AEDC team conducts first test on a reusable space plane

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  When an expensive and critically-needed U.S. satellite abruptly stops functioning, a replacement is urgently needed. People may assume there is a quick fix.

But the real answer is no, according to Dr. Richard Roberts, 716th Test Squadron project manager for flight systems and aerodynamics. He said there is no way to currently conduct a quick launch of a fully reusable spacecraft, even an unmanned one, to replace a disabled satellite or put a payload into space.

The Air Force Research Laboratory worked with an Arnold Engineering Development Center team at the von Kàrmàn Gas Dynamics Facility (VKF) Supersonic Wind Tunnel A recently to conduct the first aerodynamic effects test on a Fully Reusable Access to Space Technology (FAST) proof-of-concept launch vehicle.

Dr. Roberts said his team put the FAST launch vehicle through a complex quick flip turn known in aerospace parlance as a rocketback maneuver.

"The primary objective of the test was to obtain jet interaction data to characterize the aerodynamics of the rocketback maneuver," he explained. "This reusable launch vehicle could be used to transport an expendable upper stage to put equipment into orbit and then it would do a quick flip turn to come back the way it came, returning to the launch site.

"The purpose of this vehicle and its rocketback capability is to allow shorter turn-around times between flights," he continued. "You can get it up there, flip it around and send it back where it came from and then, within a few days, you refuel, re-equip it and send it back up to space rather than having to ship it across country from an alternate landing site.

"To date, NASA's space shuttle is the closest we have come to this capability, which involves considerable operational expenses and a long time to turn-around the vehicle for the next flight."

Currently, all other booster systems are entirely expendable and require long lead times prior to launch.

The Air Force and Air Force Research Laboratory (AFRL) is pursuing the Reusable Booster System (RBS) concept as the potential next step for a low-cost access to space capability. Development of the rocketback capability for RBS could result in reduced cost per flight by reducing required vehicle turnaround time.

After the vehicle is launched, the rocketback maneuver is completed to return the vehicle to the launch site where it can be turned around within 48 hours. After turnaround is complete, the vehicle can be prepared for launch in under eight hours. This time table is greatly reduced compared to the time required to complete these tasks after shipping the vehicle across the country from an alternative landing site.

Dr. Roberts said the test of this capability involved the use of a 4-percent scale model of the concept vehicle.

"We used high pressure air to simulate the exhaust coming out of it and we tested extreme angles of attack, 90 degrees plus some, and actually flew this thing backwards in the tunnel," he said.

Dr. Roberts acknowledged the test posed some hurdles the team had to overcome.

"The high pressure air is always the big challenge because we don't do it a whole lot, even though we just did two tests [with a similar maneuver] back to back," he said. "[We have the additional challenge of] keeping that equipment ready to use and staff trained on it. The physics involved are complex and we're also dealing with the air flow blockage in the tunnel and the mechanics of getting the air to go the way we want it to.

"We try to keep it [the test article] out of the boundary layer as best as we can," he continued. "It is tough flying [the model] at extreme angles while using the high pressure jet simulation and avoiding the flow near the side of the tunnel, it can be tricky."

Aerospace Testing Alliance Project Engineer John Hopf agreed that the challenges the team faced during the test provided a learning curve for everyone involved.

"We went into the test knowing that a lot of what we were going to try to do wasn't proven," Hopf said. "In the wind tunnel, we had lots of blockage issues with a large model and the mass flow and running the test at the edge of the tunnel envelope.

We approached it as an experiment more than a production wind tunnel test," he added. "We did get quite a bit of good data. I think we can identify any of the questionable data."

Information gleaned from the test will go into AFRL's computational fluid dynamics database and possibly support future wind tunnel testing.