Fault Tolerant Relative Navigation Using Inertial and Relative Sensors

Abstract

Many emerging applications of space, ground, marine, and air vehicles require relative automated navigation with respect to other vehicles and objects. Disturbances in the environment may cause faults in relative navigation sensors. For sensors based on cameras or laser range finders, events as common as lighting changes, glint, or obstruction by debris could potentially cause spurious responses. Relative navigation is safety critical-fault tolerance must be addressed. We propose a fault detection, identification, and recovery architecture using multiple moving horizon estimators, each for a separate hypothesis of the fault state of the system. The hypothesis with maximum empirical likelihood is selected. Detected and identified faults are reported to the main navigation filter, which may then discard the relative navigation sensor data, and instead temporarily rely on the inertial navigation system. The guidance system may also act on the identified fault state, taking actions to recover the system to a safe state. This logic is demonstrated in simulation for the automated rendezvous and docking (AR&D) of spacecraft-a key technology for the near future demands of the space program. The simulation results demonstrate that faulty relative sensors may seriously affect the navigation solution. The proposed fault detection scheme has demonstrated an ability to identify faults in these sensors and take them offline before they disrupt navigation and lead to mission failure.

Fault Tolerance of Relative Navigation Sensing in Docking Approach of Spacecraft

“…The chaser and target spacecraft were simulated with 6 degrees of freedom each, in low earth orbit. A visualization of the approach scenario is shown in Figure 6, and described in detail in [10]. The spacecraft pictures and error ellipses are magnified in the picture.…”

“…The FDIR algorithms and the simulation scenario are described in our earlier paper [10] FDIR model and Monte Carlo simulation…”

“…This answer is based on our earlier study [10]. Achieving the fault tolerance requires (i) being able to detect a fault of the relative navigation sensor and (ii) having a redundancy management and fault recovery capability.…”

“…The second failure would require aborting the AR&D approach (Fail Safe). A brief discussion ofthe Guidance and Control (G&C) for the abort is contained in [10]. The analysis in this paper assumes that a safe abort of the docking approach is always possible.…”

“…Achieving the fault tolerance requires (i) being able to detect a fault of the relative navigation sensor and (ii) having a redundancy management and fault recovery capability. The relative sensor fault detection approach based on analytical redundancy is discussed in detail in [10]. It relies on fault-tolerant inertial navigation.…”