No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
NASA RASC-AL 1st Place Winning Paper: Discovery and Endeavour - Ceres Interplanetary Pathway for Human Exploration and Research (DECIPHER)
This article explores the feasibility of crewed missions to Mars and Ceres, addressing key challenges such as defining vehicle boundaries within Earth's domain and ensuring radiation protection during interplanetary transit. Given the importance of preserving life in space and safeguarding the health of astronauts, the study delves into mission-specific details and innovative concepts, including NASA's Artemis program and solar-electric propulsion. It highlights the interplay between seemingly isolated design decisions and overarching mission goals, revealing critical trade-offs between mission duration, crew density, and resource utilization. Drawing from the Artemis program and advanced testing methodologies, the feasibility of joint operations between Mars and Ceres is evaluated, with a focus on mission duration, crew safety, and in-situ resource utilization (ISRU). The study concludes with recommendations for a flexible and adaptable design model for future missions.
View Video Presentation: https://doi.org/10.2514/6.2022-2587.vid The concept of a crewed expedition to Ceres seems feasible within the next few decades as modern space explorers have been planning to send humans through the 2040s. The scientific drive resulted in the conception of various sorts of human mission architectures with competent scientific objectives at the end of 2021, where our discrete roundtrip exploration architecture holds significance. Therefore, to show the feasibility of our architecture, we present possible trajectories and communication approaches required for the mission. The analyses include an approximation of transit and surface stay durations, delta-velocity requirement, and mission windows for launch and crew return. In addition, we present two communication approaches along with their uplink and downlink data transfer rates, bandwidth, and other significant parameters.
View Video Presentation: https://doi.org/10.2514/6.2022-2004.vid The Lunar surface stands as a proximal destination for numerous space exploratory missions in terms of the robotic and manned expedition. Since the Apollo mission, we have had a prolonged technological gap in returning humans to the Moon. But, NASA has been progressing its ARTEMIS mission to land the next generation astronauts through early 2025, where the astronauts may encounter different sorts of habitability challenges from both lunar and space environments. Therefore, to address this challenge in terms of thermal stability and habitation systems, we present a Lunar Underground Habitation System (LUHS) concept for affording a sustainable environment for lunar astronauts against the complex environment and longer nights. Further, the design ensures additional protection from being exposed to surface radiations and micrometeoroid impacts. In this paper, we discuss the architecture overview, technical aspects, working mechanism, and mission scenarios along with the applicability for future crewed lunar exploratory missions.
View Video Presentation: https://doi.org/10.2514/6.2022-0720.vid The prospect for long-term human missions and permanent settlement on Mars explicitly requires some perfect habitation systems for sustainable presence. So, this paper presents an overview of the Mars Underground Habitation System (MUHS) concept. The MUHS affords three planetary habitats and two life support systems to enable the Martian crew independent against periodic cargo re-supply from the Earth. In addition, the habitation systems may remain favorable against surface hazards, radiations, meteoroid impact, persistent weather, and atmospheric fluctuations. The prime intent behind this habitat proposal is to sustain the thermal stability against the Martian environment after sunset.
Launched onboard the BepiColombo Mercury Planetary Orbiter (MPO) in October 2018, the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) is on its way to planet Mercury. MERTIS consists of a push-broom IR-spectrometer (TIS) and a radiometer (TIR), which operate in the wavelength regions of 7-14 μm and 7-40 μm, respectively. This wavelength region is characterized by several diagnostic spectral signatures: the Christiansen feature (CF), Reststrahlen bands (RB), and the Transparency feature (TF), which will allow us to identify and map rock-forming silicates, sulfides as well as other minerals. Thus, the instrument is particularly well-suited to study the mineralogy and composition of the hermean surface at a spatial resolution of about 500 m globally and better than 500 m for approximately 5-10% of the surface. The instrument is fully functional onboard the BepiColombo spacecraft and exceeds all requirements (e.g., mass, power, performance). To prepare for the science phase at Mercury, the team developed an innovative operations plan to maximize the scientific output while at the same time saving spacecraft resources (e.g., data downlink). The upcoming fly-bys will be excellent opportunities to further test and adapt our software and operational procedures. In summary, the team is undertaking action at multiple levels, including performing a comprehensive suite of spectroscopic measurements in our laboratories on relevant analog materials, performing extensive spectral modeling, examining space weathering effects, and modeling the thermal behavior of the hermean surface.
Hydrothermal processes in impact environments on water-rich bodies such as Mars and Earth are relevant to the origins of life. Dawn mapping of dwarf planet (1) Ceres has identified similar deposits within Occator crater. Here we show using Dawn high-resolution stereo imaging and topography that Ceres’ unique composition has resulted in widespread mantling by solidified water- and salt-rich mud-like impact melts with scattered endogenic pits, troughs, and bright mounds indicative of outgassing of volatiles and periglacial-style activity during solidification. These features are distinct from and less extensive than on Mars, indicating that Occator melts may be less gas-rich or volatiles partially inhibited from reaching the surface. Bright salts at Vinalia Faculae form thin surficial precipitates sourced from hydrothermal brine effusion at many individual sites, coalescing in several larger centers, but their ages are statistically indistinguishable from floor materials, allowing for but not requiring migration of brines from deep crustal source(s). Dawn mission’s second extended phase provided high resolution observations of Occator crater of the dwarf planet Ceres. Here, the authors show stereo imaging and topographic maps of this crater revealing the influence of crustal composition on impact related melt and hydrothermal processes, and compare features to those on Mars, Earth and the Moon.
