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100 votes
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Why doesn't the Falcon-9 first stage use three legs to land?

I can't speak for why SpaceX made the decision. However, while three legs won't wobble, four legs are less likely to tip over. SpaceX has demonstrated tipping over is a major problem. Dr. Peterson of ...
Schwern's user avatar
  • 8,016
92 votes

How does the SpaceX Falcon 9 first-stage straighten for landing?

Ironically, the answer is in his own (or rather SpaceX's) video. Still from 0:49 of the video showing cold gas thruster firing The first stage of the Falcon 9 uses a set of nitrogen cold gas ...
ForgeMonkey's user avatar
  • 7,119
67 votes
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Why doesn't SpaceX land boosters in Africa?

The boosters do not have the range to get to Africa because they aren't going fast enough. If you look at the graphic below it shows a Falcon Heavy mission. The side boosters do not get very far ...
GdD's user avatar
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59 votes
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Why can't Falcon 9 fairings touch the water?

The fairings are not boats. While they appear to float (at least for some time), there will also be water on the inside of the fairing. That results in some issues. Inside the fairing, there are ...
DaGroove's user avatar
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56 votes
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Why is Falcon 9's fairing so big?

One of the keys to SpaceX's cost advantage is standardization on common parts. One example is the Merlin engine, which is used on both the first and second stages of the Falcon 9 and Falcon Heavy (...
SafeFastExpressive's user avatar
55 votes
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Falcon 9 design: Why is the cargo fairing so much wider than the lower parts?

The diameter of the stages is the largest size that can be transported by road without extensive "outsize load" issues (permits, having to move traffic lights and signs out of the way etc.). This ...
Hobbes's user avatar
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50 votes
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Why was there only a single Falcon 9 landing on ground-pad in 2021?

Whenever possible, SpaceX prefers Return To Launch Site (RTLS) landings over Autonomous Spaceport Droneship (ASDS) landings, since they get the booster back immediately instead of having to wait for a ...
Jörg W Mittag's user avatar
50 votes
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What is SpaceX doing differently with their Falcon 9 so that it doesn't cost as much as the Space Shuttle?

A few factors: First, the shuttle had extreme capability and performance requirements that Falcon 9 didn't have, for example: Recovery of a 100-ton vehicle from orbit, with a reusable thermal ...
Russell Borogove's user avatar
49 votes
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Is a SpaceX launch completely automated?

The rocket is autonomous, it flies itself. The navigational math, engine, and flight dynamics of a Earth-based orbital class rocket in operation are far too complex for manual operation, especially ...
Saiboogu's user avatar
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48 votes
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Why does the SpaceX Falcon 9 rocket do a 180 flip for reentry?

Hobbes has already showed you a diagram of the Falcon 9 launch profile, so I won't repeat that. Note: This answer is not intended to be a complete, scientific treatment of the subject. I knowingly ...
user's user avatar
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48 votes
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Falcon 9: engines stabilize spin

The other answers are great demonstrations of F9's capabilities, but I'll be the contrarian here and say they're all wrong and perhaps Elon oversimplified things for a tweet. This was a one engine ...
Saiboogu's user avatar
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47 votes
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Why would NOAA restrict the ability of SpaceX to live stream the second stage?

Because beaming down images of the earth from space is restricted, and Companies and Universities require a Commercial Remote Sensing Licence (weirdly these are issued by NOAA) to do so. SpaceX has ...
Mark Omo's user avatar
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45 votes

Why does the SpaceX Falcon 9 rocket do a 180 flip for reentry?

Trajectory of the Falcon 9 first stage: Graphic courtesy ZLSA Design (zlsa.github.io) As you can see, before the boostback burn, the stage flips so the engines point in the direction of travel. When ...
Hobbes's user avatar
  • 128k
45 votes

What holds SpaceX’s rocket in place in this launch?

The Falcon 9 (and Falcon Heavy) use launch clamps at the base of the vehicle to hold it steady pre-launch. In fact, the gantry and umbilicals don't actually provide much support even before they ...
Jack's user avatar
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45 votes

Falcon 9 launch process - perception of launch speed

Aside from thrust/weight ratio, I suspect at least part of this conditioning came from a peculiarity with the Space Shuttle and its launch process. The Space Shuttle's launch process was different ...
reirab's user avatar
  • 1,639
42 votes
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How are the SpaceX Falcon 9 Mod 3 and Mod 4 grid fins different?

