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.

Scheduled for September 2014, the flight test will take an Orion test article through a highly elliptical orbital trajectory designed to bring it back into the atmosphere at about 80% of the velocity it would see returning from the Moon or beyond.

“That is enough to start to tell us what we need to do from a heat-shield standpoint, and where we can reduce weight, or where we might have to add weight, depending upon what we learn,” Dumbacher says, adding that the flight test also will help designers decide whether they can take weight out of the capsule structure.

A press conference is scheduled during the Jan. 16 session of the integrated review to announce the formal agreement of the European Space Agency’s (ESA) participation in developing the Orion service module, using propulsion-system hardware from ESA’s Automated Transfer Vehicle.

“We’re somewhere between systems definition review level and PDR level on the maturity of that service module design from ESA,” Dumbacher says. “There are still technical and programmatic issues and questions that have to be worked. We are not going to be able to lay out all the nuts and bolts and all the detailed designs, nor are we going to be able to lay out all the specific impacts to all the suppliers, down to the second, third and fourth tier. We still have work to do on it.”