Withdrawing From TSP Without Paying The Penalty, is it Possible?

I am eligible to retire from fed service at 57 1/2. I will have 36 years of service. I plan on using my TSP to supplement my retirement. I cant seem to find a straight answer on withdrawing my money prior to 59 1/2 without paying the 10% penalty. Some sites say I can access all of it anytime, others say I have to use the SEPP plan, and others say I can access all of it but only 4 times per year. I understand the tax paid on it is variable to my overall income. - Tim