Hot answers tagged

35

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 possible, which means no stronger than necessary. If the pressure inside them gets too high, it must be released to keep the hull from rupturing. The device ...


31

The reason for the transparency of the Space Shuttle Main Engine's flame is the fuel it's burning. SSMEs burn liquid hydrogen and liquid oxygen, and when hydrogen and oxygen burn the flame is nearly invisible to the human eye. i.e. it's hardly emitting any visible light, the gases themselves are colorless, and the product of the reaction, H2O (water vapor),...


31

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 chamber wall location and which occur at completely random intervals is called rough combustion. It's different from "combustion instability" defined as ...


27

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 plume. At high altitude the plume is nearly invisible. You can look at a number of shuttle launch photos and see the different appearances the main engine plume ...


25

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 space shuttle. As the SRBs produce 83% of the thrust at lift-off, a counter-force was needed to go straight-up. With shuttle engines off, I am not sure the whole ...


21

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, the plume expands and dissipates faster, and less free oxygen is available for combustion with the fuel rich exhaust (which is the source of the bright yellow ...


17

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 . The jet noise is produced directly from the formation, propagation and dissipation of vortices or eddies that are formed in the shear ...


15

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 Shuttle launch shows some of those (at 9:40, for example). The audio commentary mentions (around 9:00) that the cameras on the platform and tower are inside ...


15

Sure, it's entirely possible. Not unusual in model rocketry (where style points can count for something), for example:


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

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 of the rocket, which changes the flow of propellant in the lines fuel and oxidizer lines, which then causes a change in the thrust, which is now a loop. Pogo ...


14

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 the exhaust, which glows yellow as it combusts with oxygen in the atmosphere. The oxidizer:fuel mass ratio for complete combustion of kerosene with hydrogen ...


13

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 staging) often operate at the lowest possible exhaust pressure that prevents the flow from detaching from the nozzle walls. Historically, the Summerfield ...


12

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 plumbing wraps around the nozzle completely so it can form an even "curtain". This allows the nozzle extension to be lighter and simpler as it doesn't need to pass ...


11

Sorry, no bulb-shaped exhaust plume, at least not in true vacuum. But you might see something similar to an incandescent light bulb shaped exhaust plume at high altitudes that first stages reach, up to about 135 km high (exact altitude depends on launch vehicle and its ascent profile) above sea-level where there is still some, albeit tenuous atmospheric ...


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

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 ...


9

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 phenomenon. The term $\color{blue}{\text{blue radiation}}$ is suggested as the best available. While there are several narrow spectral lines int the near UV (...


9

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 visible SSME plume at this altitude, just a glow inside the nozzles.


9

@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). For a better comparison, I combined the two images and adjusted size and contrast to be roughly the same: My impression: There is a slight difference in the ...


9

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 used about 55 years ago. They cause extra drag (2 to 5% less Is; drag increases with larger vane deflections) and erosion of the vane material. Graphite jet ...


9

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 $$\mathrm{CH_2+3H_2O_2}\to\mathrm{CO_2+4H_2O},$$ and you can see that the exhaust is mostly water, which results in a clean, transparent flame and increases thrust ...


8

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 can then cause atoms and molecules in the plume to fluoresce, seen against a dark sky. Keep in mind that there can be a huge amount of yellow/white blackbody ...


7

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 vent them to space.


7

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, and holding umbilical connectors for launch vehicle fueling, power and purging gas. On its own, it doesn't enable crew or service personnel access to the launch ...


7

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 a high velocity relative to the atmosphere, so there's a narrow, turbulent exhaust trail which "wanders" due to winds and the gimbaling of the rocket's engines ...


6

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 the 'rectangle shape' may form by way of circular harmonics and the like. If viewed from just the right angle, the rectangular corner appearance can be replicated....


6

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 above the nozzle exit plane looking down, not below and looking across the plume as most of the available shots were taken). It's clear that the base of the shock ...


6

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 with the images from 1981 and 2015 here is a video of another test from 2017. So here it is as a GIF, and then as the video. The GIF is 30 fps from about 00:55 to ...


6

Flame color should not be directly related to hypergolic...ity(?). Rather, it's dependent on the chemical properties of the particular fuel and oxidizer, and their products. Wikipedia says: The Titan II also used storable propellants: Aerozine 50, which is a 1:1 mixture of hydrazine and unsymmetrical dimethylhydrazine (UDMH), and dinitrogen tetroxide. ...


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