Elon Musk and SpaceX are big winners in Donald J. Trump’s 2026 spending plan.

President Trump is delivering on Mr. Musk’s wish list at both NASA and the Pentagon to reorient federal spending on space in a way likely to drive billions of dollars in new business to Mr. Musk’s space technology company, if Congress signs off on the budget plan.

At the Pentagon, Mr. Trump is calling for a massive jump in spending, an extraordinary 13 percent increase, almost entirely through allocations in a Congressional budget reconciliation plan under consideration.

The jump would happen while many other federal agencies would be slashed, in part to supercharge federal spending in two areas where SpaceX is positioned to profit: a vast missile defense system and space missions to Mars and the moon.

Mr. Trump has proposed a Golden Dome defense system to track and kill missiles headed toward U.S. targets, possibly sent by China, Russia, North Korea or other rivals.