Talk:Comparison of orbital rocket engines

Citations and sources are needed
Please be sure that the many assertions made in this new article are verifiable. Especially any new items added to the article should have inline citations for each claim made. As a courtesy to the editor who has put a lot of work into this article to date, and who is in the middle of getting it in good order right now, a couple of the existing unsourced claims have been tagged citation needed to allow some time for sources to be added. But the entire article will need to be sourced. Cheers. N2e (talk) 16:00, 23 December 2011 (UTC)
 * Great job Savemaxim, for getting those few requested items sourced so quickly. I have an idea for the citation metadata that I find makes it easier when reusing refs, and also a slight change for adding the citation info in Wikipedia edit mode, as it makes it easier to separate the article claims from the citation, in subsequent edits.  If you're interested, ask.  But what you've done is fine, and definitely meets the essentials of WP:V. N2e (talk) 21:49, 23 December 2011 (UTC)

Missing engines, could someone include them?
The LR-87 and especially the most powerful liquid Hydrogen fuelled engine, the M-1 (rocket engine), need to be included in the table. I am not tech savvy so don't know how to include both in the table. help is required. — Preceding unsigned comment added by 86.45.64.216 (talk) 11:48, 27 January 2012 (UTC)


 * Any design on paper could be considered "the most powerful". The M-1 only got to component level testing... and since it hasn't been funded in over 40 years, i don't think i can be considered "in development". Look at page 11: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680006392_1968006392.pdf — Preceding unsigned comment added by Auroranaut (talk • contribs) 03:27, 10 February 2012 (UTC)

The RD-270 engine is missing. It's mentioned on Wikipedia in its own article as retired, development stopped during testing. Can it be added?Avmich (talk) 02:40, 7 April 2014 (UTC)

LE-7A rocket engine is where?
Hello, I seem to be there is not any descriptions of the LE-7A rocket engine on the table. There is missing rocket engine LE-7A on Japanese H-2A/B launch vehicle, where is? Could you someone tell me why? Is there any reasons? thanks.--純之助 (talk) 02:25, 29 February 2012 (UTC)


 * Don't be so pushy :). Added. Savemaxim (talk) 12:43, 29 February 2012 (UTC)


 * Savemaxim, not sure I see how anything that the editor who asked the question did was being pushy. Please assume good faith, and let's not bite the newcomers.  Cheers.  N2e (talk) 22:35, 29 February 2012 (UTC)


 * Yeah, sorry, pushy was a wrong word here, I just tried to look funny. Cannot understand how it comes that people find time to write comments but have no time (or afraid of) to edit article themselves. Cheers. Savemaxim (talk) 09:36, 1 March 2012 (UTC)


 * Savemaxim, thank you to write the article of LE-7A. N2e, I don't care of it, thank you. The reason why I do not edit this article belongs to my poorly English skills. Maybe, I loook like so funny in 'Engrish' from you...--純之助 (talk) 14:23, 1 March 2012 (UTC)

Formatting - itallic - 2012
The entire table is in italics for no discernable reason. If italics have a purpose here their use should be made clear and consistent. 24.58.54.118 (talk) 20:10, 25 June 2012 (UTC)

Thrusts
This might be just me being thick. Some figures for the "vacuum thrust" column were calculated by including Earth's surface G. Isn't that used for sea-level thrust? Marasmusine (talk) 08:02, 2 May 2013 (UTC) Worse, it seems that the thrusts given are for multiple engines in a stage not single ones. Yet another example of needing to take Wikipedia with a grain of salt. — Preceding unsigned comment added by 67.87.243.175 (talk) 19:33, 17 September 2013 (UTC)


 * When a thrust is given in pounds force, or kilograms force, there is an implicit factor of the earth's surface gravity in the value. The thrusts in the table are given in Newtons. Hence any factors in the calculation are to remove the implicit earth's acceleration that occurs in the other units from the value in Newtons.  The values in the table appear to be correct, and are given for a single engine.   Multiple engines may be used on a stage, but the thrust values in the table are for a single engine.  For the thrust to weight ratio, the weight is mass times earth's acceleration. Therefore when the mass is given in kilograms, it needs to be multiplied by earth's gravity to get the weight in Newtons. --66.41.154.0 (talk) 20:21, 26 September 2013 (UTC)

Thrust-to-weight ratio
Some of the entries for the TTW ratios aren't cited directly, but calculated based on other parameters. However, there ought to be a clarification as to what thrust figure is actually taken into account for the TTW ratios that are cited directly from references (and not calculated on the article page): Sea-level thrust? Vacuum thrust?

