Major Areas of Opportunity - Implications of Emerging Micro-and Nanotechnologies - page 95

• to protect space-based assets from man-made threats—for example, anti-

satellite weapons and space debris

Propulsion is at the heart of aerospace vehicle design since the propulsion
system and its fuel account for between 40 and 95 percent of the initial system
mass. Propulsion is needed to power vehicles ranging in size from grams (for
unobtrusive airborne and spaceborne sensors) to hundreds of tons (for large air-
craft and launch vehicles). Modern warfare also requires energy—energy in mod-
est quantities for C 3 I (watts to kilowatts) and in very much larger quantities for
weapons (megawatts and above). Micro- and nanotechnology applied to propul-
sion and power may offer the opportunity for significant evolutionary improve-
ments to current systems and may enable revolutionary new systems and capa-
bilities.
The technical challenges may be met by utilizing a combination of micro-
and nanoelectronics for communications and information processing, MEMS and
NEMS for sensors and distributed actuators, and molecularly engineered materi-
als for ultralightweight structures. Batch fabrication, self-assembly, and high
levels of functional integration during the fabrication process will be required to
make these highly sophisticated systems and subsystems affordable.

Flight Vehicle Aerodynamics

Micro- and nanotechnologies offer the possibility of dramatically improving
the aerodynamics of flight vehicles in two principal ways. The first is through
direction modification of the aerodynamics by microdevices and the second is
through materials changes that achieve more favorable fluid mechanics behavior.
Although the lift and drag of large aircraft is tens or hundreds of tons, the
aerodynamics within a few millimeters of the vehicle surface has a profound
impact on vehicle performance. This so-called boundary layer is the result of the
viscous nature of air and the high characteristic speeds and length scales of man-
made vehicles. It has long been known that local manipulation of the boundary
layer can radically alter first-order vehicle performance parameters such as drag
and stability. A relatively recent research field is the active control of fluid
mechanics, which uses high-frequency, dynamical control of aerodynamic sur-
faces to alter the mean aerodynamic behavior. Subscale experiments have dem-
onstrated that such active control can be used to alter the turbulent nature of the
flow, perhaps leading to laminar flow vehicles with dramatically increased range
and payload compared with existing aircraft. A second flow control application
uses unsteady manipulation of the boundary layers to generate large forces and
moments to achieve control and maneuverability of the flight vehicle. These
controllers would supplement or replace conventional large-scale control sur-
faces, their actuators, and hydraulic lines and valves. This would alter the steady-