Hearing about lasers and raindrops puts me in mind of this recent XKCD What-If posting.

how is this ion engine more efficient than just squirting a small amount of pressurized gas out of the tank instead

It has to do with how quickly you can throw the propellant - how much momentum you can impart to it, which in return imparts a certain change in momentum to the rest of the satellite (delta-v). With conventional satellite propulsion, like fuel+oxidizer rockets or monopropellant thrusters, the energy available to impart that momentum is chemically based. That is, the propellants undergo a chemical reaction, get hot and/or change phase into a gas, and nozzles force that gas to exit at some velocity. Details vary with engine and nozzle design, but there are limits on how much thrust you can get each fuel type. Mass in, reaction energy, mass*velocity (momentum) out. Rocket designers measure this "efficiency" with a quantity called specific impulse (measured in units of seconds) For a given mass of fuel, you can pretty quickly calculate what the total delta-v the satellite has available to it.

Ion engines can impart much higher velocities to the "fuel" than chemical rockets, in part because they are using electrical energy (of which there is an arbitrarily large supply) rather than whatever you can get from chemical reactions. Again, the details vary based on the design, but ion engines tend to have specific impulses much higher than chemical rockets. The actual thrust (i.e., total force) from an ion engine tends to be miniscule, but is provided very efficiently, and can be produced for days or weeks at a time.

Google has been working on that, it's called Flu Trends. But it hasn't really proven itself out yet. See my post below.

Google tried (is still trying?) to track the spread of influenza, by watching the trends in searches for information about the disease. It's a very interesting bit of work, but as I recall, failed to be meaningfully predictive. The trouble is, there are lots of prosaic reasons why someone might search out information about the flu (or any other disease) other than actually having it. Separating that noise (general interest in the flu) from the genuine signal (particular interest from people who are infected). Doesn't mean it can't work, just that it hasn't been made to work yet.

well played.

proper Stirling engines or steam turbines are not popular in space for some reason

R&D on a nuclear-powered stirling engine for space is ongoing. It's not they they aren't popular, per se, its just that they are a very difficult engineering problem. How many devices with continuously moving parts do you know that operate maintenance-free for years or decades? It's not impossible, but is really hard.

As others have mentioned: RTGs are difficult to come by ($$$, rationed resource) compared to solar panels. Generally, they only get used when there is no other way to power the spacecraft to meet the science objectives.

The present RTG designs for spacecraft are all 1-2 orders of magnitude larger than what Philae would need.

One other thing I would note is that RTGs have useful lifespans measured in years to decades. Philae hasn't been designed to operate for that long (its long sleep until it arrived notwithstanding). What is more, even if it has electrical power (solar, nuke, or otherwise) to operate indefinitely, it will be cooked by the Sun around the time of the comet's closest approach. So an RTG would vastly outlive the useful lifespan on Philae. Given that RTG material is scarce, this would be a wasteful use.

reminds me of a similar situation that came up in an introductory CS course at Dartmouth years ago. A bunch of students, possibly abetted by the TAs, ended up with the exact same code for some problem or other. The professor (a visiting professor, if that makes any difference) went ballistic and reported every student, intent on getting all of them suspended or expelled.

In the end, the charges were dropped. It would have been a very difficult situation to adjudicate - the behavior of the students, TAs, and professor was bad all around, and some might say that it all cancelled out. Some definitely were cheating (i.e., malicious intent), and others just got caught up in stupid behavior (i.e., ignorant), and it would have been difficult to separate the two.

The usage of "United States of America" as either singular or plural has shifted over the years. The guidelines you provide are good for the general case of collected objects, but "USA" seems to be a particular case that (sometimes, maybe, mostly) breaks the rule.

"That's not a knife. This is a knife."

Well played, but wrong continent entirely.

I realize this is heresy, but even though I've been working with PCs on a daily basis for THIRTY YEARS, not everything needs to be computerized.

The advantage of introducing computers into the voting process is in making the ballot preparation easier, more flexible, and more accessible. Want the same ballot and instructions in 10 different languages? It is expensive to generate the different paper versions, and impossible to estimate how many of which type you'll need. But it is trivial with a computer. Want a "spoken" ballot for the blind? Done. Want a ballot with 200-point font? You're limited only by the computer screen size. Want to include nice big pictures, along with party-affiliation graphics, for the illiterate? Pretty cheap to do on a computer. For 80% of the population, you can still utilize hand-filled paper ballots, which will be faster and cheaper in most cases, but having machines makes it easier for the other 20% to exercise their right.

But I agree with the earlier posts - use the technology only for generating the ballot. The actual piece of paper is what is important. If you want to add mechanized/computerized tallying of the ballots (i.e., optical scanning or barcoding) to make things easier in the 90% of races where a 2% counting error doesn't matter, fine. But keep those paper ballots and do randomized, hand-counted auditing, and have thresholds that trigger automatic hand counts in close cases.

because i doubt the universe cares much about the data we generate....

Oh, I don't know. Eventually we'll have so many hard drives dedicated to it that it'll collapse into a black hole.

Or - wait for it - the computing power requirements scale so large that the only way to keep the whole enterprise going is to build a Dyson sphere.

Maybe the universe won't care even then, but we'll at least come closer to leaving our mark!

People go into business to make money. If they can do it providing a bullshit product that's fucking useless to government for huge skips full of cash, they will.

Is that what gets you out of bed each morning, or do you have a shred of professional dignity? Sure, there are people who will do the minimum possible for that payday, but there actually are people who give a damn whether they do their job well or not, and care about what happens after the next payday.

What do they care

Probably these guys didn't get into this industry just to waste money. I would imagine that most of the people actually working on this are 1) motivated by the potential profits of mastering and proliferating this technology and/or 2) have a genuine desire to develop more sustainable energy sources and/or 3) masochistic engineers that love a good challenge. All three classes of people would be disappointed with failure, and really jazzed with success. I think that they care about succeeding greatly.

Daily tides here reach 11 miles per hour, and can go as high as 18....

Well, damn! And here I thought going to 11 was really something.