Ok, I asked so I could use these awesome photos in an answer... I confess. The material has changed from Aluminium with an ablative paint to bare titanium. The specific shape, size, and mount points ...
geoffc's user avatar
  • 80k
41 votes

Why can't Falcon 9 fairings touch the water?

In addition to the water damage is the impact damage: the fairings wouldn't "touch" the water they'd hit the water, even with parachute retardation. A net slows deceleration down and spreads it more ...
GdD's user avatar
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40 votes
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Why are Falcon 9 main engines throttled down and up shortly after launch?

Why would one throttle down at a crucial time during steep ascent, way before MECO? Is it to weaken the effect of max Q? Yes, exactly that. The engines are throttled up to the highest extent possible ...
marked-down's user avatar
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40 votes
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What is the primary reason for SpaceX motion to have astronauts board Dragon before fueling up the rocket?

The Merlin-1D engines are now tuned to use the super cooled fuel and oxidizer. Thus you would be running the engines in an out of normal state, if not using it the same as all other launches with ...
geoffc's user avatar
  • 80k
39 votes
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Why won't SpaceX launch a rocket for a month?

The Eastern Range run by the Air Force has a 2 or 3 week maintenance window. Thus no one is launching from either Cape Canaveral (Where LC-39A is located), nor the CCAFS (Cape Caneveral Air Force ...
geoffc's user avatar
  • 80k
39 votes

Is a SpaceX launch completely automated?

Elon Musk made reference to the "Holy Mouse Click" that happens right before they start loading fuel. From that point forward, the rocket will launch itself at the planned time, about 2 hours in the ...
PearsonArtPhoto's user avatar
  • 121k
38 votes
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Why was AMOS-6 mounted on the rocket for a test fire?

The static test wants to be done relatively close to launch day, to minimize the likelihood of anything happening to the engines between the test and the launch. The more conservative procedure is ...
Russell Borogove's user avatar
38 votes
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Why did SpaceX retire Falcon 1?

The Falcon 1 was less profitable to maintain, and it didn't have the customer base to support using it. A Falcon 1 launch cost around $10 million, of which about 10% was profit. They also considered a ...
PearsonArtPhoto's user avatar
  • 121k
37 votes
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Do Falcon 9s get a thorough wash or a fresh coat of paint (they look clean pre-reflight)?

It's easy to see by just looking at photos and videos of launches of re-used boosters that they don't. There are only a very few very small white lines, probably where engineers inspected some weld ...
Jörg W Mittag's user avatar
34 votes
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Why does the CRS-8 Falcon 9 rocket appear to be swaying before launch?

Because it is. It is a very tall structure, first stage alone is 140 feet, plus second stage, plus fairing. It is considered at the limit of how tall and thin they can make it. Wikipedia says the ...
geoffc's user avatar
  • 80k
34 votes

Why won't they recover the Falcon 9 from CRS-14?

Earlier on Musk indicated it may be possible to fly a block 3/4 booster more than twice but it would depend on the missions flown, with LEO missions like this Commercial Cargo mission being easier ...
Evan Steinbrenner's user avatar
33 votes
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What work needs to be done before reusing Falcon 9?

At the moment no one knows, since no one has done quite this task before. SpaceX is learning alot with each recovered core. In this image of three of the recovered cores in the LC-39A HIF building ...
geoffc's user avatar
  • 80k
33 votes

What made the Earth appear to be flat during the recent SpaceX launch?

I suspect it is a combination of the fisheye effect of the camera lens and the lack of altitude. The fisheye effect is well known for making the earth appear more round than it should be. It does so ...
Quietghost's user avatar
  • 2,486
33 votes
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What holds SpaceX’s rocket in place in this launch?

The Transport Erector Launcher (TEL) is used to assemble the rocket in the assembly building, then driven out to the launch pad (The Transport part), then when it is time to launch, hyrdraulic arms ...
geoffc's user avatar
  • 80k
32 votes
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What makes 21st century fairings so valuable that they'd potentially be recovered and re-used?

It is not so much that in the 21st century it is hard or expensive to make a fairing. Rather they are just REALLY REALLY big. 13 meters by 4.6 meters. That is about 40 feet long, and 14 feet wide....
geoffc's user avatar
  • 80k

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