Note that the feasibility of all these proposals are relative to sanity: the NASA budget is $20bn, and Quicklaunch has a viable system to launch bulk materials out of a space gun for $250/kg. So 1 kiloton costs just 250 million, or 1% of the NASA budget. The space gun is dominated in cost by fixed costs of the gun, and scales up well (more volume per unit surface area of the projectile helps a space gun, because it reduces drag and drag heating, as well as the usual scale economies for a larger rocket) so if you really wanted to build a 10,000 square kilometer orbital mirror to terraform Mars, you could probably do it for less than 50% of one years’ NASA budget.
Note that the feasibility of all these proposals are relative to sanity: the NASA budget is $20bn, and Quicklaunch has a viable system to launch bulk materials out of a space gun for $250/kg. So 1 kiloton costs just 250 million, or 1% of the NASA budget. The space gun is dominated in cost by fixed costs of the gun, and scales up well (more volume per unit surface area of the projectile helps a space gun, because it reduces drag and drag heating, as well as the usual scale economies for a larger rocket) so if you really wanted to build a 10,000 square kilometer orbital mirror to terraform Mars, you could probably do it for less than 50% of one years’ NASA budget.