To aid in the discussion of orbital mechanics and orbital energies, I've included several additional fields listing various orbital energy and geometry parameters.

Orbital Energy

All orbital energies are calculated as specific (per unit mass) energies in the fictitious units of the simulation; let's call them pfargls (pf).  In these units and for a circular orbit, the specific kinetic energy is +50 pf and the specific potential energy is -100 pf yielding a total energy of -50 pf.  When a non-circular orbit is modeled, one can see the interplay between kinetic and potential energy with the kinetic energy increasing toward periapsis and decreasing toward apoapsis while the potential energy exhibits the opposite trend.  The total energy should remain reasonably constant.  

• KE = (1/2) v^2
• PE = - G M / r
• E_tot = KE + PE

Orbital Geometry

One of the fundamental characteristics of an orbit or trajectory is its eccentricity.  In order to calculate the eccentricity, we need a variety of energy and momentum parameters:

where epsilon is the total specific energy as shown above, h is the specific angular momentum (h = |r x v|), and mu is the standard gravitational parameter, mu = G M.

Once we have the eccentricity, we can calculate the periapsis (nearest distance) and the apoapsis (farthest distance).  In the fictitious units of the simulation, the velocity for a circular orbit is 10.  If the initial velocity is set to less than this, then the initial distance of 20 will be the apoaspsis and the periapsis is calculated.  If the initial velocity is set to greater than 10, then the initial distance will be the periapsis and the apoapsis is calculated.

• apoapsis = periapsis * (1 + e) / (1 - e)
• periapsis = apoapsis * (1 - e) / (1 + e)

Now one can demonstrate that circular orbits have eccentricities of zero and the KE = -(1/2) PE, that all closed (elliptical) orbits have negative total energies, that parabolic trajectories have zero total energy, and that hyperbolic trajectories have positive total energies.  You can find out more about these calculations at https://en.wikipedia.org/wiki/Orbital_eccentricity.