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Comment Re:Or just make the diesels hybrids (Score 1) 141

And even the best public transport system generally isnt going to start and stop *exactly* where you need it, so there still is going to be *some* walking. Which some people with disabilities or health problems simply can't manage. And to achieve a good public transport system - with frequent stops, densely placed stops, relatively direct routes and affordable prices - is entirely dependent on population density far more than it is on "will". In places with high density, it's a relatively straightforward process to have a good public transport system. In places with moderate to low density, it can be difficult to nearly impossible. And weaknesses in public transport system are a viscious cycle: the less frequent the stops, the further spaced out they are, the longer the transit times, and the more expensive the rides - the fewer people will ride them. The fewer that ride the less frequent you have to have the stops, the further apart they need to be, the less direct the routes, and the less affordable the prices.

Comment Re:Cost of access is key. (Score 1) 325

That was not my point. Ofc we can improve ISP. No idea how much that improves either 'performance' or drops price.

It improves performance a *lot*. As for price, it depends on how expensive that rocket system is. For first stages, an improvement in ISP's effect on the size of the rocket isn't that much greater than linear. But the further up the delta-V chain the engine is used, the more of an impact it has on everything that was used to get it there. An extra hundred sec ISP on a first stage might reduce the system mass by a third; on a second stage up to LEO, maybe cut it in half; on a kick stage for a Mars transfer orbit, maybe cut it by two thirds. On an ascent stage from the surface of Mars... well you get the idea. Shrinking down a rocket to a small fraction of its size - fuel, tankage, and engines - well, that's really significant. ISP is very, very important for upper stages. So you can afford to pay quite a bit for those top stages if it improves their performance. Just not an "unlimited" amount.

There is no way a high tech electrical engine will improve its performance by 10% regardless how much money or time you put into it: the efficiency is already between 98.5% - 99.5%, up to 99.9% in some cases.

This is getting a bit offtopic, but at least the electric engines in EVs don't usually run at nearly that high. Depending on the type they might average 85 to 94% on average. It varies over their load cycle.

Regarding rockets: there is simply not much margin anymore in changing the form of the exhaust tube, burn chamber etc

Actually you can. The general principles of how rocket engines work are fixed, of course - your exhaust will never exceed its local speed of sound in the throat, and then you want to expand it as close to ambient pressure as you want. But the details vary greatly. There's bell nozzles, linear nozzles, annular nozzles, aerospikes, throatless nozzles, atmospheric wake compression, and on and on. There's tons of different ways - developed, in development, and in theory - to pump and inject your propellants - where they need to be pumped at all. Even many propellants that are traditionally thought of as being in one state can be implemented in other states. There's various ways - developed, in development, and in theory - to prevent nozzle erosion. To improve regeneration. To reduce mass. And on and on and on. Rocket combustion is a rather complex thing and we're still trying to get a handle on it. Do you know that we still really don't know how aluminum burns in solid rocket propellant? There's something like five different competing theories. I mean, things like this are a Big Freaking Deal(TM), especially when such small improvements in upper stage ISP have such significance for lower stage mass. And even on your lower stages there's a lot of things that have a big effect on your system cost. For example, how to stop resonant shocks from ripping them up - a lot of people don't realize that one of the main benefits of adding aluminum first stage to propellant mixes is that the droplets of burning aluminum damp shocks. (yeah, it increases ISP too by raising the exhaust temperature, but it also has disadvantages, such as not contributing to expansion, slowing down gases (particularly near the nozzle), and impacting/eroding the throat (or even forming an accumulating slag)

Re, nuclear+chemical. There are proposals for this. The main issue isn't efficiency - the extra chemical energy doesn't make that much of a difference - but thrust. The downside to nuclear thermal is that the reactor is so heavy (fission is like that, unfortunately) that the mass ratio is only something like 3-4:1. That's really bad (you generally get 15-20:1 or even better for a chemical first stage). So the approach is to inject oxygen early in the ascent phase for added thrust, but only run on hydrogen higher up when gravity losses are lower. I'm really not that sanguine about nuclear thermal rockets getting a serious development program any time soon, though. The public overestimates the risk, of course - not only am I sure they'd well seal the fuel elements against whatever damage would be incurred by explosion or reentry, but there's the simple fact that the fuel is "fresh", not contaminated with the more hazardous actinides. But it's going to be a hard sell. And a really hard development project, if they ever did try again. Gigawatt-scale flying nuclear reactors that pose radiation hazards during assembly and test aren't exactly childs' play.

