An innovative combustion-chamber setup that was flight-tested last month could cut the cost of rocket engines by eliminating the need for regenerative cooling.

Orbital Technologies Corp. (Orbitec), a Madison, Wis.-based space-technology company, flight-tested a version of the 30,000-lb.-thrust liquid-propellant rocket engine it is developing for the U.S. Air Force's Advanced Upper Stage Engine Program (Ausep) and other in-space applications.

Results of the Oct. 20 sounding rocket test at Mojave, Calif., validated the company's “vortex” engine technology, which injects fuel and liquid oxygen so that the burning mixture does not touch the walls of the combustion chamber, allowing them to be thinner, lighter and lower cost, says Paul Zamprelli, business development director.

By carefully tweaking the propellant-injection parameters, the company hopes to eliminate the need for costly cooling tubes or channels that circulate unburned fuel through the combustion chamber walls to prevent them from overheating. The flight test also demonstrated Orbitec's acoustic igniter and a lightweight carbon-carbon nozzle extension developed for the flight by ATK.

“The next step is to demonstrate the performance at a larger scale and ensure that future launch vehicle requirements are captured in our design,” Zamprelli says. “Orbitec is ready and excited to compete for any future rocket engine and propulsion applications.”

In the vortex approach, oxidizer is injected into the combustion chamber at an angle that sets up a pair of coaxial vortices (see illustration). The swirling motion provides better mixing with the fuel, with combustion occurring in the innermost vortex. The outer vortex protects the chamber walls and other surfaces from the heat of the combustion.

Orbitec, which also produces environmental-control and life-support systems, fire-suppression equipment and kits that will enable astronauts on the International Space Station to start to grow fresh food next year, has been working on vortex combustion since 1998, according to propulsion director Marty Chiaverini.

“We had been conducting research on swirl-injected hybrid rockets for improving fuel-burning behavior and discovered that under the right conditions vortex flow could be used to prevent flame spreading along solid fuel surfaces, rather than enhancing it,” Chiaverini says. “We modified some existing hardware and ran some proof-of-concept experiments on the vortex-cooled liquid rocket combustion chamber concept during the summer of 1998.”

Since then the company has tested its patented concept using a number of different liquid and gaseous propellants. The flexibility, which requires tweaking the propellant flow in the chamber to accommodate the varied propellant properties, “makes the system very attractive for most applications that are called out currently, as it does not discriminate,” says Chiaverini.

Potential applications range across the spectrum of thrust levels. The approach could also include rocket-based combined-cycle engines that start off using atmospheric oxygen before shifting to liquid oxygen at high altitude, according to a joint NASA/U.S. Army Missile Command study conducted in 2000 with Orbitec input.

“So far, we have successfully scaled the vortex chambers from 10 [lb. thrust] to 7,500 [lb. thrust],” he says. “We do not see any fundamental barriers to additional scale-up. The main issue we need to deal with [regarding] scale-up is injector design and optimization.”

The 30,000-lb.-thrust VR-3A engine under development for the Ausep competition will use liquid hydrogen fuel, Zamprelli says. The Air Force is looking for “cost-effective, technically mature alternatives to the Evolved Expendable Launch Vehicle upper stage,” according to NASA, which is collaborating on the effort.

“NASA is interested in the study as the [advanced upper stage engine] could be a candidate to power the [heavy-lift Space Launch System] cryogenic propulsion stage for in-space applications to enable exploration to multiple destinations beyond low Earth orbit,” according to the civilian space agency's Marshall Space Flight Center.

During the past 15 years, Orbitec has upgraded its test facilities to accommodate more powerful vortex engine ground-testing, working with both the Air Force and NASA on advancing the technology.

The flight test was preceded by a Sept. 20 ground test with a 3,000-lb.-thrust setup that demonstrated the chamber-wall vortex cooling, acoustic igniter and the ATK lightweight nozzle extension, which uses that company's technology to join hot carbon-carbon components to an actively cooled metal housing (AW&ST Oct. 1, p. 15.

The flight test involved a smaller vortex engine, integrated into a sounding rocket airframe developed by Garvey Spacecraft Corp. of Long Beach, Calif., and California State University at Long Beach. Other subcontractors on the test included Moog, Barber Nichols, Concept NREC and Boeing.

Zamprelli says his company is ready to begin commercializing the vortex engine and other space-related technology it has developed, and is looking for “teaming partners and investment to take all of our technologies to market.”

“Orbitec has been funded by NASA and the USAF on our technology [including] 15 years on vortex-related science,” he says. “We feel we owe it to the nation to show what this technology can bring to the space industry that has been so stale in the last 30 years or more.”