Founder and CEO Elon Musk has announced that the Falcon 9 booster that made the historic first powered controlled landing of a space rocket has successfully completed a post-flight static test fire.

In a tweet on Friday, Musk said: "Conducted hold-down firing of returned Falcon rocket. Data looks good overall, but engine 9 showed thrust fluctuations." He went on to post, "Maybe some debris ingestion. Engine data looks okay. Will borescope tonight. This is one of the outer engines."

A borescope is an optical instrument made of a rigid or flexible tube that uses prisms or fiber optics to allow inspectors to see inside of tight spaces, such as rocket engines.