I am wondering if we can use footnotes to describe technologies used in a science-fiction novel instead of describing it by switching from an omniscient POV, that describes everything in a poetic way, to a "historian" POV. I understand this is not something we see usually in a novel, but I am wondering if there are historical precedents for this, and if you think it's perfectly reasonable to do so.
Can you do it? Sure.
Should you do it? Most likely, no.
It's not that you can't use footnotes as an explanatory aide. Mark Haddon’s The Curious Incident of the Dog in the Night-Time does so. It's just a matter of making use of the disruption in a constructive manner beneficial to the experience you are attempting to invoke.
There is no such thing as a bad idea in writing. It's the execution that matters. As a result, nobody can honestly tell you if it is going to be a bad idea or not to do something, because we won't know if you're able to pull it off unless we see you try it first.
Anyone who says you can't do it just hasn't succeeded at doing it. The value of the footnotes is to disrupt the reader's reading of your story in a choreographed manner or to make the reader experience first-hand the narrator's perspective of the world.
Personally, I would dissuade you from trying it. Footnotes are a great tool, but not something just anybody can pull off. It takes a level of skill that most writers don't have. If you do attempt to do so, be prepared for dozens of rewrites by virtue of footnote alone. That said, if you think you can do it, I recommend writing a sample work (a few pages in length) and using it as a proof-of-concept to see how well your beta-readers respond to your attempt at the stylistic device. If you fail to make it work, feel free to try again or feel free to give up on it. There's no shame in admitting your limitations after all. It's better that your work is good because you did your best than it is to fail because your best wasn't good enough.
There are a few points to balance with an issue like this.
What is the tone and style of the work? Does the use of footnotes aid in reinforcing the tone and style. [If the main character is technical, and the whole piece has a fairly technical tone and air to it, then the use of footnotes might actually serve as a means of reinforcing that technical feel.]
What knowledge of the technology, and its history, actually matter to the reader?
Who are your readers, and what kind of mindset are you expecting? [Are you targeting an audience who is happy to know it is a 'ray gun', or do you expect them to want to know that not only was this ray gun based on an earlier design by famed scientist Von Whathisface, but this specific model was custom made for the whosamacallem division on the... Well, we can acknowledge that some geeks get weirdly into excessively weird details. And we should also keep in mind that if you go into too much detail, then you stray into the realm where you'll be 'wrong', and lose 'geek points' as a writer.]
Footnotes were used to good effect in parts of the Discworld series, and a few other novels that I'm drawing a blank on currently, so we do have examples that they can be used to reasonably good effect at times, however I would stand strongly behind the idea that they should probably be avoided unless you have settled on an exceptionally good reason to use them. (In Discworld's case, that reason was mostly comedic.)
Rather than thinking about how you can tell details about a technology, consider focusing on showing off the details. However, this is ideally done in a casual way. "These new shuttles are so much faster and safer than old style jets. It is crazy how people put up with those deathtraps for so long..." is kind of clunky and insulting. "I'm grabbing the next shuttle from New York to LA, and should be there in about forty five minutes..." tells the reader a lot about the technology without having to actually describe the technology.
Instead, focus on how the characters uses the technology, how it impacts them, and how it ultimately affects society as a whole. [I personally standby the argument that good sci-fi is about how technology impacts people, not about the technology itself.]
Two pages of technical specifications on an amazing flying car might not really tell you nearly as much as you think it does compared to a paragraph like "He slid the door back to squeeze into shuttle pod's cramped front seat, before easing it out of the small docking space to glide off into the night. He frowned at the nearly bare front console, regretting the upgrade last year from the previous model with its cup holder... The thrill of the extra speed had faded after less than a week."
Less is often more - Think long and hard about whether or not a reader actually Needs any given info about something in a science fiction setting before you try to offer it on a plate or shove it down their throats.
Assume your readers are smart and intelligent, at least until they prove otherwise. - Then you can revisit your viewpoints on them.
It is your book and you can certainly do as you please. If you do this, you might end up interfering with the reader’s immersion.
Imagine you are reading a new sci-fi from an unfamiliar author - anything is possible. You are reading about the characters and setting and the character picks up an item with an intriguing name, but now you have a footnote. Would you read on? Might you not just put the book down and resolve never to waste your precious time reading another faux textbook?
Another risk of introducing such information in that form is that you suggest to the reader that you must hold their hand and lead them to attempt to understand your genius.
Do not insult the reader nor break the spell we seek to cast with seamless prose. Let the readers in and do not tap them on their shoulder and tell them about the technology you dreampt up.
If you want to write a faux grimoire that might work, but for a novel of any type, please leave out footnotes.
You can do this as stylistic choice
Footnotes to help explain a complex technology, add additional information or provide a humorous aside. Terry Pratchett used footnotes liberally to great effect. The key is in developing a narrative voice for the footnotes such that they aid the narrative rather than distract from it.
A dry technical footnote which only describes a technical term you used isn't adding to your narrative. Instead it simple shows that your failed to properly describe it within the prose. Conversely a footnote that adds context or humour to a page can be a brilliant addition.
Whether this is a good idea or not will depend on your narrative style. If your narrative voice is almost a character in itself, as with Pratchett's work, you can use footnotes are evidence of the narrator becoming distracted in their retelling. If your narrator is more of a invisible bystander with not influence on the story you will need to find another voice to use in the footnotes. If you can pull it off you can use the footnotes to tell an entire meta-story of their own.