KENNEDY SPACE CENTER, Fla. — A test launch of Boeing's Starliner, a capsule that will eventually carry crews to the International Space Station, from Florida's Space Coast has been pushed back.

The unmanned test flight was pushed to August from May because the CST-100 Starliner team had a tight launch window due to another launch on the same launch pad, Boeing confirmed Tuesday.

The other launch, a national security payload for the Defense Department in June, only allowed for a two-day window to launch the Starliner test flight and clear the pad for the U.S. Air Force's AEHF-5 mission, Boeing said. Both payloads are being sent into space aboard a United Launch Alliance Atlas V rocket.

"In order to avoid unnecessary schedule pressure, not interfere with a critical national security payload, and allow appropriate schedule margin to ensure the Boeing, United Launch Alliance and NASA teams are able to perform a successful first launch of Starliner, we made the most responsible decision available to us and will be ready for the next launch pad availability in August," Boeing said in a statement.

The company said the new August date for the test launch will still allow for a crewed test flight later this year.

Boeing also said the first Starliner crew will stay at the International Space Station longer than the few weeks originally planned but didn't announce a mission length.

NASA is working to end its reliance on Russian rockets to get cargo and astronauts to the ISS.

SpaceX's Dragon capsule has made several cargo missions to the ISS. Last month, it tested a crew version of Dragon, which successfully docked with the station in an unmanned test flight.