Yesterday there was a question about small commercial rocket motors for sale in the U.S.. I'm going to post an image of it in case it becomes inaccessible in a while due to deletion:

what is the market for small liquid rocket motors

TildalWave put it on hold on the grounds that there is a policy across SE against questions asking for a shopping recommendation. The argument is that any answer becomes obsolete quickly, is highly dependent on the particular needs of the asker and as such is usually not useful to others, and that if recommendations were allowed, attempts at covert advertising through fake questions and answers would immediately appear.

The question had been around for a number of hours when that happened, had received two answers, and nobody had noted the shopping issue and flagged, commented, or voted to close. In my case, I just wasn't aware of the entire issue.

Rikki-Tikki-Tavi had answered with a brief relevant list and made the case the rule doesn't apply here:

...I don't think it's fair to say that he's asking for a product recommendation. He's asking what companies manufacture these. Also, most of the arguments why product recommendation questions are bad do not apply to SE. Most of these thrusters were designed decades ago with minor upgrades (so why will they be obsolete next year?), personal preference is not much of an issue, prices are unavailable in any case, and he explained that he wanted US manufacturers first.

It is certainly easy to see why it seems doubtful that vendors or buyers of spacecraft components would use Space.SE to boost sales, or would be influenced by opinions here. Or is that entirely true? One doesn't get the feeling the asker was actually about to buy a rocket motor, because if he was, it would be very strange if he didn't already know about the market. Is that going to apply to all commercial components at all times? Can it be handled case-by-case since it seems unlikely to come up more than rarely? Is it viable to make a complete list of all products to answer such questions and have confidence it won't become obsolete?

There was enough debate on this occasion it seems to deserve examination. Since I am pretty neutral and also am trying to get used to how to handle all this kind of thing, I decided to do the asking.


2 Answers 2


Let's look at this question from a different angle than the shopping angle.

Based on the parameters in the question, we're talking about the type of engine you would have on a model rocket not bound for space. That means this question is actually off topic because it is about model rockets, not space exploration.

This is what our Help Center says on what is on topic here:

Space Exploration is primarily about spacecraft, how to send them to space, and their functions there. Specifically, questions on these topics are encouraged.

  • Space exploration
  • Satellite design and operation
  • Systems with potential use in space
  • Scientific discoveries made by space probes

From What topics can I ask about here? - Space Exploration Help Center

Since the engines being asked about are not going to be used on a space-bound rocket, then we are not talking about spacecraft or systems with potential use in space.

Thus, without even delving into the ambiguous "shopping question" issue, we can determine that this question is firmly off topic on this site.

Edited to add:

One commenter did point out this:

I think op's question was aimed towards the commercial side of things and not amateur rocketry. Maybe they could be used as an apogee kick motor or for attitude control on large spacecraft, though I could be guessing. – Mardlamock N

If it is the case that the use case of the engine was for some auxiliary purpose on a space-bound vehicle, then there is room for improvement in the question. The author would need to edit to make the question more specific.

  • $\begingroup$ However the disagreement arose over that aspect. It also wasn't clear what application the asker was seeking, it could have been regarding what motors are used as thrusters on commercial rockets. Which means it should have been put on hold as unclear. It keeps coming back to that, and that was certainly stated at the time. But broad questions are often tolerated - the question was answerable with a short list. $\endgroup$
    – kim holder
    Jun 6, 2015 at 14:40
  • 1
    $\begingroup$ @briligg If the unclear nature of a question makes it appear to be off topic, it can be closed as off topic. The close labels are just that--labels. They are assigned based on what first appears to the closer. It is not critical to have 100% accuracy in close labels; what is important is working with the poster to help them edit the question to something that can be reopened. But that is only possible if the poster is still interested in editing the question. $\endgroup$
    – called2voyage Mod
    Jun 6, 2015 at 14:42
  • $\begingroup$ @briligg The issue is not that the question is broad, but that without further clarification it appears to be off-topic (model rockets not space-bound). If the poster included more details as should have been included in a question then it might have been apparent that the use of the engines was actually on a space-bound vehicle. $\endgroup$
    – called2voyage Mod
    Jun 6, 2015 at 14:45
  • $\begingroup$ It is critical to have accurate close reasons. If the close reason isn't 100% accurate, the closer should leave a comment as to why. (This is why a flag is auto generated if you close without comment... I hope you're not simply dismissing those when they come up!) The whole point of the close reason is to tell the user what they did wrong so they don't do it again. To simply close something that appears on topic without saying why is a waste of everyone's time. $\endgroup$
    – corsiKa
    Jun 15, 2015 at 14:50
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    $\begingroup$ @corsiKa The user did say why they thought it was off topic. That reason is now up for debate, but my point is that there are other reasons that post was (or might have been) off topic. Yes, it would be nice if someone dropped a note about those reasons under normal circumstances, but in this case it was an unregistered user who hasn't even returned to the site since they posted the question. $\endgroup$
    – called2voyage Mod
    Jun 16, 2015 at 14:07

Thank you briligg, for posting this question.

I admit that I was unaware of the shopping question issue, as I was unaware when someone previously asked about attitude control systems for cubesats.

For the consumer electronics oriented stacexchanges I can easily see why these questions are problematic. Additionally to the reasons listed here, they show very limited research effort, since these companies spend a lot of money to make their products known.

This is different for SE products. Companies making these spend very little on untargeted marketing, like websites. As a consequence their sites often don't have very high google page rank, and are hard to find, especially among the manufacturers of hobbyist components who do spend on such things.

Now, I am not against closing/deleting that particular question. I think it is unclear what the purpose really is. I answered as best I could on the assumption that it is a valid question (i.e. not about a model rocket). The links I posted all concern storables, so no normal hobbyist material.

But departing from this particular question, I think talking about suppliers is important to understand things about how the space industry works. If we ban all questions about "Who manufactures component XY?" we miss out on a lot of possible insights on things like monopolies and ITAR regulations.

Edit 2015/09/28:

I think this is another legitimate question about suppliers:

Who sells RP-1 to SpaceX and other commercial launch companies?

  • 2
    $\begingroup$ Good point in the last paragraph +1 $\endgroup$
    – called2voyage Mod
    Jun 8, 2015 at 15:07

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