Volume 46 | Issue 5 | June 2004
Spike fetches first
By Jay Levine
Spike made his masters proud on the prairie lands of West Texas.
Spike isn't a doggie but the mascot of the Dryden Aerospike Rocket Test, which provided the first known flight data from a solid-fuel aerospike rocket. Researchers from Dryden, the Air Force Flight Test Center and blacksky Corp., Carlsbad, Calif., joined forces this spring to test the rocket concept during two successful flights.
The project logo shows a dog in a harness being carried by a rocket powered by an aerospike nozzle. The advantage of an aerospike nozzle is that "it really shines as it adjusts for atmospheric pressures as it flies; this is known as altitude compensation," said Trong Bui, Dryden's principal investigator.
Spike fetched evidence that an axisymmetric, or toroidal (round), aerospike rocket can be launched successfully. Valuable aerospike nozzle performance flight data were obtained after the research vehicle rocketed skyward off its 16-foot launch rail and attained an altitude of about 26,000 feet at speeds of up to Mach 1.5.
Two 10-foot, solid-fueled rockets with aerospike nozzles, each weighing about 100 pounds fueled, flew successfully on two consecutive flights March 30 and 31. Under cloudless skies and with winds calm, the rockets ascended from the King Ranch launch site at the Pecos County Aerospace Development Corp.'s flight test range in Fort Stockton, Texas. A third rocket flight with a conventional conical nozzle was unable to launch due to weather.
In addition to the altitude compensation advantage, the aerospike technology could result in development of a more compact and higher expansion-ratio nozzle for the upper stage vehicle, which will offer greater efficiency for space flight applications. The aerospike nozzle also can be as short as one quarter the length of a conventional nozzle. The use of aerospike nozzles could result in as much as a nine percent decrease in propellant requirements and total system weight for a mission to the Moon or Mars, said Air Force project investigator Chuck Rogers.
That makes the bone Spike brought home worth a whole lot of kibble.
Now, Bui said, the team seeks a customer to help fund additional research vital to determining the limits of the technology under various conditions.
"We are using a two-prong approach, depending on funding," Bui said. "We'd like to flight test the aerospike nozzle at different truncation (increasingly shorter) levels. The ideal spike that we flew is long, and we want to chop off as much as 75 percent of that length and use it on the same rocket testbed. That way we'd have a real comparison to the database we established on the vehicle we flew on the first two flights. We also want to try a higher-performance solid rocket fuel."
Partnering possibilities - including other NASA centers, government agencies and industry - are key to how far the research can be taken, he said. For example, given Bui's first choice, he said, he believes cost-effective aerospike nozzle flight research can be achieved by using the aerospikes on the hybrid sounding rockets similar to the Hyperion 2 launched from the Goddard Space Flight Center's Wallops Flight Facility, Wallops Island, Va.
"The Hyperion 2 rocket has a hybrid rocket motor that uses solid fuel and a liquid oxidizer, and it burns a long time," Trong explained. "Our current solid rocket motor fires from zero to 7,000 feet and stops, and the vehicle coasts up to 26,000. That does not provide a wide range of altitudes. The Hyperion motor burns from zero to 140,000 feet - now that's a big range of altitudes.
"What's more, it peaks out at 100 miles - that's in space. Ultimately, we would like a second stage - also with an aerospike motor - to fire at 100 miles."
The interesting question, Bui continued, is "what happens to this nozzle if we take it up to space? Would it hold the efficiency, or would it drop? We want to see if it holds its efficiency in space - if so, we're on to something."
Aerospike nozzles can be thought of as "inside-out" rocket nozzles. Rather than the rocket engine's exhaust plume exiting from a conventional bell-shaped nozzle, the plume travels externally. The main advantage of aerospike nozzles is that, as the rocket climbs, atmospheric and airstream pressure act on the plume to keep it at an optimum setting along the entire trajectory. This allows very efficient engine performance in flight. With traditional rocket engines, the bell nozzle is most efficient at only one point in the rocket's trajectory.
