wire without superconductivity breaking down is proportional to the cross-section of the wire.

Multiply that cross-section by the several thousand lightyears to the closest magnetar and you have a LOT of wire.

That means you need a lot of energy to position it. Simply dropping it off from a moving rocket isn't good enough, the wire needs to be stationary.

In fact, it's probably more energy than you could ever hope to transfer even in millions of years of operation.

Once you have the wire in place, you still need to worry about things like galactic drift, objects passing through the space occupied by the wire etc. so it's unlikely you could actually keep the wire in place for millions of years without needing to re-string it.

Oh, and the dynamo might not work as well as you want it to because superconductivity also breaks down in intense magnetic fields.

[Mando Knight]

The amount of current we can get through the wire without superconductivity breaking down is proportional to the cross-section of the wire.

Multiply that cross-section by the several thousand lightyears to the closest magnetar and you have a LOT of wire.

That means you need a lot of energy to position it. Simply dropping it off from a moving rocket isn't good enough, the wire needs to be stationary.

In fact, it's probably more energy than you could ever hope to transfer even in millions of years of operation.

Once you have the wire in place, you still need to worry about things like galactic drift, objects passing through the space occupied by the wire etc. so it's unlikely you could actually keep the wire in place for millions of years without needing to re-string it.

Oh, and the dynamo might not work as well as you want it to because superconductivity also breaks down in intense magnetic fields.

I think that at the point where you're literally building a dynamo out of a hyper-condensed star, maintaining superconductivity in the wire you're using might not actually be the most ridiculous feat you're attempting.

[factotum]

Using a super-long wire to transport power in that situation would not be practical. The relative motion of the magnetar and Sol would render it impossible. Likewise, transmitting power through some other means (say, a honkin' great laser) wouldn't work because your aim point would keep changing--you're essentially trying to hit a target moving at several hundred metres per second from information you have from several thousand years ago!

It has to be said, though, once we're at a point in our development where we could reasonably consider such a thing, we'd have to be a galaxy-spanning civilisation anyway, so send the power to somewhere much closer where we can make better use of it.