I know for a fact that having a felony conviction is not the end of the world. I personally know a man who was convicted of a pretty stiff crime back in 1994. At the time he was working for DOD/DON at Charleston Naval Shipyard and held a secret clearance. Since he fully acknowledged and took full responsibility for the crime the powers that be did not take away his clearance (his punishment was 20 yrs imprisonment suspended upon completion of 5yrs probation, 500 hrs community service, completion of a 3 years perpetrators psychological counseling.) After the Shipyard was shutdown by the shortsighted and ignorant BRAC (base realignment and closure committee), he went back to college and got a degree. He worked in another field (at less pay than he was getting at the shipyard) until his probation was over. He then secured a rent-a-tech job at DOE Savannah River Site. After the contract there ended, he went on the road to other DOE facilities and worked commercial outages. He is now "house" at a DOE facility. I do know that most DOE and commercial sites will not allow a person on site while still serving probation or parole.
It is still a difficult road to travel. My friend has been turned down for many jobs. His persistence has got him where he is today. Send me a PM if you would like to know more details.