A roll program or tilt maneuver is an aerodynamic maneuver that alters the attitude of a vertically launched space launch vehicle. The maneuver is used to place the spacecraft on a proper heading toward its intended orbit.
A roll program is completed shortly after the vehicle clears the tower. In the case of a crewed mission, a crew member (usually the commander) reports the roll to mission control which is then acknowledged by the capsule communicator.
Space Shuttle launch
The roll program occurred during a shuttle launch for the following reasons:
- To place the shuttle in a heads down position
- Increasing the mass that can be carried into orbit (this was actually the initial reason - a 20% payload increase due to more efficient aerodynamics and moment balancing between the boosters and main engines)
- Increasing the orbital altitude
- Simplifying the trajectory of a possible Return to Launch site abort maneuver
- Improving radio line-of-sight propagation
- Orienting the shuttle more parallel toward the ground with the nose to the east
The RAGMOP computer program (Northrop) in 1971-1972 discovered a ~20% payload increase by rolling upside down. It went from ~40,000 lb to ~48,000 lb to a 150 NM equatorial orbit without violating any constraints (max Q, 3 G limit, etc.). So the incentive to roll was initially for the payload increase by minimizing drag losses and moment balancing losses by keeping the main engine thrust vectors more parallel to the SRBs.
Titan II and Saturn V launch
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