Robust Nonlinear Optimal Solution to the Lunar Landing Guidance by Using Neighboring Optimal Control

A closed-loop time-optimal control strategy for the highly nonlinear problem of the lunar landing mission by using the perturbation technique is developed in this study. The first part of the study considers analytical solution for an optimal control policy of variable mass spacecraft, while it descents on the surface of the moon in the variable gravitational field of it. To validate the accuracy of perturbation solution, a numerical approach based on steepest descent method is employed. The second part considers analytical derivation of an optimal feedback guidance solution by employing the neighboring optimal control (NOC) law when effects of imperfection in the dynamic model or disturbing noises have been taken into account. The technique of NOC produces time-varying feedback gains that minimize the performance index to the second order for perturbations from a nominal optimal path. The robustness of the designed NOC law is examined with applying sinusoidal noises. From the study of the simulation results, it may be concluded that the developed optimal guidance laws may be used in real world spacecraft applications.     

Preparing to Bridge the Lunar Gap

The United States is committed to the exploration of and the expansion into space. A manned earth‐orbiting space station is planned for the next decade and studies continue looking at manned lunar bases. Appropriate planning should be initiated for such a mission now as a high national priority. Many systems must be examined and technologies developed as soon as possible. Some of these include types of power sources, life support systems, construction equipment and techniques, construction methods, lunar mapping, and logistical constraints.     

Technical Requirements for Lunar Structures

The moon has recently regained the interest of many of the world’s space agencies. Lunar missions are the first steps in expanding manned and unmanned exploration inside our solar system. The moon represents various options; it can be used as a laboratory in low gravity, it is the closest and most accessible planetary object from the Earth, and it possesses many resources that humans could potentially exploit. This paper has two objectives: to review the current status of the knowledge of lunar environmental requirements for future lunar structures, and to attempt to classify different future lunar structures based on the current knowledge of the subject. The paper divides lunar development into three phases. The first phase is building shelters for equipment only; in the second phase, small temporary habitats will be built, and finally in the third phase, habitable lunar bases will be built with observatories, laboratories, or production plants. Initially, the main aspects of the lunar environment that will cause concerns will be lunar dust and meteoroids, and later will include effects due to the vacuum environment, lunar gravity, radiation, a rapid change of temperature, and the length of the lunar day. This paper presents a classification of technical requirements based on the current knowledge of these factors, and their importance in each of the phases of construction. It gives recommendations for future research in relation to the development of conceptual plans for lunar structures, and for the evolution of a lunar construction code to direct these structural designs. Some examples are presented along with the current status of the bibliography of the subject.     

Characterization of Lunar Dust for Toxicological Studies. II: Texture and Shape Characteristics

The morphology (shape and texture) of dust fractions of five Apollo lunar soils and a lunar dust simulant, JSC-1Avf, was studied using scanning electron microscopy. Shape (aspect ratio and complexity) of particles was described based on the two-dimensional projection images. The distributions of aspect ratio and complexity of particles are reported. It was determined that the Apollo lunar dust particles consist mainly of impact-produced glass, with complicated morphologies, extensive surface areas per grain, and sharp, jagged edges. Importantly, many grains contain elaborate vesicular textures, representing minute agglutinates. Dust simulant JSC-1Avf also has similar shapes as lunar dust, but differs in surface texture and area (smooth and nonvesicular). These data provide information for toxicity studies of lunar dust and for selecting a suitable lunar dust simulant.     

Geotechnical Properties of NT-LHT-2M Lunar Highland Simulant

Future lunar explorations require a thorough understanding of the geotechnical properties of lunar soils. However, the small amount of lunar soil that was brought back to earth cannot satisfy the needs. A new lunar soil simulant, NU-LHT-2M, has been developed to simulate lunar regolith in the lunar highlands region. It is characterized to help the development of regolith-moving machines and vehicles that will be used in future missions to the moon. The simulant’s particle size distribution, specific gravity, maximum and minimum densities, compaction characteristics, shear strength parameters and compressibility have been studied; and the results are compared with the information about lunar regolith provided in the Lunar Sourcebook.     

