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50 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 ...
Organic Marble's user avatar
30 votes
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Why is the X-37B's large nozzle offset to right from the spacecraft's mid-plane?

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 --...
Russell Borogove's user avatar
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 ...
SF.'s user avatar
  • 55k
25 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 ...
David Hammen's user avatar
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 ...
Organic Marble's user avatar
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 ...
Organic Marble's user avatar
16 votes

Where does the thrust act in a rocket engine and how is it transferred to rocket structure?

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 ...
Tristan's user avatar
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16 votes
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Red color in the nozzles of Soyuz-2 rocket engines RD-107 and RD-108, is it only a decoration?

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 ...
Russell Borogove's user avatar
15 votes

Why should the velocity through the nozzle throat be sonic?

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 ...
Organic Marble's user avatar
14 votes
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Sea level static test of an upper stage possible?

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 ...
Organic Marble's user avatar
12 votes
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Ribbed rocket nozzles

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 ...
DarkDust's user avatar
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12 votes
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How can phenolic (resin?) handle rocket engine nozzle temperatures?

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;...
Organic Marble's user avatar
12 votes

Is it always one nozzle per combustion chamber and one combustion chamber per nozzle?

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 ...
Organic Marble's user avatar
12 votes

What is the area of the SSME nozzle knowing only thrust at sea level and in vacuum?

You can use the method I explained at the start of this answer: Falcon 9 Merlin 1d thrust calculated through every moment of flight Quoting from that, you use the thrust equation: $ \ \ \ F = \dot{m}_\...
Organic Marble's user avatar
11 votes
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Contracting rocket engine nozzles

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 ...
Organic Marble's user avatar
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 ...
Saiboogu's user avatar
  • 6,417
10 votes

Do converging-diverging engine nozzles need to be bell-shaped?

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 ...
ikrase's user avatar
  • 8,873
10 votes
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Conversion of heat into electricity in rocket nozzles

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 ...
Christopher James Huff's user avatar
10 votes
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Are nozzle plugs taken out before launch or are they ejected upon ignition?

In general, nozzle plugs like those depicted in the linked question, as well as other assorted engine protection setups like these nozzle FOD covers are almost always removed prior to flight, during ...
ecfedele's user avatar
  • 527
10 votes

Are nozzle plugs taken out before launch or are they ejected upon ignition?

Certainly all the big shuttle engines: OMS, SSME and SRB covers and plugs were, ahem, "removed before flight". However some of the shuttle Reaction Control System engines had covers applied ...
Organic Marble's user avatar
10 votes
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What happens if the mass flow rate is increased continuously in a converging nozzle?

This subject can indeed be quite confusing, as I got confused a bit myself as well reviewing the theory. So lets review the basics first: The Basics The complete formula for the mass flow through a ...
Ruben's user avatar
  • 1,154
9 votes

Why is the Merlin 1D Vacuum nozzle bigger than the Merlin 1D nozzle?

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 ...
Russell Borogove's user avatar
9 votes
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TR-106 under-expansion in sea-level test?

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 ...
Russell Borogove's user avatar
9 votes
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Aerospike with solid fuel

It's been tried at least once at the research level, as the paper Flight Research of an Aerospike Nozzle Using High Power Solid Rockets details. A comparison was made between conventional and ...
Organic Marble's user avatar
8 votes

Why do rocket nozzles flare?

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 ...
Andreas's user avatar
  • 1,385
8 votes
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Are there rocket nozzles that use non-elliptical shapes?

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 ...
Organic Marble's user avatar
8 votes
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What are these big shiny metallic "lumps" on the bottom edge of each Falcon Heavy nozzle?

They are bumpers, to prevent damage during gimbaling. These were added after an incident in testing where engine nozzles were damaged after they banged into each other. The bumper functions as a ...
Hobbes's user avatar
  • 128k
8 votes
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Why does the Superdraco exhaust seem so under-expanded in this photo?

In this photo, the exhaust doesn't expand so much. The nozzle looks to be a bit longer. So they've played with various nozzles. (cropped and adjusted for visibility) And the Ars Technica article ...
Hobbes's user avatar
  • 128k
8 votes

Aerospike with solid fuel

Short answer is mixing aerospike and solid fuel is probably not particularly useful The possible advantage of the mass and complexity of an aerospike is efficient operation from sea level to vacuum, ...
GremlinWranger's user avatar
7 votes
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Can exit pressure of nozzle be less than atmospheric pressure?

Sure! That's called "overexpansion" because the flow is expanded too much to match the ambient pressure. ME 239: Rocket Propulsion: Over- and Under-expanded Nozzles and Nozzle ...
Organic Marble's user avatar

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