Enter your current altitude, orbital velocity, and periapsis distance into the calculator at right. The calculator will give the time in (d, h, m, s) till atmospheric entry, max drag, v = 250 m/s, and landing, or atmospheric exit (where applicable).

The calculator assumes that your ship is headed down toward periapsis. To use this calculator when your ship is headed up toward apoapsis, add twice the 'time to apoapsis' from the game to the results.

How to Use the Solution

This calculator is primarily meant for use with mods like RemoteTech where craft cannot be controlled instantly; rather, burns and actions must be pre-programmed.

Program the ship it to retract fragile solar panels, antennas, etc before atmospheric entry, and to deploy parachutes after slowing to ~250 m/s. Remember to wait longer before opening solar panels, else they may break when the chutes fully open.

If your goal is an aerocapture, program the ship to circularize its orbit at the appropriate time.

Suggestions for Best Results

The calculator will probably not work for ships with lift surfaces, because the lift force depends on the craft's orientation in the atmosphere. Lift forces are not considered.

Sometimes, when coming out of timewarp, the periapsis will jump around a bit, potentially messing up the re-entry maneuver...

How it Works

Given a current altitude, orbital velocity, and periapsis, we have enough information to resolve the orbit of the ship (there are some ambiguities in orientation, but they do not matter for this problem). The point of intersection of this orbit with the atmosphere and the velocity of the ship at that point are calculated. Using these data, the trajectory in the atmosphere is determined using numerical methods. If the ship reaches the ground, the time and altitude of maximum drag and of reaching 250 m/s (in the Orbital frame, not the Surface frame) will be given, and the time of landing/impact (assuming no parachutes) will be given. If the ship escapes, the velocity at which the ship escapes the atmosphere is found, and used to compute the new orbit.

Q&A