Realistic STL Interstellar Missions

[Flyndaran]

I thought ramscoops were not feasible for propulsion in our local bubble, because the interstellar medium was too sparse. But I thought they could work in other denser regions of space.

[AlexanderHowl]

Ramscoops are feasible up to 0.05c. The low density is an issue for a ramscoop that would not depend on a power plant. One power point per ramscoop should be sufficient though to correct for the low density.

[Johnny1A.2]

Originally Posted by Joseph Paul

How vast? More than what it takes to build a city?

Today? Yes. In fact, we can't do it today, as both I and David noted. It's beyond us, just as a 747 wide body would be beyond the full resources of Classical Civilization at its Roman height of power.

But cost is relative to the size of the civilization and the size and wealth of the subgroup doing the project. A 747 is still beyond the resources of most individuals and groups, but costs very little relative to the size of Western Civilization.

When STL starships first appear, they'll almost surely be staggeringly expensive. But things change.

[David Johnston2]

Originally Posted by Joseph Paul

How vast? More than what it takes to build a city?

The investment to build a city would be nothing compared to what it would cost to accelerate a small city to a significant fraction of the speed of light.

[Flyndaran]

A city can be built over time and adjusted on the fly. A city can also easily be developed from earlier technologies.
An manned interstellar ship must be fully developed and tested long before first use. It's a massive fundamental difference in kind not degree, IMO.