AAWSAP DIRD, Laser Lightcraft Nanosatellites, November 2010

Text

This text came with the file. It may have mistakes. When the text and the image disagree, the image is right.

UNCLASSIFIED//fOR. 8FFl&IAk W&li ,HIia¥
Figure 1. Air Force X-25LR Laser Lightcraft {courtesy of F. Mead, AFRL/ PRSP, Edwards AFB,
CA).
In the two-mode propulsion concept, a forebody aeroshell acts as an external
compression surface for the airbreathing engine inlet. Affixed to the bottom of the craft
is a parabolic-shaped afterbody mirror, which serves as a primary receptive optic for
the laser beam and as an external plug nozzle expansion surface. The primary thrust
structure is the centrally located annular shroud, which provides air through the inlet
and also acts as a ring-shaped energy "absorption/propulsion" chamber for plasma
formation. The air inlet is closed when the Lightcraft operates in the rocket mode.
The Lightcraft is very lightweight and uses its shape to facilitate vertical flight. The
craft has the appearance of a fat acorn when viewed from the side. The lower portion
of the craft is a very highly polished metal mirror, whereby the lower point of the
acorn-shape is the midpoint of a stretched-out parabolic mirror (see Figure 2). The
Lightcraft receives kilojoule pulses from a ground-based infrared laser at a rate of 25
times per second. The axisymmetric, off-axis parabolic collection mirror facilitates flight
by concentrating the pulsed laser light into an annular focus. The laser beam's pulse
interacts with the mirror, spreading out and focusing into an annular area inside the
circumference of the craft. The intensity of the 18 microsecond pulsed laser is
sufficiently high that atmospheric breakdown occurs in the annular area causing inlet air
to momentarily burst into a highly luminous plasma (10,000 - 30,000 K), thereby
producing a superheated plasma shock wave (with instantaneous pressures reaching
tens of atmospheres) that generates thrust in the direction of the laser beam. A lip
around the craft's circumference, akin to a plug nozzle, directs the expansion of the
UNCLASSIFIED,<,<FOA QFFI&IAL HSI!! OHLY
12