Not sarcastic. Hmm. I probably read that a long time ago, but I don't remember a thing about it. It's certainly not a new idea. Others have suggested having a big rock in front, but water seems like a better solution IMHO.

So a Thorium-based molten salt reactor fuel cycle, whose power levels can easily be throttled up and down (or even off), providing a few (hundred, thousand?) megawatts ... :) Or someday fusion or antimatter ...

Thorium is nice because it's only minimally radioactive, can be stored in huge piles without getting 'hot', and won't sustain a reaction without encouragement - hence throttling ability.

I think a ship with a multi-megawatt Thorium reactor could carry enough fuel to run for 100 years pretty easily.

Well, it took 20 to 30 years (depending on POV) before Unix became the accepted OS. :) I can't think of one right now, but there have been many scientific theories and experimentally proven technologies that didn't get any love for decades. I'm not sure how difficult it would be to build one of these experiments, but they don't look that difficult from the tiny pictures I've seen. So I suspect that there are several folks right now trying to build a higher power version in their garages, and planning to pump a lot more power into the rig to see what happens. The maker types are less interested in getting the official scientific stamp of approval than in making something 'go'. So I'm optimistically awaiting the first hobbyist version that is hooked up to some supercapacitors and gets a megawatt jammed through it. Maybe it'll blow up, maybe it'll work, maybe it'll do nothing.

I know, I'm just hoping. :)

Yes, IMHO that's a definite problem. It's very much like standing at the business end of a particle accelerator. As one approaches C that very thin interstellar gas is becoming much more like a bunch of cosmic rays. In the Great SF Novel that I think about writing, I figure I'll put a few hundred feet of water ice at the front end of the ship to absorb those. I'm not sure about 0.71c though - it's certainly better but I'm not sure how much better. One of the unknowns is how many actual rocks are out there as well ... is 100 feet of ice enough?

"Dear Valve: Please go to http://ka.je/ to see a solution to your authentication problem. The Kaje Picture Password SAAS removes all passwords from your website, eliminates transmission of passwords across the net - they are converted to an encrypted hash in the browser - and prevents phishing attacks. The Kaje SAAS never knows anything about the user, so there is no way (short of hacking two different operating systems run by two different companies on completely separate networks, at least one of which is designed to prevent even a hack from being useful) for a black hat to get the user's info and password or other Proof of Knowledge. Kaje has built-in features to prevent keyboard and mouse snooping as well, and the vendor works diligently to know nothing about the user. There is no more private and secure method for user authentication or step-up authorization. And since the user uploads his/her own test challenge (picture or other), it acts automatically as two-factor authentication - much better than that "site key" that some banks are using, while being easier to remember."

Proofs of Knowledge include picture passwords, text passwords, cognitive self-tests, Captcha's and a bunch of others. NB - I work for the company. The founder is also the inventor of Self Encrypting Drives and has several patents related to online security.

A friend of mine points out that the only thing preventing us from colonizing the stars is the ability to generate 1G acceleration for a year, and do the same at the other end.

In one year at 1G a vehicle can be traveling at about 0.71c, which is an optimal speed for getting there quickly while minimizing the effect of time dilation - the traveler will only age about one less year in 16 vs. the observer.

From very long ago, I recall a similar calculation based on solar sails. IIRC if you can get 0.01G (= 0.1 m/s/s), you can achieve a significant fraction of C by the time you have gotten to the Oort Cloud. Quicky Wolfram Alpha : 3154 km/s or 7 million miles/hour. At 0.1G, that would be 31,540 km/sec = about 0.1c.

Ahem ... that would be an _ostensible_ propulsion device, the working principle for which is (according to mainstream physicists) poorly described and violates commonly accepted physical principles. OTOH, I hope it works. I'll believe it when they cram a couple of megawatts in, and get it to lift its own weight - or better, 100 times its own weight.

