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SpaceX To Attempt Falcon 9 Landing On Autonomous Spaceport Drone Ship

drerwk Re:Someone doesn't understand basic relativity (80 comments)

Right, but the sentence you are make fun of is talking about stabilizing the rocket as it is coming back into the atmosphere, ass first in a no longer particularly aerodynamic configuration as it is missing the whole second stage and payload section. Flight stability in the nose going first direction is much better than in the engine going first direction. They are not complaining how hard it is to go that last 10m to the landing; I agree with you that stability control at that point is pretty easy. You know the first attempt they made for power re-entry failed because the axial rotation of the booster caused fuel starvation to the engine due to centrifigal force. Full tanks and no rotation at launch save you from that worry.
And as for less mass being easier to stabilize - can you balance a pencil on your finger? How 'bout a broomstick?

yesterday
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SpaceX To Attempt Falcon 9 Landing On Autonomous Spaceport Drone Ship

drerwk Re:Someone doesn't understand basic relativity (80 comments)

And I don't mean the speed of light kind.

At 14 stories tall and traveling upwards of 1300 m/s (nearly 1 mi/s), stabilizing the Falcon 9 first stage for reentry is like trying to balance a rubber broomstick on your hand in the middle of a wind storm.

EXACTLY the same as takeoff. NO difference.

Same amount of fuel? No, so not the same moments of inertia. During launch the engine is pushing in the direction of travel, during re-entry no. During launch, the aerodynamics include that nice fairing on the nose, which should be a bit less chaotic than coming engine first down. The period of 1300 m/s travel that you quote and compare to launch is not during launch (0 m/s) - it is probably closer to the period of maximum dynamic load and clearly during super sonic travel. The reverse part of that travel, the period of maximal dynamic load during re-entry in a non-aerodynamic configuration is rather more difficult than getting off the pad.

yesterday
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Apple Wins iTunes DRM Case

drerwk Re:The video game crash of 1983 (178 comments)

The crash happened across platforms, though I have a limited view of it - I co-wrote Repton for Sirius Software, available on Apple II, C-64, and Atari 400/800. Sirius went out of business because 20th Century Fox failed a promised payment of $20mil. But I also worked for Infocom around '85 - and they were also crushed - maybe due to being text based.

2 days ago
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Physicist Kip Thorne On the Physics of "Interstellar"

drerwk alumni - please up vote (289 comments)

Maybe when the editors are finally fully automated we could get the Cal Tech ==> Caltech rule running.

about two weeks ago
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Mathematical Proof That the Universe Could Come From Nothing

drerwk Re:Nothing? (429 comments)

I suppose I am to some degree being pedantic, but if the term causality had occurred in his explanation, or he'd said "X causes Y" is invariant I'd not have replied.

about a month ago
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Mathematical Proof That the Universe Could Come From Nothing

drerwk Re:Nothing? (429 comments)

As long as there's no faster-than-light travel, "X happens before Y" is an invariant - it's true in all reference frames.

No. http://math.ucr.edu/home/baez/... and for the longer version http://en.wikipedia.org/wiki/L.... In these examples, the doors either close at the same time for the observer stationary with respect to the barn, or at different times for the observer running with the pole.

OK, sorry, should have said ""X doesn't happen after Y" is an invariant" (there don't exist reference frames such that X happens before Y in one frame and X happens after Y in another frame).

Again no. A running coming from the other direction would see the doors close in the other order. I think the AC parallel to this post explains it pretty well.

about a month ago
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Mathematical Proof That the Universe Could Come From Nothing

drerwk Re:Nothing? (429 comments)

As long as there's no faster-than-light travel, "X happens before Y" is an invariant - it's true in all reference frames.

No. http://math.ucr.edu/home/baez/... and for the longer version http://en.wikipedia.org/wiki/L.... In these examples, the doors either close at the same time for the observer stationary with respect to the barn, or at different times for the observer running with the pole.

about a month ago
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Scientists Seen As Competent But Not Trusted By Americans

drerwk Re:Science is not about trust (460 comments)

Always enjoy reading his lectures - thanks. Had the pleasure of hearing a couple as well.
Maybe I was not clear in my statement - the LHC itself is not so much an experiment as a source of high energy collisions - the experiments are the detectors placed in the beam line, and with respect to the detection of the Higgs, there are the two: http://en.wikipedia.org/wiki/A... http://en.wikipedia.org/wiki/C.... While they are similar in that they detect collisions and take careful account of the collision products they do so differently. So they are effectively in a position to reproduce each others results as they have done with the detection of the Higgs.

about 3 months ago
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Scientists Seen As Competent But Not Trusted By Americans

drerwk Re:Science is not about trust (460 comments)

Science is about reproducible results. Publish the details of your experiment, so I can perform your experiment (and variations on it) myself. Your claim is strengthened if I get the same results you do.

But I don't have a Large Hadron Collider! How am I supposed to reproduce this?

The fact is that many experiments are expensive to reproduce and will not be; and there are scientists who do poor work either intentionally or due to institutional reasons. The desire to do great science is only part of the motivation of a scientist; the desire to feed one's family can influence anyone thinking, as can the desire for fame, or other desires.
Addressing the LHC argument - The LHC requires thousands of scientists, the results will be examined to see if they match previous results at the appropriate energies, and it is worth noting that the LHC has detectors ATLAS and CMS which effectively check each others results regarding detection of the Higgs. And there are other detectors looking for new physics, that are not presently worth the cost of double coverage.

