1. The problem statement, all variables and given/known data I am given Rp=.6AU and need to find the eccentricity. 2. Relevant equations Rp=a(1-e) 3. The attempt at a solution I can find what Halley's comet eccentricity is (0.967) but I need to actually calculate it. What is the equation I need? I know I need to know Ra, or a, or p.