I note that the Dr. Tajmar, the researcher whose name is on the paper, is still using terms like "... if true ...". This is not yet a tried-and-true propulsion device. The articles I saw just now did not show actual numbers, but the NASA experiment used such low power that the apparent thrust was well below several of the potentially confounding effects; i.e. the noise was much higher than the signal. It may still turn out to be the result of some experimental error, an unexpected issue with the apparatus, etc. Again though, one hopes. :)

I suppose more like 50 people all pissing at once, starting such that the water arrives at the ground before the expected time of arrival and continuing past that time.

By way of evidence (in addition to the facts from Viet Nam), long ago when I was young and foolish, some other young'uns and I were staying on the 12th floor of a hotel in NYC during a field trip. We started playing around with water in the wastebasket, and after a few tries were able to dump a bucket full of water out the window so that by the time it fell 12 floors, someone walking by got dosed. We had to drop the water when they had just stepped onto the curb from the street. They walked about 1/2 block during the drop. We nailed a couple of unfortunate sailors, and immediately closed the window and played dumb.

I've read that in practice, the weight of a bicycle in use doesn't vary - the lighter the frame & hardware, the heavier the lock required! :)

The price of carbon fiber has been a major factor, along with the difficulty of using it in manufacturing. Both of those have improved by orders of magnitude, and if one company I'm familiar with succeeds, they'll cut the cost of the fiber by another factor of 10 while greatly improving the quality. These incremental advances are truly changing the equations for many of the things you're pointing out.

As someone peripherally involved in "New Space", I'll say that the advances in technology really are making some of those fanciful ideas possible, even economically feasible. People right now are putting their money into those new ventures, and they're not doing it for entertainment but because the numbers pan out at least as well as many of the dotcom ventures. SpaceX has cut the cost of launch by 50% just by using well-tried industrial cost management methods - faced with exorbitant pricing for turbine pumps, the company built their own at 1/10 the cost. If the reusable first stage pans out, that will cut the cost by about another 1/2 (they think it will be better than that, but I think their long term costs will be higher as they transition their systems to support the more rigorous requirements of manned launches - that will affect all of their systems, even the unmanned launch ones.)

Another example, 3D printing has already proven itself with multiple different entities successfully printing components and even entire rocket engines, with costs and production times reduced by 90%.

Bottom line - much of the extremely high cost of space has been the government-run cost-plus market structure and extremely careful engineering practices. In fairness, I think this was necessary for the early days, but now we can move past that and into a more market-driven economic model with fixed prices on off-the-shelf products. Consider that development costs on a rocket engine are going to be on the order of a billion dollars, regardless of whether 10 or 10,000 of that engine are produced; but if 10,000 are built the amortized cost is $100,000 vs. $100,000,000 per engine.

If reusability pans out, the fuel cost of a launch is less than $500,000.

I learned a while back that the cost of an F-18 was more than 1/2 software. The plane had 1600 VME boards. (VME was a common instrumentation/computer bus, back in the 1970s and 1980s). All that fancy over-the-horizon radar, integrated electronics, head up displays, etc. takes a lot of computing power and software. I'm sure that is even more true for the newer planes.

On the Titanic, steerage pasengers paid IIRC $8, while the top tickets were $30,000. I think that's the equivalent of $1,000,000 or so today.

I read somewhere that flying NYC to LA on a corporate jet costs about $30,000 - not sure if that is total or per passenger. So that's something close to the cost target. If they can get you there in 1/2 the time, is it worth $60,000? These are the numbers they're probably working with. Note that Virgin Galactic has flights booked solid for seven years worth of flights at $200,000 each, and those flights are just up and down for entertainment.

The major US air carriers have definitely gotten out of their repeating-bankruptcy spiral and are registering record profits these days. Through mergers and other tactics, they have eliminated almost all of the low cost alternatives, and at nearly all major airports the majority of the gates and flights are 'owned' by one or two airlines, eliminating effective competition. Note that they raised prices when fuel prices went up, and kept them their afterwards, and added baggage fees, etc. - soon they will be charging extra for the right to breathe actual air, I'm sure.

I saw the SR-71 at the Abbottsford Air Show in British Columbia a long time ago. The plane took less than an hour from takeoff in San Francisco to arrival in BC. They did a 'slow' fly by, which was deafening. Then they did a faster fly by and went vertical into the low hanging clouds.