While that is very good, at the same time 2% is pretty much nothing. Why not make it so that 50% is payers choice? (I wouldn't make it 100% only because there are too many people who wouldn't want to fund the military).
According to a slapdash google search, the 2015 federal income due to taxes is $3.9 trillion, and about half of that comes from income tax. 2% of that is $20 million dollars.
I want to say that that's not nothing, but the Rosetta equipment alone cost €220 million. I'm not even sure how much of an impact $20m would have if you spread it across, e.g., the New York public school system.