Similarly, the TTW of an upper stage engine might use a weight-at-altitude; although I don't think this is the case. — Preceding unsigned comment added by 123.237.156.169 (talk) 17:16, 22 January 2014 (UTC)

Since the table does not have a column "Weight" only a column "Mass" and since "Weight" only has a meaning in vertical motion at sea-level, this column should be relabelled "Thrust-to-mass" ratio and should represent Newtons per kilogram, that is m/s squared. Note that SpaceX, and every manufacturer outside the United States, uses only metric units. So this includes the RD-180 used the ULA. Similarly the specific impulse unit for performance is a consequence of confusiong pounds of thrust with pounds of mass. Thrust is a force, but fuel is measured in terms of mass. Because of the thousands of American aerospace engineers who have had their minds cluttered by this mistake it is necessary to report the performance of a propulsion system in seconds for Americans and in effective velocity, v sub eff, in m/s for the other six billion people in the world. — Preceding unsigned comment added by Jamescobban (talk • contribs) 21:03, 5 December 2020 (UTC)

It has been two months since I pointed out that the columns Thrust per Weight and Specific Impulse reference information which is not supplied in any of the other columns. Thrust per weight compares the thrust of the engine in pounds force to the weight of the engine in pounds force. In common speech pounds of force and pounds of mass are confused, leading to scientific gibberish such as Specific Impulse. It is muddled thought like that which leads to plowing billion dollar spacecraft into Mars and blowing up Ariane rockets. Specific Impulse is the number of pounds (force) of thrust divided by the fuel rate in pounds (mass) per second, resulting in a measurement in seconds! Thrust per weight is the number of pounds of thrust divided by the force exerted by gravity acting on the engine under an imaginary standard mean acceleration of gravity. Even that magic constant, is defined by standard as 9.80665 m/ss (about 32.17405 ft/ss). That is the number being used by American engineers in performing this calculation is itself an approximate conversion, like "normal body temperature" in which 98.6F is simply the result of converting the international standard value 37C to the American system of units. The chart does not give any of the American measurements from which one could calculate the specific impulse or the thrust per weight. The thrust of these engines is consistently given in SI newtons not American pounds force, and the mass (not weight) of the engines is given in kilograms, not pounds mass. One could interpret the dimensionless thrust per weight column as the number of newtons of thrust divided by the number of newtons exerted by the mass of the engine under the standard "mean gravity". However except for a very few seconds when the engine is lifting a spacecraft away from the launch pad the thrust is NOT aligned with the force of gravity. Most of the time the thrust is at nearly right angles to the force of gravity so the most logical measurement for comparing these engines is the acceleration which is produced by applying the thrust in newtons to the mass of the engine in the absence of irrelevant (because at right-angles to acceleration) forces. That is simply thrust in newtons divided by mass with the result in metres per second per second. Note that result is 9.80665 times the value in the "Thrust per Weight" column, eliminating the need for footnote b. And again the proper SI metric equivalent to specific impulse is the effective velocity of the exhaust which is the thrust in newtons divided by the fuel rate in kilograms (mass) per second.

Note that on a simplified spheroidal Earth and ignoring tides due to the Sun and Moon the actual acceleration of gravity is gn = 978031.85 (1.0 + 0.005278895 sin(lat)2 + 0.000023462 sin(lat)4).

I want to see a productive discussion of this issue. I do not want to be forced to unilaterally rewrite the columns to meet my personal non-American point of view. I want to see reasonable arguments of why the current American-specific values should be retained. — Preceding unsigned comment added by Jamescobban (talk • contribs) 05:25, 29 January 2021 (UTC)

The claim "This page exposes the full list of orbital rocket engines."
This is obviously not true (and the missing engines are numerous: from old ones, through the Chinese, to the most recent developments like in Europe).

