Background on the Falcon 9 Launch • Hacker News Board

Re: Background on the Falcon 9 Launch

#111

Post by chrisseaton » Wed, Dec 23, 2015, 2:22 PM UTC

logicallee wrote: post #99

yellowbeard wrote: post #15

Earlier quoted context omitted.

There is an XKCD "what if" that explains this: https://what-if.xkcd.com/58/ "The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast."

How fast do you have to go? Easy. Look out at the horizon far enough that you can see it drop (for example a mountain etc). You have to go so fast that in the time it takes you to reach that point, you only drop by the amount the horizon falls.

Could you make a cruise missile that didn't need any wings or other surfaces for lift - only forward propulsion - that just went so fast that it was effectively in orbit, but nor far above the ground?

Re: Background on the Falcon 9 Launch

#112

Post by johnm1019 » Wed, Dec 23, 2015, 2:25 PM UTC

caio1982 wrote: post #103

Just for the record, the biggest newspaper in Brazil has an incredible picture of the launch/landing on its front page today :-) http://f.i.uol.com.br/folha/homepage/images/1535742.jpeg

Fantastic picture! I bet editors in the newsroom took a collective breath when they saw that email from the field.

Re: Background on the Falcon 9 Launch

#113

Post by lordnacho » Wed, Dec 23, 2015, 2:35 PM UTC

chrisseaton wrote: post #111

logicallee wrote: post #99

Earlier quoted context omitted.

How fast do you have to go? Easy. Look out at the horizon far enough that you can see it drop (for example a mountain etc). You have to go so fast that in the time it takes you to reach that point, you only drop by the amount the horizon falls.

Could you make a cruise missile that didn't need any wings or other surfaces for lift - only forward propulsion - that just went so fast that it was effectively in orbit, but nor far above the ground?

The loss from atmospheric drag would be enormous. If you were on a planet with no atmosphere it would be no different from any other orbit though.

Re: Background on the Falcon 9 Launch

#114

Post by madaxe_again » Wed, Dec 23, 2015, 2:38 PM UTC

marktangotango wrote: post #37

the_economist wrote: post #18

Earlier quoted context omitted.

He has a reputation for being an extremely hard worker.

Indeed, I'd wager that raw intelligence is highly overrated. Hard work trumps intelligence. Hard work and intelligence are an unbeatable combination. >> What can us, mere mortals learn from him? We can't change our baseline raw intelligence (which effects how quickly and deeply you can learn new things), but are there other patterns we can replicate in our lives? Become an autodidact, and study, study, study.

Intelligence undermines hard work all too often. I wasted years of my life coasting, as coming top of the class in everything was easy, and only actually started applying myself after university, when it rapidly became clear that intelligence alone doesn't cut it.

You've gotta be smart, you've gotta be prepared to work insane and thankless hours, you've gotta be tough as nails to hear but ignore the naysayers, you've gotta be willing to lose everything, and above all, you've gotta believe in yourself.

Only when you put all of those together (with krazy glue, of course), only when you are leading yourself, can you hope to lead others.

Re: Background on the Falcon 9 Launch

#115

Post by 4ad » Wed, Dec 23, 2015, 2:45 PM UTC

idlewords wrote: post #26

I'm having some trouble with the opening salvo here: "Now imagine placing a marble somewhere on that slippery sheet -- it is guaranteed to fall into one of the funnels. " This holds for the case where there are two objects initially at rest, but I don't see it as obviously true if there are more than two objects in the universe.

You're right, it's not obviously true. In fact it's quite complicated. But you can prove it mathematically.

Re: Background on the Falcon 9 Launch

#116

Post by marcosscriven » Wed, Dec 23, 2015, 2:47 PM UTC

zodiac wrote: post #109

marcosscriven wrote: post #88

This all seemed reasonable except this paragraph: "The reason they are floating around is that they have no net acceleration. The outward acceleration of (apparent) circular motion, which wants to sling them out into deep space, exactly balances the inward acceleration of gravity that wants to pull them down to Earth." There is no "outward acceleration". The weightlessness is because the craft they are in is accelera…

Both you and the article are right - you are analyzing it in the frame of reference where the center of the earth is stationary, while the article analyzes in the frame of motion where the center of the rocket is stationary. Since the frame where the center of the rocket is stationary is a non-inertial frame, Newton's law doesn't apply [1]. However a modification of Newton's law that includes a so-called "ficticious…

Right, of course I understand that - but two points.

