This isn't about what kind of technology would make spaceflight easier, this is about what kind of a discovery would incentivize world superpowers to aggressively invest in spaceflight.
I'm asking this question because I'm thinking about creating a alternate history setting where the moment humanity goes to space, they just really go for it and push hard for space colonization, instead of just scaling back after the moon landings like in our world. I looked to the closest analogy to it, with the colonization of the Americas, but all it does is point out how un-viable space colonization is. Basically, as I understand it, what made colonizing the Americas viable wasn't because there were natural resources and wealth there, but because there were millions of people who already lived there who made those resources valuable, with the Native American fur traders, the domestication of turkeys, potatoes, maize, tomatoes, and most importantly, gold and silver mines. The initial promises of vast amounts of gold and silver fueled the initial Spanish colonization efforts. And the immense luck, cunning, and perfect timing of Pizzaro and Cortes really sealed the deal with the vast wealth of their conquests inspiring many others to come to the Americas seeking riches. Here's a video by AlternateHistoryHub explaining in detail how important the Native Americans were to "making the Americas worth colonizing."
Now, in space there's good news and bad news. The good news is that as far as we can tell, there are no indigenous Martians or Venusians or Moonies, etc to genocide, so that's always a major plus. The bad news is, without someone to "make it valuable," there is not much worth up there worth colonizing space for. Not in the near term, anyhow, without truly gargantuan investment, which is the problem I wanna solve here. I've got some ideas for how to get spaceflight to happen earlier, and more extensively, such as Tunguska hitting somewhere more populated, ASBs making other planets habitable, or the transistor being invented later, so they have to build transmission space stations instead of small satellites, but in my opinion, that's still not enough motivation to spur on the kind of investment that would lead to a rapid development of space colonization.
Basically, I want to create that gold rush. Give the new space explorers a taste of something so valuable that they cannot resist the temptation to go just a little bit further, and to build all the infrastructure necessary to support that rush skywards. And so the only thing I could think of was little bits of technology left behind by ASBs across the solar system, nothing too revolutionary, but enough to make the powers that be think that there's much more up there.
Just two rules here if I may add:
Not computer/AI related: I'm trying to make a realistic, gunslinging, rocketpunk space opera, and so I want to slow down the development of computing tech as much as possible, so if they discover the alien equivalent of "How to create an AGI for dummies," that kinda defeats the point of accelerating spaceflight technology. Unless the computing tech will lead them down a dead end, and will delay computer tech even more.
Preferably a technology that currently exists the world today: Some kind of technology that was invented after the 1950s/60s that would be revolutionary to them, and very profitable to make. Maybe the ruins of a more efficient nuclear reactor, or insulin if they don't develop it by then?
(Also don't worry about why the aliens dropped this tech here. Maybe there's a logical reason, or maybe they're just messing with the cute little apes from Earth.)
Thanks!