Hacker News new | comments | show | ask | jobs | submit | dandelany's comments login

How about the fact that index funds consistently outperform actively managed funds?

And the relevance of this is...?

You asked for evidence backing up the statement "People whose day job is to predict this stuff can't even make good predictions". Managers of active mutual funds are exactly these people. The fact that they can't beat the market is clear evidence they can't make good predictions.

Of course you could say "well, the good managers beat the market, even though on average they don't". But you could also say that the few people who correctly predict three coin flips in a row are "good at predicting coin flips" - it's easy to say this in retrospect but impossible to predict who the "good ones" are upfront.


The atmospheric pressure is so low that you don't need a tube at all (<1% of Earth). And you'll have to use wheels instead of hovering because you can't suck in enough air to eject out the bottom. At that point, you no longer have a Hyperloop, you have a car (or train).

The second picture in the article shows the countdown clock. The article just confuses it by calling it "analog" and comparing it to a wristwatch, but in fact most people would consider it digital.

"Digital [adj]: (of a clock or watch) showing the time by means of displayed digits rather than hands or a pointer."

Imagine the confusion in an alternate universe where the clockmakers of old decided to call the pointing sticks "fingers" instead of "hands".

In addition to the link posted by celoyd, you can get access to the full data stream you mentioned by filling out this application form[0].

There are also some heavily processed images from that data available from NOAA[1] - the "Geocolor Full Disk" is the best, it's half-resolution (5500x5500). The green filter on Himawari's camera doesn't correctly capture the green color of vegetation, which is why OP's video looks browner than you might expect. So this product attempts to correct for that by creating an artificial green channel made of a combination of other channels[2]. It also attempts to correct for Rayleigh scattering[3], so this is basically what the Earth would look like if the atmosphere suddenly disappeared (except for the clouds :P). The night portions of these images are a different kind of false color composite: the clouds come from two infrared channels, white are high ice clouds and red are low wet clouds; the city lights are (sadly) just a static overlay from existing data.

And (shameless plug) I've been playing with applying motion interpolation algorithms to these NOAA images to create smooth, high resolution video that can be played much slower. The Farneback optical flow algorithm[4][5] seems to work very well. (Lots of) videos available on my Youtube channel[6], code/details available here[7][8], blog post coming soon :)

[0] http://www.eorc.jaxa.jp/ptree/registration_top.html [1] http://rammb.cira.colostate.edu/ramsdis/online/himawari-8.as... [2] http://www.goes-r.gov/downloads/ScienceWeek/2015/Presentatio... [3] http://rammb.cira.colostate.edu/research/goes-r/proving_grou... [4] http://www.diva-portal.org/smash/get/diva2:273847/FULLTEXT01... [5] https://github.com/dthpham/butterflow [6] https://www.youtube.com/watch?v=6rOwjn87edI&list=PLrmCQL5hEL... [7] https://github.com/dandelany/animate-earth [8] http://www.unmannedspaceflight.com/index.php?showtopic=8063&...

-----


Wow. Great stuff! Is there a good way to use one a video at a very low framerate (perhaps 0.1-1 fps) with low resource requirements as animated wallpaper on Ubuntu/Linux?

-----


Oh, hello! I enjoyed your motion interpolation experiments, and I look forward to the blog post.

-----


Awesome work and thanks for the helpful links. Would make a really cool background / screensaver to loop the prior days imagery in HD :)

-----


Here are details from the docs: https://docs.npmjs.com/how-npm-works/npm3-nondet

-----


> You can reliably get the same dependency tree by removing your node_modules directory and running npm install whenever you make a change to your package.json.

https://docs.npmjs.com/how-npm-works/npm3-nondet

-----


That explains why I haven't experienced it -- our projects' npm scripts to build packages wipe out that folder before building.

-----


> The thrust vector has stable orientation relative to the rocket (if you don't gimbal)

This is what makes your argument moot - because they do gimbal, and the gimbaling is what creates the moment/torque. In a way that is very nearly analogous to twisting your hand around slightly to balance a broomstick.

> The yardstick is unstable in inclination if it isn't vertical. The rocket is unstable in horizontal position if it isn't vertical.

The rocket is unstable in position and inclination (attitude). So you're right that there's more to it, but it's still the inverted pendulum problem for attitude, plus the rocket formulas for translation and added constraints of landing location. Are you saying Bezos is lying in this post when he explicitly says "When you do a vertical landing, you’re solving the classic inverted pendulum problem"? He would know, and I don't see a reason for him to lie about it.

-----


Fair call on the gimbaling at the end, in that instance it does impart a moment around the CoM and will invoke a torque, though that's really only at the end once much of the vertical velocity is cancelled. As a result it does represent the inverted pendulum right before landing.

Interestingly, because the CoM is so low due to the low volume of fuel by the time of landing, it's likely not as big a torque as you'd first expect (all the mass is down the base where the engines are). In that case, rocket height isn't going to have as a big an impact because it's not like it's equally dense up the entire rocket structure. I'd argue he's likely overstating the effect of rocket size on how difficult it is to achieve.

-----


> This is what makes your argument moot - because they do gimbal, and the gimbaling is what creates the moment/torque. In a way that is very nearly analogous to twisting your hand around slightly to balance a broomstick.

The point of the inverted pendulum problem is that the torque on a long, thin, ground-supported object (or even just any ground-supported object with a narrow base or a hinge on its bottom) is a function of its orientation. That gives you a second order differential equation for tilt. This is NOT the case with the free-flying rocket because the engine is rotating along with the rocket. You could simulate the inverted pendulum actively, by rotating the engine so that it has a fixed orientation relative to the ground (up to the gimbaling limit, which is usually <10 degrees), but you actually want to do the opposite with the landing rocket (with significant damping to boot). Basically, you want the active control system to simulate a normal pendulum, just turned upside down (but with the damping so that it doesn't actually oscillate).