1) The whole original post appears to be worded for the layman to try and dispel myths around what orbit is. I don't think the layman is going to think about inertial frames of reference, rather I genuinely think the common misconception that there's really something 'pulling' the astronauts up will continue, much like many people think a car is throwing them out of a bend in the road, rather than the vehicle pushing them away from a straight line.

2) In any case, even if Musk implies the frame of reference, there's a reason a 'centrifugal force' is also referred to as a 'fictitious force' [1]

[1]: https://en.wikipedia.org/wiki/Fictitious_force

Re: Background on the Falcon 9 Launch

#117

Post by marcosscriven » Wed, Dec 23, 2015, 2:55 PM UTC

simbilou_ wrote: post #110

marcosscriven wrote: post #101

Earlier quoted context omitted.

Nothing is accelerating outward. There's only one acceleration here, and that's towards the centre of the mass of Earth.

A laughable claim, mister Bond, perpetuated by overzealous teachers of science.

:) https://www.explainxkcd.com/wiki/index.php/123:_Centrifugal_...

Re: Background on the Falcon 9 Launch

#118

Post by leonroy » Wed, Dec 23, 2015, 3:05 PM UTC

blizkreeg wrote: post #17

Clearly this man's intellect is through the roof. Reading this post and him explaining these concepts in such first-principle terms (despite not being a physicist/rocket engineer) indicates his in-depth understanding (nothing new there). I know he has a Bachelors in Physics but bear with me. But, I'm just in awe and I keep thinking 'how does he do it?'. He's running two intensely technical and risky companies. Yet he…

> We can't change our baseline raw intelligence.

Hmm. I used to believe this until a book recommendation by Bill Gates no less opened my mind a little to the thought that intelligence isn't a fixed or capped (to any level most of us hit anyways) attribute.

I would strongly recommend at least a read of Gates' book review and at best purchasing a copy of the book and applying it. Certainly one of the best books I've read of late.

http://www.gatesnotes.com/Books/Mindset-The-New-Psychology-o...

Re: Background on the Falcon 9 Launch

#119

Post by ohitsdom » Wed, Dec 23, 2015, 3:13 PM UTC

sillysaurus3 wrote: post #83

blizkreeg wrote: post #17

Clearly this man's intellect is through the roof. Reading this post and him explaining these concepts in such first-principle terms (despite not being a physicist/rocket engineer) indicates his in-depth understanding (nothing new there). I know he has a Bachelors in Physics but bear with me. But, I'm just in awe and I keep thinking 'how does he do it?'. He's running two intensely technical and risky companies. Yet he…

This hero worship is utterly stupid. It's also a disservice to children. We're teaching them that there are heroes, and then everyone else. Bull. Work as hard as Elon did, and you'd make the same progress. It also required luck. No PayPal, no Elon. And there could only be one PayPal, at precisely that time in history. A better question is, why did Carmack fail where Elon succeeded? Armadillo Aerospace was supposed to…

Hero worship is stupid, but everyone is different. We all couldn't be Elon if we worked as hard as he does.

Re: Background on the Falcon 9 Launch

#120

Post by jerf » Wed, Dec 23, 2015, 3:16 PM UTC

chrisseaton wrote: post #111

logicallee wrote: post #99

Earlier quoted context omitted.

How fast do you have to go? Easy. Look out at the horizon far enough that you can see it drop (for example a mountain etc). You have to go so fast that in the time it takes you to reach that point, you only drop by the amount the horizon falls.

Could you make a cruise missile that didn't need any wings or other surfaces for lift - only forward propulsion - that just went so fast that it was effectively in orbit, but nor far above the ground?

In addition to lordnacho's point, see things like https://en.wikipedia.org/wiki/North_American_X-15 .

You can't stay in orbit with plane wings because of air resistance, and with so little air you need rocket propulsion (for now, at least). But that's not to say there aren't some interesting games to be played with wings on the way up.