WASHINGTON — The scheduled June 28 launch of a U.S. national security satellite aboard a United Launch Alliance (ULA) Delta 4 Heavy rocket will debut a new and more-powerful variant of the vehicle’s RS-68 main engine that the company says will help cut costs and add flexibility to its fleet.
The RS-68A, also featuring better fuel efficiency than current versions of the engine, was designed specifically for the Delta 4 Heavy rocket that is used to loft the U.S. government’s biggest satellites. But ULA plans to incorporate the RS-68A on all versions of the Delta 4 starting around 2015, thus eliminating manufacturing variability — both on the engine itself and on related first-stage hardware — that drives up costs, ULA spokeswoman Jessica F. Rye said in a written response to questions.
The upcoming launch of the NROL-15 mission from Cape Canaveral Air Force Station, Fla., is one of four launches scheduled this year for the U.S. National Reconnaissance Office, which buys and operates the nation’s spy satellites. The payload is classified.
Denver-based ULA, a Boeing-Lockheed Martin joint venture, builds and operates the Delta 4 and Atlas 5 rockets that today launch the vast majority of government payloads under the U.S. Air Force’s Evolved Expendable Launch Vehicle (EELV) program. The program has come under increased scrutiny in recent years due to rising costs that have drawn pointed criticism from its two most important customers besides the Air Force: NASA and the National Reconnaissance Office.
The Air Force has devised a strategy for reducing the EELV costs, the main thrust of which is a so-called block buy under which the service would commit to purchasing a combined six to 10 Atlas 5 and Delta 4 booster cores during a three- to five-year period. But in a report released in September, the U.S. Government Accountability Office urged the service to hold off on the block buy until it gets better cost data from ULA. The report argued, among other things, that the service could wind up with excess rocket inventory by committing to a multiyear block buy.
In a congressionally mandated response to the report, which was dated March, the Air Force cited a number of factors that would help keep launches on schedule and thereby keep inventories down. Among them are the Atlas “white tail” and Delta Fleet Standardization initiatives — the latter entailing the common RS-68 engine — which the service said would “increase flexibility in booster assignment, which further reduces the likelihood of launch delays.”
Rye said the Atlas 5’s main booster core is common to all configurations of the vehicle.
“Until final processing for launch, such things as the number of solid rocket motors attached to the booster can be changed since all the hardware and wiring necessary to reconfigure the booster for a particular payload are present,” she said. “This is achievable because of the high performance of the RD-180 booster engine.”
The Russian-built RD-180 is capable of generating nearly 1 million pounds of thrust, versus 670,000 pounds of thrust for the standard RS-68, which is built by Pratt & Whitney Rocketdyne of Canoga Park, Calif.
The Delta 4’s lower main-engine performance means that, for medium-class versions of the vehicle, different core-stage configurations are needed depending on the mission and payload size. Including the attachment points, wiring and other hardware necessary to accommodate solid-rocket motors, for example, adds weight to the booster core.
The Atlas 5 can easily handle the additional weight of solid-rocket motor accommodations, enabling ULA to include them on all of its booster cores, whether or not the mission requires thrust augmentation. For the Delta 4, booster cores must be tailored more precisely to the mission at hand: A Delta 4 saddled with the added weight of attachment points and related hardware has difficulty lofting certain payloads without the additional thrust provided by the solids.
The RS-68A engine, capable of generating 720,000 pounds of thrust, will take care of this problem, Rye said.
For the Atlas 5, Rye said, payloads do not have to be committed to specific rocket hardware until six months prior to launch. “The current program strategy is to have multiple backup missions for each Atlas launch vehicle until 12 months before launch, with a single backup for each launch slot down to six months before launch,” she said. “This allows for the greatest probability that the final mission selected for each Atlas launch slot will be there for launch.”
With the Delta 4, rocket hardware currently must be committed to a specific mission 17 months before the launch, limiting the Air Force flexibility to swap out payloads if one is delayed. The goal of the Fleet Standardization Program is to reduce that time period to six months, similar to that of the Atlas 5, she said.
“Fleet Standardization is currently in the Final Design phase, with a Critical Design Review coming up in October with fleet cut-in and first launch planned in mid 2015,” Rye said. “There was no effort in the Fleet Standardization program to address any specific commonality with the Heavy; however there are many components which are already common between them.
The Delta 4 Heavy is a unique configuration featuring three core stages aligned side by side, with no solid-fuel strap-on motors.
