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49

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 ...


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 ...


28

They might appear as the flame is detached from the nozzle, but that's in essence merely an illusion and the burn is there, all over the plume of the nozzle exhaust. It is however nearly translucent due to high purity of cryogenic propellants and by the chemical reaction producing molecules having high translucency. Visibility of the plume, unless you're ...


27

First off, it's absolutely an engine nozzle. Some sources say X-37B has a storable biprop propulsion system with ~900N thrust. The Aerojet R-42 is such an engine and the dimensions look about right -- 24" long bell with 15" exit diameter. This engine uses MMH and NTO as propellants, which are toxic, requiring the use of hazmat suits by ground crew. The X-...


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 ...


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 ...


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....


17

What you see is the first Mach disk (a standing shock wave), which causes a sudden increase in temperature, pressure, and density. At the nozzle exit, the exhaust gases have a comparably low temperature due to the high expansion ratio. In case of your SSME, the temperature is about 1200 K. The hydrogen-oxygen flame plume does not soot, and the water vapor ...


16

The thrust acts on the nozzle and combustion chamber walls by virtue of the pressure differential they contain. Using the RS-25 (SSME) as an example, with illustrations from this pdf, I can highlight a few of the components. Page 11 (pdf page 17) shows the gimbal bearing assembly, a ball-and-socket joint assembly made from a titanium forging. That is ...


16

They aren't painted red. If you zoom in on the picture, you'll see that the red parts are actually protective inserts clipped onto the nozzles to keep debris out of them during transport. It's a widespread aerospace-industry convention to make such "remove before flight" items bright red so it's obvious if you've left one on. Apparently the covers stay ...


15

According to comments on this thread, the shape of the nozzle on SpaceShip Two is to provide "free pitch-up" during the short powered flight period. That nozzle shape would direct thrust force downward slightly, under the craft's center of gravity, causing it to slowly rotate nose-upward. Presumably modifying the nozzle shape was easier than tilting the ...


15

The most numerous launcher is the Soyuz-U, with more than 700 launched. Its 4 boosters use the RD-107 engine (manufactured by Energomash), so you'd have ca. 2800 engines of a single type. PDF with some drawings of RD-107 The RD-107 is maybe not the best engine to find details on, being a soviet-era design. Other rocket engines may have been built in smaller ...


15

Uwe's comment on the question is spot on. The characteristics of the flow through the nozzle depend critically on the pressure ratio - the two pressures being the pressure at the entrance to and exit from the nozzle. Above the critical pressure ratio flow through the nozzle is subsonic and it is not choked at the throat. Below the critical pressure ratio, ...


14

You need a massive facility that can maintain a near vacuum while dealing with the engine exhaust. There are (were) a couple in the US. Plum Brook Station (Part of NASA Glenn) includes the In-Space Propulsion Facility (picture from this informative paper) Arnold Engineering Development Center (run by the DOD) includes the J-6 Large Rocket Motor Test ...


13

It's because of black body radiation; as the temperature increases the maximum light wavelength gets shifted to ultraviolet (near blue) regions which humans cannot see. This article says: Hydrogen flame, like alcohol flame emits little visible radiation but yet emits UV radiation. According to Wikipedia: With increasing oxygen supply, less black body-...


12

Obviously there are differences between implementations that will make a general rule very hard to define. For example, on the Space Shuttle, the 3 SSME engines were close together, and the two SRB's offset nearby. But when they looked at 4 or 6 RS-68A engines between the two SRB's for one of the many SLS/Ares iterations they found the heat load was too ...


12

Rocket engine nozzles often are cooled by pumping (some of) the propellant through pipes inside the nozzle wall or outside of it before they are burned inside the engine. An example of this is the Saturn V's F-1 rocket engine. This is called regenerative cooling. It's likely these "ribs" you were seeing.


12

There is a great writeup on this in the wonderful book "Development of the Space Shuttle 1972-1981" by T. R. Heppenheimer. Highly recommended, as is his prior volume "The Space Shuttle Decision". tl;dr: They did melt/burn. That was the whole idea. Page 178-179: Nozzle: The flame within a solid motor burned at 5,700 degrees Fahrenheit, which was hot ...


11

If you were able to change a booster rocket engine nozzle's area ratio at will, you would want it to expand, not contract1. Best performance is achieved when the exit plane pressure matches the ambient pressure. As the rocket ascends, the ambient pressure drops, and more expansion is needed, not less. Why don't they do this? The usual aerospace reasons: ...


11

Partial answer: This engine from the 1970s vintage Viking Lander is a liquid engine featuring one combustion chamber and many nozzles. (you can ignore the red arrow, it's from another question). The reason for this design was to prevent exhaust plume erosion of the Martian surface below the lander, to prevent degradation of the science results. Source ...


10

It varies tremendously based on the engine involved and what's being protected. Back in the day when Shuttle deployed comsats with solid fuel boost stages, the satellite would be tens of miles away at ignition but the Shuttle would maneuver to protect the windows. For Shuttle EVA, the Space Shuttle Flight Rules show that the safe distance for a suited ...


10

Those are Mach diamonds. They form due to the interaction of the exhaust flow with its own supersonic shockwaves. All rockets and some jet engines produce them; their visibility varies with the propellant combination, mixture ratio and environmental conditions. The flow pattern doesn't appreciably affect thrust since it takes place after the exhaust has ...


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 ...


10

You don't need a "bell-shaped" nozzle for a rocket -- a simple cone (often with an included angle of 30 degrees, it seems) is sufficient. Cones are easier to design (they only have one design parameter, which isn't even that sensitive) and easier to construct (they can be made with the simplest machining methods). For this reason, many early rockets used ...


10

This would not be useful in general. Thermoelectric converters don't convert heat into electrical power, they generate electrical power from the flow of heat across them. You still need to cool the cold side, or the thermoelectric junctions will just burn up. The low efficiency of thermoelectric conversion means you're only removing a small fraction of the ...


9

There's no good reason to run a production rocket engine underexpanded at ground level; it loses efficiency and will only become more underexpanded as it gains altitude. If you compare the shape of that nozzle and the size of the combustion chamber to pretty much any other rocket engine, it's clear that this is a very short nozzle. The curve of the ...


8

The NK-33 has been used successfully on two different rockets' first stages (Antares and Soyuz-1), and was planned to be used on several more, including the Soviet N-1F, and I think for Rocketplane Kistler as well. The RD-170 family of engines have been used on a number of different launch vehicles as a first stage. It was used for the boosters of the ...


8

The combustion of propellants is an exothermic process, it mainly provides heat. Initial velocity (think of the turbo pumps) and the changed specific gas constant of the combustion product are negligible. Heat also translates into pressure via the gas law. Heat and pressure are somewhat useless once the exhaust gas does not interact with our rocket any more....


8

For maximum thrust, the pressure of the exhaust at the "exit plane" (the end of the nozzle) should be equal to the ambient air pressure it's exhausting into. The larger the area of the nozzle's cross section, the lower the pressure of the exhaust stream at that point. Intuitively, if the exhaust is at higher pressure than the air when it leaves the nozzle, ...


8

Yes, aerospike engines don't have to be elliptical, since their "nozzle boundary" is just a line of equal pressure. Even the little nozzles at the top of the ramp appear to be rectangular. As far as why normal nozzles are circular, it allows for a nice smooth expansion. Flow in ducts with corners has a lot of nonuniformities. The author states in ...


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