Although the advantages of aerospike nozzles are well understood through analysis and ground test data, the lack of actual flight test data has precluded their use in current as well as next-generation space launch vehicles. In addition, the configuration of an aerospike nozzle presents unique challenges to both designer and fabricator. The goals of the current project were to obtain aerospike rocket nozzle performance data in flight and to investigate the effects of transonic flow and transient rocket flight conditions on aerospike nozzle performance.
"The successful planning and integration of the Dryden Aerospike Rocket Test project clearly demonstrates the capability of the low-cost technology approach used," said Scott Bartel of blacksky, builder of the rockets.
"The flight operations support from the Tripoli Rocketry Association and Fort Stockton shows that enthusiasm for aerospace research is universal."
With a few flights notched, Bui said research must continue to build on the database created with the first two flights.
"We'd like to fly this, fly this often and fly it into space. The key here is to include analysis, ground testing and flight testing in a complementary way and bring things to flight quickly," he said.
"It seems people think flight research is 10 years of paper study, then 20 years of ground and wind tunnel research and then a miracle happens and we fly X-planes. But if you look deeper, researchers work on flight research testbeds and make contributions that might not be as high profile as X-planes, but add to databases and create tools and procedures for X-planes. This type of research keeps us sharp for when we do have X-planes because we use the same tools, procedures and practices."
The success of the Dryden Aerospike Rocket Test project, Bui said, "furthers our ability to obtain flight research data for not only the aerospike nozzles, but for other rocket technologies as well, such as dual-bell nozzles. This inexpensive, high-speed flight research platform allows us to take new ideas to flight quickly and, at the same time, increases the technology readiness level of new aerospace concepts."
Blacksky Corp. coordinated development of the experimental aerospike nozzles and solid propellant motors used in the tests with Cesaroni Technology Inc. of Ontario, Canada.
Cesaroni provided key support to the project with the rapid design and development of both aerospike nozzles as well as the custom solid-propellant rocket motors. The configuration of the nozzles presented unique design and fabrication challenges for Cesaroni.
"For many years NASA Dryden has built small radio-controlled and remotely piloted research models flown at subsonic speeds, to explore new concepts such as lifting bodies, parafoil landing systems and the testing of hypersonic shapes for landing feasibility," said the Air Force's Rogers. "With the demonstration of this rocket flight test technique these models can now be tested at transonic and supersonic flight conditions at very low cost."
Dryden funded the project and instrumented the rockets. Bui noted that a variety of Dryden personnel and resources were tapped for the project, including:
· Jim Murray, of the Aerodynamics branch, for design and fabrication of the data acquisition system.
· Howard Ng and Gary Williams (Aerotherm), of the Instrumentation branch, who performed the electronics integration and instrumentation wiring for the rockets.
· Keith Day of the Dryden machine shop, for machining work on the rocket hardware.
· Claudia Herrera, a former Propulsion branch co-op, for design and analysis work.
· Roy Compton, Donald Griffith, Steven Patterson, Anthony Lorek, David Martin and Richard Rowland, all of the calibration/environmental lab, who assisted with calibration and environmental testing of the rocket hardware.
· Harry Miller, Julie Baca Haley and Sandy McWilliams, of the electronics fabrication lab, who provided key assistance in the fabrication of the data acquisition electronics.
· Thanks also to Carla Thomas, Arcata Associates, for photo support and Casey Donohue and Chris Ashburn, both AS&M, of the Aerodynamics branch for their meteorological support.
And since the aerospike nozzle uses a centered Prandtl-Meyer all-external expansion design, with a handshake at the launch site on the day of the test, the project team dedicated the second flight to the memories of early 20th century German engineer and physicist Ludwig Prandtl and his doctoral student at the University of Göttingen, Theodor Meyer, whose work on expansion and oblique shock waves provided the theoretical foundation for the present aerospike nozzles.
Dryden public affairs writer Gray Creech contributed to this report.