[ RadSafe ] Fission, Fusion, Mars, Spacecraft...

[Brennan, Mike (DOH)]

Hi, Joe.

Given that I will be attending a science fiction convention this
weekend, and one of the panels I am on is about spaceship combat, I've
given a fair amount of thought to things like this.

With current, or near term technology, getting mass into orbit is the
expensive part.  This is the first big problem with using some type of
nuclear reactor for propulsion in space: there is a minimum size you can
make a reactor, and it is fairly big.  When you include the reactor, its
auxiliary systems, and the reaction mass, you need a very large system
before it has higher energy density than a chemical rocket system.  To
use a down-to-earth example, it is clearly a good idea to make aircraft
carriers nuclear powered, it is a reasonable idea to make cruisers
nuclear powered, it makes no sense at all to make patrol boats nuclear
powered.  

When thinking about space travel, it is important to not confuse
acceleration with velocity.  The propulsion plant determines what
acceleration your ship is capable of, but velocity is only limited by
time and reaction mass/fuel.  (yes, I can hear you shout, "But what
about relativity!"  By the time you can sustain accelerations that get
you to relativistic velocities in fairly short lengths of time, you are
not working with anything we could build with our current understanding
of physics).  I don't foresee us building a ship where acceleration will
be a challenge for people (once it gets out of the gravity well, of
course).

I love nuclear power in space, but we are at least two scientific
breakthroughs away from needing it for manned ships.



-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of
JPreisig at aol.com
Sent: Monday, March 25, 2013 10:07 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] Fission, Fusion, Mars, Spacecraft...

Dear Radsafe,
 
     Hi.  Hope you all are well.
 
 
     Chemical Propulsion Energy --- about 1   keV
 
     Fission Propulsion Energy (reactor enrichment) ---  about 1 MeV
 
     Fission Propulsion Energy (100% enriched???)  ---  about 20 x  1
MeV
 
     These are crude energy levels associated with  these various rocket
etc. propulsion systems.
You can do better calculations of these levels at home.
 
     Some rather crude calculations involving rocket  kinetic energy
show me that a fully enriched Uranium propulsion system  might go 100
times faster in velocity than a chemically based propulsion  system.
Of course, spaceship/rocket materials considerations and limitations of
astronauts's ability to endure/survive very large g forces may limit the
velocities and/or accelerations a spaceship or rocket can use.
 
   A ground launched rocket using chemical propulsion could  place a
spaceship using fission/fusion/chemical propulsion into space.  One
might then be able to use enriched fission propulsion to increase a
spaceship's  velocity to get to Mars sooner than just using chemical
propulsion.
 
  The Tito/Zubrin??? 2018 flyby (only???)mission to Mars is expected  to
take 501 days or so.  Maybe adding fission propulsion to this spaceship,
one could reduce this trip time to 250 days.  This starts to sound more
do-able all the time.  If fully enriched Uranium propulsion could be
fully  used (not likely), the trip time might take only 5 days.
 
   The propulsion systems we are used to include: chemical  propulsion,
fission propulsion, fusion propulsion, enriched fission propulsion  and
perhaps several other propulsion systems which are being developed/used
now.  The UFO and Ancient Alien shows allude to these several other
(advanced???) propulsion systems.
One you might be able to figure out yourself.  The other is directly
described on one of these Ancient Alien/UFO shows (see shows on the H2
Channel ---USA).
 
    Perhaps someday soon we?? will be able to use an  enriched
fission/chemical hybrid system to propel an Earth atmosphere spaceship
which is robotically controlled from the Earth's surface.  Such a
spaceship could go significantly faster than a spacecraft with human
beings  aboard.  
Is all this starting to sound familiar???
 
   Wonder if Dr. Von Braun was a student of Goddard and others,  by
studying the literature???  One UFO/Ancient Alien show describes another
source of Von Braun's Advanced Flight Systems (not necessarily Rockets)
knowledge.  
Won't go into it here.
 
   Have a good week...
 
                Joe Preisig
 
 
    
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