Pin-point Landing Research Articles

Moon Diver: Exploring a pit's exposed strata to understand lunar volcanism

Natural pits on the Moon expose deep cross-sections of the lunar maria, enabling direct investigation of the Moon's volcanic history and providing potential access to subsurface lava tubes. The Moon Diver mission concept seeks to explore the Mare Tranquillitatis pit, which exposes the largest wall of bedrock of the mare pits (∼65 m). The concept is enabled by two innovative capabilities: pinpoint landing near the pit and robotic access to its near-vertical wall with an instrument package to examine the elemental chemistry, mineralogy, and morphology of these bedrock layers. Pinpoint landing uses closed-loop guidance with terrain-relative navigation (TRN), which was advanced by Perseverance landing on Mars, to deliver the lander within a 100-m ellipse. The Axel robotic explorer, which remains tethered to the lander, would egress onto the lunar surface and traverse the relatively flat terrain to the pit's funnel entrance. The lander, which is the data link to Earth, also serves as an anchor and provides power and communication to the rover through its tether. The rover is a novel two-wheeled platform with a trailing boom and a spool that pays out the tether as the rover traverses toward the pit. The 300-m long tether is well margined for the rover to scale the pit wall. The rover carries a surface preparation tool and three additional instrument types: (a) three high-resolution cameras for acquiring context images of the near and far walls with the near-wall pair in a stereoscopic configuration, (b) an alpha-particle-X-ray spectrometer (APXS) for elemental composition, and (c) a multi-spectral microscopic imager (MMI) that uses controlled lighting for mineralogy. The surface-preparation tool removes dust and patina from the rock wall by grinding a small area. This tool, the MMI, and the APXS would be deployed from an instrument bay inside the wheel wells. The rover would independently point each instrument at the same target on the wall with millimeter repeatability. Landing shortly after sunrise, the surface mission timeline is just shy of a lunar daytime (14 Earth days). Beyond the primary mission, the rover would be capable of descending from the overhang and peering into the void that may open to a large cave or lava tube. Lunar pits provide an exciting new target for exploration using innovative robotic capabilities that have been tested with integrated science instruments at multiple terrestrial analogue sites including a pit with basaltic layers in Arizona.

Japanese Lunar Lander SLIM and Its Optical Navigation for Pinpoint Landing

Japanese Lunar Lander SLIM and Its Optical Navigation for Pinpoint Landing

Comparison of powered descent guidance laws for planetary pin-point landing

This paper conducts a comparison study of constrained powered descent guidance laws for planetary pin-point landing from the viewpoints of guidance performance and algorithm structure. All considered algorithms are reformulated to incorporate the critical elements of the powered descent problem, such as the free flight time, thrust limitation and terrain constraint. With these requirements to meet, the performance of guidance laws is evaluated and compared via simulations. Specifically, the nominal landing simulation verifies the guidance accuracy, fuel consumption, and real-time performance, as well as the hazard avoidance capability. Meanwhile, the robustness of guidance laws is evaluated by the Monte Carlo simulation, and the performance difference in final landing dispersion is interpreted by analyzing the algorithm structure and characteristics. Lastly, the discussion on practicability indicates the promise of optimization-based algorithms in future planetary landing missions.

A Distributed Radio Beacon/IMU/Altimeter Integrated Localization Scheme with Uncertain Initial Beacon Locations for Lunar Pinpoint Landing.

As a growing number of exploration missions have successfully landed on the Moon in recent decades, ground infrastructures, such as radio beacons, have attracted a great deal of attention in the design of navigation systems. None of the available studies regarding integrating beacon measurements for pinpoint landing have considered uncertain initial beacon locations, which are quite common in practice. In this paper, we propose a radio beacon/inertial measurement unit (IMU)/altimeter localization scheme that is sufficiently robust regarding uncertain initial beacon locations. This scheme was designed based on the sparse extended information filter (SEIF) to locate the lander and update the beacon configuration at the same time. Then, an adaptive iterated sparse extended hybrid filter (AISEHF) was devised by modifying the prediction and update stage of SEIF with a hybrid-form propagation and a damping iteration algorithm, respectively. The simulation results indicated that the proposed method effectively reduced the error in the position estimations caused by uncertain beacon locations and made an effective trade-off between the estimation accuracy and the computational efficiency. Thus, this method is a potential candidate for future lunar exploration activities.