I suspect that there are backwaters of science, where someone may find gain in having published many papers, and have low risk of being caught because the value of the results is such that they will not be replicated; but when you cheat like Jan Hendrik Schön with results that would be quite valuable then you can expect work attempting to extend the experiment to be done, and when it fails the original work will be re-checked.

about 3 months ago
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Physicist Claims Black Holes Mathematically Don't Exist

drerwk Re:Hmmm ... (356 comments)

Thanks - a little looking has been fun http://www.physics.montana.edu... But, one order of magnitude in density from outer core to center for a neutron star compares to about nine orders of magnitude from center to envelope on our own Sun.

about 3 months ago
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Physicist Claims Black Holes Mathematically Don't Exist

drerwk Re:Hmmm ... (356 comments)

Read the conclusion where the author directly addresses your concerns. But, I will also point out that at the stage of collapse the authors are talking about the star more closely resembles a neutron star rather than a hydrogen fusing star. Because a neutron star is supported by Pauli exclusion, it seems to me that the density may well be close to constant through out a majority of the star.

about 3 months ago
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Ask Slashdot: Is iOS 8 a Pig?

drerwk Re: Alright smart guy (504 comments)

I use safari too - which is what is failing to load all kinds of things - I'm going to give tenfourfox a try. I mostly like to have a 'puter that the two year old can tear the keys off of and I don't get stressed out. But it would also be nice if the browser worked well enough for the seven year old to run his blog.

about 3 months ago
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Ask Slashdot: Is iOS 8 a Pig?

drerwk Re: Alright smart guy (504 comments)

What browser? I can't get most sites to load anymore due to js / html5 use most places. I'd love to keep my g4 power book running.

about 3 months ago
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Ask Slashdot: How To Pick Up Astronomy and Physics As an Adult?

drerwk Re:Just do it. (234 comments)

To add to the Galaxy Zoo suggestion:
Have a look at this book: "Statistics, data mining and machine learning in astronomy" http://www.britastro.org/journ...
I have my BS in Physics, but I write software. I think it would be pretty hard at 10 hours a week to pick up the math of most of the advanced topics - even mechanics. But, learning statistics and data mining and having public access to data like the Sloan Survey would put you in the position to make real discoveries as an amateur. And, a modicum of competence in statistics and data mining may give you some good options for paying gigs.

about 2 months ago
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Universal Big Bang Lithium Deficit Confirmed

drerwk Re:3 times less? (171 comments)

Yes, exactly.

about 3 months ago
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Information Theory Places New Limits On Origin of Life

drerwk Re:Thermodynamic equilibrium is not required (211 comments)

There's this "Sun" bombarding the planet with energy, constantly.

Then take the two-body system given by the Earth and the Sun as the closed system.

If it was a closed system the Earth would have cooked by now coming to equilibrium with the Sun - fortunately we have the cold bath of the rest of the universe to which most of the Sun's energy flows, as well as some heat from the night side of the Earth - so it is not a closed system.

about 3 months ago
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How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

drerwk Re:mini-explosion? (74 comments)

You might enjoy reading http://www.ast.leeds.ac.uk/Aug... for an introduction. But to answer your question, the incoming cosmic rays usually (always?) begin interacting in the upper atmosphere, I don't know the cross sections particularly well, but it is possible that only very rarely do they make it to the ground. What we detect down here is the cascade of particles - like an avalanche - initiated in the upper atmosphere. The resultant cascade can affect detectors across hundreds of square kms.

about 3 months ago
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Big Bang Actors To Earn $1M Per Episode

drerwk Re:Nerd Blackface (442 comments)

Do you really think that an IRL Sheldon without script immunity would be able to do the same? The TV Sheldon also seems to be a pretty crap physicist, given to conspiracy theories, junk science, and an inability to distinguish between fiction and reality.

I was an undergrad Physics major at Caltech. Other than the crap physicist qualifier, I knew professors in the department who were given to conspiracy theories, junk science, and an inability to distinguish between fiction and reality, though not all in a single individual.

about 4 months ago
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Perlan II Project Aims To Fly a Glider To the Edge of Space

drerwk Re:"and designed to fly near transonic speed" (44 comments)

The lift produced by a wing is partly a function of the rate of air mass that passes over the wing. Keeping density constant an increase in velocity will increase lift. If the density of the air decreases, as it does with altitude, then one must increase velocity to get the same air mass to pass over the wing and generate the same lift. At the altitude they will be flying, they may well have to fly near the speed of sound to get enough air over the wing to provide sufficient lift. The higher they go, the higher their stall speed so they end up flying in a decreasing envelope between speed of sound and stall. The typical airspeed indicator is a static ram pressure transducer, which is also dependent on the mass of air impinging on it, so it will indicate 'normal' stall and flying speed even though the plane is going much faster.

about 4 months ago

Submissions

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Powering the Planet

drerwk drerwk writes  |  more than 7 years ago

drerwk writes "An article in the Caltech magazine Engineering and Science by Prof. Nathan Lewis gives a clear and cogent argument that solar is the only likely solution in the next fifty years to the clean energy problem. Discussions on /. regarding clean energy run the gamut and include arguments regarding nuclear, fusion, solar, coal and so on. In contrast, Prof. Lewis's article covers the pros and cons of these same arguments with actual journal references. Let's hope those paint on solar cells are coming soon!

This talk was the opening keynote speech at the first annual California Clean Innovation Conference, held at Caltech on May 11, 2007. The event, a partnership with UCLA and UC San Diego, included discussions on the futures of assorted energy technologies and how to finance them. In other sessions, clean-energy startup companies were given the opportunity to "fast pitch" their business plans, in three to five minutes each, to a panel of venture capitalists. Nathan S. Lewis (BS '77, MS '77) is Caltech's Argyros Professor and professor of chemistry. Much more on global energy issues and on his own research in solar power can be found at http://nsl.caltech.edu./
"

Link to Original Source

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