Space Exploration Technologies Corp. said on Wednesday it has invested about $500 million in commercial-space ventures, shedding light on the closely held company's efforts to develop private rockets and capsules even as congressional skepticism about such projects grows.

The figure is substantially larger than founder and Chief Executive Elon Musk previously spelled out to lawmakers and goes beyond earlier statements that he has invested $100 million of his personal wealth in the Southern California-based maker of launchers...