An integrated systems definition review of NASA’s three human exploration elements — launcher, capsule and ground systems — kicks off next week, with major items of discussion to include the schedule for developing the Space Launch System (SLS) core stage and the Orion crew capsule’s weight.

The three-day review at Johnson Space Center will build on previous design work on the SLS, Orion and modifications at Kennedy Space Center, Fla., to make sure all of the requirements and interface control documents match up.

The SLS core stage is the “critical path” to the first flight test of an unmanned Orion multipurpose crew vehicle atop an early variant of the SLS in 2017, according to Dan Dumbacher, deputy associate administrator for exploration systems, and the Orion capsule weighs about 4,000 lb. more than its recovery parachutes can handle. Both issues are tractable, he says.

“Just before the holidays they completed the preliminary design review [PDR] on the core stage,” he said Jan. 7. “Doing the review, we actually came through pretty clean, so we’re gaining some confidence. Obviously, we have hardware in front of us [and] Mother Nature has a wonderful way of keeping us all humble.”

'Acceptable risk'

The PDR determined the big rocket’s main stage can meet requirements “within acceptable risk,” and can be integrated with the surplus RS-25D space shuttle main engines that will power it for the first few flights. Combined with the solid-fuel, shuttle-derived boosters and other planned launch hardware, the initial SLS variant has enough extra capability to handle the overweight Orion capsule.

Specifications call for the Orion capsule and its service module to weigh 73,500 lb. at liftoff. Lately the capsule has been running “something like 4,000” lb. over its allotted weight, Dumbacher says. The service module is about 1,200 lb. too heavy.

While the baseline SLS probably can handle the extra weight, the parachutes that will bring the capsule back to a water landing after re-entry cannot, Dumbacher says. Going into the integrated review, design teams have been wringing out the extra weight on the capsule, he says, and an upcoming flight test atop a Delta IV heavy may allow engineers to cut their margins to save more weight.