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Comment Re:Thought Experiment (Score 1) 162

I was out walking today through a forest that was originally planted

Was it used for that purpose? The fact that it's still there suggests not.

I carefully used the word "originally" when I originally wrote that. Not because I expected your response, but it suffices.

You seem to be thinking that the trees I was walking amongst were the ones that were planted in the 1300s? No - they had been harvested one at a time, according to their individual shape and size and the lumber needed for a particular ship, from around 200 to 450 years after planting. In each gap left by each harvested tree, others were planted according to the needs of that century while continuing to serve the needs of centuries past. That century's trees were local use as the re-forestation efforts of the 14th century had relieved the military's shortages, and changed ship building techniques reduced the need for particular shapes of lumber. Without the drive of legislation, the new plantings were changed from oak to the more useful (locally) ash and elm. At least, that's what the owner's tax and payment records tell the historians. Those smaller trees were managed by "coppicing" (check your local forester's dialect for their word) with the trees in a continuous state of replenishment from then until the woodland fell out of use in the early 1900s. (There are a few dozen larger uncoppiced trees ; no one knows why they were treated differently. But they change the ecology of the forest considerably.)

Most (not all, "most") coppiced broadleaved forests in the country were grubbed out and replaced with imported conifer species for clear-felling on a 1-2 century cycle during the last century, particularly in the immediate aftermath of the great pit-prop crisis of Word War 1. Which is precisely why this particular piece of woodland was saved from being grubbed out in the early 1970s (for arable, not forestry ; meh), to be used instead as a nature reserve. Then we had the nightmare of Dutch Elm Disease, which I grew up fighting to control in that wood, and which has now been replaced as a bogey-man by Ash Dieback. Fortunately, since we have a range of tree species in the wood, we can lose any one species without losing the woodland as a whole. That's judgement, not luck.

Forest management is a lot more complex than "see it, fell it, move on to the next mountain". Particularly if you don't have a next mountain to move on to.

Comment Re: Lots of children have the wrong DNA. (Score 1) 233

It seemes very reasonable to suggest that

any concept supported by claims as strong as "It seemes very reasonable to suggest that ..." is screaming out to be tested, because if there's one thing we know about people, it's that people are very good at fooling other people. That is why the professions of "confidence trickster" and "politician" exist.

Where I'd look for data would be cases where the volition of the (putative) parents isn't involved in selecting the children to be tested - when checking siblings (cousins, IIRC going further out isn't much better than random chance) as organ or particularly bone marrow donors for a victim.

Good luck getting your proposal to access such data past the ethics committee.

Comment Re:Sail Problems (Score 1) 162

In either case, the solar wind and the sun's gravity can alter the trajectory of the sails.

The influence of other star's gravity is calculable. (Unless there's something gravitating and dark out there.) The influence of interstellar winds ... is a fair question. So you send your first few probes off to see how they behave. It's not as if they'll contain anything you're more emotionaly attached to than some bits of wiring and (maybe) an AI.

The Oort cloud also requires consideration. If the sails are not punctured by the particles in the Oort cloud, impacts of those particles on the sails will decelerate them.

In the days before the first probes to Jupiter, exactly the same concerns were raised about going through the Asteroid Belt. We've not had a probe damaged out of - is it about a dozen that have gone through? We have every reason to expect the Oort Cloud to be more diffuse. In either case, suck it and see. Send probes out. Once you've built the lunching lasers (or while you're building them), the incremental cost of each launch is going to be pretty small.

If the sails are punctured, they will become useless in decelerating the sensors when the target star is approached.

They don't work like wind sails. Yes, you'd lose some efficiency. The triangle bounded by the three nearest shroud anchor points would limit the damage. A factor to include in your sail design, certainly. But not a show-stopper.

Comment Re:Quantum entanglement (Score 1) 162

we can send one every week

Well, not quite. You're constrained by the efficiency of your reflector, the maximum temperature your (electronics, mirror coatings, sail, shrouds, whatever is the most temperature-sensitive component of your actual vehicle design) can stand, and your launch laser. So you fire the laser until the probe has the velocity you can dispose of at the destination (which is what this paper is about), then leave it to fly. Re-point laser and launch again. You might not get one launched a week, but several a year is probably feasible. By the time they're flying past Eris, they're probably at cruising speed already.

Comment Re:Thought Experiment (Score 1) 162

The missions being envisioned here are for small robots that can be accelerated and decelerated with reasonably foreseeable technologies

No. The only forces being modelled for deceleration in the target systems are those of light pressure and gravity - which we can calculate from the light flux (observed at Earth), the range (parallax), and orbital mechanics.

Once someone has a design for a probe (mass, sail area, reflectivity) then the analysis can be re-done to calculate the travel times (and important things, like how much ahead of the proper motion of the target object you have to aim. to hit the target) with your actual device. This analysis compared travel times for otherwise identical probes dispatched to different targets, and an optimal course strategy for getting there quickest and slowing down to orbital speeds at the far end. There are a few other constraints (e.g., a maximum probe temperature of 100C / 373K, to allow plausible electronics to survive) which could be revisited with an actual "release to manufacturing" design, but this paper provides a road map for how to optimise the trajectory once you get to that point.

Comment Re:Thought Experiment (Score 2) 162

the time frame isn't useful, the data wouldn't be obtained in our lifetime, and then what?

Coincidentally, I was out walking today through a forest that was originally planted in the 1300s, in order to provide timber for the anticipated navy of the 1600s. Even though the people who planted the trees wouldn't see them grow to a usable size.

