COLORADO SPRINGS — United Launch Alliance CEO Tory Bruno says his choice of planning to reuse only the BE-4 engines – not the entire first stage – of the company’s new Vulcan rocket was driven purely by the economics.

The cost equation also favors the Blue Origin BE-4 engine, he says, because it employs “clean burning” methane fuel, he says.

“It takes a good seven to eight reuses before you can pay off the additional cost of all the extra equipment and the logistics of recovering it and then bringing it back to the factory with a reasonable amount of refurbishment that you have to do,” Bruno told Aviation Week in an April 15 interview. “You can’t just dust it off and reuse it. You have got to do plumbing and new cables and insulation and all this kind of stuff. Our calculations say [it takes] 7-8 uses to break even … To really make it worth while, you have really got to reuse it about 15 times.”

ULA’s rival, SpaceX, failed to successfully land a Falcon 9 v1.1 first stage after an April 14 launch. “I’m surprised they didn’t make it yesterday,” Bruno said. The company plans to attempt its fourth first-stage recovery during NASA’s seventh Commercial Resupply mission, slated for the summer. SpaceX is attempting to land the first stage on a barge at sea to prove the concept, before eventually landing it back at Cape Canaveral Air Force Station, Florida.

In the April 14 attempt, “We seem to have landed a little bit too hard,” said Hans Koenigsmann, chief engineer for the mission at SpaceX, during a post-mission briefing at NASA. “Looking at the data, everything seemed to be fine. It is not quite clear what happened.”

SpaceX founder and Chief Technical Officer Elon Musk posted on Twitter that “Falcon landed fine, but excess lateral velocity caused it to tip over post-landing.” Koenigsmann said this third landing attempt “targeted the barge more accurately this time.”

“We applaud all efforts to bring reusability into today’s launch systems,” a SpaceX spokesman said. “However, SpaceX is thinking beyond just saving money. We are also working towards making human life multi-planetary.”

ULA, however, is embracing a different form of reusability with its newly unveiled Vulcan rocket that should pay off within only three reuses, Bruno says. ULA intends to reuse only the main engine of the first stage for Vulcan; Bruno plans to downselect between its primary choice, the Blue Origin BE-4, and the alternate Aerojet Rocketdyne AR-1 within the next 18 months.

“The issues around reusability in the kind of lift we are doing now are all economic … it is about the money,” Bruno says, acknowledging that eventually a goal is to achieve single-stage-to-orbit reusability.

“You can accomplish the economic advantage in about five or so” reuses, Bruno says of a methane engine, such as the BE-4. “If you happen to use a very clean-burning propellant like liquid natural gas or methane, then the refurbishment is even less and the ultimate number of reuses is even greater.”

Bruno says after main engine cut-off the paired BE-4s will be physically detached from the base of the core by a shaped explosive charge. The device will sever the propulsion systems at a specially designed separation interface built into the thrust structure between the engine mounts and the base of the stage. “We are literally cutting the thrust structure,” says Bruno, who adds the device also will sever the large feed pipes supplying oxygen and fuel to the thrust chamber, be it methane or kerosene. “We cut that loose and the whole structure separates very cleanly,” he says.

Following separation the joined engines will be cocooned to protect them during re-entry by a 12-meter-dia. device called a hypersonic inflatable aerodynamic decelerator (HIAD), comprising a set of concentric, doughnut-shaped rings made of braided Kevlar. Each tube in the ring, or torus, will be lined internally with silicon and held to its neighboring torus by Kevlar straps.

Studied by NASA for several years, versions of the decelerator are under development to enable larger payloads to be delivered to the surface of other planets or, as in the Vulcan concept, to be returned to Earth. Vulcan’s engine re-entry plan will build specifically on results from the Terrestrial HIAD Orbital Reentry (THOR) program, which plans to test a second generation, 3.5-meter-dia. unit as a secondary payload on an Orbital ATK Cygnus commercial resupply mission to the International Space Station.

Originally planned for 2016, though now delayed as a result of the Antares launch failure last year, the test will involve THOR launching with its HIAD stowed as a small cylinder between the second stage motor and the launch vehicle fairing. Following separation of the Cygnus cargo vehicle from the second stage, THOR will separate, perform a deorbit burn, then inflate the HIAD before re-entering the atmosphere. The work, which builds on flight tests in 2012, aims to develop the decelerator to a technology readiness level suitable for an industrial user to take it to operational use.

“We’ve been working closely with NASA on their HIAD program,” Bruno says, adding that the larger diameter required for the Vulcan will be “one more step above” the version due to be tested in THOR.

Once slowed to low subsonic speed, the engine unit will deploy a parafoil to slow its descent further and guide the engine to a rendezvous point. A helicopter would then pluck the engine out of the sky for return to ULA for refurbishment. Though seemingly complex, this is not unlike the operational concept used to retrieve film canisters from early spy satellites; those were retrieved in mid-air by C-130s after being expended by orbiting spacecraft.

Bruno did not specify either the weight of the BE-4 engine shipset after use or the type of helicopter it is studying for the recovery phase. “It is within the capability of what we can recover with the helicopter,” Bruno says. ULA graphics of the mid-air capture phase indicate the use of a large, tandem-rotor Boeing CH-46, which has a cargo hook capacity of 10,000 lb. Other suitable models could include the CH-47, which has a single point load capability of 17,000 lb. on its forward hook or a center cargo hook capacity of 26,000 lb. The Sikorsky CH-53E, which has a single hook capacity of 20,000 lb., could provide another option.

By not reusing the entire Vulcan first stage, the design also calls for fewer modifications compared to reusing the entire section, Bruno says. In the case of the BE-4, ULA is planning only to include a separation interface with a shaped charge for decoupling the engine from the rest of the stage, the inflatable heat shield and the parafoil for recovery. “It is not going to be bathed in plasma and recirculating rocket exhaust on the way down because there is no rocket exhaust. It is covered up in this conical heat shield; it experiences a very benign environment on the way in,” Bruno says.  “Our approach is such that the engine, during its recovery, will see less severe environments than it does in its normal operation.”