Visual navigation algorithm based on line geomorphic feature matching for Mars landing

In order to satisfy the requirement of precise pin-point landing mission in Mars exploration, this paper proposes an innovative visual navigation algorithm based on feature lines extraction and matching to estimate the attitude and position of the lander during descent phase. Currently, common navigation landmarks are feature points and craters. But, the number of feature points extracted from landing image is so large that the image process is complex and time-consuming, and they do not usually have absolute coordinate information to absolute navigation. Meanwhile, crater is matched difficultly. Hence, ridges, fissures and other surface textures similar to lines are most common visual features of Mars and can be used as navigation landmarks for visual absolute and relative navigation. Firstly, that feature lines matching based on the EDLine algorithm remains invariant to scaling, rotation, and illumination, etc. provides the basis for visual navigation by using feature line. Secondly, feature lines selected as navigation landmarks can be used to absolute navigation and relative navigation respectively, which can implement integrated navigation. In this paper, a novel integrated visual navigation has been designed to finish the precise pin-point landing and overcome the accumulated errors of relative navigation and the limited application range of absolute navigation. Experimental simulation results show that the integrated navigation algorithm solves the limitation of single navigation mode and improves the effectiveness and stability of the algorithm.

A Novel Approach to Visual Navigation based on Feature Line Correspondences for Precision Landing

To satisfy the needs of precise pin-point landing missions in deep space exploration, this paper proposes a method based on feature line extraction and matching to estimate the attitude and position of a lander during the descent phase. Linear equations for a lander's motion parameters are given by using at least three feature lines on the planetary surface and their two-dimensional projections. Then, by taking advantage of Singular Value Decomposition (SVD), candidate solutions are obtained. Lastly, the unique lander's attitude and position relative to the landing site are selected from the candidate solutions. Simulation results show that the proposed algorithm is able to estimate a lander's attitude and position robustly and quickly. Without an extended Kalman filter, the average errors of attitude are less than 1°and the average errors of position are less than 10 m at an altitude of 2,000 m. With an extended Kalman filter, attitude errors are within 0·5°and position errors are within 1 m at an altitude of 247·9 m.

Visual navigation using edge curve matching for pinpoint planetary landing

Pinpoint landing is challenging for future Mars and asteroid exploration missions. Vision-based navigation scheme based on feature detection and matching is practical and can achieve the required precision. However, existing algorithms are computationally prohibitive and utilize poor-performance measurements, which pose great challenges for the application of visual navigation. This paper proposes an innovative visual navigation scheme using crater edge curves during descent and landing phase. In the algorithm, the edge curves of the craters tracked from two sequential images are utilized to determine the relative attitude and position of the lander through a normalized method. Then, considering error accumulation of relative navigation, a method is developed. That is to integrate the crater-based relative navigation method with crater-based absolute navigation method that identifies craters using a georeferenced database for continuous estimation of absolute states. In addition, expressions of the relative state estimate bias are derived. Novel necessary and sufficient observability criteria based on error analysis are provided to improve the navigation performance, which hold true for similar navigation systems. Simulation results demonstrate the effectiveness and high accuracy of the proposed navigation method.

Hybrid optical navigation by crater detection for lunar pin-point landing: trajectories from helicopter flight tests