Should it read "this page aims to expose a full list"? aegis maelstrom δ 16:28, 23 January 2014 (UTC)

I changed to 'This page exposes the list of orbital rocket engines (list is not full!).' Savemaxim (talk) 11:11, 30 January 2014 (UTC)

Thrust-to-weight ratio of Merlin 1D
Still do not have an official source saying that Merlin 1D has a 150 TTW ratio. Smb, please add.Savemaxim (talk) 11:18, 30 January 2014 (UTC)
 * False alarm. Found a source. Savemaxim (talk) 11:31, 30 January 2014 (UTC)

Some new information on merlin 1d
https://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable

Merlin 1D (current) TWR is 157.7, not 150 as listed. Weight is 1030lb / 467kg

I suggest we change the entry. Also, have in mind that the listed iSP and thrust is from the Merlin 1D vac, which is a different engine (different nozzle, optimized for 2nd stage use only). I think it needs a second entry really, especially since both engines are updated right now and will fly on this November on SES-9.

The TWR will go up to 180+ then. For reference, the new merlin 1D vac full thrust is rated for 934kN / 210.000lbf, and has an ISP of 348s. The new merlin 1D full thrust is rated for 756kN / 170.000lbf (SL) and 825kN / 185.500lbf (vac). According to Tom Mueller on quora, it seems like the weight will remain the same.

source: http://www.spacex.com/falcon9

85.72.73.49 (talk) 11:22, 21 September 2015 (UTC)

Adding source column
Just wanted to know what is your opinion on adding a column for sources in order to make the table more neat? Also not the biggest deal of course, the page has become leaner

Please check it in my sandbox and compare side by side with current page. User:Hammer5000/sandbox - Hammer5000 (talk) 18:28, 12 January 2016 (UTC)


 * I'm all for it. Oefe (talk) 19:46, 12 July 2016 (UTC)

Scope of the Table
This article provides great context for understanding both historical and upcoming rocket developments. Thanks to the many contributions of several editors, this table is large enough that scope is becoming an issue. I appreciate its comprehensive nature, but a table where 80% of the entries should measure thrust in kilo-newtons while the rest are best measured in milli-newtons loses some meaning and utility. Because this discrepancy in thrust matches another Order of magnitude discrepancy in specific impulse, we have two distinct tables randomly mixed together.

You could also find significant performance differences between the hydrogen, liquid, and solid rocket engines, but these classes have enough overlap in practice (see Antares,PSLV,H-IIB) to belong in the same the table. Some examples of "rocket engines" that do Not belong in this table could include cold gas thrusters, vernier thrusters, and solar sails, which have very low, medium, and very high specific impulse. If we were to include research projects (with actual test fires), NERVA and the Russian experiments with methane might be useful in the table. The Space Shuttle is an example where the high performance RS-25 engines are already in the table, but the less glamorous yet equally important Orbital Maneuvering System is missing. I just realized we also forgot the Apollo Ascent Propulsion System, the only engine to carry humans from the surface of the moon to orbit.

This isn't a criticism of ion thrusters, but merely some observations that might inspire creative improvements to an article we already enjoy. I see that Savemaxim included ion thrusters when he started this article in 2011, so I expect ion thrusters to remain an important part of this article. My first thought was to break the engine tables into 2 to 4 classes by specific impulse (secs), < 250 (optional), 250-500 (conventional chemistry), 500-1200 (optional), 1200+ (electric engines). A different approach would be to separate boosters, engines that made design trades to compensate for gravity and air drag, from maneuvering engines, which are designed to fire at least twice in orbit (and made trades for hours of operating time).

