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Background on the Falcon 9 Launch

spacex.com

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Re: Background on the Falcon 9 Launch

#91

Post by thomashabets2 »

fixermark wrote: post #56
mikeash wrote: post #12

Earlier quoted context omitted.

Blue Origin is cool but it's certainly not astonishing to me that a billionaire is able to send a rocket on a suborbital trajectory and recover it. It's certainly more than I've ever done by a long shot, but it's not a very interesting achievement unless you're interested in five-minute space tourism. I don't think BO's achievement here has many implications for space travel.

I wonder its implications for terrestrial travel, though? We are in a post-Concord era, after all, but suborbital flight could get you to any point on the planet pretty quickly if the price is right.

This may be interesting to you: http://www.antipope.org/charlie/blog-static/2015/01/why-were...

Re: Background on the Falcon 9 Launch

#92

Post by exDM69 »

v4n4d1s wrote: post #90

Great and easy to understand article, thanks for posting it. Does anyone know it the spacex team uses the imperial or the metric system for development? Elon switches between both systems and it's messing with my head.

Fwiw, on their public webcast, they had on-screen telemetry showing km/h for speed and km for altitude (and no downrange distance). Not necessarily what they use internally, though.

Aerospace engineers traditionally uses knots, thousands of feet and nautical miles. SI units typically have km/s (not /h).

Re: Background on the Falcon 9 Launch

#93

Post by lmm »

ChuckMcM wrote: post #69
Alain-lf wrote: post #65

Earlier quoted context omitted.

SpaceX own the first stage. You pay to get your payload delivered to a specified orbit. You don't actually buy the rocket. It's like flying, you buy a ticket, not the plane.

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 truly "own" something you don't have the right to destroy, but obviously you don't have the right to destroy a flat with someone else's above it).

> And the math there would no doubt be really interesting to an insurance company since you have the possibility that the launch is a success and the first stage lands, the launch is a success and the first stage crashes, the launch effectively fails (second stage failure) but the first stage successfully returns, and both stages are lost. That is a number of different outcomes to insure.

The insurance industry already deals with far more complex scenarios. A ship on an ocean voyage will often have the hull and cargo insured separately, different loss layers insured separately (e.g. first 10% of losses, 10-20%, 20-100% all separate), with multiple underwriters on each layer (and sometimes the same underwriter on multiple stamps).

Re: Background on the Falcon 9 Launch

#94

Post by w_t_payne »

ggreer wrote: post #31
w_t_payne wrote: post #23

If we can land the rocket accurately enough to put it down on a tiny barge only slightly larger than the rocket itself, then why do we need to tolerate the weight of the landing legs? We already have industrial robots that can move and grasp heavy weights relatively quickly over distances of several metres -- it doesn't take much imagination to conceive of a similar contraption being used to arrest the descent of the…

There are several reasons why landing legs make more sense: – Any flat chunk of cement is a landing spot. That means more places to land in case of contingencies. For yesterday's mission, SpaceX had one primary and four alternate landing zones.[1] – I doubt industrial robots can withstand rocket exhaust. As helicopter footage shows, the landing pad got lit-up pretty good.[2] Remember, the first stage is over 40 meter…

Who cares about what makes more sense ... giant robots, dude! :-)

Re: Background on the Falcon 9 Launch

#95

Post by 1stop »

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…

Is "tangential velocity" not just another way of saying "outward acceleration"?

Re: Background on the Falcon 9 Launch

#96

Post by lmm »

kibwen wrote: post #24

The article mentions that the water landing requires less fuel to return the rocket because it doesn't have to spend fuel overcoming its initial ballistic trajectory. In the water landing scenario, how far away from the launchpad is the landing barge? I'm wondering about the economics of launching from a site where your first stage trajectory is entirely overland, to avoid the complications of landing on a barge that…

It's important that the trajectory be fail-safe in terms of avoiding land - if the falcon were to explode early on it could sprinkle debris over a large area around the intended landing zone. So it'd have to be a small unpopulated island - a barge is probably easier. If they need more area or stability I'd think it's relatively easy to expand the barge or add more mass/sea anchors underneath.

Re: Background on the Falcon 9 Launch

#97

Post by timbre »

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…

It's describing the dynamics in the (non-inertial) reference frame of the satellite (the reference frame in which the astronauts can be described as "floating around"). In this reference frame, the centrifugal force balances the gravitational force, leading to zero net acceleration.

Re: Background on the Falcon 9 Launch

#98

Post by marcosscriven »

1stop wrote: post #95
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…

Is "tangential velocity" not just another way of saying "outward acceleration"?

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?

Re: Background on the Falcon 9 Launch

#99

Post by logicallee »

yellowbeard wrote: post #15
nathanielc wrote: post #9

My favorite way to describe orbits is 'constantly throwing yourself at the ground but moving so fast that you just keep missing', hence the constant free-fall/zero-g.

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.

Re: Background on the Falcon 9 Launch

#100

Post by 1stop »

marcosscriven wrote: post #98
1stop wrote: post #95

Earlier quoted context omitted.

Is "tangential velocity" not just another way of saying "outward acceleration"?

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" force usually comes from a massive rocket... It is then maintained by the inward force of gravity.

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