For journeys in the outer solar system, or further, you need to supply your own light. You shine some kind of beam (laser light most likely) at the sail from back home.
Of course stopping at another star is still a bit tricky. Robert Forward proposed detaching part of the sail and using it to reflect the beam back onto the rest, Larry Niven & Jerry Pournelle just had the probe diving in very close to the star. I've also seen the suggestion of using the galactic magnetic field to take you around the back of the target system so that you can decelerate back down your original beam.
They work fine in normal light if you buy a half-way decent projector. Direct sunlight on the screen is a problem, but it is with a black- or white-board as well.
It seems I was over by a factor of 3. I remembered the number of feet and reported it as metres. A quick google for "icecap volume" found this in a course handout from a course at UIUC.
Most of Earth's ice is found in Antarctica, where permanent ice caps cover approximately 0.5% of Earth's total surface area and are 3km thick, on average. [ Earth's oceans cover roughly 70% of our planet, to an average depth of 4.0km. Assuming that water and ice have roughly the same density, estimate by how much sea level would rise if global warming were to cause the Antarctic ice caps to melt. Comment on the effects the melting of the Arctic ice cap (which floats upon the Arctic ocean) would have on sea level (hint: you do not need to know how large the Arctic ice cap is to answer this question). ]
The calculation is then easy. If you melt this icecap it is spread 140 times thinner, so will be about 20m thick,
I should remark that no one expects significant melting of the East Antarctic icecap in the forseeable future.
The Antarctic icecap is in two pieces: East and West. The West is much warmer, and does seem to be melting faster in recent years. If it melts completely sea levels rise by about 6 metres (20 feet). Melting the East antarctic icecap would eb a lot harder -- it's much colder and higher and further from the sea -- but if it happened sea levels rise about 60m (200 feet).
There are (at least) two kinds of GRB: long ones (minutes) which are believed to be giant single stars collapsing directly to black holes and short ones (milliseconds) which are believed to be colliding neutron stars.
I'm not sure, but I don't think so. I think that instead of using "magnetic fields pointing left or right (or forwards or backwards)" for 1 or 0, they will use "magnetic fields pointing up or down". Why does this make a difference, I hear you yell -- because the magnetic crystals are needle-shaped and the magnetic field points along the needle, so up/down packs them in more tightly.
I bought a laptop from Emperor Linux last December, with Linux pre-installed. They ship to the UK. I bought power cables separately, and could have bought a UK keyboard from IBM, but didn't bother. I'm very happy with it. Suspend to RAM works most of the time, accelerated graphics I'm still working on when I feel like it, but drivers allegedly exist, DVD playing worked find when I installed mplayer. Emperor sent instructions but no software. ACPI is fine, wireless is fine, bluetooth allegedly works, but I have no other bluetooth device to try it with, power-saving works. I haven't played with the buttons much, but the speaker volume & mute buttons work.
It wasn't cheap, but I did buy absolutely top-of-the-range (good year for grants).
Neutron stars generally have huge magnetic fields. The neutron liquid which makes up the star has small numbers of protons on electrons in it. These move very freely (I think it's a superfluid, so actually frictionless), and so conduct electricity very easily.
The type of star considered likely to be respnsible for SGRs has an even huger magnetic field, possibly created by a "dynamo" effect similar to that responsible for the Earth's magnetic field which operated during the first 10 seconds or so of the neutron star's life. A google search on magnetar finds several excellent articles.
It's not any particular lump(s) of Pu that are missing. I think they took in some used fuel rods and estimated somehow how much Pu was in it. Then, when they reprocessed them they found they had slightly less Pu than they expected.
This is basically what happened to the bulk of Earth's carbon -- it is in rocks. I know this reaction is very slow on Earth (so it is not going to remove the carbon we're adding to atmosphere in any useful timescale) but it might be possible to make it happen quicker on Vewnus. Not sure how, maybe smash the rock to powder (with nukes, say) and then immerse it in hot supercritical CO2. Don't know.
The simplest thing is to simply shade Venus entirely from the Sun. It then takes about 200 years for the atmosphere to freeze out as solid CO2. Now you can build heated domes, or whatever you like on top of this, or cover it with a layer of something like diamond strong enought to keep it solid (or liquid) at your favourite temperature an put a breathable atmosphere over that,
Nuclear rockets for take off from ground level really are a rather worrying idea. A nuclear upper stage is conceivable, in particular for boosting from LEO to Mars transfer orbit or something like that, and nuclear/ion is a great idea for long slow deep-space missions, but to get a takeoff you'd need a reactor core close to the melting point of Uranium oxide with a hell of a lot of hydrogen being pumped through it very fast and not too much mass wasted on the shielding. While I usually fairly pro-nuclear, this seems reckless.
