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35 votes
Accepted

Do spacecraft ever release unneeded gases into space?

You bet. Not only gases, but astronaut pee as well! Which could result in spectacular light shows. This happens for several reasons: Spacecraft and the tanks inside them are built to be as light as ...
Organic Marble's user avatar
31 votes
Accepted

Do liquid propellant rocket engines experience thrust oscillation?

Yes, in liquid engines this phenomenon is called "rough combustion". Sutton (4th edition) says Combustion that gives pressure fluctuations greater than about +/- 5% of the mean pressure at a ...
Organic Marble's user avatar
30 votes
Accepted

Were the Space Shuttle's Main Engines ever off while the Solid Rocket Boosters were firing?

Hydrogen-oxygen engines produce a relatively faint blue flame, with visible blue-white shock discs or diamonds under certain circumstances, particularly low altitudes where air pressure confines the ...
Russell Borogove's user avatar
27 votes

Were the Space Shuttle's Main Engines ever off while the Solid Rocket Boosters were firing?

No, they were never off. Here is my explanation: have you ever noticed that the top engine is tilted down? This is us to keep the center of thrust more or less aligned with center of mass of the ...
le_daim's user avatar
  • 2,060
21 votes

Apollo 4 vs Apollo 8 plume

In addition to the foreshortening illustrated by Organic Marble, the appearance of rocket plumes changes significantly with altitude. At higher altitudes, the pressure of the surrounding air is lower, ...
Russell Borogove's user avatar
19 votes
Accepted

Why are rocket launches so loud?

From Prediction of Acoustic Loads Generated by Propulsion Systems The primary noise source during rocket engine testing is the jet noise generated by the rocket exhaust plume . ...
Organic Marble's user avatar
15 votes
Accepted

Why do the shapes of these two exhaust plumes from an Atlas V 411 look different?

Yes, the pressure of the first stage exhaust is always at least slightly subatmospheric, because that gives the maximum average ISP over the whole burn time. Rockets with boosters attached (parallel ...
Rikki-Tikki-Tavi's user avatar
15 votes
Accepted

Do strongbacks/launch towers have to be repainted or refurbished after a launch?

On e.g. the Saturn and Shuttle launches, vulnerable items like umbilicals are retracted into closed spaces, with a door closing over them in time to protect them. This very detailed video of a ...
Hobbes's user avatar
  • 127k
15 votes
Accepted

Is it possible to create different colors in rocket exhaust?

Sure, it's entirely possible. Not unusual in model rocketry (where style points can count for something), for example:
ceejayoz's user avatar
  • 1,278
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
Accepted

Why does Merlin 1D Vac turbopump drive exhaust go around the nozzle?

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 ...
Russell Borogove's user avatar
14 votes

Do liquid propellant rocket engines experience thrust oscillation?

In addition to the "rough combustion" that Organic Marble mentions, liquid engines also characteristically suffer from pogo oscillation. This is the phenomenon in which the thrust causes acceleration ...
dotancohen's user avatar
  • 6,734
14 votes
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How did the kerosene-burning Black Arrow have transparent exhaust? (seems to just "hover" in photos)

Typically, kerosene-LOX engines run fuel-rich, with an oxidizer:fuel mass ratio of about 2.5:1 (as compared to 3.5:1 for complete combustion), leaving significant amounts of unburned carbon soot in ...
Russell Borogove's user avatar
10 votes

Were the Space Shuttle's Main Engines ever off while the Solid Rocket Boosters were firing?

Offered as a supplement to the other answers - here's a frame from an SRB mounted camera (post-separation) showing the SSMEs running in the absence of SRB plumes. As stated by others, there's no real ...
Organic Marble's user avatar
10 votes

ISP losses associated with exhaust vane TVC

Sutton edition 7 mentions them without too much detail Jet vanes are pairs of heat-resistant, aerodynamic wing-shaped surfaces submerged in the exhaust jet of a fixed rocket nozzle. They were first ...
Organic Marble's user avatar
10 votes

What is this South Korean rocket and why does it have separate yellow and blue exhaust plumes?

