An advanced ascent guidance algorithm for rocketpowered launch vehicles is developed. The algorithm cyclically solves the calculus-of-variations two-point boundary-value problem starting at vertical rise completion through main engine cutoff, taking into account atmospheric effects. This is different from traditional ascent guidance algorithms which operate in a simple open-loop mode until the high dynamic pressure portion of the trajectory is over, at which time guidance operates under the assumption of negligible aerodynamic acceleration (i.e., vacuum dynamics). Judicious approximations are made to reduce the order and complexity of the state/costate system. Multiple shooting is shown to be a very effective numerical technique for this application. In particular, just one intermediate shooting point, in addition to the initial shooting point, is sufficient to significantly reduce sensitivity to the guessed initial costates. An abort to downrange landing site formulation of the algorithm is presented. Results comparing guided launch vehicle trajectories with POST open-loop trajectories, for both sub-orbital cutoff conditions and orbit insertion conditions, are given verifying the basic formulation of the algorithm.
Enhancements to an advanced ascent guidance algorithm for rocket-powered launch vehicles are described. A general method has been developed for conveniently and efficiently handling the common case of (asymmetric) launch vehicles with unbalanced thrust and aerodynamic moments. The new part of this development concerns the treatment of endo-atmosperic flight. An alternative method for handing the transversality conditions has been developed that eliminates the need for a priori elimination of the constant multipliers that adjoin the terminal state constraints to the performance index. As a result, new constraints can be formulated and implemented with relative ease.The problem of bum-coast-bum trajectory optimization is treated using a modified multiple shooting technique.
Flight Center flown by a more traditional guidance method. trajectory problems onboard. Although research into algorithms with numerical solution capability is not new 2"4, their use as actual flight software remains untapped. This is due mainly https://ntrs.nasa.gov/search.jsp?R=20020065568 2017-11-06T21:15:02+00:00Z to issues of computational complexity that accompany all numerical procedures of this nature. EGuide addresses some of these issues with an architecture that combines the best of traditional guidance methods with the advantage of onboard solution capability. EGuide uses a classic shooting method as its solver. When solving a specific entry problem, EGuide adjusts parameters to meet specified goals using a Newton method that has been configured to generate [7] Hanson,
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.
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