Accurate autonomous navigation capabilities are essential for future lunar robotic landing missions with a pin-point landing requirement, since in the absence of direct line of sight to ground control during critical approach and landing phases, or when facing long signal delays the herein before mentioned capability is needed to establish a guidance solution to reach the landing site reliably. This paper focuses on the processing and evaluation of data collected from flight tests that consisted of scaled descent scenarios where the unmanned helicopter of approximately 85 kg approached a landing site from altitudes of 50 m down to 1 m for a downrange distance of 200 m. Printed crater targets were distributed along the ground track and their detection provided earth-fixed measurements. The Crater Navigation (CNav) algorithm used to detect and match the crater targets is an unmodified method used for real lunar imagery. We analyze the absolute position and attitude solutions of CNav obtained and recorded during these flight tests, and investigate the attainable quality of vehicle pose estimation using both CNav and measurements from a tactical-grade inertial measurement unit. The navigation filter proposed for this end corrects and calibrates the high-rate inertial propagation with the less frequent crater navigation fixes through a closed-loop, loosely coupled hybrid setup. Finally, the attainable accuracy of the fused solution is evaluated by comparison with the on-board ground-truth solution of a dual-antenna high-grade GNSS receiver. It is shown that the CNav is an enabler for building autonomous navigation systems with high quality and suitability for exploration mission scenarios.

Database construction for vision aided navigation in planetary landing

In this paper, a novel database construction method for passive-image based navigation system within the planetary precise pin-point landing (PPL) background is presented. The key concept is selecting qualified visual features to construct the visual database by examining their contribution to the navigation system. We first define a metric named feature exploitability to evaluate the visual feature's distinctiveness and its spatial imagery distribution. After that, a greedy selection method is employed to construct the database by selecting features with high feature-exploitability scores. Then, a hierarchical feature retrieval method is proposed to achieve the adaptation of image-scale variation during landing and improve the efficiency of feature retrieval. To evaluate our proposed approach, the Monte Carlo simulation and an experimental test are conducted, simulation results show the advantage of the feature exploitability driven database construction method over other database construction methods and the necessity of proper database construction in a vision-aided navigation system for PPL mission.

A novel crater recognition based visual navigation approach for asteroid precise pin-point landing

This paper proposes a novel terrain-relative navigation (TRN) approach for the asteroid pin-point landing mission. The key concept is encapsulating efficient crater matching with active LiDAR ranging. Importantly, a novel crater to 3D crater model matching approach is proposed. Then, the line-of-sight from lander to crater is employed to guide the LiDAR ranging, and parameters of the matched 3D crater model is efficiently fused with LiDAR ranging to compensate its measurement, resulting in the robustness against the variation of terrain relief. In addition, a crater selection mechanism is proposed to reduce the estimation uncertainty. Monte Carlo simulation results show that the proposed approach is able to provide an adequate navigation performance under a high terrain relief, which is an evident improvement over the traditional methods.

Dynamic boundary layer based neural network quasi-sliding mode control for soft touching down on asteroid

Pinpoint landing is a critical step in some asteroid exploring missions. This paper is concerned with the descent trajectory control for soft touching down on a small irregularly-shaped asteroid. A dynamic boundary layer based neural network quasi-sliding mode control law is proposed to track a desired descending path. The asteroid’s gravitational acceleration acting on the spacecraft is described by the polyhedron method. Considering the presence of input constraint and unmodeled acceleration, the dynamic equation of relative motion is presented first. The desired descending path is planned using cubic polynomial method, and a collision detection algorithm is designed. To perform trajectory tracking, a neural network sliding mode control law is given first, where the sliding mode control is used to ensure the convergence of system states. Two radial basis function neural networks (RBFNNs) are respectively used as an approximator for the unmodeled term and a compensator for the difference between the actual control input with magnitude constraint and nominal control. To improve the chattering induced by the traditional sliding mode control and guarantee the reachability of the system, a specific saturation function with dynamic boundary layer is proposed to replace the sign function in the preceding control law. Through the Lyapunov approach, the reachability condition of the control system is given. The improved control law can guarantee the system state move within a gradually shrinking quasi-sliding mode band. Numerical simulation results demonstrate the effectiveness of the proposed control strategy.

