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Hi Everyone, I'm having geeky fun with my HP-50g calculator, keying in all sorts of equations found on the Wiki pages. I know almost nothing in algebra/mathematics, but isn't KSP a nice place to learn? I'm on Entroper's Basic Orbiting (Math) Wiki page and there's something I don't get. If I know the altitudes of my apo- and periapsis, I can solve for the orbital speeds at the apsides with the orbital speed equation velocity = body_radius * sqrt( 9.80665 / ( body_radius + altitude ) ) which would yield one velocity for the apo- and another for the periapsis. Right? Now, further down the tutorial page, there are equations useful to solve for numbers in elliptical orbits, and they use a variable l (lowercase L) for the angular momentum. It is said that "l = m * r * v at apoapsis or periapsis", where I understand that m means the orbiting vehicle's mass, r its orbit radius (body radius + altitude) and v its orbital velocity. It says "at apoapsis or periapsis", so I understand value of variable l should be equal whether it is calculated at apo- or periapsis, but, using the two values for v found using the velocity equation discussed above, I don't get equal numbers. Are they not supposed to be equal? What am I not understanding?