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RE: starship-design: Interstellar mission within fifty years

L. Parker writes:
 > > Only because of the very small amount of antimatter contained.
 > > Do you thing you may propel the starship with the amount
 > > of antimatter that when annihilated will make the engine
 > > "only a little hot"?
 > If you take common "flash powder" and put some in your hand and touch a
 > match to it, it will flash burn, you will not be seriously injured although
 > your hand may be scorched. If you take the same powder compress it into a
 > tight package and light it with a suitable spark, it will quite neatly blow
 > your hand off...
 > To say that a few picograms of antimatter are not dangerous in a rather
 > loose concentration in a Penning trap does not mean that they cannot be
 > quite deadly when properly utilized.

One million antiprotons are about (1/6.023*10^23)*10^6 grams of
mass; twice that mass converted to energy is about 3*10^-4
Joules.  Admittedly that turns out to be a fair amount of hard
radiation (gamma rays plus pions and such) if you annihilate them
all at once; perhaps you could give someone cancer or radiation
poisoning if you direct them properly.  But you'd need many
billions of antiprotons before you could blow anyone's hand off.

However, it does seem as if antiproton-catalyzed fusion will
require a fairly hefty supply of antiprotons.  Neither does it
seem likely that you can generate enough antiprotons from the
energy released by fusion to have a self-sustaining system.