Hi, everyone! I'm trying to find the period of a satellite orbiting the earth by the next formulas with: miu= 398600.5; a=36770.48 km; I. 2*pi*(a^3/miu)^1/2 II. 84.489*(a/Re)^(3/2)min III. 0.00016587*a^(3/2)min And I got aprox. 19 hours from both formulas (I. and III.) which is correct. Can anyone please explain to me how do you get from the first formula to the second and third,what transformations should I make and also who is Re? Another problem that I have is that I'm trying to get from cartesian system to orbital and I have reached a point where I have to: Compute the time of periapse passage, T (note that EA must be in radians), with the formula T=t-(1/n)*(EA-ecc*sin(EA)); where EA=eccentric anomaly=0.0335 ecc=eccentricity=0.80324; n=sqrt(miu/a^3); I have taken t=270; With the following result:-73.7766 which I know is bad but I don't know where I've done wrong.Can anyone explain to me ,please? Also, Is this time the same as the period?