Orbiter Scenario Editor

# Changing the simulation date

The Date button on the editor main page opens the date selection page. Here you can change the date of a running simulation, and specifiy how vessels will be propagated from the current to the new date.

The simulation date is displayed in different formats:

- Universal Time (UT): A global reference time based on siderial time. Corresponds to the local time at longitude 0°.
- Julian Date (JD): The interval of time in days and fractions of a day since 1 January 4713 BC, Greenwich noon.
- Modified Julian Date (MJD): The Julian date minus 240 0000.5.
- Julian Century (JC2000): The interval of time in centuries and fractions of a century since 1 January 2000, Greenwich midnight.
- Epoch: Year and fraction of a year.

If any of the date fields is modified, all other date formats are adjusted automatically. Clicking the Refresh button updates the dialog fields with the current simulation time. Clicking the Apply button sets a new simulation time, and clicking the Now button sets the simulation time to the current computer system time. By using the spin controls in the UT section, the simulation time is updated directly.

Before changing the simulation time, you should specify how vessels are propagated in time to the new date. Different time propagation modes can be selected for orbiting vessels (with orbits that don’t intersect the central body) and for suborbital vessels (with trajectories that intersect the surface). The following options are available for orbital vessels:

- Maintain fixed state vectors: keep the vessel’s relative position and velocity with respect to the central body fixed in a non-rotating frame. This means that the planet is rotating underneath, while the vessel keeps its location and attitude.
- Maintain fixed surface position: keep the vessel’s position velocity and attitude fixed relative to the planet surface. This means that the vessel is rotating together with the planet, and stays fixed above the same point of the surface.
- Propagate along osculating elements: move the vessel along its current orbital trajectory, assuming that no forces other than the central body’s gravitational force are acting on the vessel.

For suborbital vessels, in addition to the above one further option is available:

- Destroy vessels: destroy any suborbital vessels (i.e. assume that the vessels impacted on the ground during time propagation).

You can adjust the time forwards as well as backwards, but remember that moving back in time will not necessarily restore the simulation to a previous state, because the vessel propagation does not take into account events such as engine burns.