The only improvement that seems obvious to me is to drop the distinction for sea level performance. Sea vs Vacuum impulse applies to stages 0 and 1 where the actual performance is a non-trivial calculation involving strap-on boosters, gravity drag, max-Q, and payload g-limits. On boosters that only burn 2 minutes, we just have the Sea Level numbers, because they don't burn much vacuum. Comparisons between high performance engines like the RS-25, RD-180, and Merlin 1D are inherently difficult, and unless we also include the mass fraction of fuel that the engine is pushing, the only fair comparison is at the margin (the highest quoted specific impulse). This isn't because a 20% higher vacuum impulse will automatically mean a net 20% higher performance, it just means that the hypothetical limits for that engine are relatively high.

The chamber pressure, mass, and TWR columns can be difficult to fill in for certain organizations and could be slightly consolidated. For liquid rocket engines, the choice of turbo pump and flow design shows us where a particular rocket company might find performance improvements, regardless of whether they bother to publish their chamber pressures. Likewise, advances in the casing (or lack thereof) would be more relevant to performance than chamber pressure for solids. Basically chamber pressure could be replaced with design features. When it comes to the mass, TWR, and thrust collumns, we only need to pick two. Without knowing the dry mass that the engine is pushing, the TWR is more important than the mass of a single engine, although the (best) real world mass ratio of the entire rocket stage that the engine is attached would be more interesting, if inaccessible.

I think it would also be interesting to move the power requirements for each ion thruster from the thrust column to the propellant entry (interpreting kWatts electric as an oxidizer). I find integrating the area of the solar panels over the time of thrust to be an amusing volume for the "oxidizer tank" and the local solar flux a funny way to measure density. This is more of a cosmetic idea than a useful one.

This article is full of useful data and to a lesser extent, less useful data. We can probably find an idea or two to better organize and or consolidate the data.

108.89.136.155 (talk) 09:47, 17 January 2016 (UTC) Will


 * Surprised to see the ion engines (Xenon & Argon) on this page ("orbital" I took to mean orbital launch) but if we have them, perhaps have as a separate table so they can have different columns ? Would prefer to see a separate ion-thruster list page.
 * Also surprised to see solid fuel boosters in an 'engine' list - They are so different they could be in a separate table if not page. - Rod57 (talk) 09:17, 4 October 2018 (UTC)

"Under development"
Would one or more of the editors involved in creating this page (which is very good already, and very useful, so thanks for putting in the work) please explain their intended interpretation of "under development"? Obviously there's a spectrum of possible intentions and interpretations of the phrase, but no definitions have yet been offered.

As a result, it's hard to say whether engines such as the F-1A and F-1B should be considered. I'll just spell out the obvious so no one thinks I'm trying to hide it: these engines would share the "most powerful" honor among liquid-propellant engines if considered eligible for this table. That may influence some people's thinking about whether they should be included or not, but I'll assume we can all concentrate on the principles at issue here instead of how we may want the results to turn out.

The F-1A was developed to a fairly high technical readiness level back in the 1960s, with significant amounts of component manufacture and testing having been completed. On the other hand, significant amounts of development work remained. Rocketdyne was prepared to begin delivering them on fairly short notice (a couple of years) for some time thereafter.

The F-1B also isn't just a paper project. It has been under active development by Dynetics and Rocketdyne within the last five years, and could be delivered within another few years. Significant parts have been built and tested, but more development work is needed. I have no idea whether anyone is currently working on it, though.

Personally I would err on the side of including more data rather than less data in a table that is already so sizable and well-researched. I also think a project's state of technical readiness, particularly including component manufacture and testing, is a more relevant criterion for inclusion than whether that work is currently going on. But I'm also a fan of consensus-based decision making around here, so I figured I'd see if this is something people would like to discuss before making changes. 98.247.224.9 (talk) 06:39, 20 September 2017 (UTC)

RD-0110
The RD-0110 is not listed yet, this upperstage engine has flown more than 1000! times and was the predecessor of the RD-0124. Link: https://en.wikipedia.org/wiki/RD-0110 VictordeHollander (talk) 16:37, 7 February 2018 (UTC)
 * Thrust (vac): 298 kN
 * ISP (vac): 326
 * Dry weight: 408.5 kg
 * Propellant: LOX / RG-1

