I gather this has a meaning related to "version". However, I have seen this term used for military and commercial aircraft and other products (generally connected to government or aerospace).

I am looking for a formal definition of the term (not opinion) as used in these industries. How is it different from "version"? What's makes a change to a design a "version" rather than a "block"? What's an "update" vs. a "block update"?

EDIT: I did see this answer prior to posting my question:

Origin of term "Block I", "Block II", etc

The difference is that what is marked as an answer there is really mostly opinion. What I am looking for here is an industry definition of the term rather than opinion. In other words, if you used the term "block" in a contract, what would it mean?

It is clear that colloquially it means "version". Yet they don't use the term "version" at all. They don't say "Falcon 9 Version 5" or "AC-130 version 10", they explicitly use the term "block".

There might be no formal definition distinct from "version". This might be a term of trade that could equate to, for example, the use of "basis points" in financial speak instead of percentage. Yes, a basis point is 0.01% and it might be more convenient in financial speak, but saying "75 basis points" and "0.75%" is the same thing (and the latter requires no mental gymnastics). Same thing with the term "thou" in machining, which means "0.001 in".

I think in both of the examples I gave there's a pretty straight forward equivalence or definition of the terms ("basis point" and "thou"). I have not been able to find such a definition for "block". Does block mean "major version"? In other words, you have "Falcon 9 block 4 version 4.99" and when you make the jump to what would be version 5.0 the language becomes "Falcon 9 block 5"?

The examples given are not meant to be perfect. No need to nit-pick them. Just trying to clarify a perspective.

EDIT 2: I also read this question and answer. Once again, no definition is provided, just opinion: Why is the word 'Block' used along with a number to indicate the rocket version?

I think a definition would require a link to a NASA (or other authoritative source) standards or nomenclature document defining how the term is to be used in programs.

What made this confusing for me is that I am working on a project where the statement of work says something like (sorry, can't quote exactly due to restrictions) "allowance for version and also block upgrades". Yes, I will ask the author but wanted to see if there's a canonical definition of the term in the space industry. A search did not return anything I can use.

  • $\begingroup$ I saw that before posting. It looks like an opinion rather than a definition. The closest it gets to a definition is the quote provided for the Ranger program. Maybe the best way to put it might be: If you had to sign a contract for aerospace work, what would be the formal definition of what each "block" deliverable entails? It is quite possible that this is just a term of trade meaning nothing more than "version" and it is defined by the scope of work in a manner relevant to the project. In other words, you make it up to suit the project/program needs or phases. $\endgroup$ – martin's Sep 5 at 0:02
  • $\begingroup$ Just because the answers are not satisfactory doesn't mean the question isn't a duplicate. There is no reason to have two of the same question open. This one got closed as a duplicate as well space.stackexchange.com/q/27045/6944 I like the answer on it better:) $\endgroup$ – Organic Marble Sep 5 at 0:03
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    $\begingroup$ It's not bad, I'll give it an upvote ;) $\endgroup$ – Russell Borogove Sep 5 at 0:07
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    $\begingroup$ @martin's rather than reaching for the insta-close button, commenters could have simply informed you that if you would like to keep your question open and attract different answers, you can simply adjust it to ask something like "I have seen the answers to W and X but so far none have pointed to a specific, citable definition of the term Y in the context of Z. Are there sources related to the industry that provide a clear, definitive definition?" By distinguishing what makes your question different than those the question can probably stay open. $\endgroup$ – uhoh Sep 5 at 1:06
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    $\begingroup$ I edited the question to include additional context. Hopefully this helps. $\endgroup$ – martin's Sep 5 at 18:50

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