Spacewalks, or extra-vehicular activities (EVAs), are a critical component of human space exploration for science activities and habitat construction and maintenance. For NASA's proposed lunar Gateway system, an airlock module is required for vehicle maintenance, repair, and exploration. Traditional airlock structures are fully metallic, with two chambers, known as an equipment lock and a crew lock. The larger volume, called the equipment lock, serves as the storage, logistics and electronics area, while the smaller volume, called the crew lock, serves as the volume to transition from the vacuum of space to the pressurized cabin. A traditional metallic structure design offers mass efficiency for these elements, but cannot offer volume efficiency. The potential to use an inflatable fabric pressure shell supplemented by a metallic support structure allows for efficiency in both mass and volume. Inflatable structures are being used for human habitable space modules, starting with the Bigelow Expandable Activities Module on the International Space Station. They are high-strength fabric-based structures that are compactly stowed for launch and then, once in space, they are expanded and rigidized with internal pressure. They provide significant launch volume savings over metallic structures. For Gateway, a hybrid airlock design is proposed with both metallic and inflatable structural elements, taking advantage of each material's capabilities. A metallic equipment lock serves as both a docking node and provides pressurized volume for pre-EVA activities including pre-breathe and suit donning/doffing. A rigid equipment lock offers stowage space during launch for integrated hardware and suits. Adding an integrated inflatable crew lock provides the volume required for EVAs with minimal use of launch volume. Using dual inflatable crew locks provides redundancy and the capability to move large pieces of equipment into and out of the vehicle for repair and maintenance. The inflatable crew lock is deflated and packaged in the launch shroud and expanded after installation on the Gateway. This packing capability allows additional volume to be added to the equipment lock and fully utilize the capability of the launch vehicle. This report outlines the work completed to design, analyze, and test the systems of a microgravity airlock with inflatable crew locks. In detail, it includes launch vehicles, structural sizing of the metallic equipment lock, the fabric layers of the inflatable crew lock, the internal structure of the crew lock, the space suit interface elements, the crew restraint system, the hatches and pass-throughs, the material and thermal elements, and the crew operations for the usage of the system. This paper is meant to offer a reference design for a hybrid microgravity airlock design for deep space human exploration.
Nuclear thermal propulsion (NTP) systems have been studied in both the USA and the former Soviet Union since the 1950s for use in space science and exploration missions. NTP uses nuclear fission to heat hydrogen to very high temperatures in a short amount of time so that the hydrogen can provide thrust as it accelerates through an engine nozzle. Benefits of NTP systems compared to conventional chemical and solar electric powered propulsion systems include higher fuel efficiency, greater mission range, shorter transit times, and a greater ability to abort missions and return to Earth in the event of system failure. As a result of these benefits, the US National Aeronautics and Space Administration (NASA) is evaluating NTP for use in crewed missions to Mars, and plans for a possible mid-2020s flight demonstration of a NTP engine are under development. The extremely harsh conditions that NTP systems must operate in present a number of significant engine design and operational challenges. The objective of this chapter will be to describe the history of NTP material development, describe current NTP material fabrication and design practices, and discuss possible future advances in space propulsion material technologies.
The future of human exploration missions to Mars is dependent on solutions to the technology challenges being worked on by the National Aeronautics and Space Administration (NASA) and industry. One of the key architecture technologies involves propulsion that can transport the human crew from Earth orbit to other planets and back to Earth with the lowest risk to crew and the mission. Nuclear thermal propulsion (NTP) is a proven technology that provides the performance required to enable benefits in greater payload mass, shorter transit time, wider launch windows, and rapid mission aborts due to its high specific impulse and high thrust.
Aerojet Rocketdyne (AR) has stayed engaged for several decades in working NTP engine systems and has worked with NASA recently to perform an extensive study on using low-enriched uranium NTP engine systems for a Mars campaign involving crewed missions from the 2030s through the 2050s. Aerojet Rocketdyne has used a consistent set of NASA ground rules and they are constantly updated as NASA adjusts its sights on obtaining a path to Mars, now via the Lunar Operations Platform-Gateway. Building on NASA’s work, AR has assessed NTP as the high-thrust propulsion option to transport the crew by looking at how it can provide more mission capability than chemical or other propulsion systems.
The impacts of the NTP engine system on the Mars transfer vehicle configuration have been assessed via several trade studies since 2016, including thrust size, number of engine systems, liquid hydrogen stage size, reaction control system sizing, propellant losses, NASA Space Launch System (SLS) payload fairing size impact, and aggregation orbit.
An AR study activity in 2018 included examining NTP stages derived from Mars crew mission elements to deliver extremely large cargo via multiple launches or directly off the NASA SLS. This paper provides an update on the results of the ongoing engine system and mission trade studies.
