starship-design: Antimatter

[Steve VanDevender <stevev@darkwing.uoregon.edu>]

Ken Wharton writes:
 > As for antimatter, I guess the more energy sources the better.  Keep in mind,
 > though, that the result of antimatter annihilation is two photons, and
 > photons are the worst possible way to turn energy into momentum.

Why do you people keep saying this?  Photons are the _best_ way to turn
energy into momentum.  What's the momentum of 1 kg of mass converted
into photons vs. the momentum of 1 kg of mass converted to energy and
used to accelerate another 1 kg of mass?