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

[Jerry Lahti]

I worked at NASA from 1963-1973 on the fission powered nuclear propulsion 
system that you describe below. The propulsion reactor, NERVA, was built and 
tested.  The project was cancelled in 1972. 

For more details and an interesting summary, see the "Proceedings of the 
National Symposium on Natural and Manmade Radiation in Space" held March 1-
5, 1971. The specific reference for the proceedings is NASA-TM X-2440, Jan 
1972, 1020 pages. This document summarized many aspects of nuclear power in 
space just prior to cancellation of virtually all of these programs. In 
particular, yours truly contributed a paper regarding radiation doses duse 
to solar flares on a typical Mars mission. 

It's interesting to see that this subject is being revisited. 

--
Jerry Lahti
Naperville IL


---------- Original Message -----------
From: JPreisig at aol.com
To: radsafe at radlab.nl
Sent: Mon, 3 Nov 2008 00:49:12 EST
Subject: [ RadSafe ] [RadSafe]Mission to Mars---Fission Propulsion

> Dear Radsafe:
> 
>      This is from:  jpreisig at aol.com     .
> 
>      Hello Radsafe:
> 
>           If a fission-propelled spaceship cannot escape the Earth's 
> gravity on its own, then perhaps such a spaceship could be launched 
> <initially> into space with a chemically propelled rocket <old,
>  dependable, familiar>. The fission-propelled spaceship might be 
> launched into space with one rocket, or it might be launched into 
> space in several pieces, and assembled together in space.  Assembly 
> crews could be housed in a space station, which the USA and Russians 
> have already had in space.  Once the fission- spacecraft is in space,
>  it could use various chemically driven <smaller> spaceships to get 
> to the Earth or to other planet surfaces.  The fission-spacecraft 
> could be left in space for a long time, if necessary.
> 
>       Apparently NASA-USA is working on a new rocket launch system 
> which is expected to be ready in the next 5 to 7 years.  The mission 
> objectives are eventual trips to the Moon and/or Mars.  So, indeed,
>  astronaut flight crews may eventually be spending up to three years 
> in space.  Oh my.
> 
>      A fission reactor for the fission-propelled spaceship could be 
> designed using MCNP, MCNPXX or whatever computer codes are available 
> for this purpose. There is some self-shielding in the reactor due to 
> water or whatever other fluid <and reactor solid parts> is used to 
> moderate the neutrons.  Fission neutrons are pretty much knocked 
> down to thermal neutron energies <approximately> by a twelve inch 
> Bonner <spectrometer> sphere, so I don't think neutrons are too bad 
> of a radiation problem for such a spaceship.
> 
>      Gamma radiation from the reactor is a whole another issue.  As 
> the reactor is turned on, there will be growth of the gamma 
> generating radioisotopes during any space trip, with not much decay-
> off during the trip.  Gamma shielding needs to be well planned, in 
> accordance with the length of the mission<s>.  One can place the 
> reactor at some distance from most of the crew, but some 
> astronauts/crew members will have to deal with the reactor in close 
> proximity.  Guess everyone will have to assume their fair share of 
> the doses.
> 
>      Geez, a central reactor with the crew placed radially at some 
> distance from the reactor.  Wonder what that would look like???
> 
>      The notion of a saucer shaped spaceship springs from mechanical
> stabilty considerations.  That's classical mechanics <i.e. physics> -
> -- see books by Kleppner and Kolenkow and or Jerry Marion.  A cylindrical
> shaped spacecraft is not mechanically stable.  The saucer shape 
> allows the crew to normally be at some distance from the reactor.  
> Time, distance and shielding, don't you know....
> 
>      The spaceship will probably have to carry some water, or 
> whatever fluid, which will be used for cooling and/or propulsion 
> associated with the reactor. By the way, how does one cool a reactor 
> in space???  I guess I have my own ideas about cooling a fission 
> reactor in space.  Space is very cold, no???? Some water in the 
> reactor is necessary for neutron moderation. Some other water may be 
> fed into the reactor <in a separate water loop>, heated in the 
> reactor and eventually be forced out of the reactor, exiting the 
> spacecraft to propel the spacecraft.  Relatively clean water exits 
> the spacecraft as propellant.  Clearly other spacecraft drive 
> mechanisms are possible.
> 
>      So, that's all for now.  I've NEVER read any Heinlin/Heinlein.....
> 
>      The <Asian> Indians are starting to launch rockets into space now.
> Very interesting.
> 
>      I hope you all are having a great day and/or week.  And if you 
> have the notion that someone is paying me right now to work on this 
> stuff, that notion is not correct.  See you <ALL????> on OUR spacecraft....
> 
>      Regards,      Joseph R. <Joe> Preisig, Ph.D.
> 
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------- End of Original Message -------