One of the key goals of the Rosetta mission was to understand how, where and when comets formed in our solar system. There are two major hypotheses for the origin of comets, both pre-Rosetta: (1) hierarchical accretion of dust and ice grains in the Solar Nebula and (2) the growth of pebbles, which are then brought together by streaming instabilities in the Solar Nebula to form larger bodies. Rosetta provided a wealth of new information on comet nuclei and confirmed many past ideas on comets, e.g., high volatile content, lack of aqueous alteration of grains, and the low bulk density of the nucleus. Rosetta also provided new data on the nature of cometary activity, the active geology on the nucleus surface and the interior structure and bulk density of the nucleus. Supporters of the above-mentioned origin hypotheses each find confirmation of their ideas in the Rosetta results. But the question of which hypothesis is preferred, or if there are other, better hypotheses that could be invoked, could not be answered. Theoretical studies suggest that comet nuclei were collisionally processed in the Primordial Disk though it is not clear that the nuclei we see today display the effects of that process. Both theoretical and observational studies suggest that the major end-states for cometary nuclei are dynamical ejection, random disruption and disintegration, and/or evolution of nuclei to inactive, asteroidal-appearing objects. Rosetta has provided us with many new insights that will help to guide future cometary missions, observations, experiments and theoretical investigations that will lead to answers to the fundamental questions with regard to cometary origin.
Aims. We model thermal evolution and water-rock differentiation of small ice-rock objects that accreted at different heliocentric distances, while also considering migration into the asteroid belt for Ceres. We investigate how water-rock separation and various cooling processes influence Ceres’ structure and its thermal conditions at present. We also draw conclusions about the presence of liquids and the possibility of cryovolcanism.
Methods. We calculated energy balance in bodies heated by radioactive decay and compaction-driven water-rock separation in a three-component dust-water/ice-empty pores mixture, while also taking into consideration second-order processes, such as accretional heating, hydrothermal circulation, and ocean or ice convection. Calculations were performed for varying accretion duration, final size, surface temperature, and dust/ice ratio to survey the range of possible internal states for precursors of Ceres. Subsequently, the evolution of Ceres was considered in five sets of simulated models, covering different accretion and evolution orbits and dust/ice ratios.
Results. We find that Ceres’ precursors in the inner solar system could have been both wet and dry, while in the Kuiper belt, they retain the bulk of their water content. For plausible accretion scenarios, a thick primordial crust may be retained over several Gyr, following a slow differentiation within a few hundreds of Myr, assuming an absence of destabilizing impacts. The resulting thermal conditions at present allow for various salt solutions at depths of ≲10 km. The warmest present subsurface is obtained for an accretion in the Kuiper belt and migration to the present orbit.
Conclusions. Our results indicate that Ceres’ material could have been aqueously altered on small precursors. The modeled structure of Ceres suggests that a liquid layer could still be present between the crust and the core, which is consistent with Dawn observations and, thus, suggests accretion in the Kuiper belt. While the crust stability calculations indicate crust retention, the convection analysis and interior evolution imply that the crust could still be evolving.
Future human exploration missions to Mars are being studied by NASA and industry.
Several approaches to the Mars mission are being examined that use various
types of propulsion for the different phases of the mission. The choice and
implementation of certain propulsion systems can significantly impact mission
performance in terms of trip time, spacecraft mass, and especially mission abort
capability. Understanding the trajectory requirements relative to the round-trip
Earth to Mars mission opportunities in the 2030’s and beyond is important in
order to determine the impact of trajectory abort capability. Additionally, some
propulsion choices for the crew vehicle can enable mission abort trajectories
while others will most likely provide less flexibility and increase mission risk.
This paper focuses on recent modeling of Earth to Mars abort scenarios for human
missions to determine the capability to provide fast returns to Earth. The
modeling assumed that the abort would occur after the Mars crew vehicle has
been injected along the path to Mars (i.e., after the Trans Mars Injection (TMI)
burn). These aborts have been defined as well as the timing of fly-by aborts to
quickly return crew to Earth.
These abort trajectory studies are based on missions NASA defined during the
Evolvable Mars Campaign (EMC) with crew going to Mars in 2033, 2039, 2043
and 2048. Detailed trajectory analysis was performed with the NASA Copernicus
program for the several crew missions that were in the EMC as well as other
new missions being considered using finite-burn low thrust electric propulsion.
The goal was to determine how the heliocentric trajectory elements change and
the “abort trajectory” impulse requirements.
Abort scenarios that were studied included fast returns N-days after TMI as well
as fly-by aborts and multiple revolution cases, using all available propellants
(e.g., main propulsion system and reaction control system (RCS)) to provide the
required abort velocity change. Trajectories were investigated for impulsive maneuvers
and for finite burn cases and the abort timelines for each are examined
and compared.
This paper and presentation will focus on the Copernicus trajectory analysis results
that were performed to determine the abort trajectories that altered the primary
mission to return to Earth as soon as possible.
