For months, a powerful U.S. senator has been pushing for details of a murky deal under which a Russian manufacturer supplies the rocket engines used to launch America's spy satellites into space.

At issue: how much the U.S. Air Force pays for the engines, how much the Russians receive, and whether members of the elite in President Vladimir Putin's Russia are secretly profiting by inflating the price.

Now, documents uncovered by Reuters provide some answers. A tiny Florida-based company, acting as a middleman in the deal, is marking up the price by millions of dollars per engine.