[ RadSafe ] [RadSafe]Mission to Mars---Fission Propulsion

Tue Sep 30 14:59:55 CDT 2008

As I recall, the principal doses were delivered by cascaded nuclei from high 
energy proton bombardmant.  The first several g/cm**2 acted as a dose 
AMPLIFIER rather than shielding.

--
Jerry Lahti
Naperville IL

---------- Original Message -----------
From: <Rainer.Facius at dlr.de>
To: <radsafe at radlab.nl>
Sent: Tue, 30 Sep 2008 19:02:40 +0200
Subject: [ RadSafe ] [RadSafe]Mission to Mars---Fission Propulsion

> Mike,
> 
> to my knowledge Bremsstrahlung intensities from charged particles 
> other than electrons are negligible. Hence only during passages 
> through the (mainly outer) radiation belts, Bremsstrahlung photons 
> contribute to space radiation doses. While operating, nuclear 
> propulsion engines of course are intense sources of gamma rays and 
> neutrons. After engine shutdown, decay of fission products by 
> predominantly beta decay will be the source for rather soft and 
> hence negligible Bremsstrahlung photons. Fission product decay 
> ceases quite rapidly.
> 
> So, for all space flight mission scenarios other than geostationary 
> orbits (and of course in the vicinity of Jupiter :-), Bremsstrahlung 
> contributes only negligibly to space radiation exposures.
> 
> Regards, Rainer
> 
> Dr. Rainer Facius
> German Aerospace Center
> Institute of Aerospace Medicine
> Linder Hoehe
> 51147 Koeln
> GERMANY
> Voice: +49 2203 601 3147 or 3150
> FAX:   +49 2203 61970
> 
> -----Ursprüngliche Nachricht-----
> Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im 
> Auftrag von Brennan, Mike (DOH) Gesendet: Dienstag, 30. September 
> 2008 18:05 An: radsafe at radlab.nl Betreff: RE: [ RadSafe ] 
> [RadSafe]Mission to Mars---Fission Propulsion
> 
> I suspect that the key to using nuclear propulsion in space is 
> getting in and out of our gravity well.  Most of the schemes for 
> using reactors to accelerate reaction mass can not achieve the 
> acceleration needed to go from Earth's surface to orbit.  Even if a 
> nuclear rocket could develop that kind of acceleration, I foresee 
> non-trivial political obstacles to such a launch.  I am also a fan 
> of having the spacecraft for the trip be rather larger than it would 
> be practical to launch as a single package.
> 
> I believe that a necessary first step for a manned mission to Mars 
> is development of a way to put packages in orbit for tens or 
> hundreds of dollars per kilo, rather than thousands or tens of 
> thousands of dollars per kilo.  It would be nice if it could be done 
> without high accelerations, too.  Of the systems I've seen proposed 
> (and as a science fiction fan, I've seen a fair few), the Space 
> Elevator concept looks the best.  Although some very interesting 
> work has been done, and I think it has potential for actually coming 
> to pass, I decline to hold my breath until it happens.
> 
> Rather than focusing on sending people to Mars, I think we should 
> send progressively more sophisticated robots, all the way up to 
> robots build some of the infrastructure that will be needed for an 
> extended stay by people.
> 
> As for the radiation issue during the trip; I read an interesting 
> article that contended a big source of radiation would be 
> Bremsstrahlung radiation from the interaction of high energy 
> particles and the metal ship around the crew.  The proposed fix was 
> to use a very large inflated spaceship for the voyage, with small 
> landers for the trips to and from the surface of Mars.  Selling the 
> "balloons in Space" concept may take some work, however.
> 
> -----Original Message-----
> From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] 
> On Behalf Of Rainer.Facius at dlr.de Sent: Tuesday, September 30, 2008 
> 5:58 AM To: JPreisig at aol.com; radsafe at radlab.nl Subject: AW: [ 
> RadSafe ] [RadSafe]Mission to Mars---Fission Propulsion
> 
> Joe,
> 
> as long as human astronauts (instead of chimpanzees) are manning the 
> spacecraft, mission duration is the NUMBER ONE factor driving the 
> risks to their health and hence the (counter-) measures to be taken 
> to ensure a safe and healthy return.
> 
> The probabilities of encountering life-threatening medical 
> conditions (physiological and psychological) or critical technical 
> equipment failures are roughly proportional to mission duration. The 
> risk of acute early radiation effects (and secondary risks from 
> associated performance decrements) due to unforeseen large solar 
> energetic particle events adds to these risks for untoward mission 
> outcomes and is again roughly proportional to mission duration 
> (solar activity held constant). The risk for late radiogenic cancer 
> from (chronic) exposure to galactic cosmic radiation again is 
> proportional to mission duration. For reference missions to Mars of 
> about 1000 d duration during phases of minimum solar activity (such 
> as now), galactic cosmic ray exposures behind conventional mass 
> shielding can accumulate to 1 Sv.
> 
> So, dollars spent into attempts to reduce mission duration are by 
> far the most cost effective in reducing the health risks of Mars 
> travelling astronauts.
> 
> Fundamental physical/technical constraints limit the specific 
> impulse achievable by chemical propulsion to somewhere between 400 
> to 500 seconds. With solid nuclear power propulsion, specific 
> impulses between 500 and 1000 s are achievable whereas with a gas 
> core nuclear rocket specific impulses between 1000 and 6000 s can be 
> obtained, thereby reducing mission durations by the respective 
> factors. The technologies for solid nuclear power propulsion - and 
> hence for a reduction of mission duration by a factor of two - are 
> at hand but certainly not the limit. Los Alamos has spent quite some 
