Various emergency return trajectories

If one of the engines of Energia refuses to function correctly, the Buran shuttle enter in the emergency return phase. This is done by the instantaneous calculation of a new trajectory and by the landing of Buran by the on-board computer (which is an alternative of the normal software of Buran flight).

The emergency return operation occurs if the engine undergoes various damages during the putting into orbit (sudden refusal to function, impossibility of ejecting the first stage...) until a certain threshold from which a putting into orbit is possible. The zone of the emergency return finishes to 125-130 s from the departure for a damage on the second stage engine and can last up to 180-190 s for a damage on the first stage engine.

Descriptive diagram of various scenarios following a damage:
A-Normal trajectory; B-Abnormal trajectory; C-Ejection of the crew after a damage of Energia; 1-Buran-Energia couple on the launching pad; 2-of the catapult-launching zone (102 s of flight); 3-Threshold of the emergency return area (125-190 s of flight); 4-Buran-Energia in flight; 5-Normal flight of Buran; 6-Trajectory in low altitude; 7-Beginning of the braking impulse; 8-End of the braking impulse; 9-Re-entry in the atmosphere; 10-Landing on the aerodrome by the on-board computer; 11-Shutdownof of Energia's engines at the appearance of a damage and separation of Buran; 12-Begining of the return trajectory of Buran-Energia ; 13-Turn around; 14-Separation of Buran; 15-16-Descent of Buran; 17-Best able aerodrome to receive the shuttle

The emergency return trajectory is made after a disconnection problem of the first stage's engines, but not after 190 s. Energia is then turned around and started to slow down, by calculating with the Buran's computer the constraints undergone by the structure until the landing. The distance between the Buran-Energia couple and the landing strip can reach 480 km for an altitude of 120 km. During the return phase, the engines of Energia are turned off, then it is detached from Buran to enable it to land (the engines of Buran are then ignited).

The flight in low orbit will occur if a damage occurs after 190 s. Energia continues its trajectory in order to put Buran into low orbit, then separates from it. The characteristic of the on-board system is that it determines the operation automatically according to the reserve of fuel and the distance covered. Then Buran starts the brake impulses automatically (according to the kinematics parameters) to be in return condition and lands finally on the aerodrome in automatic mode.