The science and origins of asteroids is deemed high priority in the Planetary Science Decadal Survey. Major scientific goals for the study of planetesimals are to decipher geological processes in SSSBs not determinable from investigation via in situ experimentation, and to understand how planetesimals contribute to the formation of planets. Ground based observations are not sufficient to examine SSSBs, as they are only able to measure what is on the surface of the body; however, in situ analysis allows for further, close up investigation as to the surface characteristics and the inner composure of the body. To this end, the Asteroid Mobile Imager and Geologic Observer (AMIGO) an autonomous semi-inflatable robot will operate in a swarm to efficiently characterize the surface of an asteroid. The stowed package is 10×10×10 cm (equivalent to a 1U CubeSat) that deploys an inflatable sphere of ~1m in diameter. Three mobility modes are identified and designed: ballistic hopping, rotation during hops, and up-righting maneuvers. Ballistic hops provide the AMIGO robot the ability to explore a larger portion of the asteroid's surface to sample a larger area than a stationary lander. Rotation during the hop entails attitude control of the robot, utilizing propulsion and reaction wheel actuation. In the event of the robot tipping or not landing upright, a combination of thrusters and reaction wheels will correct the ro-bot's attitude. The AMIGO propulsion system utilizes sublimate-based micro-electro-mechanical systems (MEMS) technology as a means of lightweight, low-thrust ballistic hopping and coarse attitude control. Each deployed AMIGO will hop across the surface of the asteroid multiple times. Individual actuation of each microvalve on the MEMS chip provides control torque for rough attitude control with only slight alteration to the hop path en-route to its destination. For optimal use of instrumentation, namely the top mounted stereo cameras utilized in local surface mapping and navigation planning, the robot must remain as upright as possible during data acquisition. Should AMIGO land in an improper orientation, thrusters and reaction wheels will attempt to correct the positioning. Several inflatable structures will be evaluated including a soft inflatable and an inflatable that ri-gidizes under UV light. The inflatable will be compared under operational scenarios to determine if it produces disturbances torque and an unsteady view for the stereo cameras. Future work is focused on raising the TRL by real world testing system performance and utilizing hardware-in-the-loop simulation models. The thruster assembly can be evaluated on a test stand mounted inside a vacuum chamber. To simulate milli-gravity, the entire robot will be analyzed in either parabolic flight tests or in buoyancy chambers. A combination of experimentation will validate simulations and provide insight in areas to improve on the design and control algorithms for milli-gravity asteroid surface environments.
Dwarf planet Ceres, the largest object in the Main Asteroid Belt, has a surface that exhibits a range of crater densities for a crater diameter range of 5–300 km. In all areas the shape of the craters’ size-frequency distribution is very similar to those of the most ancient heavily cratered surfaces on the terrestrial planets. The most heavily cratered terrain on Ceres covers ∼15% of its surface and has a crater density similar to the highest crater density on <1% of the lunar highlands. This region of higher crater density on Ceres probably records the high impact rate at early times and indicates that the other 85% of Ceres was partly resurfaced after the Late Heavy Bombardment (LHB) at ∼4 Ga. The Ceres cratering record strongly indicates that the period of Late Heavy Bombardment originated from an impactor population whose size-frequency distribution resembles that of the Main Belt Asteroids.
The otherwise homogeneous surface of Ceres is dotted with hundreds of anomalously bright, predominantly carbonate-bearing areas, termed “faculae,” with Bond albedos ranging from ∼0.02 to >0.5. Here, we classify and map faculae globally to characterize their geological setting, assess potential mechanisms for their formation and destruction, and gain insight into the processes affecting the Ceres surface and near-surface. Faculae were found to occur in four distinct geological settings, associated predominantly with impact craters: (1) crater pits, peaks, or floor fractures (floor faculae), (2) crater rims or walls (rim/wall faculae), (3) bright ejecta blankets, and (4) the mountain Ahuna Mons. Floor faculae were identified in eight large, deep, and geologically young (asteroid-derived model (ADM) ages of <420 ± 60 Ma) craters: Occator, Haulani, Dantu, Ikapati, Urvara, Gaue, Ernutet, and Azacca. The geometry and geomorphic features of the eight craters with floor faculae are consistent with facula formation via impact-induced heating and upwelling of volatile-rich materials, upwelling/excavation of heterogeneously distributed subsurface brines or their precipitation products, or a combination of both processes. Rim/wall faculae and bright ejecta occur in and around hundreds of relatively young craters of all sizes, and the geometry of exposures is consistent with facula formation via the excavation of subsurface bright material, possibly from floor faculae that were previously emplaced and buried. A negative correlation between rim/wall facula albedo and crater age indicates that faculae darken over time. Models using the Ceres crater production function suggest initial production or exposure of faculae by large impacts, subsequent dissemination of facula materials to form additional small faculae, and then burial by impact-induced lateral mixing, which destroys faculae over timescales of less than 1.25 Gyr. Cumulatively, these models and the observation of faculae limited to geologically young craters indicate relatively modern formation or exposure of faculae, indicating that Ceres’ surface remains active and that the near surface may support brines in the present day.
