Successful AEDC arc heater test is significant step toward filling hypersonic capability gap

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  Twenty-five minutes may not seem like much time to many people, but for engineers conducting a recent test in AEDC's 70 megawatts segmented arc heater, H3, it set a record.

"The longest run in H3 to date, until Aug. 17, was about nine minutes," said Carrie Reinholtz, AEDC's project manager for the three-phased test program. "They almost tripled their longest run time in H3."

Reinholtz said the real significance of the long run time is it may provide engineers at AEDC with advanced arc heater technology to eventually fill a long-standing ground testing capability gap between facilities at Arnold and NASA.

According to Dr. Joe Sheeley, ATA project manager and technology engineer, the DOD segmented arc heater facilities, located at AEDC, have traditionally been used to simulate the high shear, low altitude portion of a ballistic vehicle's flight. At the other end, the arc heaters at the NASA centers like Ames, Johnson and Langley have been used to simulate the high altitude regime of a vehicle flight where high lift vehicles such as the shuttle fly.

Since 2008, the arc heater developers in the Technology and High Temperature Lab (HTL) have been working on a range of arc heater technologies to fill the mid-range capability gap. They hope to ultimately incorporate the total package of these technologies into AEDC's H2 cell, replacing the existing Huels heater design with a segmented heater of the H3 design. This would provide the 60-year-old facility with a cutting edge, segmented arc heater with longer runs times capable of simulating higher enthalpies at mid-altitude shear conditions, like those experienced by long-range global strike vehicles.

In the Huels heater, the electric arc is struck across a single insulator and establishes its own length while in a segmented heater, copper segments separated by insulators are used between the electrodes. The segmentation allows the heater to be operated at higher voltages - and therefore higher enthalpies - since more segments and insulators can be added to the heater to cause the arc to be longer. The segmented heater is also cleaner, produces less copper in the test gas, heats the gas more efficiently and creates more repeatable conditions.

"[At AEDC] we want to be able to run at high enthalpy conditions in the mid-altitude range," Reinholtz said. "Before the program began they had only demonstrated these conditions for very, very short periods of time. The short run times aren't providing a sufficient duplication of flight test conditions.

"For example, say a customer wants to perform bonding, thermal protection, or nose materials testing. If you're able to run simulated flight conditions for 25 minutes, you'll have a more realistic understanding of what the materials will experience and determine whether the materials will survive re-entry."

Reinholtz said the next part of this first phase will involve testing a new electrode in H3. Testing will be conducted to determine whether the new design further reduces the wear rate on the electrode. Reducing wear rates would increase electrode life and allow for longer run times with multiple test articles, which in turn, increases test efficiency.

"The long term vision of this project is to be able to take the H3 segmented heater technology and replace the H2 Huels heater with that specific technology," she said. "The upgrade to the H2 facility will then provide the long run times in the mid pressure test envelope."

"That capability is required for re-entry and boost glide vehicles. Providing this test envelope for ground testing will help to reduce the overall program risk."

Reinholtz added, "This effort is funded by OSD's T&E/S&T (Office of the Secretary of Defense Test and Evaluation/Science and Technology) Advanced Propulsion Test Technology (APTT) program. This funding is not 'internal' to AEDC. It is also worth noting the goal of T&E/S&T is not to perform the H2 upgrade. That upgrade, if selected, would be funded by a CTEIP (Central Test and Evaluation Investment Program) project."

"Hypersonic flight test programs can easily cost $100 million per flight and are becoming more difficult to perform due to treaties and test range availability issues," Sheeley said. "They are also very visible, with a failure possibly resulting in the cancelation of a program. It is worth a significant investment in ground test infrastructure if it will allow vehicle developers to down-select materials and improve material models in ground test programs costing only hundreds of thousands."

Regarding H2's transformation into a segmented arc heater for future ground testing, Reinholtz said, "Additional work and funding is required before H2 transformation can be completed. However, this is a necessary first step."