69 votes
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SpaceX merlin engine failure

The Falcon 9 can shut off a faulty engine, re-configure the remaining engines (change thrust levels, vector direction) and update its flight profile in real-time. This happened on the SpaceX CRS-1 ...
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  • 12.2k
50 votes
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If rocket engines only need fuel and oxidizer, then why there are so many pipe lines on the engines?

While an ideal engine would just ingest fuel and oxidizer and produce exhaust gas real world engines will have some combination of regenerative cooling, film cooling, turbine exhaust, hydraulic power, ...
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35 votes
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How can a 9-engine Falcon rocket be cheaper than single engine rockets?

No, on the contrary. The larger the engines get, the more expensive they get. Just look at the massive amount of full-scale tests they needed to get the F-1 engines of the Saturn V main stage running ...
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27 votes
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What are the differences between a standard Merlin engine and the Merlin Vacuum engine?

The biggest difference is the nozzle. For optimal performance in vacuum, you want a much larger one. According to Spaceflight 101, the chamber pressure is the same, but the expansion ratio (throat ...
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20 votes
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How hot do rocket engine nozzles get?

Direct measurement is difficult; I've seen some optical methods used but can't put a hand on them at the moment. Here are some calculated inner and outer wall temperatures for the Space Shuttle Main ...
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18 votes

How do the Falcon 9 engines re-ignite?

Falcon 9 uses TEA-TEB to ignite its engines both on launch and during all the landing burns. The mixture is pyrophoric - it ignites spontaneously when it comes to contact with oxygen (both in air or ...
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  • 5,027
18 votes

SpaceX merlin engine failure

The engines can be vectored to manage this. They actually have had an engine failure and still made it to orbit in the CRS-1 mission. Note that there are some points in the mission that an engine ...
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  • 118k
17 votes
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How does SpaceX plan to achieve reusability of the Falcon 9 *second* stage?

Old/Original Proposal for Second Stage Reuse Second stage reuse for Falcon 9 was a planned feature that has been discontinued. In this old render(Shows a Falcon 9v1.0 with square engine block) you ...
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15 votes
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Merlin engine stoichiometry

Fuel-rich operation is common in hydrocarbon engines and improves specific impulse, although there's some confusion about the mechanism by which that occurs. According to Sutton & Biblarz' Rocket ...
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14 votes
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If it is difficult for Merlin engine to have deeper throttling, could it be as an option a different engine at the center of the rocket?

The question presumes that lower landing thrust for Falcon 9 is desirable, which I believe is false. The landing thrust is a compromise between opposing requirements. With lower thrust, the rocket ...
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14 votes
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Why does Merlin 1D Vac turbopump drive exhaust go around the nozzle?

The turbopump exhaust in the Merlin 1D vacuum versions is directed into the nozzle where it acts as a cooling layer between the very hot chamber exhaust and the wall of the nozzle extension. The ...
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11 votes

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

Revisiting this question 4 years later, it seems clear that while they had this estimate of the engine build rate, they did not hit it. There was an Instagram post of the 400th completed engine Dec ...
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11 votes
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Does anyone know how to calculate the KG per second of RP-1 and LOX from the 9 Merlin 1D engines?

As @RussellBorogove points out in his excellent answer, Isp or "mass-specific impulse" is the number that expresses the relationship between thrust and mass flow rate. Mass specific impulse with ...
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10 votes

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

In addition to the other answers, I think its also worth noting a few extra points: Landing. It takes just one of those engines, throttled all the way down to its minimum thrust to land the stage ...
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10 votes

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

Traditionally, engines are expensive because they require lots of manual labor to build. Because they are built in small numbers, there's no point in investing in an automated factory that can build ...
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  • 121k
10 votes
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GSLV MK2 vs Falcon 9 - Reasons for Huge performance difference

The biggest factor is probably the "inside-out" staging design, where the solid core burns out but is not jettisoned, while the liquid boosters continue to run. Spaceflight101 gives the empty mass of ...
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10 votes
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What is the white spray-pattern residue inside these Falcon Heavy nozzles?

I believe it is residue from the TEA-TEB starting fluid. Triethylaluminum combustion produces aluminum oxides, Triethylborane produces boron oxides. Both are shades of white and grey, matching the ...
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9 votes
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How many engine firings can a SpaceX Falcon handle?

After the first few landings of the first stage, Elon Musk said that the first core (landed on land) from the Orbcomm OG2 mission will become a static display outside the SpaceX factory in Hawthorne. (...
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  • 76.4k
9 votes

SpaceX merlin engine failure

Per the specs on the F9 page it has about a 1.4 to 1 thrust to weight ratio at takeoff and it goes up from there as the vehicle burns fuel getting lighter and the engines start to generate more thrust ...
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8 votes

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

It depends on so many things. SpaceX chose many instances of a smaller engine, which is generally simpler than a single larger one to build and complexity is related to cost. They chose a fuel and ...
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8 votes

SuperDraco Dragon V2 vs Merlin 1D Falcon

The thrust of the engines (for any launcher or spacecraft, really) is nowhere near as important as the amount of fuel feeding them. It takes about 9400-10000m/s of ∆v, depending on trajectory, to ...
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8 votes
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What are the challenges in Falcon 9 "full thrust" (v1.2) with densified propellant?

The Merlin 1D's are claimed to have been able to run at the Falcon 9 1.1 Full Thurst level all along. However to get them into initial use on the Falcon 9 1.1 earlier, they were initially certified ...
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8 votes

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

Some engines will be used on the grass hopper platforms. Some engines will presumably fail during qualification/smoke (pun not intended*) testing. Some engines will end up in the stock pile for ...
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8 votes

Pintle Injector Face Shut Off - Merlin

Here is an image on how this can be done. It can be done using a sleeve that covers the central pintle. The sleeve also has a "bump" in it that controls the gap around the annular gap. So the sleeve ...
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8 votes
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How did SpaceX achieve such a high Thrust to Weight ratio with the Merlin engine?

As I understand the two major items are continuous refinement of the design, and 3-d manufacture of key components of the engine. The Merlin is the most recently designed engine used on a large scale, ...
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  • 118k
8 votes

Does anyone know how to calculate the KG per second of RP-1 and LOX from the 9 Merlin 1D engines?

I think uhoh's answer (7607000/2570=2959 Kg/s) is in the ballpark. Here's another (less precise) approach: First stage has 245,620 L of liquid oxygen and 146,020 L of RP-1 fuel (1) Let's assume ...
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  • 2,093
7 votes

What are the differences between a standard Merlin engine and the Merlin Vacuum engine?

There are several reasons for having deep throttling in the vacuum engine but not the first stage engine. (1) The first stage cannot use a large expansion bell, and couldn't even if the mechanicals ...
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7 votes

What are the challenges in Falcon 9 "full thrust" (v1.2) with densified propellant?

We saw one of the major drawbacks of using the condensed propellant tonight. First, the LOX and RP-1 are not loaded until last minute (-10:00) so that they heat up at a minimum. This led to tonight's ...
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  • 198
7 votes
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What is wrong with this burn time calculation?

The equation works for a straight-line burn with no gravity losses, but the first-stage burn of an orbital launcher arcs from vertical to nearly horizontal, and loses velocity to gravity. To compute ...
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7 votes

From what material and how are the Merlin engines and nozzles of it (sea level) manufactured?

Tl;Dr; Nickel-cobalt with a copper cooling jacket. Spacenews interviewed Elon Musk where he said ".... The hardest part of the engine to mass produce is the electro-plating of nickel cobalt on ...
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