Orion Reentry Guidance with Extended Range Capability Using PredGuid

Skip Entry Trajectory Planning and Guidance

“…However, certain gains and constants were unavailable in that document. Reference [9] lists these constants and gains, but they appear to be from the earlier version, reference [12] of the Apollo skip guidance. For this work, the gains and constants are used from a more recent document [30].…”

“…Once such a reference trajectory is found, the Apollo guidance system commands the bank angle to track the reference velocity and rate of altitude profiles by a linear guidance law. The various approximations and linearization assumptions have been found to limit the accuracy of the guidance, especially in the case where the downrange is relative long in this work and others [9,10]. This inaccuracy can have a significant adverse impact on the success of the mission.…”

“…For entry vehicles with relatively low lift-to-drag (L/D) ratios, a known strategy since the Apollo era for achieving long downrange is to allow the vehicle to skip out of the atmosphere [4,5,6,7,8,9,10,11]. Figure 1.1 shows an illustration of this concept with the first entry, skip, then reentry of the atmosphere and final entry phase to the landing site.…”

“…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.…”

Skip Entry Trajectory Planning and Guidance

“…The Apollo skip algorithm was designed for shorter ranges, thus the long time spent in the Kepler phase adds a significant amount of unexpected drag to the trajectory. Extensive further analysis and details are available in the work by Bairstow [9] and were discussed in Chapter 3.…”