SLS Boosters Raise Hope For Kerosene

By Frank Morring, Jr.

Advanced kerosene-fueled rocket engines will be a serious subtext this week when launch-industry representatives gather for briefings on NASA’s plans to compete the strap-on boosters for its next heavy-lift rocket.

The Space Launch System (SLS) needs new boosters to meet the 130-metric-ton capability that Congress has ordered. While NASA is careful not to specify what kind of propulsion it wants in the boosters, there is a hope among many in the launch industry, and within the U.S. government, that a new kerosene engine is the ultimate choice.

The reason is not hard to see. Regardless of which U.S. commercial crew vehicle replaces Russia’s Soyuz capsule as the ride to orbit for U.S. astronauts now that the space shuttle era is over, kerosene—or more precisely, Refined Petroleum-1 (RP-1)—will fuel it off the launch pad. And the U.S. government is not spending much now on advanced kerosene rockets, even though kerosene can provide more thrust for the volume of fuel and thus reduce the size and weight of first-stage fuel tanks.

The Falcon 9 rocket built by Space Exploration Technologies Inc. (SpaceX) to carry its Dragon capsule uses kerosene. So does the Atlas V, which has been picked by Blue Origin, Boeing and Sierra Nevada Corp. to launch their commercial crew spacecraft: Space Vehicle, CST-100 and Dream Chaser, respectively. Given Blue Origin’s recent inflight loss of a test vehicle, the Dragon, CST-100 and Dream Chaser are leading the pack to become NASA’s commercial shuttle follow-on.

The Falcon 9 mounts a gang of nine Merlin rocket engines Space X developed in-house. The iconoclastic startup is at work on an advanced Merlin 1D variant and has plans for an even more powerful Merlin 2.

The Atlas V uses a Russian-built RD-180 as its main-stage propulsion system. United Launch Alliance (ULA), the Boeing/Lockheed Martin joint venture that flies the Atlas V and Delta IV, says it has enough RD-180s to operate for 4.5 years, with a steady supply chain running to replenish that stock.

But, given ULA’s lead role in launching U.S. military and intelligence satellites, having a foreign engine in the critical path for any of its launches is less than optimal and drives a lot of the interest in a new engine. President/CEO Michael G. Gass is quick to point out that the SLS booster competition is a way to get some government money behind a new RP-1 propulsion system, even as he is careful to praise his Russian engine supplier, NPO Energomash, as a reliable business partner.

“We’ve bought the rights to manufacture the existing RD-180 here, but I’ve been advocating let’s not manufacture an old engine; let’s move the technology the next 15 or 20 years,” Gass says. “There’s things we would want to do. There’s things the Russians would want to do. . . . Let’s spend money building the next-generation engine, whether it’s our money, the Russian money, but as a space community let’s move the ball forward.”

Kerosene also will fuel NASA cargo missions to the International Space Station as early as next year under the Commercial Resupply Services program, which will spend up to $3.5 billion to send unmanned commercial cargo carriers to the orbiting outpost. SpaceX plans its first ISS flight early next year, and Orbital Sciences Corp. also plans to fly its kerosene-fueled Taurus II with a Cygnus resupply vehicle in 2012.

The Taurus II first-stage engine is the Aerojet AJ26, a modification of surplus Russian NK-33 engines originally built for the Soviet N-1 Moon rocket. Some of them are 40 years old, and age was a factor in a fuel leak that triggered a test-stand fire during an acceptance test last summer that destroyed one engine and slowed the Taurus II development.

“Some of the engines do require some repair, and we’re in that process right now,” says Julie Van Kleeck, vice president of the space and launch systems business at Aerojet in Sacramento, Calif. “There were some small cracks in the manifolds, and we had to go develop inspection techniques and then repair techniques, and then we had to validate those. We’ve gone through that process, and have a method of screening now.”

Aerojet has a relatively small Air Force Research Laboratory (AFRL) contract to develop advanced kerosene rocket technology under the Hydrocarbon Boost Technology Demonstrator program, a competitively awarded effort to build a flight-like oxygen-rich staged combustion cycle test engine that can be ready in 2018. In addition to that work, the company has an in-house architecture study for a kerosene engine that could play in the NASA booster competition.

Informally dubbed the “500,” Aerojet’s engine would be scalable, up to a point, in increments of 500,000-lb. thrust and be capable of powering an SLS strap-on booster. Aerojet already has a deal with Teledyne Brown Engineering to manufacture the engines in Huntsville, Ala., and backing for the plan from the U.S. senators from Alabama and California.

“We’re definitely advocates of a kerosene engine in this country,” says Van Kleeck. “We’ve got the ongoing program with AFRL to work the technology side of it. We’re now looking at variants of an engine that might be suitable for the advanced booster competition NASA’s having, so we are looking at an engine variant that we think can make that competitive.”

In its first budget request for NASA, the Obama administration called for development of a new kerosene-fueled engine, but it ultimately decided to maintain the U.S. lead in liquid oxygen/liquid hydrogen propulsion represented by the RS-25 space shuttle main engine, the RS-68 that powers the Delta IV and the J-2X under development for the SLS (AW&ST Nov. 14, p. 39).

Top SLS managers will conduct an industry day Dec. 15 at Marshall Space Flight Center to outline NASA’s plans for procuring advanced boosters for the big new launch vehicle, which will start with a research announcement. The first two SLS flight tests will use five-segment versions of the four-segment solid-fuel boosters that powered the shuttle.

Alliant Techsystems, the manufacturer of those boosters, has indicated it probably will offer a solid-fuel entry in the advanced-booster competition, and other entrants are likely as well. So the prospect of more government funding for kerosene rocket propulsion is far from assured. And even if a kerosene engine is picked for the SLS booster, there still won’t be coordination with the Air Force on the effort.

In the wake of the shuttle retirement, a group of propulsion experts at NASA is trying to find a more coordinated approach for U.S. government research across the rocket-propulsion field. Known as the National Institute for Rocket Propulsion Systems (Nirps), the organization has set up a series of teams led by experts from NASA and the U.S. Army to map ways government agencies and industry can work together.

The Nirps aims to cut development and sustainment costs for missile and rocket propulsion systems, maintain the U.S. industrial base and advance research in all types of rocket propulsion. For kerosene-fueled rockets, the hope is that NASA and the AFRL can find a way to work together toward common goals.

“We’ll try to sit down with AFRL and . . . figure out if you took it as one body, how would you make it coherent, assess the gaps and overlaps, and do something from an integrated perspective,” says Dale Thomas, associate director for technical issues and Marshall lead for the Nirps.

NASA Concept

Credit: Aviation Week and Space Technology

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