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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49 votes
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Why are rocket engines operating above 100% often considered nominal?

The original design called for say 500,000lbs of thrust. After years of development, tweaks, changes in the real world (bonuses, like the pressure of the fuel in the line from the entire length of ...
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  • 76.5k
49 votes
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Why do rocket nozzles flare?

The purpose of this nozzle is to achieve maximum acceleration of the flow to obtain the highest possible exit velocity. The shape of convergent / divergent (de Laval) nozzles is dictated by the ...
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47 votes

Why is SpaceX considering Methane as fuel for their next engine, the Raptor?

Methane (CH4) and RP-1 are roughly equivalent in realizable performance. As previously mentioned by other posters, CH4 has slightly higher impulse – about 370 s in vacuum vs the 360 s – at the same ...
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44 votes
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Why are Rocket engines at the base of the rocket?

..what reason is there for having the engine at the bottom, .. For the fundamental logical flaw in the desire to move the engines, please see this answer of Russell Borogove - it comes down to The ...
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43 votes

Why are Rocket engines at the base of the rocket?

Putting the rocket nozzles nearer the top wouldn't make the rocket any more stable; this is the well-known pendulum rocket fallacy. In fact, some rockets have used a tractor (engine on top) ...
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43 votes
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Why cool engines with fuel as opposed to oxidizer?

Whatever you use as a coolant will become hot. Hot oxygen will (a) vaporize, making the plumbing somewhat more difficult, and (b) react with and erode (or maybe even ignite) the cooling channels, ...
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43 votes

Why can solid rockets be both the skinniest and most spherical launch vehicles while liquid fuel rockets have a more limited range of aspect ratios?

The squat end of the spectrum has little to do with solids versus liquids and everything to do with aerodynamics. Spherical tankage is most weight-efficient, so you'd expect squat stages in cases ...
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40 votes
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Why did it take so long for methane to be used as a rocket propellant?

Or am I wrong and have there been attempts to build a methane rocket in the past? Well, if there were, I figured that John D. Clark's famous book Ignition! (1972, free online copy) would be the place ...
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38 votes

Why did it take so long for methane to be used as a rocket propellant?

The three main competitors for liquid fuel choices to date have been: Hypergolics - easiest to get started with Kerosene/LOX - Good thrust, low performance, but dense LH/LOX - Best performance, ...
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  • 76.5k
36 votes
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Would a grinding machine be a simple and workable propulsion system for an interplanetary spacecraft?

The main engineering challenge in implementing your proposal is that in order to be competitive with a chemical rocket engine, the grinding wheel must rotate at an extremely high velocity. A typical ...
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  • 476
34 votes

Is it common and good engineering for a pair of cables to be easily plugged into each other's connectors in modern spacecraft

Off the top of my head I can think of several failures caused by miscabling. On Apollo 6 the signal to shutdown a malfunctioning second stage engine was cabled to a different engine, resulting in two ...
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34 votes
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What is a "Major Component Failure" referred to in news reports about the unsuccessful Space Launch System core stage test firing?

tl;dr Each engine reports a self-test status to the vehicle it's attached to. "MCF" is one of the possible statuses and indicates that the engine controller has detected a serious - but not ...
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33 votes

Why doesn't the US use European rocket engines?

The primary reason is one of competence. The Russians have a series of pretty darn good rockets. The RD-171, a 4 engine bell, one turbopump engine (used on Zenit first stage) is an impressive ...
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32 votes
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Was the third shuttle engine any different from the others?

The engines themselves were identical within manufacturing tolerances, but there were some installation differences, mostly due to "packaging" constraints in the crowded aft compartment of the shuttle....
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30 votes
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Why doesn't the US use European rocket engines?

Initially, every country that built rockets built their own. After WW2, the design of ICBMs and space rockets was related closely enough that the capability to design and build rockets was seen as ...
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  • 121k
30 votes
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The principle behind regenerative cooling?

You are missing how heat is distributed in exhaust. Most of propellant ejected through the nozzle never makes contact with the nozzle surface or walls of the combustion chamber, and as result never ...
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  • 52.6k
30 votes
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Performance of a pumpless liquid rocket engine

The performance of a rocket engine - its specific impulse - is directly proportional to the velocity of exhaust gas (and nothing else!). That velocity is achieved by releasing the combustion products ...
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  • 52.6k
29 votes

Why design new rocket engines instead of using the existing types?

Ars Technica has a pair of articles that give some insight in why it's desirable to use new designs: NASA has been working on an updated version of the F-1 (the first stage engine for the Saturn V). ...
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  • 121k
26 votes
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How realistic would the Sea Dragon engine be to produce given today's technology?

Has any research into actually producing anything larger than the F1 been seriously carried out? The M-1 was a hydrogen engine just a little larger than the F-1. Parts of it were built and tested and ...
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26 votes
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Did any rockets use differential throttling instead of gimbal?

The first stage of the Soviet N-1 moon rocket (Block A) used this type of differential thrust system. It had 30 engines in 2 rings. The outer ring of 24 engines used differential thrust control to ...
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  • 2,211
26 votes

Is it common and good engineering for a pair of cables to be easily plugged into each other's connectors in modern spacecraft

Not in flight but this 1996 NASA lesson learned document lists multiple instances of mis connected cables during ground assembly and test including on Galileo. It in turn references JPL documents ...
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25 votes
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Why is the SABRE engine curved?

According to Mark Hempsell, formerly Future Programmes Director at Reaction Engines Ltd., now CEO of Hempsell Astronautics Ltd., explaining the reason for SABRE's curved nacelle over at ...
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  • 75.5k
25 votes
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What is that second (smoke) exhaust on a rocket engine for?

That is the exhaust of the turbopump drive. They burn a small amount of propellant, those exhaust gases are used to drive the turbopump that pumps the propellant and oxygen to the engine. There are ...
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  • 121k
24 votes

Why do rocket nozzles flare?

The gas at the narrowest part (the throat) of a convergent-divergent nozzle used in a rocket engine is ideally moving at the Mach 1, the speed of sound. This creates a choked flow condition. After the ...
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  • 64.2k
24 votes

Using of the rocket propellant for engine cooling

Really, there is nothing particularly special about it. Any liquid flowing through pipes in the engine wall will carry heat away from the engine as it heats up. Obviously, some liquids will be more ...
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  • 7,924
22 votes
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Can ion thrusters be scaled up?

Assuming you mean "quite small" in terms of mass as well as thrust output. Fundamentally, current ion drives are limited by the amount of power available to them - it takes many, many ...
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  • 8,717
22 votes
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Have Air-breathing Engines ever been used on a reentry vehicle, could they be?

As @OrganicMarble alluded to, the Buran Soviet shuttle was designed with turbojet engines (see here; and here, under "The engines") to extend the range of possible landing locations given the re-entry ...
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  • 17.9k
21 votes
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What NASA documents did SpaceX use to design their engines?

The Merlin uses a pintle injector, a design first used in the Lunar Module Descent Engine, developed from original work at Caltech and JPL. Its design was publicized as U.S. Patent 3,699,772. It's a ...
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  • 121k
21 votes
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How are rocket nozzles made?

There are many kinds of nozzles, and many ways to manufacture them. Here is a sampling. Actively cooled nozzles such as the the SSME and F-1 nozzles were constructed by fabricating the individual ...
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