Characterization of Lunar Dust for Toxicological Studies. I: Particle Size Distribution

The particle size distribution (PSD) of lunar dust, the <20?μm portion of the regolith, was determined as an initial step in the study of the possible toxicological effects it may have on the human respiratory and pulmonary systems. Utilizing scanning electron microscopy, PSDs were determined for Apollo 11 (10084) and 17 (70051) dust samples, as well as lunar dust simulant JSC-1Avf. The novel methodology employed is described in detail. All measured PSDs feature a log-normal distribution having a single mode in a range 100–300?nm for lunar dust samples, but the lunar simulant has a mode at ～ 600?nm.     

Dependence of Lunar Bases on Phobos and Deimos

The Moon is nearly devoid of essential biogenic resources such as water, hydrocarbons, and nitrogen. Lunar bases must have a ready supply of these vital resources since they are easily lost to the vacuum of space. Also, wet chemical processes dominate the chemical industries. Extraterrestrial sources of these materials must be found to provide for life support, construction, and manufacturing. If Phobos and Deimos have carbonaceous chondritic compositions, they are ideal targets for extraterrestrial exploitation. They may contain biogenic resources such as water, hydrocarbons, and nitrogen, as well as easily recoverable structural materials.     

Microwave Sintering of Lunar Soil: Properties, Theory, and Practice

The unique properties of lunar regolith make for the extreme coupling of the soil to microwave radiation. Space weathering of lunar regolith has produced myriads of nanophase-sized Fe0 grains set within silicate glass, especially on the surfaces of grains, but also within the abundant agglutinitic glass of the soil. It is possible to melt lunar soil (i.e., 1,200–1,500°C) in minutes in a normal kitchen-type 2.45?GHz microwave, almost as fast as your tea-water is heated. No lunar simulants exist to study these microwave effects; in fact, previous studies of the effects of microwave radiation on lunar simulants, MLS-1 and JSC-1, have been misleading. Using real Apollo 17 soil has demonstrated the uniqueness of the interaction of microwave radiation with the soil. The applications that can be made of the microwave treatment of lunar soil for in situ resource utilization on the Moon are unlimited.     

Lunar Astronomical Observatories: Design Studies

The best location in the inner solar system for the grand observatories of the 21st century may be the Moon. A multidisciplinary team including university students and faculty in engineering, astronomy, physics, and geology, and engineers from industry is investigating the Moon as a site for astronomical observatories and is doing conceptual and preliminary designs for these future observatories. Studies encompass lunar facilities for radio astronomy and astronomy at optical, ultraviolet, and infrared wavelengths of the electromagnetic spectrum. Although there are significant engineering challenges in design and construction on the Moon, the rewards for astronomy can be great, such as detection and study of Earth‐like planets orbiting nearby stars, and the task for engineers promises to stimulate advances in analysis and design, materials and structures, automation and robotics, foundations, and controls. Fabricating structures in the reduced‐gravity environment of the Moon will be easier than in the zero‐gravity environment of Earth orbit, as Apollo and space‐shuttle missions have revealed. Construction of observatories on the Moon can be adapted from techniques developed on the Earth, with the advantage that the Moon's weaker gravitational pull makes it possible to build larger devices than are practical on Earth.     

Solar Thermal Power for Lunar Materials Processing

Lunar in situ resource utilization (ISRU) processes require thermal energy at various temperatures. Chemical recovery processes (pyrolysis, gas-solid reactions, gas-liquid or three-phase reactions and desorption) require thermal energy at temperatures from 1,000?K?to?2,500?K. Manufacturing processes (hot liquid processing, sinter forming, composite forming, welding, etc.) can be accomplished with thermal energy at temperatures 1,200?K–1,800?K. For these materials, process applications or solar thermal power can be effectively utilized. Physical Sciences Inc. has been developing an innovative solar power system in which solar radiation is collected by the concentrator, which transfers the concentrated solar radiation to the optical waveguide transmission line made of low loss optical fiber. In this paper, we will review our work on the development of the solar thermal power system and its application to a lunar ISRU process.     

Technical Issues for Lunar Base Structures

The establishment of a permanent human presence on other planets will require establishing permanent infrastructure in new environments. Civil engineers select, define, and implement solutions to infrastructure design problems in unique environmental contexts. Wind and seismic loading are two examples of constraints long familiar to terrestrial civil engineering. Designing structures for lunar exploration, development and eventual settlement will make use of the same design processes already practiced by the civil engineering profession. However, the extensive experience base resulting from centuries of terrestrial work does not adequately prepare civil engineers for the unprecedented constraints and environmental conditions that are encountered in space. The limited knowledge we already have about the Moon (mostly from the Apollo program) is a place to start. By assimilating and working with this knowledge, those pursuing the design of lunar base structures can begin to produce realistic and valid design solutions. The paper presents technical, operations, and programmatic issues that the writers consider fundamental to understanding the facts of life in this promising new design arena.     

Structural Design of a Lunar Habitat

A lunar base is an essential part of all the new space exploration programs because the Moon is the most logical first destination in space. Its hazardous environment will pose challenges for all engineering disciplines involved. A structural engineer’s approach is outlined in this paper, discussing possible materials and structural concepts for second-generation construction on the Moon. Several different concepts are evaluated and the most reasonable is chosen for a detailed design. During the design process, different solutions—for example, for the connections—were found. Although lunar construction is difficult, the proposed design offers a relatively simple structural frame for erection. A habitat on the Moon can be built with a reasonable factor of safety and existing technology. Even so, we recognize the very significant difficulties that await our return to the Moon.     

Atmospheric Pressure within Lunar Structure

Design and construction of a structure on the Moon requires addressing a host of issues not encountered on Earth. Since there is no atmosphere on the Moon, a lunar structure must contain an artificial atmosphere. One critical design issue is the magnitude of the pressure of this atmosphere. Much of the current literature on the design of lunar structures assumes a pressure of 101.3 kPa (14.7 psi), corresponding to that at sea level on Earth, which is an order of magnitude larger than any other loading on the structure. An assessment of the outcome of lowering the internal pressure for a lunar structure is presented that accounts for human physiology, plant growth, mechanical equipment for gas circulation, structural aspects, leak rate, decompression, flammability, combustion, and economic issues. Options for the magnitude and content of an internal atmosphere for a lunar structure are given. Results clearly show that there is a great savings if the pressure is lowered by an amount that does not greatly affect the inhabitants' physiology or safety.     

Behavior of Compacted Lunar Simulants Using New Vacuum Triaxial Device

Development and study of mechanical properties of engineering materials from locally available materials in space is a vital endeavor toward establishment of bases on the Moon and other planets. The objectives of this study are to create a lunar simulant locally from a basaltic rock, and to design and develop a new vacuum triaxial test device that can permit testing of compacted lunar simulant under cyclic loading with different levels of initial vacuum. Then, triaxial testing is performed in the device itself without removing the compacted specimen; this is achieved by a special mechanism installed within the device. Preliminary constrained compression and triaxial shear tests are performed to identify effects of initial confinements and vacuums. The results are used to define deformation and strength parameters. At this time, vacuum levels up to 10?4 are possible; subsequent research should involve higher vacuum levels, e.g., 10?14?torr as they occur on the Moon. The research can have significant potential toward development of methodology so as to develop compacted materials for various construction applications, and also toward stress‐strain‐strength testing of lunar simulants with different vacuum levels.     

Cable Structures and Lunar Environment

Lunar environmental characteristics, such as the lack of atmosphere, the smaller gravitational acceleration, and the weaker regolith, place different requirements on structural systems than the earth environment does. Some of these requirements are the internal pressurization of structures, emphasis on details, and careful design of foundation systems. Popular structural systems on the Earth environment, such as steel and reinforced concrete frames and trusses with traditional rigid connections may be inefficient for the lunar environment. Cable structures can be shown to meet the different and sometimes conflicting requirements of the lunar environment. The behavior of three different groups of cable structures in the lunar environment (differentiated by their small, medium and long spans) are studied in this paper. The structural systems can be designed to meet the main requirements in an efficient way. Foundation uplift problem is of particular interest, especially in the early lunar colonization stage. It was shown that with a slight modification in the cable system, the uplift problem can be solved, thus saving manpower and costs, while improving the overall system behavior.     