Comment Re:The guy aint no Sagan... (Score 1) 325

You forgot to exclude operational expenses.

Yes, people to run robots and comm time on the DSN. We're not talking about massive expenses here. The real expenses are the capital costs.

And also didn't mention that you can't just lob chunks of metal straight to Earth's surface,

Actually, you really just can. Even random rocks from space - not shaped for optimal entry shape, not cemented together by anything yet what nature chose to gie them - do this all the time. They have to be between a certain size range (too little and the whole thing ablates; too large and it explodes, either in the atmosphere or on impact), but the random creations of nature do it; delberately shaped and sintered projectiles should have no trouble with it, with (proportional to their mass) relatively little burnoff.

You would, of course, need a rather large area designated as the impact area; even with very precise aiming, by the time they get to Earth and undergo reentry the random variables will spread them out over a sizeable chunk of land. A large salar might be ideal, since they get resurfaced periodically so the impacts wouldn't be damaging the landscape.

By your same logic, the mining of minerals on Earth would be zero dollars per gram if the equipment was solar powered and automated

It's almost as if I didn't discuss capital and ongoing costs in my above post.

Launch costs really are key to the rate of development at the very least, in that they limit the rate in which funding can be raised for the necessary exploratory and test craft to be launched. Even if the economics for operating a mine on a NEO works out really well at present launch costs, you have to prove that you can do it before you can raise the billions to build it. And to prove that you can do it you have to launch a number of missions while you're still relatively poorly funded. They face the same problem that Bigelow has faced - a probably reasonable business plan but the early phases hinging around factors that they don't control.

It does nobody any good to pretend that the lack of a space economy is because investors are cowards and morons

I think you need to go back and read my last post again, particularly all of the "it's too early to say"/""we don't know"/"but time will tell"/etc lines. I'm not saying that at all. I'm saying that there very well could be a compelling case for asteroid mining even without any radical changes in space technologies. But there's a great deal of work to prove that before we can get to that point.

Comment Re:Less service? (Score 1) 447

Mine tend to last under 20k miles, and I seem to need new discs every 30-40k.

Yikes. I replaced one of the rotors on the truck when I did the brakes, but that was mostly because it was faster and more convenient for me to replace the rotor than to take it someplace and have it resurfaced. The other three were fine.

What kind of pads do you have? My truck came with semi-metallics and I replaced them with the same, but a lot of cars come with cheap organic pads that don't last very long.

Comment Re:I've never found it quick or easy to buy any ca (Score 1) 447

It took me nearly screaming at him to tear everything up before he would give in inch. Still pissed at myself for giving in to the "mandatory" processing fee and agreeing to 19.2K.

No need to scream. Just say, "the agreement was 19K out the door. Not a penny more.", and walk the moment they refuse to honor that. For bonus points (and because I'm a horrible human being), tell the closer that it makes you smile thinking about him explaining to the sales manager how he let you get away that late in the deal.

Comment Re:Someday electric cars may be the norm (Score 1) 447

The one thing limiting the transition to plug in electric cars is the infrastructure of charging stations or battery exchange locations allowing long distance travel.

And charging time. Unless you've got a Tesla, you're going to be waiting a few hours to recharge your car. Even if you *do* have a Tesla, it's still far longer to charge than it is to fill up a gas tank.

Comment Re:Better Question (Score 1) 447

These companies don't publish sales numbers but I'm willing to bet he's taken at least 1/4 of their business by how quickly they are trying to respond to a market they all said was pointless two years ago

Yes, the companies do publish sales numbers. You just have to know where to look.

According to Elon Musk, Tesla sold a little over 33,000 cars by the end of Q3 this year. Cadillac sells more than that in less than two months. Lexus and Mercedes are at 249,956 and 249,890 respectively for the year through Q3.

1/4 of their business? Hardly.

"I've seen the forgeries I've sent out." -- John F. Haugh II (jfh@rpp386.Dallas.TX.US), about forging net news articles