NASA is gearing up for risk-reduction in developing its heavy-lift Space Launch System (SLS), setting up a hardware-in-the-loop laboratory at Marshall Space Flight Center to exercise avionics for the big new human-rated rocket with the thrust-vector control-actuators they will be controlling in flight. The center's Propulsion Research Laboratory is running real-time simulations as hardware and software become available and can be quickly converted to accommodate new test articles.

In addition to the recycled Space Shuttle Main Engines that will be used on early SLS flights, the laboratory setups will be able to handle the strap-on boosters that are just starting to take shape with some advanced engineering study contracts from NASA.

A lot of that effort is going to liquid-fuel technology, including composite tankage and a look at updating the F-1 engine that powered the Saturn V first stage (AW&ST Oct. 29, p. 40). But ATK—which is building solid-rocket boosters (SRB) for early SLS flight tests based on its space shuttle solid-fuel boosters—is also at work on upgraded versions designed to take the SLS to the 130-metric-ton capability Congress has ordered, while lowering the cost of producing them from shuttle-era levels.

“Our advanced manufacturing techniques and streamlined processes, combined with an innovative design, results in a booster that is 40% lower in cost than the previous five-segment SRBs,” writes Don Sauvageau, director of advanced space systems at ATK, in a paper presented at the 63rd International Astronautical Congress in Naples, Italy, last month.

The company is building the five-segment boosters for early SLS flights with the basic design it developed for the first stage of the terminated Ares I crew launch vehicle, but with a cost-saving wrinkle. After the shuttle stopped flying, ATK went through an extensive bottom-up review of the production processes at its sprawling plant in Promontory, Utah. The value-stream mapping process continues, but it has already produced significant cost-savings in the qualification boosters it is building to prepare for the early SLS flight tests, according to ATK manufacturing executives and their NASA customer.

The new design ATK is wringing out with its $51.3 million NASA study contract is expected to help increase performance to the point that the company's advanced booster will require only four solid-fuel segments instead of five (see artist's concept). That will simplify stacking at Kennedy Space Center, where the SLS will be assembled in the Vehicle Assembly Building originally built for the Saturn V and later used by the shuttle fleet. And it will eliminate one joint between segments, a safety consideration. While the shuttle-booster joints were redesigned and performed perfectly after the 1986 Challenger disaster was traced down to hot gas passing through one of them, the fewer joints the better from a safety standpoint.

A number of new design elements enable the return of a four-segment configuration. Chief among them is the planned use of a fiber/resin composite case instead of the steel casing used on the shuttle and the five-segment boosters. The composite case is lighter, permits integral damage-detection sensors for additional safety, and is cheaper than steel, according to Sauvageau's paper. The composite case also contributes to a 15.1-metric-ton increase in booster performance by allowing a higher operating pressure.

Also enhancing liftoff performance is a more energetic solid-propellant mixture, a “tailored” thrust profile and an increased expansion profile. The new ATK booster will use electric thrust-vector-control actuators instead of hydraulics, which permit a common controller across the vehicle. To save more on the advanced design, commercial avionics components are planned, as well as a single-unit forward structure and new nozzle materials.

With the ATK improvements, Sauvageau says, only those reference missions requiring the full 130-metric-ton capability—a lunar landing and a long-term mission to an asteroid—will require an upper stage. Others, including a lunar orbit flight with a crew and an “advanced” asteroid mission reaching “close proximity” to the target for two weeks, can be accomplished with an SLS core stage carrying four shuttle main engines or their throw-away successors.

“Since the more difficult missions are not anticipated until into the late 2020s or early 2030s, the cost of the upper stage can be deferred for a number of years, thus allowing NASA to develop the other exploration elements necessary to have defined missions,” Sauvageau says.