Electrostatic Cleaning System for Removing Lunar Dust Adhering to Space Suits

Removing lunar dust adhering to astronaut space suits is critically important for long-term lunar exploration. We are developing an automatic cleaning system that uses electrostatic force. It employs an alternating electrostatic field that forms a barrier on the surface of fabrics. In this study, we applied single-phase rectangular voltage to parallel wire electrodes stitched into the insulating fabric of space suits. By applying mechanical vibration and operating the system in a vacuum, we realized high performance: the cleaning rate exceeded 80%. Flicking out particles smaller than 10?μm in diameter that were trapped between fibers was difficult, but this system can perform preliminary space suit cleaning and save precious time for astronauts on the moon.     

Conceptual Design of Unpressurized Shelters on Lunar Surface

Three concepts for the shelters on the moon are presented here. It is envisaged that the first robots will land on the moon and start preparing sites for advanced bases and also for future human presence. These robots will encounter severe radiation and micrometeor hits when they are exposed to the lunar atmosphere. During the period of intense solar radiation these robots have to be temporarily sheltered, since shielding on the robots may not be adequate to protect the instruments. The construction of these shelters has to be performed with very little equipment support. This paper presents concepts and their feasibility analysis for the fabrication of shelters under such stringent constraints.     

Design and Construction of Shielded Lunar Outpost

The construction of an outpost on the Moon in which humans can live and work for periods exceeding six months will require special countermeasures to adapt to the hostile environment present at the lunar surface. Various inherent dangers such as meteoroids, galactic cosmic radiation, solar proton events, and large thermal extremes will drive the design configuration of the outpost. Other considerations such as lunar soil mechanics, equipment performance, mass delivery, risk, reliability, and tele‐operability act strongly as constraints that shape and control the design alternatives. Analysis of these fundamental relationships have resulted in lunar civil engineering guidelines, which are unique to this domain, and these in turn have pointed to research areas needing further attention. A preliminary design is presented for a lunar outpost shelter. Additionally, the design methodology is explored, and early enabling technologies are identified to facilitate an understanding of lunar shelter designs from an integrated system standpoint.     

Top-Level Considerations for Planning Lunar/Planetary Habitat Structures

This paper highlights important considerations to guide overall planning and element design of lunar/planetary surface habitat structures. Driving influences include stringent launch/landing payload limitations; high costs of human time for surface deployment and operational readiness; influences of the harsh environment on structures, devices and crews; and a paucity of equipment and human and consumable resources that necessitates extreme economies. General habitat concept options are proposed along with desired attributes for comparative assessments of figure of merit (FOM) rankings. Eight broad FOM categories are applied as a basis for top-level option evaluations: (1)?launch optimization features, (2)?landing optimization features, (3)?habitat capacity and functionality, (4)?environmental factors and features, (5)?deployment and operational readiness, (6)?reliability and maintainability, (7)?commonality with other surface systems, and (8)?pathways and potentials for growth. Much of the content of this paper draws on investigations conducted by the Sasakawa International Center for Space Architecture (SICSA) in support of separate National Aeronautics and Space Administration (NASA) contracts awarded to teams headed by Boeing and ILC-Dover for a “Minimum Functionality Habitation Systems Concept Study.” Comprehensive team study results were presented to NASA in February 2009 and have been publicly released to all interested parties.     

Multiterrain Earth Landing Systems Applicable for Manned Space Capsules

A key element of the President’s Vision for Space Exploration is the development of a new space transportation system to replace Shuttle that will enable manned exploration of the moon, Mars, and beyond. The National Aeronautics and Space Administration has created the Constellation Program to develop this architecture, which includes the Ares launch vehicle and Orion manned spacecraft. The Orion spacecraft must carry six astronauts and its primary structure should be reusable, if practical. These requirements led the Constellation Program to consider a baseline land landing on return to earth. To assess the landing system options for Orion, a review of current operational parachute landing systems such as those used for the F-111 escape module and the Soyuz is performed. In particular, landing systems with airbags and retrorockets that would enable reusability of the Orion capsule are investigated. In addition, Apollo tests and analyses conducted in the 1960s for both water and land landings are reviewed. Finally, test data and dynamic finite-element simulations are presented to understand land landings for the Orion spacecraft.