You have to tear the spaceplance idea into pieces and evaluate them all separately.
1. wings and a runway landing -- is a lot of mass to take up to orbital speeds and back again -- hard to see this as a winner until we find a way to use non-chemical boosters
2. air-breathing propulsion -- could win, but no one has made it do so yet. The problem is that the big win (lower on-board fuel mass) comes if you can use air-breathing for the later parts of your acceleration. That makes the engine design really, really hard, and means that you have to reach high speed while still in some reasonable density of atmosphere, which is also a problem.
3. A fully reusable vehicle -- this is appealing, DC-X was a step in this direction. The problem is the physics, unless you can make 2 above work, you need roughly 90% of your take-off mass to be LH2 and LO2. This is really hard, making tanks, plumbing and engines this light is a huge problem.
SpaceShipOne was NOT an LEO vehicle. It got to 100km, which is the easy part but didn't make any attempt to get to orbital velocity, which is what takes most of the fuel, and imposes most of the mass restrictions. Boosting a set of wings and an undercarriage up to orbital velocity just so you can slow them down again and then land on a runway consumes an insane amount of fuel for too little purpose. Until we find a lauch fuel significantly more energy dense than LH2 and LO2 then the dry mass cost of wings and wheels will always be too high.
The Scaled Composites people are involved in one of the bids and they are not proposing a space plane.
There's another example due in part to John Conway. If you measure the squared angular momentum of a spin 1/2 particle along three perpendicular axes, you will always get (up to scale) 0,0 and 1, for the three results. These observations commute, so order doesn't matter. Conway showed that you can arrange some moderate number of sets of coordinate axes around a sphere sharing various individual axes in such a way that there is no way to label the axes with ones and zeros so that each set of three contains a 1 and two 0s. Any hidden variable for these results would give such a labelling, so you're stuffed.
This is the "hidden variable" concept. That the particles have properties, but we cannot know all of them simultaneously -- so we can fix the position using a suitable experiment, at the cost of losing all information about what the momentum was, and so on. Unfortunately, it doesn't work. You can construct more complex experiments which make it clear that there is no possible set of hidden values that the particle could start with that is consistent with all the possible experiements. The details are a little complex, but if you work through them, they are completely convincing.
And you missed my point "modern engines using basically the same fuels and principles". I'm talking about a century or two of engineering refinement, not some completely new idea.
Kim Stanley Robinson aside, actually terraforming Mars looks almost insanely difficult. You need huge amounts of heat, and probably to add huge amount of light elements to make a useable atmosphere. Someone may come up with something new, but none of the proposed methods will actually get you there in any reasonable timescale.
What I have seeen proposed, with numbers, is the "world-house" concept. Essentially you build a tent perhaps 1 mile high over possibly quite large areas of Mars. The tent fabric is chosen to be transparent to light, opaque to UV and reflective to IR, and its weight is supported by the pressure of the gas underneath it. A few pilons or mountains hold it in place. This helps warm the surface by keeping in the IR, and drastically reduces the amount of atmosphere you need (because it stops 1 mile up) and is a whole lot quicker and cheaper to make than making the rest of an atmosphere.
In this context, of course, the Martian "national" parks are easy to achieve. Just don't biuld that section of the world-house! There would be some problems with disruption to wind patterns, leakage of subsurface heat and so on, but probably nothing that couldn't be managed in a suitable "buffer zone".
The sun is burning protons, which is really hard to do.
You can burn deuterium in a gravity-confined reactor not that much larger than Jupiter (called a brown dwarf). D+He3 is easier still, D+T even easier.
The first steam engines were huge, for reasons not so unlike current fusion reactors (usuing the square-cube law to control losses). More modern engines using basically the same fuels and principles can be tiny. Why -- because we have better materials and better understanding of the process. I don't see why the same won't be possible for fusion reactors over time. The first ones will be huge power stations, but 100 years later they could easily be truck sized and 100 years after that they may be too small to see.
Sure raising gasoline/kerosene prices to sane values brings in tax from all across the economy, but you can put most of that money straight back into the economy, if you wish, by lowering (for instance) income taxes. The effect is that things which require a lot of oil get more expensive (relative to incomes) and things that require little oil get cheaper. People's buying habits adjust top this, and you have an overall less polluting economy.
I'd be more worried about "open source smallpox vaccine", "lump of plutonium, 1kg, copies=10" or "fluorine, 1000 litres, output device='Joe's desktop fabricator'".
Slashdot Mirror
For journeys in the outer solar system, or further, you need to supply your own light. You shine some kind of beam (laser light most likely) at the sail from back home.
