Richard W. Powell

Mars Science Laboratory Entry, Descent, and Landing System Overview

In 2010, the Mars science laboratory (MSL) mission will pioneer the next generation of robotic entry, descent, and landing (EDL) systems by delivering the largest and most capable rover to date to the surface of Mars. In addition to landing more mass than prior missions to Mars, MSL will offer access to regions of Mars that have been previously unreachable. The MSL EDL sequence is a result of a more stringent requirement set than any of its predecessors. Notable among these requirements is landing a 900 kg rover in a landing ellipse much smaller than that of any previous Mars lander. In meeting these requirements, MSL is extending the limits of the EDL technologies qualified by the Mars viking, Mars pathfinder, and Mars exploration rover missions. Thus, there are many design challenges that must be solved for the mission to be successful. Several pieces of the EDL design are technological firsts, such as guided entry and precision landing on another planet, as well as the entire sky crane maneuver. This paper discusses the MSL EDL architecture and discusses some of the challenges faced in delivering an unprecedented rover payload to the surface of Mars.

Mars Science Laboratory entry, descent, and landing system

In 2010, the Mars Science Laboratory (MSL) mission will pioneer the next generation of robotic entry, descent, and landing (EDL) systems by delivering the largest and most capable rover to date to the surface of Mars. In addition to landing more mass than prior missions to Mars, MSL will offer access to regions of Mars that have been previously unreachable. By providing an EDL system capable of landing at altitudes as high as 2 km above the reference areoid, as defined by the Mars Orbiting Laser Altimeter (MOLA) program, MSL will demonstrate sufficient performance to land on a large fraction of the Martian surface. By contrast, the highest altitude landing to date on Mars has been the Mars Exploration Rover (MER) MER-B at 1.44 km below the areoid. The coupling of this improved altitude performance with latitude limits as large as 60 degrees off of the equator and a precise delivery to within 10 km of a surface target will allow the science community to select the MSL landing site from thousands of scientifically interesting possibilities. In meeting these requirements, MSL is extending the limits of the EDL technologies qualified by the Mars Viking, Mars Pathfinder, and MER missions. This paper discusses the MSL EDL architecture, system, and subsystem design and discusses some of the challenges faced in delivering such an unprecedented rover payload to the surface of Mars

Mars Science Laboratory: Entry, Descent, and Landing System Performance

In 2010, the Mars Science Laboratory (MSL) mission will pioneer the next generation of robotic entry, descent, and landing (EDL) systems, by delivering the largest and most capable rover to date to the surface of Mars. To do so, MSL will fly a guided lifting entry at a lift-to-drag ratio in excess of that ever flown at Mars, deploy the largest parachute ever at Mars, and perform a novel Sky Crane maneuver. Through improved altitude capability, increased latitude coverage, and more accurate payload delivery, MSL is allowing the science community to consider the exploration of previously inaccessible regions of the planet.

Entry Configurations and Performance Comparisons for the Mars Smart Lander

The Mars Smart Lander (MSL, renamed and redefined as the Mars Science Laboratory) will provide scientists with access to previously unachievable landing sites by providing precision landing to less than 10 km of a target landing site with landing altitude capability to 2.5 km above the Mars Orbiter Laser Altimeter geoid. Precision landing is achieved by using the aerodynamic forces on the entry body to aeromaneuver through the Martian atmosphere during the entry phase of flight. The entry body is designed to provide aerodynamic lift. The direction of the aerodynamic lift vector, defined by the vehicle bank angle, is commanded by the onboard entry guidance, to converge downrange and crossrange errors by parachute deploy, while meeting the parachute deploy constraints. Several approaches and entry body configurations for providing aerodynamic lift can be considered, including axisymmetric capsule configurations with offset c.g.s using ballast or packaging, aerodynamically shaped capsule-type configurations, and alternate configurations such as mid-lift-to-drag-ratio vehicles. The design considerations, entry configurations, and entry performance of the Mars Smart Lander are described.

Entry, Descent and Landing Systems Analysis: Exploration Class Simulation Overview and Results

NASA senior management commissioned the Entry, Descent and Landing Systems Analysis (EDL-SA) Study in 2008 to identify and roadmap the Entry, Descent and Landing (EDL) technology investments that the agency needed to make in order to successfully land large payloads at Mars for both robotic and exploration or human-scale missions. The year one exploration class mission activity considered technologies capable of delivering a 40-mt payload. This paper provides an overview of the exploration class mission study, including technologies considered, models developed and initial simulation results from the EDL-SA year one effort.

