I wanted to submit this to ATSNN, but I don't know how. I went to www.atsnn.com and I couldn't find any link to submit a story.
According the International Herald Tribune, the US is planning re-opening production of Pu-238, for the first time since the end of the Cold War.
Note: Pu-238 is NOT the more well known Pu-239, which is the predominant ingredient in the fissile cores of implosion-based nuclear warheads.
Instead, it has entirely the opposite quality as Pu-239, namely that Pu-238 has a very large rate of spontaneous fission---meaning without extra
implosion or a neutron trigger used in a nuclear weapon. The spontaneous fission would thwart a proper detonation of a nuclear weapon, and keeping
spontaneous fission neutrons down is a key design constraint, and is what distinguishes reactor-grade from weapons-grade plutonium.
It gets hot all on its own and stays that way for years. It has thus been used on NASA's probes to outer planets, Jupiter and Saturn, as a power
source via thermo-electric generation for situations where solar power would be inadequate. That usually means "farther than Mars".
However, in this case, the intended uses are being kept entirely secret, and it's not clear why. I invite the readership to speculate and deny
ignorance about the potential uses of new Pu-238 and intents of such a move. I think it's fairly safe to ignore the denials of the official quoted
in the IHT article as being definitive.
Here's my list:
1) there is some secret deep space mission. This seems very unlikely---what national security implications are there on Jupiter or Saturn---unless
"2001" is right.
2) This is intended as a power source for a very long-term UAV project, e.g. a stealth surveillance platform which could remain aloft for months. Why
solar power would be inadequate isn't clear, unless they believe that the performance and battery capacity (for night-time use) would be
insufficient. This would have to be substantial advantage as a Pu-238 source would add enormously to cost, complexity and weight. And the neutrons
may make it quite visible to remote sensors.
3) A power source for a spy satellite. Question: again, why is such a difficult think like a themoelectric generator necessary when solar is known
to work well in near Earth orbit, and the efficiency of solar is increasing rapidly and the power requirements of electronics decreasing.
4) This is intended as a neutron generator for homeland security for detecting fissile uranium or plutonium in a transportation scanner or emergency
response situation. Here, the idea is that the neutrons from Pu-238 would set off additional neutrons from Uranium or Plutonium in a fissile weapons
configuration, and the distinct signatures could be detected.
But, there are already neutron generators using conventional technology (mini accelerators) well known in seismology and oil exploration that run on
normal electricity and other things, which have a very great advantage that they can be turned off. Unless very large fluxes (and thus requiring
Pu238 versus a neutron generator) are necessary---but this seems unlikely given a detection mission. Also, a neutron generator's output could be far
better *aimed*---critical for detection, as opposed to Pu238 which would radiate essentially isotropically unless somehow and expensively reflected
(e.g. beryllium). This is a use not covered by the official's denials.
5) there is some strategic missile defense use, in that the Pu-238 would be used to try to ensure predetonation of an incoming nuclear warhead. But
really this would only work if the Pu-238 were glued to the warhead, and stayed stuck with it all the way down and stayed during the detonation
sequence, and only right before the moment of maximum implosion were there too many neutrons to have a proper detonation. Again, this seems extremely
unlikely. It's very hard to hit and detect an incoming warhead to begin with.
It's possible there is a SDI use somehwere between #4 and #5, i.e. detecting true incoming warheads from fake ones by using their response to high
levels of neutrons generated by Pu238. There the in-orbit power capacities may be too low to use conventional neutron generators. But I seriously
questoin the range at which this would be possible could be any use in a missile defense area, where incoming velocities are tens of kilometers per
In sum, though I am perplexed. The only really scientifically logical and justifiable mission is deep space exploration, as far as I can tell, and
I see no reason to keep it a secret. Why not say we're considering it to support NASA's future Mars and Jupiter missions. I believe the next Mars
Science Laboratory lander may have a nuclear source like Pu-238 to generate more power for its experiments.