🚀 go-pugleaf

In article <93008.103356DOCTORJ@SLACVM.SLAC.STANFORD.EDU> Jon J Thaler <DOCTORJ@SLACVM.SLAC.STANFORD.EDU> writes:
>> Current antiproton production is geared towards physics, not
>> rocketry.  It is probably possible to create antimatter more
>> efficiently if that is the primary goal.
>
>This is probably incorrect, for two reasons:
>* Antiproton production and capture  efficiency limits the rate
>  at which antiproton storage rings can be filled.  If easily
>  obtainable improvements were available, I expect that they
>  would have been used already.

As I understand it, there are other constraints that also have to be
observed.  For example, they want antiprotons with more or less the
same energy.  Robert Forward, who studied the issue on contract for
the USAF, said production rates *could* be improved considerably if
you custom-built the hardware for it.

>* A rocket fuel needs to be cheaply contained.  Storage rings
>  are expensive.  Unfortuantely, antiprotons are created moving,
>  so they will need to be brought to rest to simplify the containment
>  problem.  This is an additional manipulation that the physicists
>  don't need to perform.

It doesn't look like a hard problem, however.  There has been work
done in that direction for various physics projects.  For example,
there was a LANL project -- no longer funded -- to decelerate and cool
antiprotons to essentially zero energy for measuring their gravitational
mass.  (If you believe general relativity, it should be identical to
their well-known inertial mass... but some of the weirder theories of
gravity say it should be different.)  I heard a talk by one of the
folks involved; he said that it was interesting physics to be sure,
but it was also a way to do antimatter-handling work with an eye on
longer-term practical uses.

If memory serves, first estimates for propulsion efforts say that the
trickiest problem is the latent heat of freezing when you try to
convert antihydrogen gas to solid pellets.  There is no shortage of
possible methods for most of the handling problems, although a good
bit of engineering development would have to be done to find out which
ones will work best.

>There is no free lunch.  Baryon number is conserved...

Well, unless you believe in proton decay, in which case it isn't...

>This means it costs
>the same 2mc^2 (at least) to make an antiproton that one gets back when
>it annihilates.

Indeed so.  Antimatter is a *storage* system, not an energy source per se.
But it's an outstandingly lightweight storage system, assuming the handling
gear's mass isn't too bad.
-- 
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  henry@zoo.toronto.edu  utzoo!henry