### Re-entry to earth

The Re-entry processor manages the de-orbit burn and sets a trajectory that will bring us in to Baikonur for landing.

The re-entry process is the longest single phase that must be run at real-time (about 30 minutes). After de-orbit burn you can accelerate time until the vessel hits the very upper layers of atmosphere.

When the atmosphere is reached, the vessel will keep the attitude so that the specified "Angle Of Attack" is maintained all the way through.

The time graph shows a profile for Altitude (brown) and aerodynamic stress (red). You can see the point of maxQ for re-entry on the left very clearly.

The processor will guide the vessel until a altitude of 30 km is reached.

### Process definition

    <Step>
      <Label>Reentry</Label>
      <Processor type="Reentry">
        <Var name="StartAt"> T = 51984.0953375 </Var>
        <Var name="AOA"> 40.0 </Var>
        <Var name="CompleteAt"> H = 30k </Var>
      </Processor>
    </Step>

StartAt defines the time of the de-orbit burn. Like the launch time this time is not calculated by REDSHIFT but must be computed (or estimated) in advance by other means. A correct time for de-orbit burn is much more critical than setting a correct launch time (we can correct a launch error later during align and sync operations), but after reentry we will have to land the ship as soon as possible, so the re-entry trajectory must put us close to the desired target.

AOA defines the Angle Of Attack to be maintained during re-entry.

CompleteAt defines an altitude where re-entry is considered complete. This should be low enough that the point of maxQ is far behind and high enough that ground is far away. 30km seems to be a good starting point (halfway between maxQ and ground).