[jsprogrammer]

If my comments are pointless arguing, so are Elon's.

Worse, Elon's are just factually incorrect (e.g. "The energy needed is the square, i.e. 9 units for space and 900 for orbit.") [and, yet, it remains, uncontested, at the top of this thread].

>It is, however, important to clear up the difference between "space" and "orbit", as described well by https://what-if.xkcd.com/58/

is a non-sequitor because no one seems to have confused space and orbit. Additionally, the comparable part of SpaceX's machines (the first stage of the Falcon 9) doesn't go into orbit (it is supposed to land not far from the launch site and does not loop around the Earth to do it).

What is the import of "orbit"? Elon is the one that brought the word into the conversation, not me.

>You are focusing on the word 'orbit' and not the overall meaning.

Then, please, what is the overall meaning of those tweets?

[ChrisClark]

Everyone else has already told you, but I'll tell you again. The media is saying Elon was just beat at his own game. Elon tweeted to point out that it's a horrible comparison, what he's been trying to do is much harder.

End of story. If you can't see that, I don't care any more. I was just trying to help.

[jsprogrammer]

>The media is saying Elon was just beat at his own game.

The media is not a single, conscious entity. Some Gizmodo blog may have claimed as such, but I think you'll have a very hard time producing any other person who would claim that what a Gizmodo blog says is what the entire media is saying.

>Elon tweeted to point out that it's a horrible comparison

Not really. There are comparables: stick goes up, stick goes down without crashing.

Elon only appears to have made a non-sequitor argument (unless someone shows where the media made the claim that space and orbit were the same thing).

Ultimately, this is probably a defect of Twitter's character limit. It is extremely difficult to put a fully reasoned argument into a single tweet.

[mikeash]

> There are comparables: stick goes up, stick goes down without crashing.

SpaceX did that years ago:

https://en.wikipedia.org/wiki/Grasshopper_(rocket)

[dtparr]

Regarding the factually incorrect bit, could you elaborate? I was under the impression that the energy required was proportional to the square of the velocity, so a 10x increase in velocity (from ~Mach 3 to ~Mach 30) would result in a 100x increase in energy required, which seems to be what he's saying.

Is my understanding inaccurate?

[InclinedPlane]

Energy is proportional to the square of the velocity, but the fuel required to reach a given delta-V scales exponentially.

[jsprogrammer]

Well, if you take the sentence:

>The energy needed is the square, i.e. 9 units for space and 900 for orbit.

at face value. It is either claiming that 9^2 = 900 or, it either mistated the units for space or mistated the units for orbit. This is incorrect.

If you take into account the context of the prior sentence:

>Getting to space needs ~Mach 3, but GTO orbit requires ~Mach 30.

you can probably work out 3^2 = 9 and 30^2 = 900. However, as InclinedPlane said, that's only in an idealized number, in reality, you must expend even more energy than that to achieve Mach 30 from the surface of the Earth.

We can check back to the prior contexts:

>Congrats to Jeff Bezos and the BO team for achieving VTOL on their booster

>It is, however, important to clear up the difference between "space" and "orbit", as described well by https://what-if.xkcd.com/58/

To be short: you'd need to find where Jeff Bezos or the BO team claimed anything about "orbit".

Since others have already given up on this conversation, I probably will too.

[mikeash]

You simply misunderstand the "square" statement. It is factually correct.

You seem to understand it later, where you say that 3^2 = 9 and 30^2 = 900, so what's the deal?

[jsprogrammer]

>so what's the deal?

I assume you stopped reading mid-sentence.

Getting to orbit from the surface of the earth requires more energy expenditure than "the square" of getting to space.