- Spacecraft/Aircraft Aerodynamics and Flight Dynamics
ACI has nationally and internationally recognized expertise in estimating aerodynamic forces and
moments from free-flight data obtained in aeroballistic ranges. Aeroballistic ranges provide
invaluable data for aerodynamic and flow-physics studies and for verification of computational fluid
dynamics codes. These facilities are operated over a wide range of flight conditions, and they have
several advantages over other types of facilities, including: 1) The freestreams are known and
uncontaminated. 2) The models are in free-flight; hence there are no sting effects and the base
flows are correct. And 3) Dynamic as well as static aerodynamic characteristics can be measured.
The data obtained from aeroballistic ranges is typically a series of orthogonal, or nearly orthogonal,
images of the model taken at known times. ACI developed a turn-key system, the Comprehensive
Aerodynamic Data Reduction system for Aeroballistic Ranges (CADRA) that translates images of
the model into 3-D position and orientation measurements. CADRA automatically identifies image
pixels associated with the model and the reference system (typically grid lines, wires, or other
objects, such as beads), and calculates their relative locations and orientations. CADRA also has
algorithms for .repairing. images when the model and another object, such as the model's shadow,
overlap. Using the known locations of the reference systems, CADRA translates the film measure-
ments into 3-D position and orientation measurements; the measurement techniques implemented
in CADRA give sub pixel resolution.
The aerodynamic coefficients are then found using a differential, iterative, least-squares technique
which fits calculated trajectories to the position and orientation measurements. An integral part of
this effort is defining the shape of the static and dynamic aerodynamic forces and moments. With
CADRA, the forces and moments can be defined as polynomials, cubic splines, and point-wise
functions, as well as other more complicated functions suitable for planetary entry and re-entry.
The CADRA system is in use by United States Air Force Wright Laboratory, NASA/Ames Research
Center, and Canadian Defense Ministry (Ministere de la Defence Nationale, Centre de Recherches
Pour la Defense de Valcatier). ACI has analyzed the engineering designs of atmospheric entry shells
used by many of NASA's and ESA's robotic planetary missions and manned spacecraft, including
the Mars Exploration Rovers, Stardust, Huygens and Orion Spacecraft Crew Exploration Vehicle.
In addition, ACI has used CADRA for analysis of data from other types of facilities and tests,
including helicopter drop tests, water tank drop tests, and vertical wind tunnels.