Thread by @HatchKolby

Landing spaceships in one piece is HARD.

I went down a rabbit-hole to understand why the @SpaceX Starship "belly flops" to land.

It's all about speed...

Here’s the 90-second answer 👇

1/Starship is not a booster rocket like Falcon

Starship is designed to return to Earth from orbit (really important)

That’s different from the Falcon boosters.

They’re job is to lift a payload high into the atmosphere, so another stage can take over.

2/Landing the boosters

Depending on the payload, the Falcon boosters can
actually land very close to where they took off.

They basically go up, flip at their highest point, then glide down with their grid fins and engines.

(This @SpaceX infographic explains it well)

3/Starship can’t really do that

Orbit is wicked fast.

Low Earth Orbit -- where most space stations and satellites are -- has a speed anywhere from 14.3k MPH to 17.4k MPH.

The ISS orbits at 4.76 miles per second (17.1k MPH)

That's 4X faster than a bullet 👀

4/Starship will be returning from the Moon, Mars, etc.

Distant (and speedy) space travel means faster speeds.

The record: Apollo 10 (pic) setting the record for the fastest crewed vehicle: 24,791 MPH during their reentry.

So assume Starship is coming in very, very fast

5/It’s all about drag

Without a ton of fuel to slow it’s descent, Starship needs to use the earth’s atmosphere to slow itself.

The goal is to create as much drag as possible.

Cue the belly flop.

The starship can lose 99.9% of it’s speed aerodynamically with the flop

6/Starship vs. Shuttle

When the space shuttle entered the atmosphere it had a 40-degree angle of attack.

(Angle of attack is a way of sayin, the nose is pointed up)

Starship will enter the atmosphere at ~90-deg angle of attack.

For context, most planes stall at a 15-degrees

10/Why belly flop?

2 alternatives are powered landing and parachutes

Powered landing: It takes lots of fuel especially at high speed. Starship does this post-flop.

Parachutes: Great, but too imprecise if your goal is to land something on the same pad, again and again

11/The flip

All that drag allows the Starship to slow itself dramatically without the use of valuable fuel or imprecise parachutes.

Then comes the flip.

12/As close to the ground as possible

The longer Starship can stay belly flopped (high drag) the more speed it can burn before using the engines = much less fuel.

That’s why the flip seems to come dramatically late.

Also these SN tests are just straight up and down flights

13/Landing

Once flipped, the ship descends under engine power.

The recent test (SN10) performed the flop, flip & powered descent, but hit the ground at about 22MPH

It doesn't look fast, but it was enough to crush it's legs and... boom.

Watch it all 👉

14/Like this?

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