> The rocket is unstable in position and inclination (attitude).

Not the latter unless you make it behave in that way. You could also check on the Apollo LM landing guidance, maybe it will become more clear if you study that.

> So you're right that there's more to it, but it's still the inverted pendulum problem for attitude

No, it's not. That's the point.

> Are you saying Bezos is lying in this post when he explicitly says "When you do a vertical landing, you’re solving the classic inverted pendulum problem"? He would know, and I don't see a reason for him to lie about it.

No, I'm saying that this phrasing makes no sense. Remember that Goddard made a similar mistake when reasoning about rockets and pendulums, so arguments to authority are demonstrably to be avoided here. A significant clarification on his part could make it more comprehensible what he actually meant, but making any kind of analogy to a ground-supported object is clearly bad when talking about a free-flying body.

-----


This is an excellent response - thanks.

Marketplace competition and non-zero-sumness are not mutually exclusive, at least not if you are a capitalist. The total money spent on spaceflight will be larger with both companies in the market than with either one alone, therefore it is not a zero-sum game.

As for acknowledging each others advancements - you don't see Sony or Dell going out of their way to mention Apple, for obvious reasons. This is normal behavior between competitors. I don't see why people are making so much out of Bezos' tweet; it was just a stupid joke.

-----


Maybe because expectations of friendliness are higher when talking about space industry. It still feels more like few entities working towards the same grand goal than companies competing with each other.

The jabs Elon and Bezos are exchanging seemed funny to me at first, but now they seem kind of serious, which makes me uncomfortable. I expected they'll have fun together, not the resentment that seems to be flying between them.

-----


You're the one turning it into a competition, in reality it is simply two separate companies doing different awesome things. Yes, obviously, going into orbit is harder than not doing so. But going to space sub-orbitally is still very difficult and cool, and the only reason there's a negative spin on BO's achievements is because people feel the need to compare it with SpaceX as if there can be only one.

Just be excited for the positive direction of spaceflight in general. Everyone benefits from both companies doing well, even if SpaceX is ahead of everyone else for awhile.

-----


I wish I had the power to turn that into a competition, but I don't think they need me for that :)

Jocking aside, I don't think there can only be one. I am comparing BO and SpaceX the same way I'd compare google and apple. In the same industry but not doing exactly the same thing. And when Apple tried to go on one of Google's turf with maps, they sucked. When Google tried to go do phones, at first they sucked. Comparison is natural and welcome.

Here, it feels to me that BO is putting themselves up for comparison for no reason.

As far as the positive direction of spaceflight, I think that transparency is key. Space exploration needs more accountability and trust that ever has been available before _in_any_industry_ever_. And there, so far SpaceX is winning hands down, including versus the old players (soyouz, ariane, ULA...). When SpaceX says "one of our struts was structurally deficient, broke down, made the rocket lose equilibrium and ultimately explode", they're also telling their competitors "Watch this. We've learned it the hard way.". Same with fog icing the leg lock. In the grand scheme of things they are making space safer, and not only for their customers. I only see bragging and borderline (note the "borderline") bullying on BO's side

-----


Bezos is also turning it into a competition: https://mobile.twitter.com/JeffBezos/status/6791166363103600...

-----


BO is making it a competition by clearly trying to one up SpaceX with the timing of their marketing releases etc.

-----


>Just be excited for the positive direction of spaceflight in general.

How about don't tell people in the comments section of HN how to feel about a story posted here?

-----


The fuel cost of a Falcon 9 launch is ~$200k. In a perfect world (tons of launches), lets say (generously) that we get launch costs down a million a pop, all things included.

BO's New Shepard is shooting for something like $100k or less per flight. The rocket is much smaller, uses less fuel, and is much easier to move around on the ground, reducing fixed launch costs. It's at least an order of magnitude lower in price, for a completely different service (suborbital tourism), which will make it accessible to a much larger market.

-----


Larger market? I think not. The space launch biz is populated by hundreds of different companies, all wanting to spend millions or billions to get a useful sat into orbit. BO is looking to a small group of billionaires with the money to throw 30-50k to spend a few minutes vomiting. And of those, only the ones young enough to participate, a rare thing amongst billionaires.

(1) The launch is not gentle. Everyone will be strapped tightly into chairs, ready for launch escape rocket thrust if necessary.

(2) Time weightless will be measured in minutes, probably less than ten. So nobody is getting out of the chairs. At best they get a few minutes of watching pens hover, unless that is everything has to be secure. In such cases only the vomit will float.

(3) The landing options are not great. Soft if all goes to plan, but parachutes/hard if no. So everyone stays in chairs. No old people and/or heart conditions need apply.

How many people pay to ride the vomit comet every year? How many of them are billionaires? That's BO's market.

-----


Well, I'm not even a millionaire and I would very gladly sell my house to go to the space, even for a few minutes.

Best thing is: with that money, I can go twice!

-----


cc. Here ya go: https://www.gozerog.com/

-----


The Falcon 9 first stage accounts for only 3/4th of the launch cost[1]. Given the $60M+ [2] total current launch cost, that still leaves $15M even if booster reuse is free.

SpaceX no longer has plans to develop second stage reusability for the Falcon[3].

[1] http://shitelonsays.com/transcript/spacex-press-conference-s... section "Question on the changes to the Falcon 9"

[2] http://www.spacex.com/about/capabilities

[3] http://space.stackexchange.com/questions/10391/how-does-spac...

-----

More

Applications are open for YC Summer 2016

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | DMCA | Apply to YC | Contact

Search: