Tye Brady

Autonomous Landing and Hazard Avoidance Technology (ALHAT)

The ALHAT project is funded by NASA to develop an integrated AGNC (autonomous guidance, navigation and control) hardware and software system capable of detecting and avoiding surface hazards and guiding humans and cargo safely, precisely and repeatedly to designated lunar landing sites. There are important interdependencies driving the design of a lunar landing system including such things as lander hazard robustness, landing site conditions (terrain and natural lighting), trajectories, sensors, crew involvement, and others. The ALHAT system must be capable of operating in a wide range of lunar environments and supporting global lunar access for both crewed and robotic missions. This paper discusses the major factors driving the design of a lunar landing system as well as the current state of the technology development. The supporting analysis and testing results will be presented that show the system interdependencies and their relative importance, as well as the trades needed to optimize the landing system. The emphasis is on the final phase of the landing where hazard detection and avoidance (HDA) and hazard relative navigation (HRN) are the primary considerations in achieving a safe landing. The current sensor options being considered and the status of the development of those sensors are discussed.

A Self Contained Method for Safe & Precise Lunar Landing

The return of humans to the Moon will require increased capability beyond that of the previous Apollo missions. Longer stay times and a greater flexibility with regard to landing locations are among the many improvements planned. A descent and landing system that can land the vehicle more accurately than Apollo with a greater ability to detect and avoid hazards is essential to the development of a Lunar outpost, and also for increasing the number of potentially accessible Lunar sortie locations. This descent and landing system should allow landings in more challenging terrain and provide more flexibility with regard to mission timing and lighting considerations, while maintaining safety as the top priority. The lunar landing system under development by the ALHAT (autonomous landing and hazard avoidance technology) project is addressing this by providing terrain-relative navigation measurements to enhance global-scale precision, an onboard hazard detection system to select safe landing locations, and an autonomous GNC (guidance, navigation, and control) capability to process these measurements and safely direct the vehicle to a landing location. This landing system will enable safe and precise lunar landings without requiring lunar infrastructure in the form of navigation aids or a priori identified hazard-free landing locations. The safe landing capability provided by ALHAT uses onboard active sensing to detect hazards that are large enough to be a danger to the vehicle but too small to be detected from orbit a priori. Algorithms to interpret raw active sensor terrain data and generate hazard maps as well as identify safe sites and recalculate new trajectories to those sites are included as part of the ALHAT System. These improvements to descent and landing will help contribute to repeated safe and precise landings for a wide variety of terrain on the Moon.

The challenge of safe lunar landing

The Apollo lunar landings were both incredibly successful and challenging. As the world watched, each of the six landing missions faced potentially mission ending hazards within each of the landing sites while simultaneously dealing with diminishing fuel reserves and a unique landing environment. Hazards in the form of rocks, craters and slopes all were perilously close to each of the successfully landed missions and brought to light the incredible challenge each mission faced.

Hazard Detection Methods for Lunar Landing

The methods and experiences from the Apollo Program are fundamental building blocks for the development of lunar landing strategies for the Constellation Program. Each of the six lunar landing Apollo missions landed under near ideal lighting conditions. The astronauts visually performed terrain relative navigation while looking out of windows, and were greatly aided by external communication and well lit scenes. As the LM approached the landing site, the astronauts performed visual hazard detection and avoidance, also under near-ideal lighting conditions. The astronauts were looking out of the windows trying to the best of their ability to avoid rocks, slopes, and craters and find a safe landing location. NASA has expressed a desire for global lunar access for both crewed and robotic sortie lunar exploration missions [2] [3]. Early NASA architecture studies have identified the lunar poles as desirable locations for early lunar missions. These polar missions provide less than ideal lighting conditions that will significantly affect the way a crewed vehicle is to land at such locales. Consequently, a variety of hazard identification methods should be considered for use by the crew to ensure a high degree of safety. This paper discusses such identification methods applicable to the poorly lit polar lunar environment, better ensuring global access for the soon to be designed Lunar Lander Vehicle (LLV).

Human Interactive Landing Point Redesignation for Lunar Landing

In order to achieve safe and precise landings anywhere on the lunar surface without the heavy involvement of mission operations required during Apollo, an autonomous flight manager (AFM) is needed to assist the crew in managing the landing mission. An essential algorithm within the AFM is the landing point redesignation (LPR) function, which determines a prioritized list of safe and precise points in the landing region from which the crew can select a landing aimpoint. The LPR function described in this paper is flexible enough to support a variety of missions and situations by allowing an operator to reach-in and modify parameters prior to and throughout the landing.

ALHAT System Architecture and Operational Concept

An autonomous lunar landing system applicable to a wide variety of crewed and robotic lunar descent vehicles is under development as part of the ALHAT (autonomous precision landing and hazard detection and avoidance technology) project. This system, referred to as the ALHAT system module (ASM) is a highly advanced integrated sensor suite that enables landing a lunar descent vehicle within tens of meters of a certified and designated landing location anywhere on the Moon, under any lighting condition. This paper describes the basic ASM architecture and its novel concept of operations, and matures this architecture through description of top level lunar landing requirements. Working closely with NASA primary stakeholders, a fully developed ASM design will enable global lunar access for exploration of unique and challenging areas on the lunar surface never before visited.

Ground validation of the inertial stellar compass

The inertial stellar compass (ISC), under development at Draper Laboratory, provides spacecraft attitude determination to 0.1 degree accuracy using just 3.5 W of power. This work describes the process of validating the performance of the instrument on the ground prior to characterizing it on orbit. Starting with subsystem-level testing of the ISCs active pixel sensor camera and MEMS (microelectromechanical system) 3-axis gyro board, we describe the operations leading up to integrated system testing of the camera and gyro sensor outputs, which are combined to provide a robust attitude solution over a wide range of operating conditions. Under the guidance of NASAs New Millennium Program, the ground validation process, which will be followed by an on-orbit demonstration, will make feasible a new class of low-power, integrated attitude sensors for small spacecraft.

Demonstration of a safe & precise planetary landing system on-board a terrestrial rocket

The Autonomous Landing and Hazard Avoidance Technology (ALHAT) Project is a multiyear NASA technology development effort focused on A(utonomous)-GNC and sensor technology to enable safe and precise planetary landings. The culmination of this project work involves field testing of the developed technology in a relevant terrestrial environment. These tests will demonstrate the capability of the ALHAT AGNC and sensor system, raising the Technology Readiness Level (TRL), in preparation for a next generation planetary lander. With this system, a next generation lander will be capable of safe and precise landings regardless of local lighting conditions. At least two independent terrestrial rocket systems will be utilized for demonstration of aspects of the ALHAT system. This paper discusses the use of the commercial Masten Space Systems terrestrial rocket for ALHAT demonstration purposes. This demonstration is being performed through the NASA Flight Opportunities program. This Terrestrial Test Rocket (TTR) will have the ALHAT AGNC software and hardware system integrated with Masten as a secondary, independent GNC system that will fly the vehicle closed-loop through highly dynamic lunar- and Mars-like approach and landing trajectories. With the AGNC system demonstrated, advanced ALHAT sensor systems will then be incorporated with the TTR, enabling autonomous hazard detection and avoidance in conjunction with a highly precise landing. Details of the hardware and software integration process with Masten are discussed along with performance results from recent tests.

Apollo looking forward: Crew task challenges

During the Apollo landings, onboard astronauts, along with analysis and instructions from mission control, performed the majority of complex tasks beyond automated Guidance, Navigation, and Control (GN&C). The crew played a significant role in the landings and were critical to navigating to the landing site, selecting a safe landing aim point, and commanding the spacecraft via a hand controller. Thus the requirements and constraints for site selection, launch dates, and GN&C design were driven in large part by human capabilities. Each of the major tasks performed by the crew will be described to provide an understanding of the functions that must be performed by either automation or people (on or off-board) for the next generation lunar lander. Additionally, several of the Apollo missions faced significant issues in identifying the landing site and assessing the safety of that landing site. These missions serve as case studies for future landing challenges that must be overcome.

Vision-based navigation and hazard detection for terrestrial rocket approach and landing

This paper introduces a compact optical payload enabling vision-based navigation and hazard detection during terrestrial rocket flights. This payload, the Terrain-Relative Navigation & Descent Imager (TRNDI), serves as an add-on module for Draper Laboratorys GENIE Autonomous-GNC system. GENIEs inertial navigation system relies on GPS during terrestrial test flights, making it insufficient for GPS-denied, extraterrestrial environments. The TRNDI system includes a horizon-pointing monochromatic camera, two downward-pointing monochromatic cameras, and a robust single-board computer. TRNDI utilizes a modular software framework, which allows multiple algorithms to run in real-time and communicate with the primary GENIE flight computer. This system enables data collection and real-time data processing for further development and evaluation of vision-based terrain-relative navigation, visual odometry, and hazard detection algorithms, with a path toward future closed-loop integration with GENIEs navigation system. This paper presents an overview of the TRNDI algorithms and hardware, as well as simulated results from two vision-based hazard detection (HD) algorithms. The first HD algorithm searches the camera field of view for suitable landing sites. The second HD algorithm creates a map of the relative safety of the landing region. The simulated results demonstrate that TRNDI can reliably find and deliver a safe landing site to GENIE in realtime during a planetary approach trajectory.