Humans are progressing slowly toward megaprojrcts in the past two centuries, so perhaps they will be spectacular by the year 2999?
Quite soon, we can send robot probes to many asteroids to separate elements and useful compounds from what the probe finds there. When and, if later a mega project in our solar system is desired, the materials can be assembled from the stock piles on many asteroids. The delta v is much less than obtaining these materials from Earth's surface and delivery often takes less than a year even by cheapest transportation. A year delay is a minor problem for a mega project, if we plan ahead. The only downside I think of, is there is no return on the investment in asteroid mining the first century, or however long it is until a mega project is willing to pay for the material. Please suggest ways to make this practical, soon, as we may not have until 2999 to establish extensive off Earth human habitats = Earth may be back in the dark ages much sooner. We won't build megaprojects, if the cost is too high. I'm reminded of the 19th century railroads that often produced no profit until the 20th century, but today's technology would be decades behind if we had not done railroads nor the interstate highway system.