Of course stopping at another star is still a bit tricky. Robert Forward proposed detaching part of the sail and using it to reflect the beam back onto the rest, Larry Niven & Jerry Pournelle just had the probe diving in very close to the star. I've also seen the suggestion of using the galactic magnetic field to take you around the back of the target system so that you can decelerate back down your original beam.
They work fine in normal light if you buy a half-way decent projector. Direct sunlight on the screen is a problem, but it is with a black- or white-board as well.
It seems I was over by a factor of 3. I remembered the number of feet and reported it as metres. A quick google for "icecap volume" found this in a course handout from a course at UIUC.
Most of Earth's ice is found in Antarctica, where permanent ice caps cover approximately 0.5% of Earth's total surface area and are 3km thick, on average.
[ Earth's oceans cover roughly 70% of our planet, to an average depth of 4.0km. Assuming that water and ice have roughly the same density, estimate by how much sea level would rise if global warming were to cause the Antarctic ice caps to melt. Comment on the effects the melting of the Arctic ice cap (which floats upon the Arctic ocean) would have on sea level (hint: you do not need to know how large the Arctic ice cap is to answer this question). ]
The calculation is then easy. If you melt this icecap it is spread 140 times thinner, so will be about 20m thick,
I should remark that no one expects significant melting of the East Antarctic icecap in the forseeable future.
Um No. You have misread your map.
The Antarctic icecap is in two pieces: East and West. The West is much warmer,
and does seem to be melting faster in recent years. If it melts completely sea levels rise by about 6 metres (20 feet). Melting the East antarctic icecap would eb a lot harder -- it's much colder and higher and further from the sea -- but if it happened sea levels rise about 60m (200 feet).
There are (at least) two kinds of GRB: long ones (minutes) which are believed to be giant single stars collapsing directly to black holes and short ones (milliseconds) which are believed to be colliding neutron stars.
I'm not sure, but I don't think so. I think that instead of using "magnetic fields pointing left or right (or forwards or backwards)" for 1 or 0, they will use "magnetic fields pointing up or down". Why does this make a difference, I hear you yell -- because the magnetic crystals are needle-shaped and the magnetic field points along the needle, so up/down packs them in more tightly.
I bought a laptop from Emperor Linux last December, with Linux pre-installed. They ship to the UK. I bought power cables separately, and could have bought a UK keyboard from IBM, but didn't bother. I'm very happy with it. Suspend to RAM works most of the time, accelerated graphics I'm still working on when I feel like it, but drivers allegedly exist, DVD playing worked find when I installed mplayer. Emperor sent instructions but no software. ACPI is fine, wireless is fine, bluetooth allegedly works, but I have no other bluetooth device to try it with, power-saving works. I haven't played with the buttons much, but the speaker volume & mute buttons work.
It wasn't cheap, but I did buy absolutely top-of-the-range (good year for grants).
Steve
Neutron stars generally have huge magnetic fields. The neutron liquid which makes up the star has small numbers of protons on electrons in it. These move very freely (I think it's a superfluid, so actually frictionless), and so conduct electricity very easily.
The type of star considered likely to be respnsible for SGRs has an even huger magnetic field, possibly created by a "dynamo" effect similar to that responsible for the Earth's magnetic field which operated during the first 10 seconds or so of the neutron star's life. A google search on magnetar finds several excellent articles.
It's not any particular lump(s) of Pu that are missing. I think they took in some used fuel rods and estimated somehow how much Pu was in it. Then, when they reprocessed them they found they had slightly less Pu than they expected.
The point is that system builders might want to bundle RME + Real (say) instead of XP Pro.
I imagine the EU will insist on RME being cheaper to system builders than full XP Pro.
This is basically what happened to the bulk of Earth's carbon -- it is in rocks.
I know this reaction is very slow on Earth (so it is not going to remove the carbon we're adding to atmosphere in any useful timescale) but it might be possible to make it happen quicker on Vewnus. Not sure how, maybe smash the rock to powder (with nukes, say) and then immerse it in hot supercritical CO2. Don't know.
The simplest thing is to simply shade Venus entirely from the Sun. It then takes about 200 years for the atmosphere to freeze out as solid CO2. Now you can build heated domes, or whatever you like on top of this, or cover it with a layer of something like diamond strong enought to keep it solid (or liquid) at your favourite temperature an put a breathable atmosphere over that,
Nuclear rockets for take off from ground level really are a rather worrying idea. A nuclear upper stage is conceivable, in particular for boosting from LEO to Mars transfer orbit or something like that, and nuclear/ion is a great idea for long slow deep-space missions, but to get a takeoff you'd need a reactor core close to the melting point of Uranium oxide with a hell of a lot of hydrogen being pumped through it very fast and not too much mass wasted on the shielding. While I usually fairly pro-nuclear, this seems reckless.