X-ray pulsars/Doppler integrated navigation for Mars final approach

The performance of the navigation system during the Mars final approach phase determines the initial accuracy of Mars entry phase, which is critical for a pin-point landing. An X-ray pulsars/Doppler integrated navigation strategy is proposed to improve the estimation accuracy of the spacecraft’s entry state, as well as to enhance the autonomy, real-time and reliability. The navigation system uses the X-ray pulsar measurements and Doppler velocity measurements which are complementary to each other. The performance degradation in velocity estimation at the end of the final approach phase for X-ray pulsar based navigation can thus be eliminated. The nonlinearity of the system and the performance of Extended Kalman Filter are analyzed in this paper. Furthermore, in order to optimize the navigation scheme, a principle for navigation beacons selection based on the Fisher information matrix is used. Finally, a navigation scenario based on the 2012 encounter at Mars of Mars Science Laboratory spacecraft is considered to demonstrate the feasibility and accuracy of the proposed scheme. Simulation results also indicate that the proposed navigation scheme has reference value for the design of the future Mars explorations.

Mars Atmospheric Entry Guidance Design by Sliding Mode Disturbance Observer-Based Control

One of the demands for future Mars exploration is pin-point landing, in which the landing precision should be less than one hundred meters and is two orders of magnitude higher than the current level. In the process of the high-speed vehicle entering a rarefied atmosphere with highly uncertainties as the Mars atmosphere, the trajectory deviation caused by entry guidance can be the major part of the total landing errors. Due to modeling errors such as the atmospheric modeling error and the vehicle's aerodynamic model inaccuracy, the more the guidance law depends on the models, the larger the trajectory dispersion can be. To reduce the impact of model errors on guidance performance, a guidance law based on the second-order sliding mode variable structure control is developed for reference trajectory tracking. The guidance law which is tested in a real entry scenario is proved to be evident in reducing the control gain and the requirement for control ability. The proposed guidance law also shows accurate tracking for the reference trajectory and high precision of the landing sites, and thus has the potential to be applied to online guidance.

An innovative navigation scheme of powered descent phase for Mars pinpoint landing

Pinpoint landing (within 100m from the target) is essential for future Mars exploration missions. This paper deals with one aspect of the pinpoint landing architecture—the navigation performance improvement during the powered descent phase, and proposes an innovative navigation scheme to obtain the vehicle complete and accurate states. On the basis of dead reckoning relying on the Inertial Measurement Unit, measurements of the Integrated Doppler Radar are adopted to correct the vehicle velocity and altitude. Distance between the vehicle and one Mars Orbiter as well as their line-of-sight relative velocity is measured by a radio sensor, and integrated in the filter to correct the vehicle horizontal position. The innovative navigation system is based on an Extend Kalman Filter. Two observation schemes are developed. One considers measurements of the Integrated Doppler Radar and radio range measurement. Another further considers radio velocity measurement. The performance of the innovative navigation scheme is greatly influenced by the position of the Mars Orbiter with respect to the target. Stochastic analyses are performed to obtain optimal locations of Mars Orbiter. Finally, the innovative navigation scheme performances are assessed through stochastic simulations. Its performance improvements are demonstrated by comparison with the Integrated Doppler Radar only navigation scheme.

Single camera absolute motion based digital elevation mapping for a next generation planetary lander

Robotic planetary surface exploration missions are becoming much more ambitious in their science goals as they attempt to answer the bigger questions relating to the possibility of life elsewhere in our solar system. Answering these questions will require scientifically rich landing sites. Such sites are unlikely to be located in relatively flat regions that are free from hazards, therefore there is a growing need for next generation entry descent and landing systems to possess highly sophisticated navigation capabilities coupled with active hazard avoidance that can enable a pin-point landing. As a first step towards achieving these goals, a multi-source, multi-rate data fusion algorithm is presented that combines single camera recursive feature-based structure from motion (SfM) estimates with measurements from an inertial measurement unit in order to overcome the scale ambiguity problem by directly estimating the unknown scale factor. This paper focuses on accurate estimation of absolute motion parameters, as well as the estimation of sparse landing site structure to provide a starting point for hazard detection. We assume no prior knowledge of the landing site terrain structure or of the landing craft motion in order to fully assess the capabilities of the proposed algorithm to allow a pin-point landing on distant solar system bodies where accurate knowledge of the desired landing site may be limited. We present results using representative synthetic images of deliberately challenging landing scenarios, which demonstrates that the proposed method has great potential.

