E. Bruce Jackson (757) 864-4060
Aircraft Guidance and Controls Branch
505-66-31
RESEARCH OBJECTIVE: The personnel launch system (PLS) concept has been proposed to ferry astronauts to and from a space station utilizing an expendable booster for vertical takeoff and performing an unpowered horizontal landing. The reusable vehicle, which could bring ailing astronauts back to earth under automatic control, is in preliminary design stages. To identify and correct flight control/flying qualities deficiencies early in the conceptual vehicle design process, a piloted simulation study of vehicle approach and landing characteristics has been initiated using the Langley Visual/Motion Simulator (VMS) cockpit. The objectives are to identify potentially beneficial vehicle configuration improvement opportunities, to define candidate controls laws, and to investigate a range of landing techniques using both manual and automatic control modes.
APPROACH: An aerodynamic model was developed from wind tunnel tests of the vehicle with appropriate corrections for landing gear and ground effects. Manual and autoland control laws and a flight director display concept were developed. The six degree-of-freedom nonlinear vehicle model was installed and validated on the VMS simulator. An approach trajectory consisting of a steep constant velocity outer glideslope, a constant "g" preflare, and a shallow inner glideslope to precision landing was developed for piloted and autoland control evaluation. LaRC & DFRC research pilots and JSC astronauts conducted evaluations of several candidate control systems and vehicle aerodynamic improvements. In addition, vehicle performance concerns, such as launch abort options and required runway lengths are being studied.
ACCOMPLISHMENTS: Successful manual landings using both the flight director display and instrument only approach techniques, under no wind, headwind, tailwind, and steady crosswind conditions were accomplished. A flight path command control system was shown to improve touchdown sink rates by 38%. Modifications to the landing gear location have resulted in smoother nosewheel touchdowns. An improvement in the lift-to-drag ratio of the HL-20 has provided a vehicle with good to excellent flying qualities. Preliminary supersonic (Mach 1.5 to 3) reentry tests show a need to refine the lateral control system for this regime and provide more aerodynamic nose-up pitching moment to avoid steep trajectories and/or control surface saturation.
SIGNIFICANCE: Early evaluation from a flight systems perspective of a conceptual PLS vehicle design have identified handling qualities & flight control problems and verified solutions to some of these problems. Basic modifications to the vehicle configuration have been identified which may result in significant program cost savings.
FUTURE PLANS: LaRC & DFRC research pilots and JSC astronauts are participating in studies of abort procedures, flying qualities and guidance and control system improvements.
(circa 1992)
Publications related to this work:
Rivers, Robert A.; and Jackson, E. Bruce: Preliminary Piloted Simulation Studies of the HL-20 Lifting Body. J. Aircraft, vol. 31, no. 3, May-June 1994.
Jackson, E. Bruce; Cruz,
Christopher I; and Ragsdale, W. A.: Real-Time Simulation Model of the
HL-20 Lifting Body. NASA TM-107580, July 1992.
[Simulation model written in C/Fortran/GL for SGI platforms is available
on request]
Jackson, E. Bruce; and Cruz, Christopher I: Preliminary Subsonic Aerodynamic Model for Simulation Studies of the HL-20 Lifting Body. NASA TM-4302 , 1992.
Rivers, Robert A.; Jackson, E. Bruce; and Ragsdale, W. A.: Preliminary Development of the HL-20 Lifting Body Design. Presented at the 35th Symposium of the Society of Experimental Test Pilots, held in Beverly Hills, CA, September 25-28, 1991.
Jackson, E. Bruce; Ragsdale, W. A.; and Powell, Richard W.: Utilization of Simulation Tools in the HL-20 Conceptual Design Process. Presented at the 1991 AIAA Simulation Technology Conference, held in New Orleans, LA, August 18-21, 1991. AIAA Paper No. 91-2955.