For the usage of liquid oxygen as a propellant in pressure-fed rocket engine systems, the propellant needs to be pressurized, for example by using an inert gas such as helium. This paper describes a practical investigation with measurement results on the pressurization and expulsion of liquid nitrogen from a 30 L pressure vessel at 30 bar. The amount of helium needed and the effect of the injection method on this amount is investigated by numerical simulations that are validated using experimental test results. The collapse factor for the system is determined. It is concluded that axial injection of the gas is more advantageous than the commonly used radial injection.
A potential spacecraft design is based around the JPL Micro Surveyor that has a mass of 75 kg (wet) including two science instruments that access >10 cm beneath the surface. The spacecraft is estimated to have a delta-V of 5 km/s sufficient for performing a tour of 2 small NEOs. After surveying the first asteroid, the spacecraft is directed into a pre-cisely guided free-fall, impacting slowly (v~10 cm/s) under milligravity (ag~0.1 mm/s2) into a selected patch of regolith. The bus comes to rest vertically on top of the Science Instruments Module which is deployed at the end of a ~3 m rigid extensible truss. The base of the SIM has two penetrators that are pushed into the subsurface to enable science that has never been done at an asteroid: subsurface volatile and organics determination and seismology.
Future space missions require bio-regenerative life-support systems. Eating fresh food is not only a fundamental requirement for survival but also influences the psychological wellbeing of astronauts operating on long duration space missions. Therefore the selection of plants to be grown in space is an important issue. Part of the EDEN ISS project entails the development and application of a methodology to select suitable plants for cultivation onboard the ISS and the Neumayer III Antarctic station, a space analogue site. A methodology was developed taking physical and physiological constraints, and human well-being (quality) aspects into account. It includes a framework for the selection process, a list of relevant criteria based on plant characteristics, engineering constraints and human nutrition and psychology. It entails a scoring system to assess and weigh these criteria for each crop, in order to rank the chosen crops. Human quality aspects, such as taste, texture and appearance were related to the well-being of astronauts. Yield aspects combined crop yield and growth efficiency in time and space, while production aspects concentrated on physical constraints of the planned growth modules and the technical aspects of cultivation. The
methodological framework used for the selection of plants was based on several approaches. Physical and physiological constraints determine whether or not the crop can be cultivated in space (and/or in Antarctica) and all other parameters are prioritized according to human quality aspects, yield or production aspects that were ranked according to pre-selected weighing factors. This yielded a ranking of the crops to be grown in a controlled ecological life support system. A description of the methodology and its results with a choice of crops related to the aims of the EDEN ISS project are given and will be discussed.
The dual-wall, Whipple shield is the shield of choice for lightweight, long-duration flight. The shield uses an initial sacrificial wall to initiate fragmentation and melt an impacting threat that expands over a void before hitting a subsequent shield wall of a critical component. The key parameters to this type of shield are the rear wall and its mass which stops the debris, as well as the minimum shock wave strength generated by the threat particle impact of the sacrificial wall and the amount of room that is available for expansion. Ensuring the shock wave strength is sufficiently high to achieve large scale fragmentation/melt of the threat particle enables the expansion of the threat and reduces the momentum flux of the debris on the rear wall. Three key factors in the shock wave strength achieved are the thickness of the sacrificial wall relative to the characteristic dimension of the impacting particle, the density and material cohesion contrast of the sacrificial wall relative to the threat particle and the impact speed. The mass of the rear wall and the sacrificial wall are desirable to minimize for launch costs making it important to have an understanding of the effects of density contrast and impact speed. An analytic model is developed here, to describe the influence of these three key factors. In addition this paper develops a description of a fourth key parameter related to fragmentation and its role in establishing the onset of projectile expansion.© 2015 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Hypervelocity Impact Society.
This paper presents a conceptual space vehicle architecture that could enable human interplanetary travel in progressively more ambitious steps. The main flight vehicle resembles the spaceship Discovery depicted in the novel and film "2001 - A Space Odyssey." Like its namesake, this spaceship could one day transport a human expedition to explore the moons of Jupiter. This spaceship Discovery is a real engineering design that could be implemented using near state-of-the-art technologies, including advanced, bi-modal nuclear thermal rocket (NTR) engines for main propulsion and electrical power. Spaceship Discovery is a modular design: Requirements, features, mass properties, and configuration layouts are presented for each module. Designs for four types of landers are presented, including requirements, mission profiles, performance data, and configuration layouts: (1) A reentry module to return the crew to Earth at the conclusion of a mission or after aborts, (2) a crew exploration lander for Ganymede, Callisto, or Earth's Moon, that utilizes only vacuum propulsive braking, and (3 and 4) Mars exploration crew and cargo landers that utilize both aerodynamic and propulsive braking. Design Reference Missions (DRMs) to the following destinations were used to develop design requirements: (1) Earth's Moon, (2 and 3) Mars, (4) Ceres, and (5, 6 and 7) Jupiter's moons Callisto and Ganymede. The Spaceship Discovery design includes dual, strap-on boosters that enable high-energy Mars and Jupiter DRMs. Mission profiles, performance data, mass properties, and configuration layouts are presented for each DRM, and then compared side-to-side. Launch requirements, mass properties, and module launch configurations are presented. Spaceship Discovery offers many advantages for human exploration of the Solar System: (1) Nuclear propulsion enables propulsive capture and escape maneuvers at Earth and target planets, eliminating the need for risky aero-capture maneuvers. (2) Strap-on NTR boosters provide robust propulsive energy, enabling Mars missions with short transit times and missions to Jupiter. (3) A backup abort propulsion system enables crew aborts at multiple points in the mission. (4) Clustered NTR engines provide "engine out" redundancy. (5) The design provides efficient implementation of omnidirectional GCR shielding using main propellant LH 2 and life support/cooling H2O. (6) The design provides artificial gravity to mitigate crew physiological problems on long-duration missions. (7) The design is modular and can be launched using proposed upgrades to EELVs. (8) High value parts of the vehicle are reusable for Lunar and Mars missions. (9) The LM1, LM2 and LM3 landers are an integral part of the Spaceship Discovery architecture but could be used in other exploration architectures. (10) The design is flexible, with inherent growth capability, and will enable an evolutionary progression to more ambitious missions "to the Moon, Mars, and beyond".
