In a relatively near future, the humanity discovered a way of commercializing space, in the sense that a project emerged that is extremely costly, but if successful, would be worth it and then some. The only problem is that the time span between the investment and the return would be significantly longer than the human life span. (For concreteness, we discovered precious mineral resoureces on one of Jovian/Saturnian/Uranian moons. We can send unmanned missions to build mining facilities, but we cannot really send enough fuel to break, so we are stuck with Hohmann transfer, that takes decades one way. We then produce fuel for the return trip on site, by an energy-costly process fueled by energy harvested on site, which also takes quite long. Then, the ore is sent back, again by Hohmann transfer, so it starts to arrive some 70-150 years later.) And, this is a risky investment, in that the mission may fail, or resources may lose their market value.
The question: what social/economical conditions allow for such a mission to be funded? As far as I understand, IRL, the longest commercial contracts we have have span of a few decades, maybe 40 years at most, and those are mortgages, a different thing completely. When investing in stock or investing directly, we typically expect return within a decade or two. We do have agreements that span, say, 100 years, but those feel more like an euphemism for "eternity" to whose who sign them, say, as in Great Britain Hong Kong deal. I am not aware of any commercial contracts that only target revenue decades later. And that is rather logical - why would someone invest their money if they have no hope of seeing returns in their lifetime?
Then again, if public money is spent, then you need to convince the public that it is worth it, and the same problem emerges, exacerbated by the riskyness. If some kind of a dictator or plutocratic elites control the public spending, then again they seem to lack incentive to spend money on such a project that they could rather spend on their villas. Etc.
So, is there a realistic mechanism such long-term missions can be funded? I'd like it to be rationally motivated, no religious cult or such.