NASA Stennis Flashback: Learning About Rocket Engine Smoke for Safe Space Travel

    

NASA’s Stennis Space Center near Bay St. Louis, Mississippi, is widely known as the nation’s largest rocket propulsion test site. More than 35 years ago, it also served as a hands-on classroom for NASA engineers seeking to improve the efficiency of space shuttle main engines.

From 1988 to the mid-1990’s, NASA Stennis engineers operated a Diagnostic Test Facility to conduct rocket engine plume exhaust diagnostics and learn more about the space shuttle main engine combustion process. The effort also laid the groundwork for the frontline research-and-development testing conducted at the center today.

“The Diagnostic Test Facility work is just another example of the can-do, will-do attitude of the NASA Stennis team and of its willingness to support the nation’s space exploration program in all ways needed and possible,” said Joe Schuyler, director of the NASA Stennis Engineering and Test Directorate.

Envision a rocket or space vehicle launching into the sky. A trail of bright exhaust, known as the engine plume, follows. As metals wear down in the engines from the intense heat of the combustion process, the flame glows with colors, some visible, such as orange or yellow, and others undetectable by the human eye.

The colors tell a story – about the health and operation of the engine and its components. For space shuttle main engines, which flew on multiple missions, engineers needed to understand that story, much as a doctor needs to understand the condition of a human body during checkup, to ensure future engine operation.

Where better place to study such details than the nation’s premier propulsion test site? Paging NASA Stennis.

NASA Stennis has long enabled and supported innovative and collaborative work to benefit both the agency and the commercial space industry. When NASA came calling in the late 1980s, site engineers went to work on a plan to study space shuttle main engine rocket exhaust.

The concept for an enabling structure about the size of a home garage was born in October 1987. Five months later, construction began on a Diagnostic Testbed Facility to provide quality research capabilities for studying rocket engine exhaust and learning more about the metals burned off during hot fire.

The completed facility featured a 1,300-square-foot control and data analysis center, as well as a rooftop observation deck. Small-scale infrastructure was located nearby for testing a 1,000-pound-thrust rocket engine that simulated the larger space shuttle main engine. The 1K engine measured about 2 feet in length and six inches in diameter. Using a small-scale engine allowed for greater flexibility and involved less cost than testing the much-larger space shuttle engine.

Engineers could quickly conduct multiple short-duration hot fires using the smaller engine. A six-second test provided ample time to collect data from engine exhaust that reached as high as 3,900 degrees Fahrenheit.

Chemical solutions simulating engine materials were injected into the engine combustion chamber for each hot fire. The exhaust plume then was analyzed using a remote camera, spectrometer, and microcomputers to determine what colors certain metals and elements emit when burning.

Each material produced a unique profile. By matching the profiles to the exhaust of space shuttle main engine tests conducted at NASA Stennis, determinations could be made about which engine components were undergoing wear and what maintenance was needed.

The Diagnostic Testbed Facility played a critical safety role for engine operations and also provided a real-time opportunity for NASA Stennis engineers to learn about exhaust diagnostics.

Multiple tests were conducted. The average turnaround time between hot fires was 18 to 20 minutes with the best turnaround from one test to another taking just 12 minutes. By January 1991, the facility had recorded a total of 588 firings for a cumulative 3,452 seconds.

As testing progressed, the facility team evolved into a collection of experts in plume diagnostics. Longtime NASA Stennis engineer Glenn Varner serves as the mechanical operations engineer at the Thad Cochran Test Stand, where he contributed to the successful testing of the first SLS (Space Launch System) core stage onsite.

However, much of Varner’s hands-on experience came at the Diagnostic Test Facility. “We learned about purging, ignition, handling propellants, high-pressure gases, and all the components you had to have to make it work,” he said. “It was a very good learning experience.”

The Diagnostic Testbed Facility impacted more than just those engineers involved in the testing. Following the initial research effort, the facility underwent modifications in January 1993. Two months later, facility operators completed a successful series of tests on a small-scale liquid hydrogen turbopump for a California-based aerospace company.

The project marked an early collaboration between the center and a commercial company and helped pave the way for the continued success of the NASA Stennis E Test Complex. Building on Diagnostic Testbed Facility knowledge and equipment, the NASA Stennis complex now supports multiple commercial aerospace projects with its versatile infrastructure and team of propulsion test experts.

“The physical remnants of the Diagnostic Testbed Facility are barely recognizable now,” Schuyler said. “But that spirit and approach embodied by that effort and its teams continues in force at the center.”

Additional Information

NASA Stennis has leveraged hardware and expertise from the Diagnostic Testbed Facility to provide benefit to NASA and industry for two decades and counting.

The facility’s thruster, run tanks, valves, regulators and instrumentation were used in developing the versatile four-stand E Test Complex at NASA Stennis that includes 12 active test cell positions capable of various component, engine, and stage test activities.

“The Diagnostic Testbed Facility was the precursor to that,” said NASA engineer Glenn Varner. “Everything but the structure still in the grass moved to the E-1 Test Stand, Cell 3. Plume diagnostics was part of the first testing there.”

When plume diagnostic testing concluded at E-1, equipment moved to the E-3 Test Stand, where the same rocket engine used for the Diagnostic Testbed Facility has since performed many test projects.

The Diagnostic Testbed Facility thruster also has been used for various projects at E-3, most recently in a project for the exploration upper stage being built for use on future Artemis missions. 

In addition to hardware, engineers who worked at the Diagnostic Testbed Facility also moved on to support E Test Complex projects. There, they helped new NASA engineers learn how to handle gaseous hydrogen and liquid hydrogen propellants. Engineers learned about purging, ignition, and handling propellants and all the components needed for a successful test.

“From an engineering perspective, the more knowledge you have of the processes and procedures to make propulsion work, the better off you are,” Varner said. “It applied then and still applies today. The Diagnostic Testbed Facility contributed to the future development of NASA Stennis infrastructure and expertise.”