> efforts for advancing the gas core nuclear rocket technology - at 
> least theoretically - and reductions of mission durations by factors 
> up to 10 are conceivable thereby.
> 
> My personal prognosis is: If manned missions to Mars will occur, 
> they will use nuclear propulsion. Given that man's strive to extend 
> his limits historically has only been limited by the laws of nature, 
> my guess is that manned missions to Mars will take place. Whether 
> this will generate sizeable job opportunities for health physicists 
> remains to be seen.
> 
> Regarding fusion propulsion, the experience of my lifetime with 
> announcements of fusion energy as lurking just around the corner of 
> the next decade makes me sceptical when or even whether we will see 
> it working. Five to six decades of such announcements have worn out 
> my 'faith' into this energy option
> 
> Thank you for your stimulating note - and good luck at your work.
> 
> Kind regards, Rainer (going back to work :-)
> 
> PS: At http://www-pub.iaea.org/MTCD/publications/PDF/Pub1197_web.pdf 
> you can download the IAEA publication STI/PUB/1197 (2005), The Role 
> of Nuclear Power and Nuclear Propulsion in the Peaceful Exploration 
> of Space. Note, in some instances they have specific impulses too 
> large by a factor of ten. Dr. Rainer Facius German Aerospace Center 
> Institute of Aerospace Medicine Linder Hoehe 51147 Koeln GERMANY 
> Voice: +49 2203 601 3147 or 3150 FAX:   +49 2203 61970
> 
> -----Ursprüngliche Nachricht-----
> Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im 
> Auftrag von JPreisig at aol.com Gesendet: Montag, 29. September 2008 23:17
> An: radsafe at radlab.nl
> Betreff: [ RadSafe ] [RadSafe]Mission to Mars---Fission Propulsion
> 
> Dear Radsafe:
> 
>      This is from:    jpreisig at aol.com    .
> 
>      Hello Again Radsafers:
> 
>      Hope you all are well today and don't require a US Federal Bailout....
> 
>           I've been thinking about space travel to Mars again using fission
>      propulsion.  I refer you to several articles by Freeman Dyson 
> in the beta     volume of the book "Adventures in Experimental 
> Physics" --- Bogdan      Maglich, editor.  I hope you can find it in 
> your library.  In one of the articles     Dyson indicates that one 
> can use fission propulsion (without resorting to     bomb propelled 
> rockets> to achieve exhaust velocities that are twice as     large 
> as the velocities that can be reached via chemical propulsion.  
> >From this,
>      I infer that a readily achieveable fission propelled rocket can 
> ultimately be      designed which can go twice as fast as chemically 
> propelled rockets (at     least>.  This would reduce the round trip 
> time to Mars from 3 years to      about 1.5 years.  This is helpful 
> if one is living in a spaceship for such a     long time.  Further 
> additional techniques used to reduce the total travel      time to 
> Mars would also be desirable.
> 
>           So, considering use of Uranium to power such a trip, how 
> could such     trip be safely made?  For takeoff, the fission 
> reactor propelling the rocket
>      (or whatever> would largely contain Uranium (and not so much Cesium
>      or Strontium which are produced via fission>.  So, let's assume 
> a safe     launch can be made.
> 
>           The rocket and astronauts (hopefully not 
> Chimpanzees???!!!> would     fly to Mars, land on the planet's 
> surface, and do whatever science and other     tasks which need to 
> be done.  If necessary, a chemically propelled      lunar/Mars type 
> lander could be used to get to Mars surface from the     original 
> rocket or Mother ship.  Upon completion of their time on Mars,     
> the astronauts would direct their spaceship towards Earth, to return 
> to home.
> 
>            However, instead of returning directly to Earth, the 
> spaceship would      land on the Moon, not using a lunar/Mars type 
> lander.  The spaceship would     land directly on the Moon's surface,
>  not to return to Earth anytime soon.     The spaceship would be 
> left on the Lunar surface, complete with its     reactor intact. 
>  There's not much weather or wind storms on the Moon, so the     
> spaceship could stay there a long time without dispersal of any fission
>      products or the original Uranium fuel.
> 
>           So, this leaves the astronauts on the Moon with the 
> scientific samples,     stored data on computers, etc.  What happens 
> next???  A second      chemically propelled rocket is sent to the 
> Moon,  and using a Lunar lander     the astronauts are picked up and 
> return to Earth in the second spacecraft.     Mission accomplished.  
> I didn't say the space mission would be inexpensive.
> 
>           In 200 years (a fair number of half-lives) the original 
> fission reactor      could be picked up from the lunar surface and 
> returned to Earth for     processing and/or storage.
> 
>           If we ever perfect a fusion propelled rocket system, much 
> of the preceding     described effort becomes unneccessary.
> 
>           Just something to think about.  I think such a fission 
> propelled rocket     system could be built in the relatively near 
> future.  Oh my, jobs for      Health Physicists and/or Nuclear 
> Engineers in space.
> 
>          The airplanes/jets which takeoff vertically are called Harriers.
> 
>          Another few years of relatively few (named> hurricanes 
> and/or          tropical storms like 2008 (so far> and I'll have to 
> say that the global         warming hypothesis is fizziling out.
> 
>          Now, get back to work????
> 
>          I hope you have a wonderful week.
> 
>          Regards,   Joseph R. (Joe> Preisig, Ph.D.
> 
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------- End of Original Message -------