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Comment by schiffern | Hacker News Reader

Incredible time-lapse of the landing, from Elon Musk's instagram: https://www.instagram.com/p/BVxysOlA04j/

The yawing motion at the beginning of the video is because they moved the drone ship to avoid stormy seas, so the stage had to thrust sideways to retarget. In calm weather SpaceX positions the ship right along the ballistic path, so the stage only needs to pitch up and "flip."

You can also see the grid fins "pulling up" through the atmosphere to bleed off as much speed as possible. I described the optimization a while back. https://news.ycombinator.com/item?id=14288431

Fantastic job to everyone at SpaceX!

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That comment is worth a read, I had no clue they were actually generating lift on the body to reduce fuel/etc. Incredible stuff.

Thanks. I made a mistake in that comment, saying the lift/drag of the Shuttle was 1. The hypersonic L/D was 1, but during subsonic approach it was 4.5. In hindsight it kinda makes sense that wings do something. :)

The maneuver is more noticeable with the new titanium grid fins (needed because the old aluminum ones caught fire from aerodynamic heating). Not only are they larger, but they use a "sawtooth" leading edge that increases control authority. New: https://twitter.com/elonmusk/status/879065552060260352 Old: http://www.spaceflightinsider.com/wp-content/uploads/2015/12...

They also happen to be the largest titanium forgings in the world. https://forum.nasaspaceflight.com/index.php?topic=42544.340#...

Well, the plan is to use forging to make them, but the ones on this rocket were cast as a blank and machined. One presumes that they are still working on the forging system. https://twitter.com/elonmusk/status/878821062326198272

Saying in aviation: If you put a big enough engine on it, even a brick will fly.

In this case, it's "given enough initial velocity and control authority, even a brick will glide", but the spirit is the same.

I believe the proper term is "brick sthouse".

A few years back a group of engineers decided to prove this by attaching a number of solid fuel rocket engines to a port-a-potty and launched it to great applause.

In RC planes community it's quite common as well :) With modern brushless engines and LiPo batteries aerodynamics becomes optional.

https://www.youtube.com/watch?v=bns5x4pvl5Y

The new and improved grid fins debuted on this flight allow them even greater capabilities in that regard (greater control authority means they can achieve a higher angle of attack).

It's sad to click on that video and see conspiracy theorists claiming that it's poor CG. Seems no matter how great your achievements there will always be people there to try to bring you down.

I love how Elon Musk feeds the trolls like saying launches are done at night because "it's much easier to do the CGI that way"

https://twitter.com/elonmusk/status/832480331496185857?lang=...

It always happens, but really, they're just trying to hook anyone they can. When it comes down to it, there is everyone, and they are the else.

There will always be some who slip between the fingers of education lifting us up.

By "pulling up" do you mean tilting? I read your other comment but had trouble understanding the effect. Do you think you could draw a quick diagram?

First off, the perspective is confusing. The camera is located on the right side of the rocket (I'm treating the zenith as "up" and the direction of flight as "forward"). So when it pulls to the left shortly after the engine shuts off, the vehicle is really pitching up while in a steep dive.

The goal of this maneuver to lengthen the descent path, which in the absence of an atmosphere would be a pure parabola (or more accurately, a suborbital ellipse). Passing through more air means shedding more velocity due to drag, and therefore less fuel is needed to land. Geometrically the best way to do that is to pitch "nose up."

No drawing skills except shitty MSPaint, but that's never stopped me before. https://i.imgur.com/VLYXDOf.jpg

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