Questions tagged [falcon-9]

Questions regarding the Falcon launch vehicle developed by SpaceX for medium payloads (15,000 lbs) to LEO and GEO (via GTO, second stage cannot inject into GEO direct)

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152
votes
2answers
250k views

What computer and software is used by the Falcon 9?

I don't know if this would be public, but what CPU / Microcontrollers are used and what software do they run on the Falcon 9? Do they use an OS or is it just bare metal programming? I found some ...
88
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3answers
124k views

What happens to the Falcon 9 second stage after payload separation?

In a Falcon 9 launch, the second stage looks like it achieves orbit along with the payload. But is that impression accurate? Does SpaceX need to do anything to deorbit the stage? I can see a few ...
66
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9answers
37k views

Why would SpaceX not use parachutes for the final descent of the first stage?

According to what I've read, SpaceX tried to use parachutes to recover the first stage of the Falcon 9, but it did not survive reentry. Now they plan to use 2 separate rocket burns to land: Reentry ...
56
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2answers
25k views

How does the Falcon 9 first stage avoid burning up on re-entry?

Now that a Falcon 9 first stage has successfully landed after a launch mission, I want to know how the first stage can avoid burning up when coming back down to earth. There doesn't appear to be any ...
54
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4answers
13k views

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

The immediate thought that would probably come into your mind would be "Because 4 legs is more stable than 3." However that is not always true. 3 legs offer the same or in some cases more stability as ...
51
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3answers
16k views

Why would NOAA restrict the ability of SpaceX to live stream the second stage?

I was watching the live stream of the Iridium-5 launch and they mentioned that NOAA had restricted their ability to live stream the second stage and that SpaceX was working to remove this restriction. ...
48
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2answers
11k views

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

I just saw this video of supposed "SpaceX Rocket Camera Landing Footage Fakery" with over a million views. The narrator repeatedly says it's complete garbage because he doesn't understand ...
44
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4answers
10k views

Why can't Falcon 9 fairings touch the water?

SpaceX is spending considerable effort to catch Falcon 9 fairings into a giant net on a ship. I am aware that salt water ruins almost everything in the long run, but the fairings are a composite ...
44
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3answers
10k views

Is a SpaceX launch completely automated?

Once the engines are ignited and liftoff occurs, are any operators/controllers on the ground making any manual changes to the flight? Or are they simply monitoring the entire event until the boosters ...
35
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3answers
4k views

Why was AMOS-6 mounted on the rocket for a test fire?

I understand that the static test is a general test of pre-launch procedures, but risking a multi-million dollar payload for a test seems remarkable. Couldn't they use a mass simulator or something? ...
35
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1answer
10k views

Why does the Falcon 9 consume hydraulic fluid?

According to many news articles, the crash of the Falcon 9 during landing on 1/10/2015 was due to running out of hydraulic fluid for the steerable hypersonic grid fins. This was seemingly confirmed ...
34
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2answers
7k views

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

On a recent launch video, the gantry is at an angle and only loose tethers are attached as the rocket is prepared for launch. What is keeping it upright and in place at this point? The engines haven'...
33
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3answers
8k views

What is the primary reason for SpaceX motion to have astronauts board Dragon before fueling up the rocket?

News piece: NASA supports SpaceX plan to fuel rockets with astronauts on board. The move is criticized by many as unnecessarily dangerous. From what I understand though, it shouldn't be necessary - ...
33
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6answers
20k views

Why did SpaceX attempt to land the booster on a barge instead of somewhere on land?

I understand the benefits of reusability for the rocket booster. But I don't understand why they're landing it on a barge. I've read tons of articles about this but not one has even hinted at an ...
32
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3answers
14k views

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

I am very new to the rockets and this can be a very dumb question, just that I am not sure if my understanding here is right? All of the rockets engines are at bottom which help it take off and ...
30
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3answers
7k views

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

According to the upcoming livestream of SpaceX CRS-14 (resupply of ISS): SpaceX will not attempt to recover Falcon 9’s first stage after launch. Why not? Wasn't that the whole point of (among ...
30
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1answer
26k views

What are the droplets/particles falling off rockets at launch?

In this picture from the AsiaSat 6 launch by Falcon 9 on 8th September 2014, the part of the rocket between the fairing and the engine appears to be surrounded by dust, water droplets or debris: And ...
29
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4answers
8k views

Why does the Falcon 9 have 9 engines?

