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Comment Re:Things that I wish wouldn't keep getting repeat (Score 3, Interesting) 141

It takes billions (not millions) of years for hydrogen atoms to fuse in the sun - that is precisely why the sun has a billions-of-years lifetime. So in building a fusion reactor, we need many orders of magnitude higher reaction rates, and to achieve them at many orders of magnitude lower densities. One way of doing this is to have much higher temperatures. The solar core temperature is about 15 million degrees and TFA has 50 million degrees for this new result, and 80 million degrees for half a second at a European reactor. This sounds unimpressive, but the reaction rates are very sensitive to temperature - proportional to about T^8 as I recall, but I didn't quickly find an online reference for this. 75 million degrees would therefore give a boost of about 5^8 which is about 400,000.

In the sun, the first reaction in the chain (proton+proton->deuterium) is the rate limiting step. In a reactor, we can provide deuterium enriched fuel and bypass this step. I don't know what the reaction rates are, but I suspect that this will be a greater benefit that the higher temperatures. You can do even better with tritium in the fuel, but your reactor becomes an intense neutron source, leading to induced radioactivity in nearby materials. Some proposed designs use these neutrons to breed more tritium from a lithium blanket around the reactor. (Once I get beyond the proton-proton chain reaction, I'm just relying on pop-science knowledge, so corrections from the more knowledgeable are welcome.)

Stars a bit more massive than the sun burn hydrogen via the CNO cycle, which has even higher temperature dependence (from memory, about T^17). I've never heard of anyone suggesting using the CNO cycle in a fusion reactor - presumably there are good reasons, but I don't know what they are. One problem is you need to wait for radioactive decays, but these have half-lives on the order of 1 to 2 minutes, and a commercial reactor would be running for much longer than that.

Comment /. Poll opportunity (Score 2) 91

Poll 1: Which nation/organization do you think will be next to land people on the moon?
* China (CNSA)
* Japan (JAXA)
* Europe (ESA)
* India (ISRO)
* Russia (RFSA)
* North Korea (KCST)
* Privately funded (e.g. SpaceX, Blue Origin or Cowboy Neal without direct state support) (ETLA)

Poll 2: Which nation/organization do you want be next to land people on the moon?
(same options)

Comment Secondary sources (Score 1) 1829

NASA discovers little green men on the moon. NASA makes a 2 page press release. Bob writes a blog post where he condenses the NASA press release to 1 page, mostly by deleting every second paragraph. (Alternatively it could be a Javascript and advertising heavy commercial news site.) Slashdot posts an article linking to Bob's blog, rather than linking directly to NASA as they should. One of the first comments provides the direct link (with title something like "This is the link you should be using") and instantaneously gets modded to +5, in reward for having done what the Slashdot editor should have done.

I'm not saying never use secondary sources - sometimes Bob has summarized 50 pages to 1 page (and done a good job of it), or added some insightful commentary. Just don't use secondary sources unless they add significant value, and always include a link to the primary source in the summary.

Comment Re:Staged chute deployment - how's that work? (Score 1) 91


It sounds like this system relies critically on the coefficient of friction between the slider grommets and the risers. Too high, and the slider never (or incompletely) slides and the chute does not fully inflate. Too low, and it inflates too fast and soon, bruising or breaking the parachutist or, worse, ripping the chute.

From the abruptness of the transition between slightly inflated and fully inflated in the space capsule chutes, and the prolonged delay before this occurs, I suspect the friction method you describe is not used. However a slider with some other release mechanism seems likely.

Comment Staged chute deployment - how's that work? (Score 3, Interesting) 91

There is a thing that these chutes do, where on initial deployment the open aperture of the chute is quite small, and the chute looks rather like a sausage. Then later on, the chute abruptly opens fully, and looks like a hemisphere. (The transition wasn't shown in the video in TFA, but I've seen it elsewhere and it is also simulated in Kerbal Space Program.)

How is this achieved? Is it some clever aerodynamics where the chute has two stable configurations and a 'catastrophic' transition? Is there some rope which constrains the aperture early on and then is somehow severed to allow fully deployment?

(I understand why - the first configuration slows the payload sufficiently so that the chute is not torn apart when it fully deploys. "How" is what I don't know.)

Comment Re:anecdotal or statistical (Score 1) 507

However, statistical evidence is just an aggregation of anecdotal evidence.

No, sorry, completely wrong.

Statistical data comes from a well defined sample which is designed to be representative of an entire population. Anecdotes have no well defined selection criteria (my grandmother smoked until she was 100, and because I don't want to believe smoking is harmful, I remember and put great importance on this, and forget all the other people I have a connection to who were damaged by smoking) or (often where the selection criterion is 'stuff that happened to me') too little data to draw a conclusion (I've never crashed while driving drunk, so it must be safe.)

"I remember really hot days 10 years ago, hotter than now" holds very little weight. It is your experience (perhaps for every person like you there are 100 with the opposite experience), it is subject to biases of memory, and you've chosen the example retroactively to support a given position. The statistical data is thousands of thermometers measuring temperatures every hour over decades.

Comment Re:It's really too soon for this post. (Score 1) 118

You can't sail a drilling platform up to a wharf to unload the rocket, like you can a barge (so your idea would require an extra transfer at sea from platform to barge), nor is it so easy to move around the landing spot to match mission requirements. Having said all that, if barge landings turn out to be sufficiently haphazard, your idea may be economical.

Comment Re:Steam Boat Willy (Score 1) 70

People could animate Hamlet with a certain mouse as the protagonist (so long as it looks like 1930s Willy not 21st century Mickey.) They could distribute the Steam Boat Willy cartoon modified so that the mouse protagonist is naked and has oversized genitalia - just so long as they never call the mouse protagonist "Mickey". I think these are the sorts of possibilities that give Disney executives sleepless nights.

Comment Missed another (Score 1) 70

Historians write a (very dubious) history book. Novelist writes a novel in which this dubious history is true. Historians sue. Historians lose.

My analysis: You can't copyright facts. If you present something as a fact (such as in a history book), you lose any copyright over that "fact" (but not over your presentation of it.) Otherwise if you wrote a SF story involving Hawking radiation then Hawking could sue you.

Comment Access to original (Score 3, Interesting) 70

This raises an interesting issue:
If I edit Anne Frank's diary, I have copyright on the edited version. If I carefully set things up and take a high quality photo of the Mona Lisa, I have copyright over that photo. If a monkey takes a selfie with my camera and then I do a bunch of post-processing to "improve" it and publish the improved picture, I have copyright due to the improvements.

In each case, somebody else could read the diaries and publish their own edition, take their own photo of the Mona Lisa, or freely distribute the original unimproved monkey selfie - but only if they have access to the diaries (or facsimile), to the Mona Lisa without plate glass in the way, or the unimproved selfie. When access to the original is restricted, reproductions can effectively exert copyright over the original when the original is out of copyright. (The monkey selfie camera owner missed this trick.)

Comment Re:There was no before (Score 1) 225

I've thought for some time that we should have video games for this. Make a game in which the speed of light is (e.g.) 30m/s and make it relativistically correct. (I've seen a simple version: run around a village collecting tokens, the more you collect the slower the speed of light.) Make a game in which quantum effects happen on a macroscopic scale. (I'm not sure how this one would work.) If you can figure out how to make 4D space into a game, I'll be impressed.

In any case, the hope is that with many childhood hours of playing such games, relativistic and quantum effects will become intuitive, and therefore as easy to learn as Newtonian mechanics.

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