That's KSLV-2 aka Nuri. The first stage uses kerolox gas generator engines so the brighter flame is almost certainly ignited fuel-rich gas generator exhaust. https://en.wikipedia.org/wiki/Nuri_(rocket)...
Organic Marble's user avatar
10 votes
Accepted

Inconsistencies in calculating exhaust velocity

You are simply calculating the wrong parameter. You are calculating exhaust velocity. You can't calculate this without knowledge of the nozzle geometry because exit plane pressure is used in the ...
Organic Marble's user avatar
9 votes
Accepted

What is the cause of the blue light from LH2/LOX rocket engines?

As pointed out by @Thomas, this nice thesis Radiation from High Pressure Hydrogen-Oxygen Flames and its Use in Assessing Rocket Combustion Instability - Ph. D. Thesis, Fiala, T., 2015 discusses this ...
uhoh's user avatar
  • 149k
9 votes

Does the luminous blue shockwave from the RS-25 engine appear to be rectangular?

This should be considered a supplementary answer. The Rectangular shape looks quite convincing, but remember we can only see the back part of the flame clearly. There are other mechanisms by which ...
Ingolifs's user avatar
  • 6,428
9 votes
Accepted

Does the luminous blue shockwave from the RS-25 engine appear to be rectangular?

The shock cone is not rectangular in any way when the engine is being tested, just as it is not in flight. I finally ran across a different camera angle view of the same test stand (from slightly ...
Organic Marble's user avatar
9 votes

Apollo 4 vs Apollo 8 plume

@russell-borogove explains that the plume changes during flight. We don't know the precise height when the two photographs were taken (both are labelled "climbing after lift-off" in the NASA archive). ...
asdfex's user avatar
  • 15k
9 votes

How did the kerosene-burning Black Arrow have transparent exhaust? (seems to just "hover" in photos)

I think Wikipedia's Bristol Siddeley Gamma; Advantages of kerosene / peroxide engines can shed some light on the missing light. The combustion formula of kerosene and hydrogen peroxide is $$\mathrm{...
Duck's user avatar
  • 327
8 votes

Is it possible to create different colors in rocket exhaust?

There are several ways to do this. Fluorescence Night time launch close to sunset or sunrise so that the rocket quickly reaches an altitude where it is illuminated by the Sun. The bright sunlight ...
uhoh's user avatar
  • 149k
7 votes
Accepted

Strongbacks vs Launch towers: Difference and definition?

Strongback is a part of TEL (Transporter Erector Launcher) that facilitates horizontal transport from horizontal Vehicle Assembly Building to the launch site, erecting the launch vehicle vertically, ...
TildalWave's user avatar
  • 75.9k
7 votes
Accepted

Is the unusual pattern/shape of SpaceX exhaust due to atmospheric pressure?

During the earlier parts of the flight, two things are different: the atmospheric pressure is higher, limiting the expansion of the exhaust, and the rocket is moving slower and ejecting its exhaust at ...
Christopher James Huff's user avatar
7 votes

Do spacecraft ever release unneeded gases into space?

Section 30.4 of this NASA document describes passivation of spacecraft at end of life. The objective is to remove all sources of stored energy including pressurized gases and the way to do it is to ...
Ross Millikan's user avatar
7 votes

What color would the exhaust of an antimatter rocket be?

As noted in the comments - there may be nothing to see. If your magic antimatter rocket is just slapping matter and anti matter together and defeating physics to get all the resulting products ...
GremlinWranger's user avatar
6 votes

Do spacecraft ever release unneeded gases into space?

There was a proposal by Mars One for a mission to Mars. It suggested using hydroponics to produce oxygen. But a MIT study reviewed it and showed that this model could not work, because the plants ...
geoffc's user avatar
  • 79.2k
6 votes
Accepted

What is the 'Summerfield criterion' regarding rocket exhaust expansion

The Ralf Stark paper linked from the answer which mentions the Summerfield and Schmucker criteria ends with a list of references; among them are a 1973 Schmucker paper (translated in 1984, here) and a ...
Russell Borogove's user avatar
6 votes

Does the luminous blue shockwave from the RS-25 engine appear to be rectangular?

tl;dr/update: The corner that makes the shock wave appear to have aspects of a rectangular top is real and it is reproducible! But @OrganicMarble's new answer now puts the issue to rest. Together ...
uhoh's user avatar
  • 149k

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