There was a lot of experience gained in the rendezvous of different vehicles in the LEO during the years of human space exploration. In the framework of the Apollo program when the astronauts landed on the surface of the Moon, the docking of the Lunar Module launched from the Moon׳s surface to the Apollo Command Module was successfully implemented in the near-Moon orbit. Presently many space agencies are considering a return to the Moon. It is necessary to solve the new task of docking the vehicle launched from the Earth to the long-term near-Moon orbital station taking into account specific constraints. Based on the ISS experience the author proposes a number of ballistic rendezvous strategies that provide for docking to the near-Moon orbital station with minimum propellant consumption. The trade-off analysis of the given rendezvous strategies is presented.
A systematic design-oriented, five-step approach to material selection is described: 1) establishing design requirements, 2) material screening, 3) ranking, 4) researching specific candidates and 5) applying specific cultural constraints to the selection process. At the core of this approach is the definition performance indices (i.e., particular combinations of material properties that embody the performance of a given component) in conjunction with material property charts. These material selection charts, which plot one property against another, are introduced and shown to provide a powerful graphical environment wherein one can apply and analyze quantitative selection criteria, such as those captured in performance indices, and make trade-offs between conflicting objectives. Finding a material with a high value of these indices maximizes the performance of the component. Two specific examples pertaining to aerospace (engine blades and pressure vessels) are examined, both at room temperature and elevated temperature (where time-dependent effects are important) to demonstrate the methodology. The discussion then turns to engineered/hybrid materials and how these can be effectively tailored to fill in holes in the material property space, so as to enable innovation and increases in performance as compared to monolithic materials. Finally, a brief discussion is presented on managing the data needed for materials selection, including collection, analysis, deployment, and maintenance issues.
SPENVIS is an ESA operational software developed and maintained at
BIRA-IASB since 1996. It provides standardized access to most of the
recent models of the hazardous space environment, through a
user-friendly Web interface (http://www.spenvis.oma.be/). The system
allows spacecraft engineers to perform a rapid analysis of environmental
problems related to natural radiation belts, solar energetic particles,
cosmic rays, plasmas, gases, magnetic fields and micro-particles.
Various reporting and graphical utilities and extensive help facilities
are included to allow engineers with relatively little familiarity to
produce reliable results. SPENVIS also contains an active, integrated
version of the ECSS Space Environment Standard and access to in-flight
data on the space environment. Although SPENVIS in the first place is
designed to help spacecraft engineers, it is also used by technical
universities in their educational programs. At present more than 4000
users are registered. With SPENVIS, one can generate a spacecraft
trajectory or a coordinate grid and then calculate: geomagnetic
coordinates; trapped proton and electron fluxes; solar proton fluences;
cosmic ray fluxes; radiation doses (ionising and non-ionising) for
simple geometries; a sectoring analysis for dose calculations in more
complex geometries; damage equivalent fluences for Si, GaAs and
multi-junction solar cells; Geant4 Monte Carlo analysis for doses and
pulse height rates in planar and spherical shields; ion LET and flux
spectra and single event upset rates; trapped proton flux anisotropy;
atmospheric and ionospheric densities and temperatures; atomic oxygen
erosion depths; surface and internal charging characteristics; solar
array current collections and power losses; wall damage. The new version
of SPENVIS (to be released in January 2009) also allows mission analysis
for Mars and Jupiter.
