I saw an article on CNN today which says that the US is looking into starting up manufacture of Pu238 again, 5 Kg/year for thirty years starting in 2011.

Is this a sign that Prometheus is really deep-sixed?

The requirements for Pu-238 are driven by mission needs independent of JIMO / Prometheus. As far as Prometheus being deep-sixed, certainly there is no more talk of JIMO, and there appears to be dwindling support for the NEP technology effort itself.

Side note on Pu-238 production -- It is not all for space missions. There are also unstated "national security" programs that require Pu-238. Press and other published accounts have stated that RTGs were used to power intelligence collection equipment in remote locations, e.g., ocean floor, Himalayas.

As I understood it, JIMO/Prometheus was to use not an RTG but a full-fledged nuclear reactor. Is there a reason why that would require Pu-238, as opposed to the same fuel used by commercial nuclear power plants? I sort of thought that Pu-238 was mostly used for RTGs, because it's the most efficient at generating heat during decay.

-the other Doug

The Prometheus nuclear reactor would not only not use Pu-238; it wouldn't use plutonium at all. It would use U-235, which is tremendously less radioactive than even Pu-239. (The latter is the isotope of Pu used in reactors -- as opposed to Pu-238, which in turn is enormously more radioactive than a non-critical mass of Pu-239, thus allowing the heat from Pu-238 to be used in RTG "nuclear batteries" without the need to build a complex reactor out of the stuff.)

U-235 is much more expensive to manufacture than Pu-239 -- but it's also about 2000 times less radioactive in a non-critical state, which means that it's infinitely better for small spacegoing reactors where you don't want to scatter dangerously radioactive material back onto Earth in the event of a launch accident.

Out of curiosity, what did the Soviet RORSATs use in their nuclear reactors? Bearing in mind that they did scatter one of those all overa stretch of ground in Canada...

-the other Doug

Highly enriched U235
http://www.daviddarling.info/encyclopedia/R/RORSAT.html

other Doug:

There were several Soviet reactor re-entries, not just the Canadian incident, although the spacecraft design *was* intended to boost the reactor core into a high 'graveyard orbit' at EOM. I seem to recall that one or more of these failed dramatically, leaving core material loose in orbit, and also that there were problems with radioactive sodium leaks too. All in all, RTGs in nice solid re-entry casks seem *much* more friendly!

Bob Shaw

Priorities in Space Science Enabled by Nuclear Power and Propulsion

Committee on Priorities for Space Science Enabled by Nuclear Power and Propulsion, National Research Council

158 pages, 8 1/2 x 11, 2006

In 2003, NASA began an R&D effort to develop nuclear power and propulsion systems for solar system exploration. This activity, renamed Project Prometheus in 2004, was initiated because of the inherent limitations in photovoltaic and chemical propulsion systems in reaching many solar system objectives. To help determine appropriate missions for a nuclear power and propulsion capability, NASA asked the NRC for an independent assessment of potentially highly meritorious missions that may be enabled if space nuclear systems became operational.

This report provides a series of space science objectives and missions that could be so enabled in the period beyond 2015 in the areas of astronomy and astrophysics, solar system exploration, and solar and space physics. It is based on but does not reprioritize the findings of previous NRC decadal surveys in those three areas.

http://www.nap.edu/catalog/11432.html

Nuclear Spacecraft Developers Borrow From Nature

http://www.spacedaily.com/reports/Nuclear_...rom_Nature.html

Oak Ridge TN (SPX) May 12, 2006 - Designing complex systems such as nuclear
reactors for space applications can be a daunting task, but researchers at Oak
Ridge National Laboratory seem to have made it less intimidating by borrowing
from nature.