NASA cut the planned missions of Boeing Co.’s Starliner spacecraft to the International Space Station from six to four, following a highly publicized botched test flight last year and as the orbiting lab heads for retirement by the end of the decade.

Originally, NASA had contracted Starliner to perform six missions that would carry crew to and from the ISS for months-long stays. Now, NASA and Boeing are mutually modifying the contract, the space agency said on Monday, with Starliner now tasked with performing four definitive missions and two optional ones.