Private-equity firms are ramping up investment in the booming space sector, with some aiming to plant flags in an industry where buyout shops haven’t previously been major players.

This year has seen by far the most deal activity ever by private equity in the space sector, according to PitchBook Data Inc., a company that tracks private-equity and venture-capital investment. Through Sept. 16, buyout firms invested about $1.22 billion in U.S.-based space companies, exceeding the second-highest annual sum ever by 59% in less than a full year, according to PitchBook data.