Talk:Rocket engine

First sentence (reprise)

The first sentence and a half, as of 2011-02-03, read:

A rocket engine, or simply "rocket," is a jet engine[1] that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines ...

I'm not quite clear on something. Does this mean that all of the energy for the reaction rocket must come from the propellant mass? If so, then would that mean that various electric propulsion rockets (e.g., ion thrusters, including the electomagnetic ion thruster called VASIMR) are NOT rockets at all? (Even though they look to a layman like a rocket. Or their plume looks like it comes out of a rocket...). N2e (talk) 20:31, 3 February 2011 (UTC)

I think the intent was to distinguish rockets (one kind of jet engine) from other kinds of jet engine.

In a rocket, all of the mass of the exhaust jet comes from the stored propellant.

In a hydrojet, all of the mass of the exhaust jet is pulled from the surrounding water.

In an airbreathing jet engine exhaust jet, some of the mass comes from stored fuel and some is pulled from the surrounding air.

So with this definition,

The mass of the Bussard ramjet exhaust jet is collected from the interstellar medium, so it is not a rocket; instead, it is arguably a kind of ramjet.

The mass of the VASIMR exhaust jet comes entirely from stored propellant, so it is a rocket. --DavidCary (talk) 02:15, 22 April 2021 (UTC)

Motors vs. Engines

This is just a thought really, but aren't engines technically based on a cycle? I was under the impression that rocket "engines" are not really engines at all (unless we are talking about pulse jets, which do have a cycle), but are in fact motors, since they use a constant injection of fuel into the combustion chamber for constant ignition and subsequent expulsion. I think it matters enough that a page move may be in order to rectify the title to indicate that rocket "engines" are in fact motors. I know that in general rocket motors refer to solid rockets, but the distinction between engine and motor is, in my humble opinion, important. ArthropodOfDoom (talk) 20:19, 12 May 2013 (UTC)

As of now, I do not understand your differentiation between motors and engines. They are both commonly defined as devices that convert energy into motion.

• I am not aware that engines are "technically based on a cycle". Can you quote some credible sources for that statement?
• You seem to have defined motors as devices that "use a constant injection of fuel into combustion chambers". Again, can you quote a credible source for that definition? Electric motors do not use any fuel and have no combustion chambers.

mbeychok (talk) 04:42, 13 May 2013 (UTC)

I suppose you are probably right, the definitions are almost synonymous in common lexicon.

My dad is a forensic engineer and once expressed his irritation to me about the incorrectness of a "motor" cycle, but the definitions have apparently since changed.

However, I guess since the fuels go through stages of injection/combustion/expulsion, rocket engines may actually have a cycle, like internal combustion engines.

If nobody else thinks it needs changing, I think that is reason enough to not do it.

ArthropodOfDoom (talk) 17:32, 19 May 2013 (UTC)

Alright, I think I have some valid info for the change. The Motor redirect page gives some basic information as to what a motor is, and some things that are motors. It also mentions Engine under Electric motors, stating that they are in fact commonly called motors. The Engine page gives the definition of a typical air-breathing engine as follows:

In modern usage, the term engine typically describes devices, like steam engines and internal combustion engines, that burn or otherwise consume fuel to perform mechanical work by exerting a torque or linear force to drive machinery that generates electricity, pumps water, or compresses gas. In the context of propulsion systems, an air-breathing engine is one that uses atmospheric air to oxidise the fuel rather than supplying an independent oxidizer, as in a rocket.

It also mentions that rockets supply their own oxidizer. The key here is that engines use cycles, as in air-breathing engines (internal combustion/jet/etc.) Motors use either a motive force of some sort (this itself stated on the wikipedia page for motors).

This comes to one specific difference between an engine and a motor, the engine uses a cycle of some sort, and the motor uses its own internal power source for movement.

Having just written all that, under close examination of the Engine page, I now see that it says as follows: ... technically, the two words have different meanings. An engine is a device that burns or otherwise consumes fuel, changing its chemical composition, whereas a motor is a device driven by electricity, which does not change the chemical composition of its energy source.

206.214.57.38 (talk) 19:06, 27 May 2013 (UTC)

You seem to be basing your comments on Wikipedia's Motor and Engine articles. If so, you have interpreted them incorrectly. This is exactly what the Motor article states:

Motor is a device that creates motion. It usually refers to an engine of some kind. It may also specifically refer to:

• Electric motor, a machine that converts electricity into a mechanical motion

(a) The first sentence clearly states that a motor "usually refers to an engine of some kind". In essence, the words "motor" and "engine" seem to be synonymic.

(b) The second sentence does not state that a motor is "a device driven by electricity" as you stated. The Motor article uses your definition only as applicable to an "Electric motor".

(c) Elsewhere in the introductory section, the Motor article clearly states that: Engines are very commonly called "motors".

