Babak E. Cohanim

Advances in POST2 End-to-End Descent and Landing Simulation for the ALHAT Project

Program to Optimize Simulated Trajectories II (POST2) is used as a basis for an end-to- end descent and landing trajectory simulation that is essential in determining design and integration capability and system performance of the lunar descent and landing system and environment models for the Autonomous Landing and Hazard Avoidance Technology (ALHAT) project. The POST2 simulation provides a six degree-of-freedom capability necessary to test, design and operate a descent and landing system for successful lunar landing. This paper presents advances in the development and model-implementation of the POST2 simulation, as well as preliminary system performance analysis, used for the testing and evaluation of ALHAT project system models.

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.

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.

Small Lunar Exploration and Delivery System Concept

This paper describes an architectural concept for a Small Lunar Exploration and Delivery System to operate as a platform for emplacing payloads into lunar orbit and onto the lunar surface, while providing mobility for surface exploration, science, and infrastructure. The concept leverages emerging services that are capable of delivering payloads to Low Earth Orbit (LEO), while utilizing new and old technologies to build a platform for transfer to Low Lunar Orbit (LLO). Advances and miniaturization in avionics, navigation, power, and propulsion systems enable a unique opportunity to develop a system that is both capable of landing on the lunar surface and providing surface mobility with the same system.

Further Development and Flight Testing of a Prototype Lunar and Planetary Surface Exploration Hopper: Update on the TALARIS Project

This paper presents an update on the Earth-based hopper prototype for autonomous planetary exploration that MIT and Draper Laboratory are developing as part of the Next Giant Leap teams efforts in the Google Lunar X-Prize. New developments and upgrades, culminating in the second-generation vehicle, are described in this paper, as well as the ongoing test program and experimental results. Recent developments include a redesign of the vehicle structure, an upgrade to the avionics system, the use of an upgraded version of the gravity-offsetting propulsion system (which uses electrically-powered ducted fans) and the incorporation of the secondary spacecraft-emulator propulsion system (which uses compressed nitrogen propellant and cold gas thrusters).

Small lunar lander/hopper performance analysis

The goal of this paper is to describe a first-order performance analysis of a lunar hopper 1,2. A hopper is a vehicle that has both landing and surface mobility capabilities on a single platform. Unlike rovers, which traverse the lunar surface while in contact with the ground, hopping reuses the landing propulsion system to lift back off again and “hop” over the lunar terrain. Hopping, as a form of surface mobility, is a novel concept. As such, analysis must be performed to assess how it would fit with an overall lunar landing system architecture. Two trajectory categories are investigated to perform this assessment: the ballistic hop, where the vehicle launches itself into a ballistic trajectory toward the destination, and the hover hop, in which the vehicle ascends and maintains a constant altitude as it travels toward its desired location. Initially, parametric studies of the ballistic and hover hop are carried out in order to make observations about the performance of each hop. Using this data, it is possible to investigate the fuel-optimal hop trajectory. The delta-V costs for the ballistic and hover hops are compared for hop distances between 500 meters and 5000 meters, and in this range it is found that the ballistic hop and hover traverse have comparable delta-V costs. For the entire hop maneuver, however, the hover hop will always be the more delta-V expensive option due to the ascent and descent phases. Nevertheless, this does not rule out the hover hop as a feasible option due to its operational advantages over the ballistic hop.

Hazard detection for small robotic landers and hoppers

Planetary hoppers are a new class of vehicle being developed that will provide planetary surface mobility by reusing the landing platform and its actuators to propulsively ascend, translate, and descend to new landing points on the surface of a planetary body. Hoppers enhance regional exploration, with the capability of rapid traverse over 100s-1000s of meters, traverse over hazardous terrain, and exploration of cliffs and craters. These planetary mobility vehicles are fuel limited and as a result, are enabled by carrying sensor payloads that require low mass, low volume, and low on board computational resources. This paper describes a method for hoppers to traverse and land safely in this constrained environment. The method uses optical detection of shadows to provide coarse hazard detection at shallow path angles and long ranges. As a hopper approaches the landing site, a short-range range sensing method is used to determine the local slope and roughness just ahead of the vehicles flight path. These two techniques are used together to safely land a hopper at downrange locations. The paper presents the method and provides analysis showing the performance and limitations of using this method for hopper traverse.

Next-Generation Maneuvering System with Control-Moment Gyroscopes for Extravehicular Activities Near Low-Gravity Objects

Looking ahead to the human exploration of Mars, NASA is planning for exploration of near-Earth asteroids and the Martian moons. Performing tasks near the surface of such low-gravity objects will likely require the use of an updated version of the Manned Maneuvering Unit (MMU) since the surface gravity is not high enough to allow astronauts to walk, or have sufficient resistance to counter reaction forces and torques during movements. The extravehicular activity (EVA) Jetpack device currently under development is based on the Simplified Aid for EVA Rescue (SAFER) unit and has maneuvering capabilities to assist EVA astronauts with their tasks. This maneuvering unit has gas thrusters for attitude control and translation. When EVA astronauts are performing tasks that require ne motor control such as sample collection and equipment placement, the current control system will re thrusters to compensate for the resulting changes in center-of-mass location and moments of inertia, adversely affecting task performance. The proposed design of a next-generation maneuvering and stability system incorporates control concepts optimized to support astronaut tasks and adds control-moment gyroscopes (CMGs) to the current Jetpack system. This design aims to reduce fuel consumption, as well as improve task performance for astronauts by providing a sti er work platform. The high-level control architecture for an EVA maneuvering system using both thrusters and CMGs considers an initial assessment of tasks to be performed by an astronaut and an evaluation of the corresponding human-system dynamics. For a scenario in which the astronaut orbits an asteroid, simulation results from the current EVA maneuvering system are compared to those from a simulation of the same system augmented with CMGs, demonstrating that the forces and torques on an astronaut can be significantly reduced with the new control system actuation while conserving onboard fuel.

Development of a Cold Gas Spacecraft Emulator System for the TALARIS Hopper

The TALARIS (Terrestrial Artificial Lunar And Reduced gravIty Simulator) hopper is a small prototype vehicle currently being developed as an Earth-based testbed for guidance, navigation, and control algorithms that will be used to explore lunar and other planetary surfaces remotely. It has two propulsion systems: (1) a system of four electric ducted fans to offset 5/6 of Earth’s gravity, and (2) a cold gas propulsion system which uses compressed nitrogen propellant in an impulsive emulation of the lunar propulsion system, flying in an environment dynamically similar to that of the Moon. This paper focuses on the second of these propulsion systems. It details the practical development of the cold gas spacecraft emulator (CGSE) system, including initial conception and design, methods of analysis, and test results. Details of the system’s integration into the broader TALARIS project are also presented. Finally, a path ahead for additional testing of the CGSE is discussed.

Talaris hopper testbed navigation analysis

This paper describes navigation techniques for a propulsive planetary hopper. 1,2 The Talaris hopper testbed, developed by Draper and MIT, is used for investigating guidance, navigation, and control techniques for planetary hoppers. The Talaris hopper currently employs an IMU and altimeter for navigation. Analysis and test results will be presented showing the predicted and achieved navigation performance. We will also describe navigation techniques that have been demonstrated to provide surface relative attitude updates and future methods of navigating hoppers for missions uniquely enabled by this platform.