SDI Program

The SDI Program is a shield you fund. When it is complete, it destroys about half of the missiles fired at you from other planets and cuts attacking jets' strength by about a quarter. It does nothing against a neighbour on your own planet, whose nuclear, chemical and biological missiles always land. Technology regions lower its upkeep. The SDI Program is a shield you fund. It answers three things, and only these three: missiles fired at you from another planet, and the jets and bombers of a strike arriving from one. It does nothing against a neighbour on your own planet — not their army, and not their nuclear, chemical or biological missiles. Technology regions lower its upkeep.

At full strength it turns aside about half the missiles aimed at you, takes 30% off an arriving realm's jets and 20% off its bombers. At half strength it does half of each. Only a strike aimed at you by name meets your shield; one aimed at the planet as a whole goes through it.

How strong it is

Strength is the funding spread over your land, not the funding alone:

strength% = the square root of (funding / (10 x (regions + 1)))

capped at 100%. Two things follow. Every region you take thins your own shield, so the same pot that shields a small realm well is nearly useless over a large one. And each further percent costs more than the last: over 8,000 regions the first 1% wants about 80,000 gold in the pot, while going from 9% to 10% wants another 1.5 million.

Funding it

The program is a pot of gold, not something you buy once. Each turn you may add up to a set amount: a fifth of what is already in the pot, and never less than 250,000 gold. Gold goes in only in whole thousands.

That amount is your allowance for the whole turn. Leaving the screen and coming back does not give you a second one.

So a shield takes many turns to build, however rich you are. You cannot buy one the turn you need it, so start early if you expect missiles.

Paying for it

Every turn the program asks for 4% of its total funding as upkeep, in the maintenance prompts, after your regions and before the Queen's tax.

Pay it in full. If you pay short, the program shrinks to what you did pay for, and the shield weakens with it. A large pot is a large bill every turn, so grow it at a pace your income can carry.