Lordy! - they must have been superhumans, those Mediaeval foresters. Able to think centuries ahead, where modern people just cannot do that any more.

Comment Re:Thought Experiment (Score 1) 162

we aren't going to travel between the stars until we figure out something a whole lot better than chemical rockets and probably FTL drive...

And just where did anyone involved with this make any suggestion that it involved any human - or even any mammal - ever reaching another star system? I as sure as hell didn't see that, and I did read the fucking paper.

It is a moot point (cue grammar Nazis who think that it's "mute") whether a VonNeumann robot with the pinnacle of 22nd century software counts as a human descendent. But that's potentially enough for "human-sourced machines" to distribute themselves across the galaxy before the Earth becomes uninhabitable. But that may not involve actual humans.

As for it being a planning optimisation study - well, yeah, it is. There are no designs for even getting any data back from this sort of mission. But for any mission that is powered from the Solar System by projected beams, the same considerations of travel time will apply, even if the actual mission takes 3 centuries rather than their theoretical 75+46 years.

Submission + - Light Sail propulsion could reach Sirius sooner than Alpha Centauri (arxiv.org)

RockDoctor writes: A recent proposition to launch probes to other star systems driven by lasers which remain in the Solar system has garnered considerable attention. But recently published work suggests that there are unexpected complexities to the system.

One would think that the closest star systems would be the easiest to reach. But unless you are content with a fly-by examination of the star system, with much reduced science returns, you will need to decelerate the probe at the far end, without any infrastructure to assist with the braking.

By combining both light-pressure braking and gravitational slingshots, a team of German, French and Chilean astronomers discover that the brightness of the destination star can significantly increase deceleration, and thus travel time (because higher flight velocities can be used. Sling-shotting around a companion star to lengthen deceleration times can help shed flight velocity to allow capture into a stable orbit.

The 4.37 light year distant binary stars Alpha Centauri A and B could be reached in 75 years from Earth. Covering the 0.24 light year distance to Proxima Centauri depends on arriving at the correct relative orientations of Alpha Centauri A and B in their mutual 80 year orbit for the sling shot to work. Without a companion star, Proxima Centauri can only absorb a final leg velocity of about 1280km/s, so that leg of the trip would take an additional 46 years.

Using the same performance characteristics for the light sail the corresponding duration for an approach to the Sirius system, almost twice as far away (8.58ly), is a mere 68.9 years, making it (and it's white dwarf companion) possibly a more attractive target.

Of course, none of this addresses the question of how to get any data from there to here. Or, indeed, how to manage a project that will last longer than a working lifetime. There are also issues of aiming — the motion of the Alpha Centauri system isn't well-enough known at the moment to achieve the precise manoeuvring needed without course corrections (and so, data transmission from there to here) en route.

Comment Re:In 1913 (Score 1) 240

There's a stream in the Scottish Highlands which has done this several times in recorded history (i.e., since the first maps were made of the area in sufficient detail, about 1830). I forget the Gaelic spelling of the originating name, but the anglicisation is "corrom," and the translation given is usually "balance", because the direction of travel of the stream in question flips from one side of the watershed (6 miles to the sea) to the other side (~30 miles to the sea) like a balance with equal weights on each pan.

Ah, there's the little bugger : "Allt a' Chothruim", the "stream of the balance" ; it's hard to see how to get from that name to the "popular" term, but that's Gaelic for you.

More recently the term "delta watershed" has replaced "corrom" - and the situation is fairly common, with a stream coming from a narrow mountain valley into wider one and building a delta (including steep ones, often termed "alluvial cones"), which happens to sit on a watershed in the larger valley. So, a relatively small change in the delta has a large consequence in the direction of water flow.

It's hardly a new phenomenon (I've seen at least one other example, in Scotland), but this sounds like a fine example.

Comment Re:Nothing to do with Hollywood (Score 1) 478

Any ratings from those addresses should just get an error message saying "this IP address has been the source of abuse and can no longer submit votes".

s/address/"range of addresses"/

And I'm sure you know that, so lets move on.

I was working in Turkey two years ago. If I were the sort to watch movies in my hotel room on my laptop (can Fedora play DVD movies yet? I've never been minded to find out, and don't have a DVD movie to find out), you would ban me from voting on the movie I've just watched? Obviously, yes.

It's hard to design such systems so that they're actually fair.

I just realised, I wasn't aware until that IMDB actually had a "star" or "ratings" system. Show how little interest I have in people's opinions, compared to things like plot summaries.

Comment Re:Not against dark matter (Score 1) 156

The experimental evidence comes from multiple independent sources spanning decades.

Not only independent sources - in the simple sense of "coming from many scientists or groups of scientists" - but also using multiple different distinct techniques from fundamental geometry on different scales (which is behind Doppler measurements of velocities) to sophisticated radiometry leading to the maps of the CMB temperature variations. The data is far wider than just having many different groups using similar techniques.

Comment Re: Not exactly direct evidence (Score 1) 156

No, that's movement of the galaxies within the universe, not expansion of the universe.

An analogy : you're in bed, and the wife rolls over and pulls the duvet off you. This is movement of the duvet within the existing place. Ripping the wall off, building walls and a new piece of roof to extend the bedroom is expanding the space within which your duvet can move, but doesn't make the duvet itself change size.

Comment Re:Fake news (Score 1) 281

Well, Britain did th same a couple of years ago, disbanding the Police's Forensic Science Service and farming it out to private companies - with the predicted loss of evidence, mis-handling of evidence, lost cases and miscarriages of justice (in both directions).

So, once again America follows a furrow already ploughed open by Britain's Incompetents-in-Chief.

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