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Background on the Falcon 9 Launch

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Re: Background on the Falcon 9 Launch

#121

Post by derekp7 »

sjburt wrote: post #86
sillysaurus3 wrote: post #83

Earlier quoted context omitted.

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…

Carmack invested about $2 million into Armadillo in its first 6 years. Elon invested $100 million in that time frame (actually, the first 4 years of SpaceX). Armadillo did OK actually, they just were on a completely different trajectory. It was very much a hobby project for Carmack.

Not only that, but wasn't Armadillo one of the "straight-up-to-100KM-and-return" (suborbital) designs? If so, then there is no money to be made in that (except for wealthy people that want a 20 minute thrill ride). It is the "lateral velocity of Mach 25" type of rocket that gets you satellite launch contracts.

Re: Background on the Falcon 9 Launch

#123

Post by IshKebab »

> Getting back to everyday reality, the impression that most people have is that gravity stops once you reach a certain altitude above Earth, at which point you start floating around in "zero g", but, as we just talked about, this is obviously not true. The force of gravity drops proportionate to the square of the distance between the centers of two objects.

I'd like to meet the person that is both uneducated enough to think that gravity suddenly stops and after that is "zero g", and also undestands what "proportionate to the square of the distance" means!

Re: Background on the Falcon 9 Launch

#124

Post by dingaling »

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…

Launch abort locations for Shuttle launches from Canaveral included Shannon in Ireland and the Azores off Spain. Both would seem ideal for recovery of eastbound first stages.

Re: Background on the Falcon 9 Launch

#125

Post by skykooler »

timdierks wrote: post #45
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…

I found a reference that the barge was 320 km downrange in the earlier tests. The Bahamas look to be an appropriate distance from Florida, although to the southeast of Cape Canaveral. From SpaceX's planned Texas spaceport, there's nothing at that range but gulf.

It would probably use much less fuel to boost the trajectory to land in Florida than to turn around and fly back to Texas.

Re: Background on the Falcon 9 Launch

#126

Post by iamjs »

lordnacho wrote: post #113
chrisseaton wrote: post #111

Earlier quoted context omitted.

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.

You could do this on the moon, for example

Re: Background on the Falcon 9 Launch

#127

Post by rguzman »

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."

From the XKCD:

> This leads us to the central problem of getting into orbit: Reaching orbital speed takes much more fuel than reaching orbital height. Getting a ship up to 8 km/s takes a lot of booster rockets. Reaching orbital speed is hard enough; reaching to orbital speed while carrying enough fuel to slow back down would be completely impractical.[5]

Did SpaceX just solve this problem and rendered this paragraph obsolete? Or is that Falcon 9 reached space and turned around without achieving orbital velocity?

Re: Background on the Falcon 9 Launch

#129

Post by ekimekim »

rguzman wrote: post #127
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."

From the XKCD: > This leads us to the central problem of getting into orbit: Reaching orbital speed takes much more fuel than reaching orbital height. Getting a ship up to 8 km/s takes a lot of booster rockets. Reaching orbital speed is hard enough; reaching to orbital speed while carrying enough fuel to slow back down would be completely impractical.[5] Did SpaceX just solve this problem and rendered this paragraph…

That paragraph was in reference to zeroing out your velocity before re-entry. The Falcon 9, iiuc, uses a combination of thrust and aerodynamic forces to slow itself down / put itself on the correct trajectory.

It's also worth noting that they only land the first stage, there's an entire next stage which isn't reusable which adds further speed to achieve full orbital velocity.

Re: Background on the Falcon 9 Launch

#130

Post by vectorjohn »

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…

The only force, and therefore the only acceleration, when you're in orbit is the force of gravity. And therefore, the only acceleration is towards the center of Earth.

The thing in orbit is already moving with a high enough velocity that it isn't able to get closer to the Earth.

I guess maybe what you're saying, is if you take the velocity vector and apply the acceleration vector over time, that changes the velocity at the same rate as the curve of the Earth.

Either way, there is exactly one force vector (which causes exactly one acceleration vector), not two.

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