Boeing Co. received consistently higher rankings than Space Exploration Technologies Corp. during NASA's recent multibillion-dollar competition to build "space taxis," according to an internal agency document.

The memo—dated Sept. 15 and reviewed by The Wall Street Journal—provides an inside look at the National Aeronautics and Space Administration's deliberations and reveals why agency officials rated Boeing's bid better across the board than the one submitted by SpaceX, as the smaller company is called.

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