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Of course, the whole discussion is somewhat moot since none of us know what an operational fusion engine might look like in terms of performance, mass or volume...

Eveyone is working on an assumption that the fusion reactor will wigh at least dozens of tons.  That's not necessarily the case:

http://depts.washington.edu/rppl/programs/stx.html]here

There are lots of alternate fusion designs that got left behind the Tokomak design.  Many of them are far better for proplulsion purposes.

As fr the Farmsworth Fusor, it's a dead-end design.  It makes a great neutron generator but the trajectory of the particles is an inherent limitation.  Because the fusion fuel nuclei are constantly yo-yoing through the center of the device, you very quickly lose all your kinetic energy to Brehmstrallung (sp) radiation.  It's only even theoretically feasible for light nuclei like He3.

One big question is whether we have enough helium to fill such an airship.  The total worldwide helium production capacity is estimated at 29 million cubic meters.  These mile long airships would eat up a significant portion of our entire helium reserves which is functionally a non-renewable resource. 

In other news, I was just reading some reports of lead selenide nanocrystal solar cells that have the capacity to boost solar cell efficiency up to 60%.

Some sort of electrodeposition mught be usable for putting metal down on a nanotube mat.  Of course, the whole adhesion problem rears its ugly head up still but at least it should be possible to combine the two phases.

You'd get a slight increase in O2 carrying capacity by polymerizing the hemiglobin but not much, the hemoglobin in your red blood cells is already packed in quite tightly.  In sickle cell anemia, low oxygen levels cause hemiglobin to polymerize and the overall reduction in the hemiglobin volume fraction doesn't change that much, the fibers are enough to completely deform the cell.

Our muscles already have quite a bit of myoglobin-like proteins.  You could up the amounta bit but you'd gain at most a few dozen seconds of oxygen carrying capacity.

The big drawback of hemiglobin is that it doesn't carry much oxygen.  Basically, youe got this big protein with a molecular mass of tens of thousands of AMUs and it carrys one O2 molecule.  If one could manufacture an artificial small molecule analogue of hemiglobin such as a modified heme poryphrin, you could theoretically expect something like a 10-fold increase in O2 carrying capacity.

Regarding makinga human vacuum survivable, those aren't bad suggestions.  However, the biggest stumbling block is the whole lack of oxygen bit.  Replacing hemiglobin withother variants, public preceptions aside, doesn't help.  It really bugs me when popular science articles talk about how whale myoglobin would allow ahuman to hold their breath for an hour, this is patently false.  Myoglobin holds exactly the same amount of oxygen as hemiglobin does - it just holds onto it tighter.  Our blood already carries about as much hemiglobin as it can so there's not much room for improvement.

One approach would be to have a sphincter that could seal off the lungs from vacuum and have some sort of surgically implanted shunt that hooked the circulatory system up to a compressed oxygen source.

A more legant but much more difficult solution would be to get rid of the need for oxygen at all.  Oxygen basically acts as an electron acceptor in the body's energy generation process.  If you have some way of wiring your mitochondria up to wires, you could dispense with O2 completely.  In that case, your human would be electrically powered.  The power requiremetns are fairly low as a human runs off the equivalent of about 100 watts of power.

Railguns are NOT easy to build.  The current densities involved make it basically impossible to launch any sizable mass at escape velocity.  Instead of trying to get all of the delta v from a high speed launch, it's much more feasible to use a cannon or railgun to get started with a km/sec or two of speed and then use small rocket boosters to get the rest of your velocity.  It's only practical for small payloads but if you want to be able to get raw materials into orbit, it's nota bad method.

True, LCD's are pretty common and cheap but they are really pretty exotic things.  I once saw a lecture about the invention of LCDs back in the 80's and it waas NOT simple.  Basically, you're setting up a semi-crystalline array of organic molecules that are charged and optically active.  When you apply a net electtrical charge to them, they all rotate and change the orientation of the light polarization through them and this causes the display to go light or dark depending on the liquid crystal orientation with respect to the polarizers next to it.

Sometimes familiarity makes us forget how amazing and exotic everyday items are.  For example your computer is basically a fleck of sand that's ramming millions of electrical charges around at billions of cycles a second ata power density greater than a kitchen electric rangetop.  THAT'S exotic, IMO. 

Or consider a tree, it's a nanotech device that's capable of creating more of itself from air, water and trace minerals from the ground.  Furthermore, it's capable of creating mobile copies of itself that are fully capable of replicating it from scratch.  It harnesses sunlight with a cascading quantum mechanical energy transfer antenna device, pulls water up with a microstructured capilllary water transfer mechanism and uses nanostructured sugar reconstituted into molecularly aligned fibers to provide structural support.

Compared to that, stuff like sapphires and diamonds are downright boring and plain! 

By that  figuring, you'd have to be about 10 million miles away from the magnetar to worry about getting your cards wiped, still a pretty respectable figure.  Imagine the kinds of science experiments you could do if you could get near one of those...

Yeah, it's a bit confusing and even though I understand the reasoning, I'm still not comfortable with the concept.  Basically, we're floating in spacetime which is growing bigger. Two stationary objects will move further apart since more space has appeared between them.  Spacetime is allowed to do that sort of stuff at arbitrary speed.

10 to the minus 35 is basically 1 divided by 10 to the 35.  So 4.5*10^-34 = 1/4.5*10^34.

Interestingly, one of the latest issues of Science was devoted to plsars and neutron stars.  I was just reading an article about neutron star/black hole formation and its much more complex than I had realized.  Once I've had a chance to digest the article a bit, I'll post an update to my earlier postings on this thread.

A fairly common tactic to reduce engine bell heating is to run the fuel through small pipes in the bell.  I know this is done on the Shuttle main engines and most likely on the F-1's.  This also preheats the fuel before it enters the combustion chamber.

Actually, higher efficiency solar cells really don't help that much for making solar energy practical.  These triple junction cells will be terribly expensive, the manufacturing process is horribly difficult.  It will have an impact on space missions where much more energy will become available for space probes. 

On the ground, cost is far more important.  Current cheap solar cells are at about 15% efficiency.  Even if triple junction cells come down to that price, you've only gotten a 3-fold increase in the cost of power/$.  On the other hand, if you can reduce the cost of colar cells, even poor ones, you suddenly open up the power market for people to start implementing the things at a local level.  There's several companies currently working on low cost polymer/nanoparticle cells that could bring a 10-fold drop in solar cell cost.   

When the cost to put solar cells drops from $10,000 to $1000, I'll be happy to slap some onto the roof of my house.