Is NASA paid for by taxpayers?

Could you elaborate on the funding mechanisms for NASA? As a publicly funded organization, I understand it relies on budgetary allocations. However, are there any other significant sources of revenue that contribute to its operations? Does NASA receive grants or donations from private entities? Additionally, does the taxpayer money that funds NASA come directly from federal taxes or are there other mechanisms involved? Clarifying these points would help me understand the financial structure of NASA and how it is sustained.