What are the reasons for using 9 engines in the first stage of the Falcon 9? Why not 8 or 10? Looking at the Raptor engine, they seem to be looking at 9 engines again. Is there some specific advantage ...
29
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4answers
2k views

What started the explosion on the crashed Jason-3 stage landing on the barge?

If you watch the truly awesome video of the Jason-3 first stage landing on the ASDS Barge Just Read The Instructions, it is pretty clear that for one thing, they landed it. Then the leg gave out, ...
29
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2answers
8k views

What is the “emergency crush core”?

In his tweet Elon Musk said: "Rocket is extra toasty and hit the deck hard (used almost all of the emergency crush core)" What is he talking about?
29
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1answer
2k views

What work needs to be done before reusing Falcon 9?

In this article Elon Musk said that first stage of Falcon 9 which landed on the barge in April will be reused in June. Launching and landing wears material down, what parts need to be replaced and ...
28
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5answers
5k views

Falcon 9: engines stabilize spin

On CRS-16, the landing Falcon 9 booster entered a spin rotation due to a stalling grid fin hydraulic pump. According to Musk, the engines stabilized the spin. How is this possible? The main engines ...
28
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3answers
10k views

What makes 21st century fairings so valuable that they'd potentially be recovered and re-used?

I've read in @geoff's answer that SpaceX is doing some experimentation that may lead to fairing recovery capability. In fact I remember hearing Elon Musk mentioning a few years ago that it was being ...
27
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4answers
3k views

Now that they can land a Falcon 9, what will they do with it?

As most of you, I am super stoked by the amazing success of SpaceX with their Falcon 9 first stage landing back on land! We also know that they have a huge backlog (over 50 flights) and are building ...
27
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2answers
27k views

What is the cost breakdown for a Falcon 9 launch?

I don't know if this was already asked, but I'm very curious about the cost breakdown of a Falcon 9 launch.
26
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3answers
4k views

Falcon 9 launch process - perception of launch speed

One of the things that drew attention from my local group of rocket-watchers with the Falcon 9/Crew Dragon launch is the perceived speed of the actual launch process. We have been conditioned for ...
26
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7answers
6k views

How can a 9-engine Falcon rocket be cheaper than single engine rockets?

From what I understand, the engine is usually the most expensive part of each rocket, excluding payload. I'm struggling to understand how SpaceX can have one of the cheapest launchers on the market ...
26
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1answer
5k views

Falcon 9 design: Why is the cargo fairing so much wider than the lower parts?

Why does the cargo fairing have a much larger diameter than the lower part of the rocket? Of course a larger diameter lets thicker payloads fit. But then the first, inter, and second stage could have ...
26
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2answers
5k views

Why did SpaceX retire Falcon 1?

Why did SpaceX retire Falcon 1? Wouldn't it have been more cost effective then Falcon 9 for lighter missions?
26
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1answer
3k views

Was Amos 6 insured for pre-launch operations?

The Falcon 9 rocket, complete with the Amos 6 payload, just blew up (Or RUDed) on the launch pad. I believe the standard language for most launch insurances is that it is only covered after "...
25
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5answers
10k views

Why doesn't SpaceX land boosters in Africa?

Apart from the obvious answer that it'd take too long to get the booster back across the Atlantic, why doesn't SpaceX leave the main or centre booster in space a little bit longer and guide it to land ...
25
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3answers
5k views

How can the reusable Falcon 9 succeed when the reusable Space Shuttle failed?

Space Shuttle was designed to be partially reusable but was later shut down because it turned out to be very expensive to run compared to disposable spacecraft. Now Falcon 9 is suddenly reusable to a ...
25
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4answers
8k views

Why was the SpaceX abort test not initiated by real booster failure?

Today (2020-01-19) SpaceX had a successful flight abort test. As far as I can understand, at a specific altitude, Crew Dragon fired its engines and escaped from the rocket. This test looks like a ...
25
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3answers
3k views

When SpaceX claims to build 4 engines/week, which engines do they mean?

In this Tweet (dated 11 Sept 2013) Peter de Selding reported that Gwynne Shotwell of SpaceX said: SpaceX's Shotwell: We're building 7 Falcon 9 fairings/yr now, 15 in 2014, & 4 engines/week ...
24
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4answers
3k views

Are SpaceX Falcon rocket boosters significantly cheaper to operate than traditional expendable boosters?

