On Mon, 08 Mar 2004 16:30:28 GMT, "George Kinley"
wrote:

Are there any way for rockets to fly in space , other then throwing mass
out in one direction and moving in other

This isn't exactly in response to the question, but what is the
current opinion on laser rockets? The idea is fairly simple, but I get
the impression that currently it is not a very strong candidate.

The latest news I found (and that was from November 2000) is that
they've lifted a 51g craft to an altitude of 71 meters using a 10kW
laser.
"The 51 g, 12 cm diameter Lightcraft is propelled skyward when the
laser beam hits a parabolic condensing reflector on its underside.
This ablates a thin plastic coating, sending the craft upwards."
(http://optics.org/articles/news/6/11/9/1)
This thing is developed by a company called Lightcraft Technologies,
Inc. (http://www.lightcrafttechnologies.com/news.html) as a method of
launching micro-satellites. I wonder how they are currently doing -
the "Latest Developements" section of their website is last updated in
Dec 2000.

The website describes the technology thus:
"The back side of the craft is a large, highly polished parabolic
mirror that is designed to capture the laser beam projected at it from
the ground. The mirror focuses the beam, rapidly heating the air to 5
TIMES the temperature of the sun, creating a blast wave out the back
that pushes the vehicle upward. As the beam is rapidly pulsed, the
vehicle is continuously propelled forward, on its way to orbit."

This seems to imply that no propellant is used as such, but the news
article mentions a platic coating. If it does need to carry some kind
of reaction mass, some easily produced and non-polluting substance
would be necessary (ice, if it was practical, would probably be superb
in terms of cost and ease of production).

Laser rockets have a kind of simplicity that appeals to me, but I lack
the knowledge of rocket or laser technology to form any concrete
opinion about their practicality.

--
Olli Wilkman