***NOTE: The data in my written work & the typed variables under "all known data" are correct. The problem statement has new values for a new submission, but I am trying to correct my work on an old submission. Sorry for the confusion! 1. The problem statement, all variables and given/known data Problem: All known data: Period (T) = 402 days = 34732800 seconds Moon's Diameter = 4900 km = 4900000 m Moon's Radius = D/2 = 2450000 m Density Moon = 4500 kg/m3 Volume of Moon = (4/3)pi(2450000m)^2 = 61600872 * 1019 m3 2. Relevant equations r3 = (T2Gm)/(4pi2) r = ((T2Gm)/(4pi2)) ^ (1/3) 3. The attempt at a solution I may have just made a math mistake, but I ran through this twice and arrived at the same result. The only thing I can think of that I may still need to do after arriving at 824250792m is somehow find the radius of the Death Star then subtract that? According to this explanation of the formula I used (http://www.dummies.com/how-to/content/how-to-calculate-the-period-and-orbiting-radius-of.html) that would not be necessary.