Need the author and story title of the hard science fiction story
matching this description:

All I know about the story is a part of the plot.

A small group of humans are on an asteroid battling, as far as I know,
a large/better equipped group of aliens/enemies.  The humans'
provisions are depleting quickly.  Among the humans is a geeky, number
crunching guy, who seems to have lost regard for the desperate
situation.  Finally, he grabs the last remaining grenade (maybe after
some arguments) and instead of throwing it towards the enemy, throws
it in the opposite direction.  But that is because he has calculated
the approx. mass of the asteroid, the speed and direction in which he
needs to throw it, etc.  The grenade goes in a tight gravitational
orbit around the asteroid and hits the enemy from their unprotected
side.  & that's how brainpower, now ammunition destroys the enemy and
saves the day.

As far as I know, the story is fairly old - at least 10-15 yrs old, if
not much more.

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Clarification of Question by stoyan-ga on 25 Aug 2003 12:46 PDT

Given the first comment, I emailed and got an e-mail from Larry Niven
himself:

Larry Niven's comment about the story:
******************************************************************************
        "It's not mine.  By flavor, it might belong to Del Rey or
Asimov. "
******************************************************************************

It's just a guess but it may be enough of a clue to some long-time,
hard-core SF fan.
Please, help.
Stoyan

I have a vague memory of this story. Somehow I think it may have been
written by Larry Niven, but I can't be any more specific than that.