SLAM-Based Navigation Scheme for Pinpoint Landing on Small Celestial Body

Addressing the need for robust pinpoint landing capabilities, this paper proposes a monocular navigation scheme based on the Rao-Blackwellized particle filter simultaneous localization and mapping (SLAM) approach. The proposed online navigation scheme provides attitude and position (or pose) estimation during the approach, descent, and landing phase for small celestial body missions. This approach relies on one navigation camera and potentially sparse readings from one or more range sensors (e.g. LIDAR (Light Detection And Ranging)). The concept of the proposed navigation scheme is to maintain several hypotheses of the most likely spacecraft pose and landmarks position and to feed the most likely one to the spacecraft controller at any given time. The proposed system uses a double staged Monte-Carlo simulation that represents the population of all possible spacecraft motions between two camera images taken at successive time steps, and that samples this population over all possible scaling factors, converting each relative motion to world-scaled coordinates in the process. The purpose of this Monte-Carlo based visual pose estimation approach is to offer an alternative solution to the drift error and inaccuracy problems of SLAM kinematic models, odometry motion models, and other conventional dead reckoning techniques.

MCAV/IMU integrated navigation for the powered descent phase of Mars EDL

Pin-point landing is considered as a key technology for future manned Mars landing and Mars base missions. The traditional inertial navigation system (INS) based guidance, navigation and control (GNC) mode used in the Mars entry, descent and landing (EDL) phase has no ability to achieve the precise and safe Mars landing, so novel EDL GNC methodologies should be investigated to meet this goal. This paper proposes the MCAV/IMU integrated navigation scheme for the powered descent phase of Mars EDL. The Miniature Coherent Altimeter and Velocimeter (MCAV) is adopted to correct the inertial bias and drift and improve the performance of integrated navigation. Altitude and velocity information derived from MCAV and the lander’s state information sensed by inertial measurement unit (IMU) are integrated in extended Kalman filter algorithm. The validity of the proposed navigation scheme is confirmed by computer simulation.

Desensitizing the Minimum-Fuel Powered Descent For Mars Pinpoint Landing

This paper aims at reducing the sensitivity of the minimum-fuel powered descent trajectory on Mars in the presence of uncertainties and perturbations, using the desensitized optimal control methodology. The lander is modeled as a point mass in a uniform gravitational field, and the engine throttle is considered the control variable, which is bounded between two nonzero settings. Unlike the conventional practice of designing separately the nominal trajectory and a feedback tracking controller, desensitized optimal control strategy incorporates the two designs in synergy, delivering a superior performance. Sensitivities of the final position and velocity with respect to perturbed states at all times are derived and augmented onto the minimum-fuel performance index through penalty factors. The linear quadratic regulator technique is used to design the feedback control gains. To reduce the likelihood of the closed-loop throttle exceeding the prescribed bounds, a multiplicative factor is applied to the feedback gains. This reshapes the nominal trajectory from the well-known maximum-minimum-maximum structure in that the nominal throttle is encouraged to stay away from the prescribed bounds, leaving room for the feedback control. Monte Carlo simulations show that the occurrence of out-of-bound closed-loop throttles is significantly reduced, leading to improved landing precision.

Minimum-Fuel Powered Descent for Mars Pinpoint Landing

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

An Analysis of Spacecraft Localization from Descent Image Data for Pinpoint Landing on Mars and Other Cratered Bodies

A pinpoint landing capability will be a critical component for many planned NASA missions to Mars and beyond. Implicit in the requirement is the ability to accurately localize the spacecraft with respect to the terrain during descent. In this paper, we present evidence that a vision-based solution using craters as landmarks is both practical and will meet the requirements of next generation missions. Our emphasis in this paper is on the feasibility of such a system in terms of (a) localization accuracy and (b) applicability to Martian terrain. We show that accuracy of well under 100 meters can be expected under suitable conditions. We also present a sensitivity analysis that makes an explicit connection between input data and robustness of our pose estimate. In addition, we present an analysis of the susceptibility of our technique to inherently ambiguous configurations of craters. We show that probability of failure due to such ambiguity is becoming increasingly small.