Show simple item record

dc.creatorChomel, Christina T. (Christina Tvrdik), 1973-en_US
dc.date.accessioned2008-08-28T23:55:21Z
dc.date.available2008-08-28T23:55:21Z
dc.date.created2007-12en_US
dc.date.issued2008-08-28T23:55:21Z
dc.identifier.urihttp://hdl.handle.net/2152/3559
dc.description.abstractIn recent years, NASA has indicated a desire to return humans to the moon. With NASA planning manned missions within the next couple of decades, the concept development for these lunar vehicles has begun. The guidance, navigation, and control (GN&C) computer programs that will perform the function of safely landing a spacecraft on the moon are part of that development. The lunar descent guidance algorithm takes the horizontally oriented spacecraft from orbital speeds hundreds of kilometers from the desired landing point to the landing point at an almost vertical orientation and very low speed. Existing lunar descent GN&C algorithms date back to the Apollo era with little work available for implementation since then. Though these algorithms met the criteria of the 1960's, they are cumbersome today. At the basis of the lunar descent phase are two elements: the targeting, which generates a reference trajectory, and the real-time guidance, which forces the spacecraft to fly that trajectory. The Apollo algorithm utilizes a complex, iterative, numerical optimization scheme for developing the reference trajectory. The real-time guidance utilizes this reference trajectory in the form of a quartic rather than a more general format to force the real-time trajectory errors to converge to zero; however, there exist no guarantees under any conditions for this convergence. The proposed algorithm implements a purely analytical targeting algorithm used to generate two-dimensional trajectories "on-the-fly" or to retarget the spacecraft to another landing site altogether. It is based on the analytical solutions to the equations for speed, downrange, and altitude as a function of flight path angle and assumes two constant thrust acceleration curves. The proposed real-time guidance algorithm has at its basis the three-dimensional non-linear equations of motion and a control law that is proven to converge under certain conditions through Lyapunov analysis to a reference trajectory formatted as a function of downrange, altitude, speed, and flight path angle. The two elements of the guidance algorithm are joined in Monte Carlo analysis to prove their robustness to initial state dispersions and mass and thrust errors. The robustness of the retargeting algorithm is also demonstrated.en_US
dc.format.mediumelectronicen_US
dc.language.isoengen_US
dc.rightsCopyright © is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en_US
dc.subject.lcshSpace vehicles--Landing--Moonen_US
dc.subject.lcshSpace vehicles--Guidance systemsen_US
dc.titleDevelopment of an analytical guidance algorithm for lunar descenten_US
dc.description.departmentAerospace Engineering and Engineering Mechanicsen_US
dc.identifier.oclc192075277en_US
dc.type.genreThesisen_US
thesis.degree.departmentAerospace Engineering and Engineering Mechanicsen_US
thesis.degree.disciplineAerospace Engineeringen_US
thesis.degree.grantorThe University of Texas at Austinen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US


Files in this item

Icon

This item appears in the following Collection(s)

Show simple item record