Nov 24 (Reuters) - NASA and Boeing ( BA ) are revising

the Starliner spacecraft contract to reduce the number of

missions from six to four, the U.S. space agency said in a

statement on Monday.

The original $4.5 billion contract, awarded to Boeing ( BA ) under

NASA's Commercial Crew Program, envisioned six

post-certification operational flights of the Starliner capsule.

With the latest modification, NASA has designated the

remaining two flights as optional.

The Starliner program has been dogged for years by

delays, technical faults and cost overruns.

The next Starliner mission will be uncrewed, NASA said,

marking the third such test in a development effort that has

cost Boeing ( BA ) more than

$2 billion

since 2016.

Propulsion system issues on the capsule during its most

recent mission last year

forced

its debut crew to remain on the International Space Station

for roughly nine months.

The next mission, known as Starliner-1, will deliver

cargo to the International Space Station, NASA added. Boeing ( BA ) and

NASA are targeting no earlier than April 2026 for the flight.