Roll program

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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.[1]

Space Shuttle launch[edit]

Space Shuttle Atlantis performs the roll maneuver shortly after launching from Kennedy Space Center on STS-129.

During the launch of a space shuttle, the roll program was simultaneously accompanied by a pitch maneuver and yaw maneuver.[2]

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)[3]
  • 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.[3]

Titan II and Saturn V launch[edit]

Titan II and Saturn V launches also required roll programs.[2]

References[edit]

  1. ^ NASA - STS-117 Lift Off! ATLANTIS: "Houston, Atlantis. Roll program." Voice 1: "Roger roll, Atlantis".
  2. ^ a b Jenks, Ken. "Why does the shuttle roll just after liftoff?".
  3. ^ a b NASA-CR-129000, TR-243-1078 (1972)