Examination of a practical aerobraking guidance algorithm

Abstract

A practical real-time guidance algorithm has been developed for aerobraking vehicles that minimizes the postaeropass A V requirement for orbit insertion while nearly minimizing the maximum heating rate and the maximum structural loads. The algorithm is general in the sense that a minimum of assumptions is made, thus greatly reducing the number of parameters that must be determined prior to a given mission. An interesting feature is that in-plane guidance performance is tuned by adjusting one mission-dependent parameter, the bank margin; similarly, the out-of*plane guidance performance is tuned by adjusting a plane controller time constant. Other features of the algorithm are simplicity, efficiency, end case of use. The algorithm is designed for, but not necessary restricted to, a trimmed vehicle with bank angle modulation as the method of trajectory control. Performance of this guidance algorithm during flight in Earth's atmosphere is examined by its use in an aerobraking testbed program. The performance inquiry extends to a wide range of entry speeds covering a number of potential mission applications. Favorable results have been obtained with a minimum of development effort, and directions for improvement of performance are indicated.

Skip Entry Trajectory Planning and Guidance

“…[9,21,22,23] This is particularly so in the presence of large atmospheric and aerodynamic uncertainties. The dispersions include those in entry condition at the first entry interface due to de-orbit condition dispersions, aerodynamics, vehicle mass, and atmospheric density.…”

“…In the literature, the usefulness of such type of measures has been long recognized in atmospheric entry and aeroassist maneuvers. [9,21,22,23] With the exception of Ref. [23], similar estimation has been applied to just drag or the L/D ratio.…”

“…[9,21,22,23] With the exception of Ref. [23], similar estimation has been applied to just drag or the L/D ratio. Experience in skip entry guidance shows that application of such estimation to shape both drag and lift acceleration profiles in the on-line trajectory planning and guidance has clear advantages over application only to D.…”

“…Analytic approaches using asymptotic expansions and optimal control techniques have been attempted for skip entry and aeroassist maneuvers [6,8,19,20]. With the advent of flight computers, onboard calculation of a trajectory has become viable through the use of numerical predictorcorrector methods [9,10,11,20,21,22,23,24,25,26]. These methods are not limited by the validity of the simplifications, approximations and empirical assumptions necessary for any analytical treatment, thus they hold greater potential to be more accurate and adaptive.…”

Optimal Aerocapture Guidance

“…16 Due to their high accuracy and flexibility, numerical predictor-corrector guidance algorithms have become popular in recent years. [17][18][19][20] While open-loop aerocapture trajectory optimization has been extensively investigated, 8,21 performance optimization in terms of post-exit propellant consumption has not been explicitly addressed in most aerocapture (closed-loop) guidance algorithms, because of the challenges involved in directly solving the nonlinear optimal control problem on-board. Still, a few guidance schemes have taken performance into design considerations in various degrees.…”