You have to tear the spaceplance idea into pieces and evaluate them all separately.
1. wings and a runway landing -- is a lot of mass to take up to orbital speeds and back again -- hard to see this as a winner until we find a way to use non-chemical boosters
2. air-breathing propulsion -- could win, but no one has made it do so yet. The problem is that the big win (lower on-board fuel mass) comes if you can use air-breathing for the later parts of your acceleration. That makes the engine design really, really hard, and means that you have to reach high speed while still in some reasonable density of atmosphere, which is also a problem.
3. A fully reusable vehicle -- this is appealing, DC-X was a step in this direction. The problem is the physics, unless you can make 2 above work, you need roughly 90% of your take-off mass to be LH2 and LO2. This is really hard, making tanks, plumbing and engines this light is a huge problem.
SpaceShipOne was NOT an LEO vehicle. It got to 100km, which is the easy part
but didn't make any attempt to get to orbital velocity, which is what takes most of the fuel, and imposes most of the mass restrictions. Boosting a set of wings and an undercarriage up to orbital velocity just so you can slow them down again and then land on a runway consumes an insane amount of fuel for too little purpose. Until we find a lauch fuel significantly more energy dense than LH2 and LO2 then the dry mass cost of wings and wheels will always be too high.
The Scaled Composites people are involved in one of the bids and they are not proposing a space plane.
There's another example due in part to John Conway. If you measure the squared angular momentum of a spin 1/2 particle along three perpendicular axes, you will always get (up to scale) 0,0 and 1, for the three results. These observations commute, so order doesn't matter. Conway showed that you can arrange some moderate number of sets of coordinate axes around a sphere sharing various individual axes in such a way that there is no way to label the axes with ones and zeros so that each set of three contains a 1 and two 0s. Any hidden variable for these results would give such a labelling, so you're stuffed.
This is the "hidden variable" concept. That the particles have properties, but we cannot know all of them simultaneously -- so we can fix the position using a suitable experiment, at the cost of losing all information about what the momentum was, and so on. Unfortunately, it doesn't work. You can construct more complex experiments which make it clear that there is no possible set of hidden values that the particle could start with that is consistent with all the possible experiements. The details are a little complex, but if you work through them, they are completely convincing.
Timescales. If you somehow could give Mars an atmosphere it would leak away over millions of years. Over thousands though, this effect is unimportant.
And you missed my point "modern engines using basically the same fuels and principles". I'm talking about a century or two of engineering refinement, not some completely new idea.
For the sake of argument, take reasonable as = 1000 years.
Kim Stanley Robinson aside, actually terraforming Mars looks almost insanely difficult. You need huge amounts of heat, and probably to add huge amount of light elements to make a useable atmosphere. Someone may come up with something new, but
none of the proposed methods will actually get you there in any reasonable timescale.
What I have seeen proposed, with numbers, is the "world-house" concept. Essentially you build a tent perhaps 1 mile high over possibly quite large areas of Mars. The tent fabric is chosen to be transparent to light, opaque to UV and reflective to IR, and its weight is supported by the pressure of the gas underneath it. A few pilons or mountains hold it in place. This helps warm the surface by keeping in the IR, and drastically reduces the amount of atmosphere you need (because it stops 1 mile up) and is a whole lot quicker and cheaper to make than making the rest of an atmosphere.
In this context, of course, the Martian "national" parks are easy to achieve. Just don't biuld that section of the world-house! There would be some problems with disruption to wind patterns, leakage of subsurface heat and so on, but probably nothing that couldn't be managed in a suitable "buffer zone".
The sun is burning protons, which is really hard to do.
You can burn deuterium in a gravity-confined reactor not that much larger than Jupiter (called a brown dwarf). D+He3 is easier still, D+T even easier.
The first steam engines were huge, for reasons not so unlike current fusion reactors (usuing the square-cube law to control losses). More modern engines using basically the same fuels and principles can be tiny. Why -- because we have better materials and better understanding of the process. I don't see why the same won't be possible for fusion reactors over time. The first ones will be huge power stations, but 100 years later they could easily be truck sized and 100 years after that they may be too small to see.
Sure raising gasoline/kerosene prices to sane values brings in tax from all across the economy, but you can put most of that money straight back into the economy, if you wish, by lowering (for instance) income taxes. The effect is that things which require a lot of oil get more expensive (relative to incomes) and things that require little oil get cheaper. People's buying habits adjust top this, and you have an overall less polluting economy.
But the DWP spends a lot MORE than $10M on their IT setup.
I'd be more worried about "open source smallpox vaccine", "lump of plutonium, 1kg, copies=10" or "fluorine, 1000 litres, output device='Joe's desktop fabricator'".