Rutherford Engines - US or New Zealand
Rocket Labs is a US company that with manufacturing plants in New Zealand where it launches its Electron launch vehicles. It will also have a launch vehicle in the US soon. So, for purposes of this chart, what is the origin of the engine, US or New Zealand or both?

user:mnw2000 16:46, 17 November 2018 (UTC)

Sea Level performance or Vacuum performance
This chart does not seem to differentiate between SL thrust and Isp, and vacuum thrust and Isp. I don't mind doing the work to add another two columns and putting the proper values in. Are there any objections? Any rules I should know? I'm usually just a casual contributor, I am not aware of all the nuances of making large edits like that. Thanks. Dotancohen (talk) 16:27, 18 February 2019 (UTC)

Missorting on thrust column
RL-10C-1 and RL-10B-2 sort before the low thrust ion motors - Rod57 (talk) 07:54, 25 March 2019 (UTC)

Proposal to remove electric engines from this page
This has been mentioned before, with several people expressing support for removing them, so I thought I'd see if that is the consensus view. In my opinion Ion engines and the like do not meet the definition of an orbital rocket engine. They are used on spacecraft, but are not a part of any orbital rocket. They are also generally not actually rocket engines, as the Electrically powered spacecraft propulsion page states, "Unlike rocket engines, these kinds of engines do not necessarily have rocket nozzles, and thus many types are not considered true rockets." Between that page, Ion thruster and List of spacecraft with electric propulsion I think they already have sufficient homes and are not needed here. — Preceding unsigned comment added by Unrulycow (talk • contribs) 12:39, 10 November 2019 (UTC)


 * Agree with removal from this page, but Disagree that ion thrusters are not rocket engines (since they do expel reaction mass) - nozzle argument seems spurious. - Rod57 (talk) 09:55, 17 June 2020 (UTC)

Should we add a power/combustion cycle column
It's not easy to find which engines use which power cycle (eg. pressure fed, combustion tap-off, staged combustion ...). This seems a more relevant property of the engine than the Vehicle(s) it was used on. The new power cycle column could go between Propellant and Specific-impulse ? Date first flown could also be added - sorting on that would show how engine designs have evolved, or is there a better page for that ? - Rod57 (talk) 10:18, 17 June 2020 (UTC)


 * I agree that a combustion cycle column would be very useful. Date first flown isn't the most relevant data in my mind, but I wouldn't be opposed if you wanted to add it. Unrulycow (talk) 21:08, 7 December 2020 (UTC)
 * It doesn't look like this ever got started so I'm happy to do it. Sevenperforce (talk) 16:10, 8 July 2021 (UTC)
 * And, done. Sevenperforce (talk) 17:44, 8 July 2021 (UTC)

RS-27
Should the RS-27 be in the retired column?

The Last Delta II flew into history and I believe they retired the line

https://en.wikipedia.org/wiki/RS-27

Space Pioneer
Chinese private launch vehicle company Space Pioneer is developing a rocket engine, Tianhuo-3, for the liquid bipropellant kerolox launch vehicle Tianlong-1.

They previously developed two other engines, and have progressed through hot fire ground testing: Tianhuo-1 and Tianhuo-2. We don't currently have all the info on the engines we might want, but seems that at least one of these--perhaps all three, since the other two are sourced--should be mentioned in the Comparison of ... article. N2e (talk) 02:43, 19 August 2021 (UTC)

Experimental engines?
Is this page an appropriate place to list experimental engines ("experimental" as in designed and tested, but never slated for use on an actual vehicle)? The NERVA engine comes to mind as something that seems like it would be interesting to learn about in this article.

155.98.131.3 (talk) 16:48, 19 January 2022 (UTC)

Canadian Hydrolox engine does not exist?
As a Canadian space geek, I was very surprised to see the G-1SL engine in this list, the only Canadian entry. A very large, staged combustion hydrolox engine of 2.4 MN thrust, an anomolously low engine mass, no reference, no listing on google searches for engine name or developer, from Canada, is extremely suspicious - I doubt it exists in any serious fashion, or at all. Dr.gregory.retzlaff (talk) 18:37, 15 April 2023 (UTC)