On Thu, 21 Dec 2006 16:49:42 GMT, Jose
wrote in :

You can not be any more wrong about this. In space craft design, weight is
EVERYTHING.
Only during launch.

After which mass is everything.

It would seem that, the mass or weight become a lot more insignificant
after the Earth's gravitational field's influence on the space craft
is reduced as a result of the increased distance between the Earth and
the space craft. But that whole discussion fails to address the issue
implicit in the question of using atomic fission for propulsion of an
aerial vehicle within the Earth's atmosphere.

Apparently the weight of a conventional atomic fission reactor and its
necessary shielding, not to mention the weight of the "steam engine"
components, make the prospect of atomic aircraft all but entirely
unfeasible for terrestrial navigation. That weight limitation would
largely be overcome in a vehicle designed for use in space under
micro-gravity conditions where there is no necessity to rely upon
aerodynamic lift to support it. So if one has the power available to
boost a heavy reactor and the requisite shielding into space, if a
suitable nuclear powered rocket can be devised, the use of nuclear
propulsion may be feasible for space travel, despite its apparent
limitations for use in conventional winged aircraft operating within
the Earth's atmosphere.

However, if a small nuclear fission reactor used to power a Sterling
engine, such as those currently used in space, could be made light
enough, powerful enough and still adequately shielded, perhaps the
dream (nightmare?) of atomic aircraft would be achievable.

Here's some information about what NASA successfully has accomplished
with nuclear power:


http://www.grc.nasa.gov/WWW/tmsb/index.html
The Thermo-Mechanical Systems Branch (5490) is responsible for
planning, conducting and directing research and technology
development to advance the state-of-the-art in a variety of
thermal systems for space, aerospace, as well as non-aerospace
applications. The systems of interest include thermal energy
conversion for power systems and solar thermal propulsion systems.
The effort involves working at the component level to develop the
technology, the subsystem level to verify the performance of the
technology, and the system level to ensure that the appropriate
system level impact is achieved with the integrated technology.
System analysis is used to identify high-impact technology areas,
define the critical aspects of the technology that need to be
developed, and characterize the system level impact of the
technology. Specific technology areas of interest include:

Dynamic Power Systems: Brayton, Rankine and Stirling Convertors,
Solar Receivers and Thermal Energy Storage
Primary Solar Concentrators: Thin film, SRP and Rigid
Secondary Solar Concentrators: Refractive and Reflective
Thermal Management: Radiators, Electronics Packaging, and Heat
Pipe Technology


http://www.grc.nasa.gov/WWW/tmsb/stirling.html
Animation of a 55 We Stirling TDC
(click on image to view)


http://www.grc.nasa.gov/WWW/tmsb/sti...adisotope.html
AVAILABLE TODAY FOR TOMORROW'S NEEDS
NASA Glenn Research Center and the Department of Energy (DOE) are
developing a Stirling convertor for an advanced radioisotope power
system to provide spacecraft on-board electric power for NASA deep
space missions. Stirling is being evaluated as an alternative to
replace Radioisotope Thermoelectric Generators (RTGs) with a
high-efficiency power source. The efficiency of the Stirling
system, in excess of 20%, will reduce the necessary isotope
inventory by a factor of at least 3 compared to RTGs. Stirling is
the most developed convertor option of the advanced power concepts
under consideration [1,2].


http://www.grc.nasa.gov/WWW/tmsb/sti...ng_bckgrd.html
However, about this time NASA became interested in development of
free-piston Stirling engines for space power applications. These
engines use helium as the working fluid, drive linear alternators
to produce electricity and are hermetically sealed. These 12.5 kWe
per cylinder engines were intended for use with a nuclear reactor
power system; the Space Demonstrator Engine (or SPDE) was the
earliest 12.5 kWe per cylinder engine that was designed, built and
tested by MTI. A later engine of this size, the Component Test
Power Convertor (or CTPC), used a "Starfish" heat-pipe heater
head, instead of the pumped-loop used by the SPDE. Recently, in
the 1992-93 time period, this work was terminated due to the
termination of the related SP-100 nuclear power system work and
NASA's new emphasis on "better, faster, cheaper" systems and
missions.


http://www.spacedaily.com/news/outerplanets-00a2.html
Europa Orbiter was replanned to use a new "Sterling" nuclear
generator design which would use less plutonium



http://www.cndyorks.gn.apc.org/yspac...heed_offer.htm
Boeing, Lockheed Offer NASA Two Choices for Nuclear Power


http://powerweb.grc.nasa.gov/doc/marsairplane.html
On February 1, 1999, NASA Administrator Daniel Goldin, announced
the "Mars Airplane Micromission," which would have been the first
NASA micromission program to launch on an Ariane 5 rocket. The
flight would have the first Mars airplane arriving on the Red
Planet around December 17, 2003, the centennial of the Wright
brother's first flight. A team composed of members from four NASA
centers (Ames, Dryden, Langley, and Glenn) was formed to generate
conceptual designs for the micromission airplane.


From the information provided at those web pages, perhaps it would be
possible to deduce whether the current state of technology would
enable the development of atomic powered aircraft today.
Unfortunately, the political and environmental concerns are probably
insurmountable even if the technology is now adequate.