The title pretty much sums it all up. I remember somebody once remarked about the space shuttle program that “the space shuttle was originally designed to be a space truck. But the shuttle is to ...
24
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2answers
15k views

How are the SpaceX Falcon 9 Mod 3 and Mod 4 grid fins different?

Elon Musk tweeted "Flying with larger & significantly upgraded hypersonic grid fins. Single piece cast & cut titanium. Can take reentry heat with no shielding." These have been commonly known ...
24
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4answers
5k views

How does the Falcon 9 know where the landing barge/pad is?

The descending Falcon 9 has got to hit (preferably gently) the tiny target of the Autonomous Spaceport Drone Ship (ASDS) in the middle of the ocean. How does the Falcon 9 know where the ASDS is? ...
24
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1answer
4k views

What makes the Merlin vacuum engine so deeply throttleable?

According to the October 2015 revision of the Falcon 9 User's Guide, the Falcon 9's first stage Merlin 1D engines have a 70%-100% throttle range, while the second stage Merlin 1D Vac engine has a 38.5%...
22
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4answers
7k views

Why does the Falcon 9 use RP-1/LOx and not LH2/LOx?

Why does SpaceX use RP-1 in the first and second stages of their rockets? In my view at least the second stage could use hydrogen as it currently is not being reused. I am aware that you have higher ...
22
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1answer
5k views

Why are Falcon 9 main engines throttled down and up shortly after launch?

On the official webcast of SpaceX's Iridium-4 mission a "throttle down and throttle back up of the Falcon 9 first stage engines" is mentioned. Why would one throttle down at a crucial time ...
21
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8answers
6k views

Why isn’t the “JRTI” barge larger?

The barge that SpaceX's Falcon 9 was trying to land on is creatively called "Just Read The Instructions"(hereafter known as JRTI). I've been told that SpaceX is using the barge to avoid a land based ...
21
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4answers
6k views

How does a simple construction keep a firing rocket on the ground?

Today I have seen this report of a SpaceX Falcon 9 rocket test firing. The force of a burning rocket is tremendous, and in the video we see an apparently simple construction keeping the rocket (or ...
21
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2answers
9k views

How did the Falcon 9's 1st stage return back to Cape Canaveral?

SpaceX's original plan was landing the 1st stage to a landing ship, that waits far away from the launch site, and it was like this: But tonight, the rocket's first stage landed at Cape Canaveral. ...
21
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1answer
7k views

How does SpaceX ignite their engines?

Based on the aborted launch on Thanksgiving 2013 of the first Falcon 9 v1.1 from Florida, we know that an issue occurred where oxygen got into the ground based TEA-TEB sources. I understand that TEA-...
21
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1answer
2k views

What does 'Rocket is in self align' mean?

I've noticed during SpaceX streams (this could happen with other LSPs but I've only noticed it with SpaceX) that shortly after the vehicle goes to internal power the controller says "Vehicle is in ...
21
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3answers
5k views

How many SpaceX Starlink Internet-service satellites could be deployed in a single Falcon 9 launch? Falcon Heavy? BFR?

The mass of the two test satellites being launched this month is 400 kg, but I don't believe that includes the antennae and the structure to hold and release them. Is total mass the only constraint or ...
21
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3answers
4k views

How does SpaceX plan to achieve reusability of the Falcon 9 *second* stage?

Update 08 April 2017: Elon Musk tweeted an indication that they're revisiting the possibility of second stage recovery, so this question is again relevant, and the details of the new solution may be ...
20
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7answers
17k views

How stable would a Falcon 9 first stage be after it has landed on a drone ship?

Presumably, the booster would be a very light, very tall tube (Most of the fuel spent) standing on 4 fairly small legs on a ship in the middle of the ocean. It would also still contain some LOX and ...
20
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2answers
6k views

Why won't SpaceX launch a rocket for a month?

The last launch of a Falcon 9 (Intelsat 35e) took place on July 5, but the next launch of a falcon 9 (CRS-12) won't take place until August 10. Elon said that SpaceX still had 12 launches to go this ...
20
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2answers
2k views

What are the two bright objects separating from the Falcon 9?

On the recent Iridium 1 launch the separation of the first and second stages can be seen at T+3:50. In the following screenshot we see the second stage burning at the lower left of the frame and the ...

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