78

Methane has the benefit of being easier to store than hydrogen. Mostly passive cooling can suffice to keep it cryogenic, whereas hydrogen needs active cooling, and will still vent over time. Which makes Methane much closer to 'storable' than hydrogen can be. This would make it useful for deep space missions, with long mission durations. Methane is less ...


49

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 the tank boosts performance (SLS has a sort of issue with this)) means the production engine actually produces 540,000lbs of thrust. Thus full power is now 108%. ...


48

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 thermodynamic properties of gases. For a subsonic gas flow, a converging passage accelerates the flow. The physics are opposite for supersonic flows: they are ...


48

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 ...


45

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 chamber pressure of 7 MPa. But, this is counterbalanced by its lower bulk density of about 830 kg/m3 vs about 1030 kg/m3. Bulk Density is the density of the ...


44

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, unless they're made of special materials.


40

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 to find it. And indeed, the index at the end of the book has a convenient entry for "methane, usefulness of" pointing to pages 8 and 191. On page 8, Clark ...


39

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) configuration (Goddard's first liquid-fueled rocket in 1926, for example), but the advantages to the pusher configuration as outlined in the other answers here are ...


38

..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 Pendulum Fallacy (the exact same fallacy I made when considering other reasons for 'engines at bottom of stack'). For more on the The Pendulum Fallacy see links ...


38

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, hardest to do So if you were starting a new space program with a clean sheet design, LOX/LH is out of the question, too hard. Hypergolics are well understood, ...


36

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 chemical rocket might have a specific impulse between about 250 and 450 seconds; therefore, the exhaust velocity is about 2500-4500 m/s. In a competitive ...


34

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 shutting down instead of one. See: Apollo 6, reason for premature engine shutdown of two engines of second stage of Saturn V? The system used to release a ...


32

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 Kerosene/LOX engine. It is a competitor for the F-1 used on the Saturn V in terms of capability. The RD-180 is a 2 engine bell, smaller turbopump version of ...


31

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. The propellant feedlines were not identical in shape and this resulted in some minor performance differences. For example, the left SSME LH2 line had a ...


30

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 has any chance to transfer its heat into them. The exhaust gas primarily cools through adiabatic expansion - high pressure and high temperature both transformed ...


30

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 from pressurized combustion chamber (pressurized by continuous production of exhaust gas by burning the fuels) and the higher the pressure the more you can ...


29

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). Some of the major differences: Another clear difference is the construction of the exhaust nozzle itself. The F-1's nozzle was made up of two parts: the first ...


28

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 having strategic value. This situation persisted throughout the Cold War. When the Soviet Union collapsed in 1989, the US government worried about the possible ...


26

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 the engine would likely have worked just fine if completed and flown. Lack of need for a super-heavy lift vehicle larger than a Saturn V prevented it from ...


25

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 engines where this exhaust is fed into the main combustion chamber (staged combustion), but this is expensive to get right so many engines use the cheaper system ...


25

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 control pitch and yaw, and was set up to shut off opposing engines in case of a single engine failure. Four launches were attempted and all failed in the first ...


25

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 attempting to avoid re-occurrence, unclear if ESA has a similar document/process. The concept here is keyed connectors, many mil spec connectors come in multiple ...


23

Logistically, methane can be easier to work with than hydrogen. Methane's boiling point is about 110K, compared to hydrogen's 20K. This means that both fuel and oxidizer lines can be purged with gaseous nitrogen. Liquid hydrogen lines can only be purged with helium, as hydrogen's boiling point is below the melting point of other inert gases.


23

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 throat, the gas expands, the temperature drops, and because of the Venturi effect, it speeds to beyond Mach 1. A convergent-divergent nozzle thusly converts ...


22

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 NasaSpaceFlight.com forum: Why a Curved nacelle? – the most frequently asked technical question. The answer is: the air intake on the front of the nacelle needs to ...


22

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 circumstances. Test versions had those engines (the same engines used in the Su-27 fighter) installed, but those were never launched into space. The version ...


21

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 design (PDF) that was used a lot by patentor TRW. A TRW employee, Tom Mueller, got bored with his day job and started working in his spare time on engines for ...


21

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 kilowatts of input power to provide tiny amounts of thrust. As you know from the answer you linked, the Dawn spacecraft is powered by 3 NSTAR ion engines which ...


21

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 tubes that made up the cooling channels (1080 tubes in the case of the SSME) and brazing them together in an autoclave. Nozzle fabrication was one of the pacing ...


21

There is a misunderstanding in your question "The engine bell(s) already support the entire compressional stress generated by the weight of the stages above it when the engine is firing..." No, the engine bells do not. (Sutton, 7th edition, Chapter 2.2) The bells mainly withstand the differential pressure forces from the gases flowing through them....


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