Navy returns to AEDC to test next-generation heat shield candidate materials for missiles, reentry vehicles

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  Once it leaves a U.S. Navy Trident II submarine and is clear of the water, a submarine-launched ballistic missile (SLBM) rapidly accelerates to more than Mach 20, on its trajectory to impact and destroy a target.

An SLBM is the Navy's sea-based equivalent to the Air Force's land-based Inter-Continental Ballistic Missile.

How do the Navy fleet commanders know for sure the sixth generation D-5 fleet ballistic missile will survive those extremely hot and severe aero-thermal flight conditions and accomplish the mission?

This is where the Navy's Drew Pathwick and the test team at the Arnold Engineering Development Complex's (AEDC) High-Enthalpy Arc-Heated facilities come into the picture.

Pathwick is the Navy Reentry Ground Test Coordinator for the Naval Surface Warfare Center's Dahlgren Division Detachment in Washington D.C.

Since 2000, he has been coming to AEDC to conduct aero-thermal testing to simulate what a missile's heat shield material candidates will experience in that flight regime - to ensure they will survive long enough and intact enough to complete the mission.

"A flight test is extremely costly, I mean we're talking about orders of magnitude more than performing a 'simple' ground test at AEDC," Pathwick said. "The Navy had decided many years ago that the data we get out of AEDC for the price is actually a steal [when] compared to a flight test. And you get a very quick turnaround with your data, whereas with a flight test, from conception to flight, you're taking about three years or something like that."

Pathwick added, "Our systems see a very extreme environment, some very high heat fluxes and pressures. Although there are many other arc heaters [ground test facilities] in the U.S., none of them can actually provide the proper conditions that we're looking for. AEDC is very unique in that respect."

Pathwick said he and his colleagues have formed a solidly professional and collaborative relationship with the test team at AEDC's Arc Heater facilities over the years.

"I interface a lot with Mark Smith and the other engineers there," he said. "They're very good at taking our requirements and ensuring that the proper test environment that we're looking for is provided, including keeping things on schedule. And the operations folks down there do a great job at meeting our, sometime unusual test requirements.

"We typically have a standard type of test configuration that we're looking for, but for some reason it seems every time we come there we have some sort of new wrinkle and the crew there is very good at helping us out and ensuring that we get the data we're looking for."

The Navy's current test entries are next-generation SLBM heat shield material candidates and these are being tested in the Complex's most cutting-edge high-pressure segmented arc heater, H3, as well as in the legacy H1 segmented arc heater.

"The data we're getting out of this test is going to be used to provide relative performance data for new build thermal protection system materials," Pathwick continued. "We're comparing that to our current thermal protection systems so that we have candidates for a new system if the opportunity arises."

He emphasized it is important to put the current material candidates testing into perspective.

"Our systems are working just fine, but there will be an end date to the service life of this system and we want to be prepared for when that day comes," he said, acknowledging some of the challenges to fielding any new weapon system or its components.

As new missiles are conceived, designed and fielded, the existing TPS materials will no longer be available and new materials will be required. Ground testing in AEDC's High-Enthalpy Arc-Hearted facilities remains the only way to gain confidence and validate these newer materials.

"We can't say this is a simulation of flight test, because it really is not, especially when you consider the Mach numbers [and considering] the aerodynamics," Pathwick said. "This is really screening from a thermal perspective. We're looking at providing flight-like heat fluxes, pressures, so we get the right thermal soak through the material as a screening process. Again, the only true way to check out a material is to eventually flight test it.

"So, this is a great screening tool so we can narrow down our candidates to a few that we can then actually put in the air and flight test."

Pathwick also said his test team has also been getting help from another group at AEDC on the Navy's test entry in H3.

"Since it's a new arc heater, we're trying to better understand the flow field that we're getting out of it," he said. "H3 is a whole different beast - we just want to make sure we understand it as well as we can. And we're getting help from AEDC's analysis branch with this facility in defining the nozzle flow conditions."

2nd Lt. Julie Sung, who is AEDC's Air Force Program Manager for the test, said that although she only recently joined the Complex's workforce, "In my short time here I have already gotten the impression that our arcs team has established many positive and outstanding relationships.

"Since NSWC has worked with AEDC on this test effort for many years now, I get the impression that each time NSWC comes to test here, all the logistics that lead up to their visit goes very smoothly and is nearly routine now. Mark, his team, and Drew Pathwick seem very knowledgeable in their jobs, and most importantly, I get the impression that they are very passionate about it as well."

Sung added, "Ground testing done at AEDC is an invaluable resource in lieu of flight testing. Having this cost effective option very likely delivers a wealth of data that can be used by the Navy to continue their efforts in maintaining progress on their SLBM programs which in turn, support the defense of our country."

Mark Smith, the ATA project engineer on the NSWC re-entry candidate materials at AEDC, has worked closely with the Navy during his 26 years at the Complex.

"The Navy has a rigorous materials test program underway in the AEDC arcs going back some 30 years, with several different Navy-related programs in the testing mix," he said. "The Navy is the single largest test customer in the AEDC arcs in terms of test workload, and they have been for many years. The collaboration between AEDC and NSWC has always been a dynamic one, with excellent communication and forward-thinking on both sides.

"[This relationship] has enabled the 'stand-up' of many new test techniques and capabilities which directly support the Navy systems and provides additional capability to the DOD warfighter for development of high-speed missiles and vehicles. In turn, the Navy has been very proactive in helping to bring these capabilities to fruition through various partnerships and most importantly, through systematic utilization of the legacy and developing arc jet capabilities at AEDC."

Asked why the Navy has continually brought their thermal protection system materials to AEDC for ground testing before subjecting the materials to a flight test, Smith said the answer is relatively straightforward.

"The AEDC arc facilities are unique in the world in their ability to simulate heat flux and pressure conditions typical of long-range ballistic missile reentry through the atmosphere," he said. "For tests such as these, the Navy as well as the Air Force (for ICBM) require high-temperature air flows lasting several minutes with turbulent boundary-layer conditions on wedge and nose tip test articles. There is no other place in the world to conduct tests of this nature."