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Comment Re:Obligatory reading (Score 4, Informative) 419

the 24,000 [year] half life

TFA refers to Pu238, which is quite active. It has a half life of about 88 years. It is an energetic alpha emitter, which is not dangerous outside the body because the skin absorbs the emission and you can wash Pu238 off pretty easily. However, once it's inside you, virtually all of the alpha emissions will be absorbed by your body unless/until you can excrete it. A good fraction of any amount ingested will eventually emit energetic radiation that you will absorb. A disaster could be bad.

Having said all that, including Pu238 in a spacecraft is a problem we have solved before, so it's not all that crazy.

Comment Re:I was wondering the same thing... (Score 1) 461

The appliance-type cookers can have a glass lid, and the pot-on-the-stove versions (always?) have a metal lid. I think that the appliance-type ones have all the pressure release valves and knobs in the pot rather than the lid which puts a glass top in play. I'm not sure about that because I've never owned an appliance-type cooker. They aren't as versatile because you can't quickly depressurize by using cold water on the lid or base.

Comment Re:Go nuclear (Score 1) 91

Including water, a SLOWPOKE reactor weighs on the order of 100 tonnes. If you could harvest water on Mars, you could probably land one on the surface with existing vehicles.

Even with water, it could be in play to get that reactor to low earth orbit in one launch and later attach a transfer vehicle in orbit. That reactor is in the ~1 MWe range.

Comment Re:Legally questionable, doomed to fail! (Score 4, Insightful) 427

Ultimately, this is an example of government not charging a high enough fee for use of a common public resource. There are lots of examples of this. Usually governments do this in order to provide the resource equally to all people, which is a noble and understandable goal. The downside risk is a tragedy of the commons, where common resources are used to depletion because there is no signal to the users that they are causing harm by depleting it.

In our economic system, we use price as a scarcity signal for buyers and sellers. Price is a ham-fisted signal that is only marginally better than rationing but without using it at all, or by using it poorly, government has opened the door for a private company to create a market in something valuable - parking turnover. Should this application take off (a big "if") government's only practical response is to raise the price of parking to the point that turnover is so high that you can usually find a parking spot quickly without paying somebody to leave. That will be a really high price which will obliterate the goal of providing access to parking for people regardless of their economic situation.

Comment Re:Still need atmospheric pressure to syphon (Score 1) 360

You are completely incorrect. The liquid may need vapour pressure to remain a liquid, but a siphon manifestly does not require any pressure to run. All you need is a full U-shaped tube and a downward force. Gravity is convenient. The U-shaped tube is often filled by using atmospheric pressure to start the siphon, but this is not a necessary condition. The way the tube gets filled in the first place has no impact on the steady state operation of the siphon.

Comment Re:Nope. People will deny that they are robots. (Score 1) 246

Well, I'll admit that the train is, in fact, in communication with a central server that controls the trains. I guess that makes them remote-controlled. I'll even admit that humans monitor the performance of the train system. However, humans only drive the trains in exceptional circumstances. I've seen it happen a few times, and you can watch up close because there is no enclosed space or seat for the driver. They just unlock the cabinet that's in the passenger compartment and tell the control center that they're taking over using their handheld radio. This is what it looks like.

As it happens, I toured the control center with my son's cub pack (younger than scouts). I asked if they employed more or fewer monitors/controllers than a system with human-driven trains. They said they had about the same number. There were less than 10 people in the control center, including supervisors and the tour guide with a few to several dozen trains running at any one time on two lines.

During the last transit strike, the trains kept running with a normal schedule. Driverless. Really, truly. Nobody there. Crickets.

You could say that the entire system is a robot (rather than each individual train), but I don't think these trains are drones under any meaningful definition. They are not driven by people. They are autonomous machines monitored by people, and the monitoring is about as rigorous as for the New York Subway.

Comment Re:waste of helium. (Score 1) 92

...even if wastefully vented just stays in the atmosphere where it can be recovered by other means.

Nope. Helium and hydrogen get fast enough at altitude to achieve escape velocity. Due to atmospheric escape, the concentration of helium in the atmosphere is relatively constant at about 5 ppm. That is a ridiculously low concentration. It is absolutely not economic to extract helium from the atmosphere. Liquid helium is less expensive than scotch, and you wouldn't try to extract a cask after it was poured into a swimming pool.

The trouble with a lot of self-made men is that they worship their creator.