The first test flight of NASA's Orion crew exploration vehicle has been delayed to early December to accommodate a U.S. military payload in United Launch Alliance's Delta 4 launch manifest, officials announced late Friday.

Two Delta 4 rocket boosters were delivered to Cape Canaveral on March 4 for the Orion EFT-1 test flight. Photo credit: NASA/Kim Shiflett
 
The unmanned Orion test flight was scheduled for launch in September or October aboard a Delta 4-Heavy rocket, the most powerful launcher in the U.S. fleet.

But NASA announced a delay Friday. A statement posted on the agency's website said the delay will "support allowing more opportunities for launches this year."

The Orion spacecraft is NASA's next-generation crew vehicle designed to carry astronauts on expeditions beyond low Earth orbit aboard the Space Launch System, a government-owned heavy-lift launcher set to debut by the end of 2017.

The Orion test flight this year, known as Exploration Flight Test-1, will prove many of the spacecraft's key systems, such as computers, software and the capsule's 16.4-foot-diameter ablative heat shield.

The first crewed Orion mission is scheduled for launch on the second Space Launch System flight in 2021.

The statement issued by NASA on Friday said the Orion team will continue on a pace to be ready for a launch in September or October.

"Completing the spacecraft according to the original schedule will allow many engineers and technicians to continue transitioning to work on the Orion spacecraft that will fly atop the agency's Space Launch System," the statement said. "It will also ensure that NASA's partners are fully ready for the launch of EFT-1 at the earliest opportunity on the manifest."

The Orion EFT-1 test flight's mock-up service module is pictured undergoing assembly inside the Operations and Checkout Building at the Kennedy Space Center in Florida. Photo credit: NASA
 
Sources indicated the Orion launch delay will make room in the Delta 4 manifest for the launch of two satellites for the Geosynchronous Space Situational Awareness Program, or GSSAP, a recently-declassified program to track and survey objects populating the geosynchronous orbital arc 22,300 miles over the equator.

The existence of the covert GSSAP satellites was announced by Gen. William Shelton, head of U.S. Space Command, in February. They were scheduled to launch in late 2014 -- after the Orion test flight -- but can now be flown sooner.

ULA delivered the core and starboard booster for Orion's Delta 4-Heavy launcher to Cape Canaveral Air Force Station on March 4. The port booster and the Delta 4's upper stage will arrive at Cape Canaveral in April, according to NASA.

Technicians will assemble the rocket components inside the Horizontal Integration Facility near the Delta 4's Complex 37 launch pad.

The Delta 4-Heavy is formed by combining three Delta 4 first stages together to compose a triple-body rocket powered by three hydrogen-fueled Aerojet Rocketdyne RS-68 engines. A single RL10 engine, also produced by Aerojet Rocketdyne, is on the Delta 4 upper stage.

The Delta 4 rocket will boost Orion approximately 3,600 miles above Earth on a four-hour unmanned test flight. The spacecraft will plunge back into the atmosphere at more than 20,000, and its heat shield will endure temperatures up to 4,000 degrees Fahrenheit.

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