Results of NASA/DARPA Automatic Probe and Drogue Refueling Flight Test Keith Schweikhard NASA Dryden Flight Research Center

Program Objective To make one demonstration fully automatic engagement (probe plugging the drogue) between the F-18 and the Omega Air B707 tanker using the Autonomous Airborne Refueling System.

Technical Background ➢ High Risk Technology ➢ Technology Demonstration not Development Program ➢ Low Cost ➢ Compressed Development Schedule ➢ Reduced number of test conditions ➢ Reduced redundancy/ error correction in the system.

Project Timeline ➢ March 05 Proposal Kickoff DFRC ➢ DARPA Kickoff Meeting ➢ Technical Kickoff Meeting ➢ System Requirements Review ➢ Preliminary Design Review ➢ Critical Design Review ➢ Risk Reduction Flight ➢ Hardware Arrives at Dryden ➢ Flight Readiness Review ➢ Airworthiness and Flight Safety Review Board ➢ Tech Brief (Surrogate Tanker) ➢ through Surrogate Tanker Flights ➢ Tech Brief (Omega Tanker) ➢ through Omega Tanker Flights ➢ Project Completion

System Architecture Data Link Pitch Stick Roll Stick Delta Throttle Rudder = 0 Command/ Status Information Push Button Display Tanker Pallet Production Support Flight Control Computers Receiver System Video Input

Refueling Geometry 20' 100' Trail Position Closure Hold Position Precontact 1&2 Position Capt

AARD Modes and States Precon t 1 Precon t 2 Trail Closur e Captur e Hold Unplug Retreat Miss Init Standb y Ready Relative GPS Relative GPS + Tracker

Accuracy Design Targets ➢ Station Keeping Mode. ➔ ±6.5' longitudinal position ➔ ±6.5' vertical position ➔ ±10' lateral position ➢ Capture Mode ➔ System must be able to reliably guide/control receiver aircraft within ±11” of desired location, in the conditions intended for demonstration, 95% of the time ➔ Requirement driven by basket dimensions: 32” outside diameter ➔ Project pilot estimates plug success rate at 95% if the probe is positioned inside 4” from outside edge of drogue

Guidance & Control Block Diagram

Omega Tanker Risk Reduction ➢ Approach to plug on left and right drogues using the cockpit and pylon camera ➢ Tanker pitch/ roll/ yaw maneuvers ➢ Varying approach rates/ trajectories ➢ Survey of capture and miss locations on the drogue ➢ Varying plug attempts at different diameters from the center of the drogue

Surrogate Tanker Flights  Surrogate tanker was used to increase test efficiency ➔ Lower cost per hour to fly ➔ Easier to schedule.  Tested engage/ disengage/ reversion modes.  Commanded Autonomous modes through Precontact 1  Gathered system performance data using sine and step inputs  Gathered system performance data for a variety of gains  Tracked Surrogate tanker through a turn in Trail and Precontact 1

Longitudinal Axis Results

Lateral Axis Results

Vertical Axis Results

Omega Tanker Flights  Tested engage/ disengage/ reversion modes.  Commanded mode transitions through unplug  Gathered/ tuned the video tracking algorithm.

Video Tracker Performance

First Plug Attempt

Second Plug Attempt

Success

Control Position Comparison

Where Do we go from here ➢ Follow on activity planned for Oct 06 through Apr 07 ➢ Added Objectives for the follow on activity ➔ Optimal tuning of controller and Drogue Motion Compensation to improve performance and robustness of the system in the capture phase ➔ Expand the envelope to include plugs and unplugs in steady turns ➔ Receiver autonomous rendezvous with the tanker from up to 2nm and ±60° off tanker heading ➔ Improve robustness of the video tracker system in the area of drogue recognition, expanded search and acquisition

Summary ➢ Designed, developed and successfully tested a prototype system to autonomously perform probe to drogue refueling. ➢ Demonstrated autonomous station keeping behind the tanker in both level flight as well as through a 20° banked turn. ➢ Demonstrated acquisition and tracking capability of the video tracking subsystem.

Questions?

System Architecture NASA Instrumentation System (AIMS) Input Signal Management Control Laws Output Signal Selected Fader logic Actuator Signal Management Disengage Logic Replication CLAW Executive Dual Port Ram A/D D/A Discrete Input 1553 I/O Surface Actuator Analog Interface Flight Control Computers Push Button Display Pilot Light Panel Instrumentation Handler Operating System Executive Process Display Handler AARD Handler Ethernet I/O 1553 Input 1553 Output RS 422 I/O Discrete Output Pilot Vehicle Interface Operating System Nav Processes Data Link Processes D/A Ethernet I/O AARD Controller GPS Ant Data Link Ant Camera (2) Analog Inputs Control Positions SLIC Bus 1 Data Recorder IMU Cockpit Analog Inputs Operating System Nav Processes Video Processes Data Link Processes PVI Processes GNC Processes Simulation Interface Processes Data Recorder IMU Data Link Ant GPS Ant Tanker Pallet Analog Multiplex Card