On that basis, one would say that the title of this article should not be changed. mbeychok (talk) 01:31, 28 May 2013 (UTC)

Ha...my general line of thinking (which is likely wrong) is that it is motors that are based on a cycle while engines derive power from reactions/heat of various forms. Thus electric motors would not be considered engines and rocket engines would not be considered motors; internal combustion engines, though, would be both. But as I said, that's likely wronng. Firejuggler86 (talk) 03:12, 9 May 2021 (UTC)

I suspect this is a case where the WP:COMMONNAME was not well defined at the time, such that both names are used, even if technically wrong. Gah4 (talk) 00:31, 15 September 2021 (UTC)

Reliability numbers

Justin: The number of flights and the number of failures is discussed in North American X-15. So, the failure rate would be WP:CALC. Would this be sufficient? It is a minor mention, would it be necessary to copy all the reference from X-15? Another question: are the figures on X-15 cited? It seems that many of these rocketry articles are probably edited by rocket scientists and engineers who cite their brains. Perhaps the OR tag should be a hat. Cheers -Jim — Preceding unsigned comment added by Jim1138 (talk • contribs) 16:24, 27 March 2015 (UTC)

I would call it WP:OR. I can't find the word "fail" anywhere in the X-15 article, or any information that would allow calculating a failure rate. (I guess 1 / 199 = 0.5 per cent.) But that statistic is irrelevant here, because the single in-flight failure ("during a ground test" is incorrect) did not have anything to do with the rocket propulsion ("Adams had lost control of the X-15 as a result of a combination of distraction, misinterpretation of his instrumentation display, and possible vertigo.") None of which has any bearing at all on rocket safety. It definitely doesn't belong here, and the standards for rocket failure rate don't seem to be well-defined. JustinTime55 (talk) 21:13, 21 September 2015 (UTC)

So you got your lack of knowledge from Wikipedia and then claim somebody else engaged in OR. I'll just leave this here. It's a published video.GliderMaven (talk) 01:42, 23 September 2015 (UTC)

If you're so damned smart, why don't you add that incident to the X-15 page, instead of engaging in personal attacks? JustinTime55 (talk) 20:51, 5 January 2017 (UTC)

Tank pressurization

Tank pressurization does not appear to be explained in the article, nor elsewhere on Wikipidia that I can find: how tank pressurization works for rocket engines, why it is needed, and how it is typically done; e.g, by Helium gas exogenous pressurization, or by autogenous pressurization as apparently Advanced Cryogenic Evolved Stage and Firefly Space Systems are pursuing (found the terms via a Wikipedia search but the term is unlinked in the article). (and maybe SpaceX too with their Raptor engine?).

In any case, I'm thinking that it would be useful to have such an explication exist somewhere on-wiki. Anyone know of something I'm missing? And is this article an okay place to do it? Cheers. N2e (talk) 13:49, 17 December 2015 (UTC)

I agree this needs to be covered, but since this article focuses on engines, and tank pressurization is an attribute of the vehicle rather than the engine, it might be more appropriate to add it to Rocket instead (which also doesn't mention it.) I also see ullage motors aren't covered; that probably could be considered to be related to pressurization. I thought the two were exclusive, in that one might expect pressurization prevents ullage, but that apparently isn't the case, as the ullage motor article gives the example of Apollo 13 using the LM's reaction control jets to provide ullage control before firing the descent engie. JustinTime55 (talk) 14:13, 17 December 2015 (UTC)

Actually, maybe pressurization should go in both articles, since one of its purposes as I see it is to allow simplification of the engine design by eliminating the need for turbopumps. For example, I don't think the Saturn V first stage uses pressurization because its engines have turbopumps and operate under at least 1g, though the third stage does even though its engines have pumps because it's restarted in zero-g. The SM and LM spacecraft need pressurization because the engines are simplified for reliability (no turbopumps). At any rate, we need RS for the topic. JustinTime55 (talk) 14:31, 17 December 2015 (UTC)

It also looks like the subject is mentioned in Liquid-propellant rocket. JustinTime55 (talk) 22:15, 17 December 2015 (UTC)

Yeah, it's an important topic for liquid-propellant rockets, so that probably is a good place for us to expand the wiki-explanation. Great suggestion!

Re ullage and tank pressurization: I think these two are rather separate things. The ullage issue becomes acute in conditions of microgravity, where the liquid/gas interface becomes unclear, and without taking action to ensure only liquid is at the end of the tank that is the tank outlet into the engine piping system, then one runs the risk of getting irregularities in the propellant mass flow to the rocket engine. Even with adequate pressure, ullage is an issue for spacecraft in orbit, and thus in microgravity.

Tank pressure is needed for both pressure-fed engines and pump-fed engines. However, since the only driver for mass flow in pressure-fed designs is tank pressure, then those tank pressures are typically much higher, compared to tank pressures in pump-fed designs. But in the case of pump-fed (generally, turbopump), one still must have adequate pressure to support fluid flow from the tank outlet, through the pipe system, and into the turbopump inlet.

The other issue of pressure in rocket engines is having sufficient pressure to overcome combustion chamber pressure so the propellants will enter the combustion chamber. But in my view, this is already explained in Wikipedia.

