Flying the Shuttle - Entry: Difference between revisions

This is accomplished by maintaining a high AoA, i.e. during the hot entry phase, the Shuttle is flown in what is technically close to a stall condition - pitched up at 40 degrees.

Once the initial vertical descent comes to a halt, the vertical velocity can be actively controlled to manage heat and deceleration force - if the shuttle is steered upward, heat load and deceleration decrease, if downward heat load and deceleration increase. In a normal airplane, one would use the elevator to control AoA and simply steer down. In the Shuttle, this is not an option, because, as explained above, the AoA is fixed by the need to have thermal protection. The solution is to roll the orbiter to a high bank angle (up to 70 degrees) to reduce lift.

The combination of 40 degree upward pitch and 70 degree roll is something not usually experienced by pilots. In such a confguration, the lift now acts <i>sideways</i>, i.e. the orbiter changes course. This may be desirable to steer the trajectory towards a landing site, or it may not. In the second case, the roll needs to be reversed periodically ('roll reversal') to steer the ground track into an S-shape around the desired trajectory.

Using a combination of high bank angle, low bank angle and roll reversals, direction and deceleration rate are managed to steer the orbiter to the landing site.

Note that the heat load is proportional to the dynamical pressure qbar times the velocity relative to the air, whereas the structural load is proportional to qbar. Thermal management is thus most important at the initial high-velocity phase in which the deceleration force is modest, and only when thermal management is over, trajectory deceleration control becomes important. For the same reason, the pitch angle can be gradually reduced with Mach number, ending in a just 14 degree pitch at Mach 2.5 where the TAEM interface is reached.