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Background on the Falcon 9 Launch

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Re: Background on the Falcon 9 Launch

#101

Post by marcosscriven »

1stop wrote: post #100
marcosscriven wrote: post #98

Earlier quoted context omitted.

I'm not sure if that's a question or a statement.Firstly, velocity and acceleration are different things. Velocity is change of distance with time (km/s), acceleration is change of velocity with time (km/s per second or km/s^2). Secondly, an acceleration on a mass requires a force. Supposing there were an 'outward acceleration', where do you propose the 'outward force' is?

... We are talking a tangent on a circle that is changing every second. So that is a change of velocity, which is acceleration. Outwards is clearly "out" of the circle. The tangent (on the curve) would be a snapshot of that "outward" velocity. As a said: Tangential velocity is the same as saying outward acceleration. Unless you were referring to just that single "snapshot" in a frozen time scenario. That "outward" fo…

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

Re: Background on the Falcon 9 Launch

#102

Post by 1stop »

marcosscriven wrote: post #101
1stop wrote: post #100

Earlier quoted context omitted.

... We are talking a tangent on a circle that is changing every second. So that is a change of velocity, which is acceleration. Outwards is clearly "out" of the circle. The tangent (on the curve) would be a snapshot of that "outward" velocity. As a said: Tangential velocity is the same as saying outward acceleration. Unless you were referring to just that single "snapshot" in a frozen time scenario. That "outward" fo…

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

If that were the case then you could get into orbit by simply going straight up. Why do they go laterally up to 8km/s then? (if not to generate an 'outward' force?).

There are two vectors being added here. One is gravity. The other is a tangental/outward vector. When added together, they form an orbit. Ignore one, and you leave orbit, either by going into space, or smashing into earth. But there are clearly two forces/vectors. And one of them, is having it's direction changed by the other, and thus is acceleration... I don't know what other words I can use to describe it. But I fail to see where I'm wrong :\

Re: Background on the Falcon 9 Launch

#104

Post by marcosscriven »

1stop wrote: post #102
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.

If that were the case then you could get into orbit by simply going straight up. Why do they go laterally up to 8km/s then? (if not to generate an 'outward' force?). There are two vectors being added here. One is gravity. The other is a tangental/outward vector. When added together, they form an orbit. Ignore one, and you leave orbit, either by going into space, or smashing into earth. But there are clearly two force…

Accidentally up voted you :)

They get to that vast 8km/s veloctiy you mention with huge rocket engines. Then they turn them off.

At that point the astronauts and their craft are in freefall.

You mention an outward 'vector'? You can only talk about forces and their effects on masses really. There's an intertia that resists the downward acceleration, but that's not a force.

Re: Background on the Falcon 9 Launch

#105

Post by 1stop »

marcosscriven wrote: post #104
1stop wrote: post #102

Earlier quoted context omitted.

If that were the case then you could get into orbit by simply going straight up. Why do they go laterally up to 8km/s then? (if not to generate an 'outward' force?). There are two vectors being added here. One is gravity. The other is a tangental/outward vector. When added together, they form an orbit. Ignore one, and you leave orbit, either by going into space, or smashing into earth. But there are clearly two force…

Accidentally up voted you :) They get to that vast 8km/s veloctiy you mention with huge rocket engines. Then they turn them off. At that point the astronauts and their craft are in freefall. You mention an outward 'vector'? You can only talk about forces and their effects on masses really. There's an intertia that resists the downward acceleration, but that's not a force.

Pretty sure inertia IS a force. But I think this point has been laboured enough.

Tomayto...Tomarto.

Re: Background on the Falcon 9 Launch

#106

Post by arethuza »

lmm wrote: post #93
ChuckMcM wrote: post #69

Earlier quoted context omitted.

Just for reference, I got an inside look at what it took to get OSCAR16[1] launched and it isn't like flying :-). Now I don't doubt things are more streamlined now but every launch starts with a basic contract and that contract has to cover everything from contingencies to insurance to liability to disposal. Trying to search for a boilerplate launch contract I found an article[1] where it discusses that Spaceflight I…

I think the real answer is that there will be a complex contractual relationship that "ownership" is too simple to describe, in either direction. E.g. I say I "own" my flat, but actually I am a shareholder in a company that owns the building and have a lease contract with that company (this is the standard (only?) way of "owning" a flat in the UK, because multiple flats stand on the same piece of land - you can't tru…

"this is the standard (only?) way of "owning" a flat in the UK"

Maybe in England - its never worked like that for any flat I've owned here in Scotland, we have completely separate legislation covering such things:

http://www.gov.scot/Topics/Justice/law/17975/11023

Re: Background on the Falcon 9 Launch

#107

Post by mannykannot »

mikeash wrote: post #8
mannykannot wrote: post #6

Earlier quoted context omitted.

I don't think you could allocate all of the landing fuel load to payload as any addition to the payload also requires additional 2nd. stage fuel.

You can run the first stage longer without any extra second stage fuel. Adding performance to either one (within limits) increases the performance of the system. Using the landing fuel for a launch would allow for a heavier payload without changing the second stage. The first stage would do more of the total work.

Ah yes, good point - I was implicitly assuming the liftoff weight was maxed out, by thinking that any upper stage weight increase would have to come from the 1st stage fuel load.

Re: Background on the Falcon 9 Launch

#108

Post by marcosscriven »

1stop wrote: post #105
marcosscriven wrote: post #104

Earlier quoted context omitted.

Accidentally up voted you :) They get to that vast 8km/s veloctiy you mention with huge rocket engines. Then they turn them off. At that point the astronauts and their craft are in freefall. You mention an outward 'vector'? You can only talk about forces and their effects on masses really. There's an intertia that resists the downward acceleration, but that's not a force.

Pretty sure inertia IS a force. But I think this point has been laboured enough. Tomayto...Tomarto.

A force is the product of mass and acceleration. Its SI units are kg.m/s^2

Inertia is an inherent property of mass. If it were the same as a force its units would be the same.

So it's really not tomayto...tomato I'm afraid. It's right and wrong.

You are right the point has been laboured, but it upsets me to think you would go on under this misconception.

Re: Background on the Falcon 9 Launch

#109

Post by zodiac »

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 force" applies [2] (I don't think this modification has a name). This is why the article says there's an outward acceleration, because in the frame where the center of the rocket is stationary, the outward acceleration is caused by the ficticious force.

[1]: https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion begins the laws with "when viewed in an inertial reference frame"

[2]: https://en.wikipedia.org/wiki/Non-inertial_reference_frame quotes, "One might say that F = ma holds in any coordinate system provided the term 'force' is redefined to include the so-called 'reversed effective forces' or 'inertia forces'."

Re: Background on the Falcon 9 Launch

#110

Post by simbilou_ »

marcosscriven wrote: post #101
1stop wrote: post #100

Earlier quoted context omitted.

... We are talking a tangent on a circle that is changing every second. So that is a change of velocity, which is acceleration. Outwards is clearly "out" of the circle. The tangent (on the curve) would be a snapshot of that "outward" velocity. As a said: Tangential velocity is the same as saying outward acceleration. Unless you were referring to just that single "snapshot" in a frozen time scenario. That "outward" fo…

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.
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