"Jerry Avins" in :

... Well, this is a cooking and chat newsgroup, so I guess it's OK so chat
about my feeling that the ion-drive SI numbers were cooked. :-)

You could almost say it was nothing but hot air. (Forgive me, bad company
lately. Physicians discussing research related to liver damage, after which
one of them said, three times, that Web-based medical advice must be viewed
with a jaundiced eye ...)

Other fuels were taxed with bringing their own energy to the game.

Yes, I suppose, Jerry: That would be important to contenders at the Rocket
Fuel Olympics, for fairness. Much as air-breathing engines (including
SCRamjets) have advantages over rockets because they poach part of their
supplies en-route. The SI number is just cited for drama. I can't think of
many situations where one could actually use a rocket in place of an ion
engine or vice versa. People have tried hard, on the other hand, to develop
air-breathing transatmospheric craft [translation: space shuttles]. One of
those people told me (at the dFVLR) in 1985 that this could potentially
replace the huge rockets the US space shuttles needed to get into orbit. A
dangerous configuration, with that big external oxygen tank. "Don't be
surprised if you wake up one morning and hear that one of the space shuttles
has exploded." (When that happened exactly, a few months later, I sent a
telegram right away, regretting that he was right. He wrote back
predicting that the disaster would be traced to some minor component, taken
for granted: "a clevis pin, or an O-ring.")