The authors present several lunar landing trajectory strategies, including those used on the Apollo, Ranger and Surveyor programs; some planned for a commercial lunar mission; and some new techniques based on artificial intelligence. The paper describes the complete strategies for trajectory design from Earth-launch to Lunar landing. This includes a comparison between using Earth and Lunar orbit strategies versus direct ascent and direct descent methods. Closed-loop landing controls for the descent to the Lunar surface are also discussed. Each of these cases is modeled with a high-precision numerical integrator using full force models. The authors document and compare the maneuvers, fuel use, and other parameters affecting the transfer and landing trajectories. In addition, the authors discuss methods to expand the launch window. The fully integrated end-to-end trajectory ephemerides are available from the authors in electronic ASCII text by request. Background
The goal of Project GAUSS is to return samples from the dwarf planet Ceres. Ceres is the most accessible
ocean world candidate and the largest reservoir of water in the inner solar system. It shows active
cryovolcanism and hydrothermal activities in recent history that resulted in minerals not found in any
other planets to date except for Earth’s upper crust. The possible occurrence of recent subsurface ocean on
Ceres and the complex geochemistry suggest possible past habitability and even the potential for ongoing
habitability. Aiming to answer a broad spectrum of questions about the origin and evolution of Ceres and
its potential habitability, GAUSS will return samples from this possible ocean world for the first time. The
project will address the following top-level scientific questions:
● What is the origin of Ceres and the origin and transfer of water and other volatiles in the inner
solar system?
● What are the physical properties and internal structure of Ceres? What do they tell us about the
evolutionary and aqueous alteration history of icy dwarf planets?
● What are the astrobiological implications of Ceres? Was it habitable in the past and is it still
today?
● What are the mineralogical connections between Ceres and our current collections of primitive
meteorites?
GAUSS will first perform a high-resolution global remote sensing investigation, characterizing the
geophysical and geochemical properties of Ceres. Candidate sampling sites will then be identified, and
observation campaigns will be run for an in-depth assessment of the candidate sites. Once the sampling
site is selected, a lander will be deployed on the surface to collect samples and return them to Earth in
cryogenic conditions that preserves the volatile and organic composition as well as the original physical
status as much as possible.
We present a light‐weight body‐terrain clearance evaluation algorithm for the automated path planning of NASA's Mars 2020 rover. Extraterrestrial path planning is challenging due to the combination of terrain roughness and severe limitation in computational resources. Path planning on cluttered and/or uneven terrains requires repeated safety checks on all the candidate paths at a small interval. Predicting the future rover state requires simulating the vehicle settling on the terrain, which involves an inverse‐kinematics problem with iterative nonlinear optimization under geometric constraints. However, such expensive computation is intractable for slow spacecraft computers, such as RAD750, which is used by the Curiosity Mars rover and upcoming Mars 2020 rover. We propose the approximate clearance evaluation (ACE) algorithm, which obtains conservative bounds on vehicle clearance, attitude, and suspension angles without iterative computation. It obtains those bounds by estimating the lowest and highest heights that each wheel may reach given the underlying terrain, and calculating the worst‐case vehicle configuration associated with those extreme wheel heights. The bounds are guaranteed to be conservative, hence ensuring vehicle safety during autonomous navigation. ACE is planned to be used as part of the new onboard path planner of the Mars 2020 rover. This paper describes the algorithm in detail and validates our claim of conservatism and fast computation through experiments.
Space launch systems and space travel require materials that push the requirements envelope. Sophisticated aluminum-lithium alloys, such as Airware 2195 and 2050, permit a stronger yet significantly lighter architecture-allowing more payload, higher orbit, or both. Alloy 2050 in either a highly formable and ductile T34 or T84 temper is being readily adopted for both cryogenic tanks and crew modules. The alloy has also been baselined for the second (upper) stages of two major space launch programs. Trade studies indicate that core stage is also a suitable candidate for conversion to 2050 from legacy 2219. Numerous other noncryogenic applications, such as intertanks, adapters, and engine sections are currently being studied for conversion. In some cases, hybrid designs with both 2195 and 2050 applications are being implemented on the same launch vehicle. In these hybrid designs, the upper stages that require lighter gauge plate favor higher strength 2195, while components of the core stage call for 3.000-4.000 inch thick 2050 plate. Similarly, a significant amount of 2050 plate with complex shapes has been successfully tested and prototyped for the Orion Crew Module. Througn its ongoing effort to provide cutting edge materials at its Ravenswood, WV, and Issoire, France facilities and C-TEC Research and Development Center near Gernoble, France, Constellium has an opportunity to play a very important role in human exploration of our planetary system.
NASA's interest in human exploration of Mars has driven it to invest in 20 K cryocooler technology to achieve zero boil-off of liquid hydrogen and 90 K cryocooler technology to achieve zero boil-off liquid oxygen or liquid methane as well as to liquefy oxygen or methane that is produced on the surface of Mars. These investments have demonstrated efficiency progress, mass reductions, and integration insights. A history of the application of cryocooler technology to zero boil-off propellant storage is presented. A trade space on distributed cooling is shown, along with the progress of reverse turbo-Brayton cycle cryocoolers, where the specific power and specific mass have dropped, decreasing the mass and power of these cryocoolers. Additionally, the cryocooler technology advancements of recuperators and compressors are described. Finally, NASA's development ideas with respect to zero boil-off technology are discussed.
