RECYCLING: SpaceX Aims for Historic Rocket Launch With Reused Booster.

Relying on the Falcon 9’s repurposed lower stage—including nine refurbished main engines intended to propel a European commercial satellite into Earth’s orbit—the blastoff slated for Thursday from Florida’s Kennedy Space Center will mark the culmination of years of intense planning, testing and public advocacy by the company.

The aim for Mr. Musk and his team is to demonstrate the viability of such “flight-proven” hardware, which they argue eventually will help usher in an unprecedented era of frequent, inexpensive flights to orbit and beyond. Ultimately, they and other space entrepreneurs, including Inc. Chairman Jeff Bezos, see re-flying rockets as the Holy Grail of exploring the solar system.

“Full reusability is a game changer,” said Mr. Bezos, whose Blue Origin LLC also has signed up commercial customers willing to put expensive satellites on top of reusable rockets.

Regardless of the outcome of Thursday’s long-awaited, first-of-its-kind mission, industry and government experts say ambitious projections of huge cost savings and other operational gains won’t be evident for at least several years, and likely much longer.

The question isn’t just “Can it be done?” The larger question is “Can it be done at a cost savings big enough to compensate for the increased risk?”