The space shuttle will re-enter the Earth's atmosphere at high angle of attack, in order to minimize total heat load, and will perform a transition to low angle of attack for increased trajectory control. The timing and shaping of this angle transition are affected by specific-control-moment boundaries, attitude instability, angle of attack, limits on various flight parameters, and the establishment of a trimmed condition for flight to the landing site. Transitions to altitudes between 45, 000 and 150, 000 ft are investigated here, with particular attention given to suitable terminal conditions and to stability and control boundaries. Angle of attack is the control variable; hence, the short-period dynamics are not modeled. Two degree-of-freedom trajectories are optimized using a steepest descent algorithm with automatic step-sizing and open end-time. It is found that trim-glide flight-path angle y becomes very steep as altitude increases and that trajectories to such flight conditions are difficult to achieve. High-altitude equilibrium conditions (y = 0) at zero y are readily obtained, and they provide suitable way points for a continued glide to low altitude. Dynamic pressure and load factor peaks associated with both types of transition are not excessive. Stability and control boundaries have significant effects on the trajectories, although peak load, dynamic pressure and load factor are not materially altered. Gliding trajectories from high to low altitude are found to be sensitive to phugoid mode excitation, and the dynamic pressure peak which occurs prior to the terminal flight condition may be excessive.
All Science Journal Classification (ASJC) codes
- Aerospace Engineering
- Space and Planetary Science