Re: Three months....
"0.5% likelihood of subsystem failure in the first three months. 10% failure chance of the whole in the first three months???
You wouldn't accept that in a commercial product let alone something being sent into space.
Space hardware does not have the option of the development cycle of a commercial product. You usually only get to make 1 or 2 units, and even then have your testing on earth in simulated environments. Your development costs are amortized over 1 unit, and every fractional increase in computed reliability costs ever more. So you make a design tradeoff for reasonable reliability and non-infinite budget.