WASHINGTON — While the upcoming test flight of NASA’s Orion spacecraft is being hailed as a major milestone in its development, agency officials emphasize that the test is just one of many before the spacecraft is ready to carry a crew.

NASA and Lockheed Martin completed a flight readiness review Nov. 20 for the Exploration Flight Test (EFT)-1 mission and gave approval to proceed with preparations for the launch, scheduled for 7:05 a.m. EST on Dec. 4 from Cape Canaveral Air Force Station, Florida.

A United Launch Alliance Delta 4 Heavy rocket will place the Orion spacecraft into an elliptical low Earth orbit of 185 by 888 kilometers. After completing one orbit, the Delta 4’s upper stage, still attached to Orion, will fire again, inserting Orion onto an elliptical trajectory with an apogee of 5,800 kilometers. Orion will then separate from the upper stage and re-enter, splashing down in the Pacific Ocean off the coast of Baja California, Mexico.

EFT-1 has a launch window lasting two-and-a-half hours, driven by launch and recovery operations, Bryan Austin, Lockheed Martin EFT-1 mission manager, said at a Nov. 6 briefing at the Kennedy Space Center. Launch is scheduled for a few minutes after sunrise to provide lighting on ascent, as well as to maximize the daylight available to recover the capsule after splashdown four and a half hours later.

The flight will mark the first time Orion, whose origins date back to the mid-2000s as part of the now-canceled Constellation program, has flown in space. NASA is promoting the flight as a major milestone in Orion’s development.

“EFT-1 is absolutely the biggest thing that this agency is going to do this year,” William Hill, NASA deputy associate administrator for Exploration Systems Development, said at the Nov. 6 briefing.

However, Garth Henning, Orion program executive at NASA headquarters, emphasized that this flight is part of a much larger set of tests needed to demonstrate the vehicle’s ability to safely carry crew beyond Earth orbit.

“Everybody loves the flight tests. They’re very exciting things,” he said in a Nov. 12 speech at a Space Transportation Association luncheon here. “EFT-1 is just one flight test, one piece of that puzzle. What we can’t test on the ground we have to do in space.”

Among those elements of Orion that cannot be tested on the ground, but will be on EFT-1, is the spacecraft’s heat shield. The spacecraft’s elliptical trajectory means it will re-enter at 32,000 kilometers per hour, faster than a normal re-entry from Earth orbit and about 80 percent of the velocity of a lunar return. “You can’t do a test like that on the ground,” Henning said.

EFT-1 also will test exposure of Orion’s electronics to radiation as it passes through the lower Van Allen radiation belts. Other components EFT-1 will test are the separation of various components, like Orion’s launch abort system, during flight, and the spacecraft’s parachutes.

“EFT-1 is basically a compilation of the riskiest events we’re going to see when we fly people,” Mark Geyer, NASA Orion program manager, said Nov. 6 at KSC. “Some of these events are difficult or impossible to test on the ground.”

If the EFT-1 flight goes well, the capsule will return to KSC the week of Dec. 22 for study by engineers, and then preparation for a second life as part of an abort test.

“One of the most stressing cases in an abort case is when the rocket is going through the maximum dynamic pressure” during launch, Geyer said. The Ascent Abort 2 test, scheduled for 2018, will launch the refurbished EFT-1 Orion capsule on a surplus Peacekeeper missile stage from Cape Canaveral to allow for an in-flight test of the abort system.

“It’s a great test for us and a great way to reuse this capsule,” he said.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...