Aerocapture Simulation and Performance for the Titan Explorer Mission

A systems study for a Titan aerocapture orbiter has been completed. The purpose of this study was to determine the feasibility and potential benefits of using aerocapture technologies for this destination. The Titan Explorer design reference mission is a follow-on to the Cassini/Huygens exploration of the Saturnian system that consists of both a lander and an orbiter. The orbiter uses aerocapture, a form of aeroassist, to replace an expensive orbit insertion maneuver with a single guided pass through the atmosphere. Key environmental assumptions addressed in this study include: the uncertainty in atmospheric density and high frequency atmospheric perturbations, approach navigation delivery errors, and vehicle aerodynamic uncertainty. The robustness of the system is evaluated through a Monte Carlo simulation. The Program to Optimize Simulated Trajectories is the basis for the simulation, though several Titan specific models were developed and implemented including: approach navigation, Titan atmosphere, hypersonic aeroshell aerodynamics, and aerocapture guidance. A navigation analysis identified the Saturn/Titan ephemeris error as major contributor to the delivery error. The Monte Carlo analysis verifies that a high-heritage, low L/D, aeroshell provides sufficient performance at a 6.5 km/s entry velocity using the Hybrid Predictor-corrector Aerocapture Scheme guidance. The current mission design demonstrates 3-sigma success without additional margin, assuming current ephemeris errors, and is therefore not dependent on the success of the Cassini/Huygens mission. However, additional margin above 3-sigma is expected along with the reduced ephemeris errors in the event of a successful Cassini mission.

Asymptotic parachute performance sensitivity

In 2010, the Mars Science Laboratory mission will pioneer the next generation of robotic Entry, Descent, and Landing systems by delivering the largest and most capable rover to date to the surface of Mars. In addition to landing more mass than any other mission to Mars, Mars Science Laboratory will also provide scientists with unprecedented access to regions of Mars that have been previously unreachable. By providing an Entry, Descent, and Landing system capable of landing at altitudes as high as 2 km above the reference gravitational equipotential surface, or areoid, as defined by the Mars Orbiting Laser Altimeter program, Mars Science Laboratory will demonstrate sufficient performance to land on 83% of the planets surface. By contrast, the highest altitude landing to date on Mars has been the Mars Exploration Rover at 1.3 km below the areoid. The coupling of this improved altitude performance with latitude limits as large as 60 degrees off of the equator and a precise delivery to within 10 km of a surface target, will allow the science community to select the Mars Science Laboratory landing site from thousands of scientifically interesting possibilities. In meeting these requirements, Mars Science Laboratory is extending the limits of the Entry, Descent, and Landing technologies qualified by the Mars Viking, Mars Pathfinder, and Mars Exploration Rover missions. Specifically, the drag deceleration provided by a Viking-heritage 16.15 m supersonic Disk-Gap-Band parachute in the thin atmosphere of Mars is insufficient, at the altitudes and ballistic coefficients under consideration by the Mars Science Laboratory project, to maintain necessary altitude performance and timeline margin. This paper defines and discusses the asymptotic parachute performance observed in Monte Carlo simulation and performance analysis and its effect on the Mars Science Laboratory entry, descent, and landing architecture

Guidance and Control Algorithms for the Mars Entry, Descent and Landing Systems Analysis

The purpose of the Mars Entry, Descent and Landing Systems Analysis (EDL-SA) study was to identify feasible technologies that will enable human exploration of Mars, specifically to deliver large payloads to the Martian surface. This paper focuses on the methods used to guide and control two of the contending technologies, a mid- lift-to-drag (L/D) rigid aeroshell and a hypersonic inflatable aerodynamic decelerator (HIAD), through the entry portion of the trajectory. The Program to Optimize Simulated Trajectories II (POST2) is used to simulate and analyze the trajectories of the contending technologies and guidance and control algorithms. Three guidance algorithms are discussed in this paper: EDL theoretical guidance, Numerical Predictor-Corrector (NPC) guidance and Analytical Predictor-Corrector (APC) guidance. EDL-SA also considered two forms of control: bank angle control, similar to that used by Apollo and the Space Shuttle, and a center-of-gravity (CG) offset control. This paper presents the performance comparison of these guidance algorithms and summarizes the results as they impact the technology recommendations for future study.

Parachute Models Used in the Mars Science Laboratory Entry, Descent, and Landing Simulation

An end-to-end simulation of the Mars Science Laboratory (MSL) entry, descent, and landing (EDL) sequence was created at the NASA Langley Research Center using the Program to Optimize Simulated Trajectories II (POST2). This simulation is capable of providing numerous MSL system and flight software responses, including Monte Carlo-derived statistics of these responses. The MSL POST2 simulation includes models of EDL system elements, including those related to the parachute system. Among these there are models for the parachute geometry, mass properties, deployment, inflation, opening force, area oscillations, aerodynamic coefficients, apparent mass, interaction with the main landing engines, and off-loading. These models were kept as simple as possible, considering the overall objectives of the simulation. The main purpose of this paper is to describe these parachute system models to the extent necessary to understand how they work and some of their limitations. A list of lessons learned during the development of the models and simulation is provided. Future improvements to the parachute system models are proposed.

Large Mass, Entry, Descent and Landing Sensitivity Results for Environmental, Performance, and Design Parameters

Landing on Mars has been a challenging task. Past NASA missions have shown resilience to increases in spacecraft mass by scaling back requirements such as landing site altitude, landing site location and arrival time. Knowledge of the partials relating requirements to mass is critical for mission designers to understand so that the project can retain margin throughout the process. Looking forward to new missions that will land 1.5 metric tons or greater, the current level of technology is insufficient, and new technologies will need to be developed. Understanding the sensitivity of these new technologies to requirements is the purpose of this paper.