[SG] Mercenary Mission Motivation

I'm writing up background & rules for a mercenary stargrunt campaign
when 
the issue of mission motivation hit me: mercenaries are not (usually) 
ideologically engaged in conflicts - so obviously their motivation is
going 
to be more...well mercenary  (and I win the prize for obvious statements
of 
the century!!)
I thought that their mission motivation would be closer tied to the
current 
status of the payment, their current state of supply and the perceived 
reliability of their employer.
The importance of the mission according to the employer will probably
have 
some impact

I'll probably not formulate a matrix to take all these factors into
account, 
and will just assign a motivation as I feel it's deserved.

Has anyone done anything like this before?
Any input from anyone, especially good accounts of mercenary operations
and 
historic motivations for modern mercenaries

Thanks
Donogh

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