The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

232 laser propulsion
Houston. Langley was also involved in investigating the
optimum shape for Gemini and Apollo spacecraft so that
they could survive reentry. Among its other projects have
been the Echo balloons, the Pegasus micrometeroid
detection satellites, Lunar Orbiter, and developing the
Mars Viking mission.
laser propulsion
Methods of propelling spacecraft using the energy of laser
beams, all of which remain conceptual or in the early stages
of experimentation. There are two main types of laser propulsion,
depending on whether the laser is off-board or
onboard the spacecraft. Off-board techniques have been
proposed to boost lightweight vehicles either from the
ground to orbit, or on interplanetary or interstellar missions.
These techniques include laser-powered launching
to orbit and laser light sails. Onboard methods involve the
use of lasers as part of a nuclear propulsion system.
Off-board laser propulsion
This is part of a larger class of propulsive methods known
as beamed-energy propulsion. Its great advantage is that
it removes the need for the spacecraft to carry its own
source of energy and onboard propulsion system. The
propulsive energy comes instead from a fixed, highpower
laser beam that is directed onto the spacecraft by a
tracking and focusing system.
Laser-powered launching. Powerful lasers developed as
part of the U.S. SDI (Strategic Defense Initiative) program
promise to have a peaceful use—to launch lightweight
spacecraft into low Earth orbit. Tests have already
been conducted by Leik Myrabo of the Rensselaer Polytechnic
Institute and other scientists from the U.S. Air
Force and NASA, using a 10-kW infrared pulsing laser at
the White Sands Missile Range and an acorn-shaped craft
laser propulsion A cold-flow propulsion test using lasers at
Marshall Space Flight Center. NASA
with a diameter of 12.2 cm and a mass of 50 g. The base
of the craft is sculpted to focus the beam from the laser
onto a propellant. In tests so far, this propellant has been
air, which is heated by the beam to a temperature of
10,000° to 30,000°C, expands violently, and pushes the
craft upward. A height of 71 m was achieved in an October
2000 trial. To orbit a 1-kg spacecraft will demand a
much more powerful, 1-MW laser and a supply of
onboard propellant, such as hydrogen, to take over at
altitudes where the air gets too thin. 163
Laser light sails. These would be interplanetary or interstellar
spacecraft powered by one or more extremely powerful,
orbiting lasers. For details, see space sail.
Onboard laser propulsion
Lasers located onboard a spacecraft could be used in a variety
of propulsion systems. In the laser-fusion concept, for
example, pellets of deuterium-tritium fuel are bombarded
by symmetrically positioned lasers for a few billionths of a
second until the nuclei fuse, releasing a sudden burst of
energy. A rapid series of such explosions could provide the
basis for a nuclear pulse rocket. Alternatively, in one form
of the interstellar ramjet, lasers are used to ionize interstellar
gas ahead of the spacecraft so that the gas can be
drawn in by a magnetic field and used as propellant.
launch
The initial motion of a space vehicle from its stationary,
prelaunch position to dynamic flight. Also, the moment
when the vehicle is no longer connected to or supported
by the launch pad structure.
launch control center
A centralized control point for all phases of prelaunch
and launch operations. The handover of control to a mission
control center occurs at the moment of separation
of the space vehicle from all hard ground connections.
Launch Escape System (LES)
See Apollo.
launch pad
(1) In a restricted sense, the load-bearing base or platform
from which a rocket vehicle is launched. This is sometimes
called the launch pedestal. (2) More generally, the
area from which a rocket vehicle is fired, including all the
necessary support facilities, such as the service tower,
safety equipment, and cooling water and flame deflectors.
Often called simply a pad.
launch support and hold-down arm
Equipment that provides direct support for a portion
of the dead weight of the space vehicle and retains the