So first of i do not think that there is any real answer to this one, but we can crunch some numbers and have a look at projected costs for different missions. This is h thought i have had for quite a while, and it is basically just: "What would we be able to do if every space agency joined forces and become one big agency?".
Combined budgets, according to wikipedia:
43400 million usd which is 43,4 billion usd which might sound like a lot, but when we compare it to the us millitary budget it is actually not that much.
But lets see what types of missions we might be able to do:
This is a calculation made by Nasa and as you might be able to see it is a bit old, but let us just use these (i can't really find anything else). If you have some newer calculations fell free to share them in the comments. But back to the topic, according to these numbers it looks like we might be able to visit our twin planet with a budget of this size. But could we visit other planets than just Mars?
YES! Well maybe...
There is a proposal for putting humans not on Venus, but in the atmosphere. The project is called HAVOC(High Altitude Venus Operational Concept), and it is a personal favorit to be honest. There is no estimated cost yet because it is only a concept for now, but i believe that a combined earth space agency would be able to do this. What do you think, and do you have some numbers or further knowledge about HAVOC? How it might look:
Maybe we could also build a knew and even bigger spacestation, with artificial gravity. If you look at the picture at the top of this article, you can see a concept for what this might look like. This could further the research and knowledge we have about space. When it comes to possible projects ESA, have this wild concept of using robots and 3D printers to create a lunar surface base. This would most likely also be possible if the budget was increased by that much. Picture of the lunar base below:
Do you have any other things that might be possible with a budget like this?
Thank you for reading