So given that the tank of a liquid propellant rocket needs some designated design pressure, there are apparently (at least) two ways of pressurizing the tanks: autogenous (like Firefly and ACES and maybe Raptor are planning to do) and exogenous (generally, from high-pressure helium by means of control valving; helium tanks may, or may not, be physically inside the volume of the tank, and may or may not, for design reasons, be immersed below the liquid interface [at launch time, in a gravity field]). It is this aspect of tank pressure, and how that pressure is created and maintained, that I believe needs explicated on Wikipedia. Cheers. N2e (talk) 06:42, 18 December 2015 (UTC)

Technically inaccurate revision

I just reverted this edit made by @Drycroft4:

A rocket engine is a form of propulsion engine that carries it own propellant (fuel) as well as a catalyst to ignite that fuel (usually oxygen). Thereby a rocket engine can operate on its own, in a vacuum such as space, since no external oxygen is required. A rocket engine differs from a jet engine in that the jet engine requires the external catalyst of air/oxygen.ref>

Several technical and logical problems with this:

• You apparently don't understand what a catalyst is; rocket engines use oxidizers, which are chemically consumed in the reaction, and thus are not "catalysts" which by definition enable a reaction without being consumed. Catalysts are rarely used in rockets.
• A rocket engine does not "carry its own propellant"; liquid propellants are carried in tanks which are not part of the engine. (Note we have a separate article, Rocket, which covers a complete vehicle.) The distinction between engine and propellant is somewhat ambiguous for solid-fuel rockets, where it's not clear whether the "engine" (just a nozzle) actually includes the propellant (i.e., is the casing holding the propellant actually part of the "combustion chamber"?)
• Wikipedia syntax: you broke the citation reference by removing the "<" from the "<ref>" tag. (See WP:Citation templates for guidance.)
• By changing text immediately before the citation reference, you have invalidated what the source (Sutton and Biblarz book) said.

If you feel strongly this change is necessary, please discuss it here first. JustinTime55 (talk) 16:25, 8 November 2016 (UTC)

• I'd agree with your reversion here.

That said though, many rocket engines have used HTP as either a monopropellant or as an oxidiser and these have used catalysts. Many have also used a consumable catalyst: it is easier in engineering terms to supply the catalyst as a fluid in excess and expel it as part of the reaction mass, rather than it is to try and maintain a rocket's high flow rate through a wire mesh or similar. A catalyst used in excess also allows an inefficient catalyst, which may also be far cheaper, compared to a metallic catalyst. Andy Dingley (talk) 16:46, 8 November 2016 (UTC)

Safety section

(This is a continuation of "Reliability numbers" above):

I'm concerned that we're conflating safety considerations of Rocket engines (the topic of this article) with those of Rocket (vehicles); this is complicated by the fact that the two can interact with each other:

• Vehicles can be lost by catastrophic failures of engine components (e.g., a turbopump bearing failure);
• Vehicle failures can be caused by propellant tank, pressurization, or line problems (engine hardware not necessarily involved);
• Vehicle loss can be caused by guidance failures; the vehicle goes off course, not necessarily attributable to engine or airframe failures, but range safety still has to abort the mission and blow up the vehicle.
• Sometimes "engine loss" is caused by no fault of engine hardware, but by problems induced by interactions with the vehicle; e.g. likely culprit is pogo oscillation (see Apollo 6, where the engine's fuel lines were damaged by the oscillation)
• We call the Challenger disaster a "Solid Rocket Booster failure"; sure, the proximate cause was flame burning through the O-rings, but the catastrophic failure was caused by the vehicle turning cross-wise into the wind, exposing it to high aerodynamic stresses, and rupture of the external tank leading to combustion of the propellant.

I think we're oversimplifying just by lumping all failures together correlated to "engine-flights". Any ideas on how to fix this? JustinTime55 (talk) 21:45, 5 January 2017 (UTC)

Infobox

User:JustinTime55 added Template:Infobox machine to the article on September 15, 2020, without any prior discussion. Although I'm generally an advocate of using infoboxes, even for certain types of bio articles where some users oppose them, infoboxes are neither required nor forbidden, but instead subject to article consensus. I believe this article is too general and confusing for an infobox to be of use, as the separate invention dates illustrates. As such, I've removed the infobox per WP:BRD. Please do not restore it without a clear consensus here to do so. Thanks. BilCat (talk) 23:51, 23 September 2020 (UTC)

Fuel Mixture in Combustion Chamber

Are there any alternatives? 41.95.23.234 (talk) 16:54, 21 June 2021 (UTC)

Isp and unit systems

Should the Isp section, and especially related to the unit of seconds, explain the connection between mass of propellant and weight (at sea level on earth) of propellant? It is a units trick, convenient in that it gives the same value in different unit systems. Gah4 (talk) 00:34, 15 September 2021 (UTC)

Consistent use of Engvar

FYI, this article is tagged to use British English, but there are 11 instances of "oxidizer" which should be "oxidiser". JustinTime55 (talk) 15:13, 11 May 2022 (UTC)