69
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 flight (see also this article).
The Merlin engines can be gimbaled (change the direction of thrust), so on the Falcon 9 all engines can slightly change the thrust ...
49
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, ignition systems, pressure sensing, tank pressurization systems, drain/purge/test lines, and electrical connections that just look like pipes for heat ...
35
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 smoothly. Now imagine, you spend all this money to design a huge engine, and you want to manufacture it. You will need a top-notch machine park to do that. ...
27
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 area to end-of-nozzle area) is 7 times larger in the vacuum variant, which (if correct) implies about 2.7 times the nozzle diameter if the throat is unchanged.
The ...
20
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 Engine, a regeneratively-cooled booster engine. The X axis is axial distance from the throat. I am pleased to see that both metric and English units are provided....
18
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 the liquid supercooled).
The rocket carries limited amount of the stuff so the number of possible re-ignitions is limited too.
Currently it needs to re-ignite ...
18
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 failure is more likely to lead to a mission failure than others. It should be noted that while a 1 engine failure has been recovered from, a 2 engine failure has ...
17
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 can see a reuse plan very similar to what you described. The second stage nozzle would retract into the tank structure, small legs would deploy, and smaller ...
16
The mass required to deliver the required $\Delta\mathrm{V}$ depends on the Isp and the dry mass ratio of the stage. It does not depend on the thrust, except to the extent that a high thrust would increase the mass required due to a large engine and feeds. For a given Isp, the thrust just determines how long it takes to use all the propellant. For an ...
13
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 could make a slower approach, giving more time to correct its trajectory and land closer to the target. But a slower approach means spending more time and thus ...
13
According to Aviation Week, it's 4 Merlin 1D engines per week. The same article says they're planning 12 Falcon 9 launches in 2014.
In October 2014, SpaceX announced they'd completed the 100th Merlin 1D. According to that article, build tempo was 4 engines per week at that point, and 80 Merlin 1Ds had flown by then.
This engine was slated to be flown on a ...
13
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 Propulsion Elements:
Rocket propulsion systems usually do not operate with the proportion of their oxidizer and fuel in the stoichiometric mixture ratio. ...
12
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 plumbing wraps around the nozzle completely so it can form an even "curtain". This allows the nozzle extension to be lighter and simpler as it doesn't need to pass ...
11
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 2017. So they clearly did not hit this run rate, nor sustain it if they meant Merlin engines.
However, in that interim they have launched 45 Falcon 9 flights, ...
11
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 units would be Newtons per kg/sec. While that has units of m/s, and may be identical or at least quite close to the average velocity of the exhaust (which will have ...
10
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 them cheaper. They are also optimized for maximum performance, requiring complex constructions and expensive materials.
SpaceX wants to change that equation. ...
10
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 for re-use (a key design feature). Any more than this amount of thrust would make the landing even more difficult. Thus if one large engine were used instead of ...
10
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 the (steel-cased) solid stage as 28 tons (with an unremarkable 83% mass fraction); this means the otherwise decent specific impulse of the strap-on engines is ...
10
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 streaks. Each engine is tested on the stand at McGregor before installation in a booster, and again in the full booster checkout, so there are several ...
9
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. (Adding to their collection of the first Dragon to reenter, a Merlin engine hanging in the ceiling. I guess a first stage is too big to hang indoors, maybe in ...
9
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 in the higher atmosphere. So theoretically if two engines failed right after lift off it would be down to ~1.1 thrust to weight ratio so it can still ...
8
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 future launches.
But I am guessing most of the remainder will be used for R&D testing, while improving the design [Merlin C => Merlin D & Merlin D => ...
8
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 reach stable orbit from Earth's surface.
The second stage of a Falcon 9 1.1, depending on payload, is responsible for the majority of that speed: 6200-6700 m/s. ...
8
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 for only 85% of the design maximum.
Thus this evolution is just to run them at full settings. If I understand it correctly, the densified propellant and oxidizer ...
8
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 fuel cycle that is simpler than most. They chose an injector that is reliable and simple. Liquid Hydrogen is very hard to work with and very expensive. So an RS-...
8
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 covers the center flow along with the annular gap. The Apollo Lunar Module Decent Engine did something similar, but cant find a good cross-section view that ...
8
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, and thus can better take advantage of modern design of such components.
Looking at some of the other top contenders, it seems that most of the very efficient ...
8
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 oxygen density as 1,1417 (2) and RP-1 density as 0,915 (average of 0.81 and 1.02 in (3)).
So we have 245620*1,1417 = 280424 Kg of Oxygen and 146020*0,915 = 133608 ...
7
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 scrub, I imagine. (My guess is they were ready to pull the umbilical and the LOX wasn't fully loaded.) Another big drawback we are seeing is that once the LOX/...
7
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 allowed it, because the exhaust flow would separate from the bell. This would cause flow instability/backflow/... that would likely destroy or damage the bell, ...
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