Human exploration of the solar system brings a host of environmental and engineering challenges. Among the most important factors in crew health and human performance is the preservation of mental health. The mental well-being of astronaut crews is a significant issue affecting the success of long-duration space missions, such as habitation on or around the Moon, Mars exploration, and eventual colonization of the solar system. If mental health is not properly addressed, these missions will be at risk. Upkeep of mental health will be especially difficult on long duration missions because many of the support systems available to crews on shorter missions will not be available. In this paper, we examine the use of immersive virtual reality (VR) simulations to maintain healthy mental states in astronaut crews who are removed from the essential comforts typically associated with terrestrial life. Various methods of simulations and their administration are analyzed in the context of current research and knowledge in the fields of psychology, medicine, and space sciences, with a specific focus on the environment faced by astronauts on long-term missions. The results of this investigation show that virtual reality should be considered a plausible measure in preventing mental state deterioration in astronauts, though more work is needed to provide a comprehensive view of the effectiveness and administration of VR methods.
Occator Crater on dwarf planet Ceres hosts the so-called faculae, several areas with material 5 to 10 times the albedo of the average Ceres surface: Cerealia Facula, the brightest and largest, and several smaller faculae, Vinalia Faculae, located on the crater floor. The mineralogy of the whole crater is analyzed in this work. Spectral analysis is performed from data of the VIR instrument on board the Dawn spacecraft. We analyse spectral parameters of all main absorption bands, photometry, and continuum slope. Because most of the absorption features are located in a spectral range affected by thermal emission, we developed a procedure for thermal removal. Moreover, quantitative modeling of the measured spectra is performed with a radiative transfer model in order to retrieve abundance and grain size of the identified minerals. Unlike the average Ceres surface that contains a dark component, Mg-Ca-carbonate, Mg-phyllosilicates, and NH4-phyllosilicates, the faculae contain mainly Na-carbonate, Al-phyllosilicates, and NH4-chloride. The present work establishes unambiguously the presence of NH4-chloride thanks to the high-spatial resolution data. Vinalia and Cerealia Faculae show significant differences in the concentrations of these minerals, which have been analyzed. Moreover, heterogeneities are also found within Cerealia Facula that might reflect different deposition events of bright material. An interesting contrast in grain size is found between the center (10-60 μm) and the crater floor/peripheral part of the faculae (100-130 μm), pointing to different cooling time of the grains, respectively faster and slower, and thus to different times of emplacement. This implies the faculae formation is more recent than the crater impact event, consistent with other observations reported in this special issue. For some ejecta, we derived larger concentrations of minerals producing the absorption bands, and smaller grains with respect to the surrounding terrain. This may be related to heterogeneities in the material pre-existent to the impact event.
Vinalia and Cerealia Faculae are bright and salt-rich localized areas in Occator crater on Ceres. The predominance of the near-infrared signature of sodium carbonate on these surfaces suggests their original material was a brine. Here we analyze Dawn Framing Camera's images and characterize the surfaces as composed of a central structure, either a possible depression (Vinalia) or a central dome (Cerealia), and a discontinuous mantling. We consider three materials enabling the ascent and formation of the faculae: ice ascent with sublimation and carbonate particle lofting, pure gas emission entraining carbonate particles, and brine extrusion. We find that a mechanism explaining the entire range of morphologies, topographies, as well as the common composition of the deposits is brine fountaining. This process consists of briny liquid extrusion, followed by flash freezing of carbonate and ice particles, particle fallback, and sublimation. Subsequent increase in briny liquid viscosity leads to doming. Dawn observations did not detect currently active water plumes, indicating the frequency of such extrusions is longer than years.
Organic compounds detected on Ceres
Water and organic molecules were delivered to the early Earth by the impacts of comets and asteroids. De Sanctis et al. examined infrared spectra taken by the Dawn spacecraft as it orbited Ceres, the largest object in the asteroid belt (see the Perspective by Küppers). In some small patches on the surface, they detected absorption bands characteristic of aliphatic organic compounds. The authors ruled out an external origin, such as an impact, suggesting that the material must have formed on Ceres. Together with other compounds detected previously, this supports the existence of a complex prebiotic chemistry at some point in Ceres' history.
Science , this issue p. 719 ; see also p. 692
The dwarf planet Ceres (equatorial diameter 963km) is the largest object that has remained in the main asteroid belt (Russell and Raymond, 2012), while most large bodies have been destroyed or removed by dynamical processes (Petit et al. 2001; Minton and Malhotra, 2009). Pre-Dawn investigations (McCord and Sotin, 2005; Castillo-Rogez and McCord, 2010; Castillo-Rogez et al., 2011) suggest that Ceres is a thermally evolved, but still volatile-rich body with potential geological activity, that was never completely molten, but possibly differentiated into a rocky core, an ice-rich mantle, and may contain remnant internal liquid water. Thermal alteration should contribute to producing a (dark) carbonaceous chondritic-like surface (McCord and Sotin, 2005; Castillo-Rogez and McCord, 2010; Castillo-Rogez et al., 2011; Nathues et al., 2015) containing ammoniated phyllosilicates (King et al., 1992; De Sanctis et al., 2015 and 2016). Here we show and analyse global contrast-rich colour mosaics, derived from a camera on-board Dawn at Ceres (Russell et al., 2016). Colours are unexpectedly more diverse on global scale than anticipated by Hubble Space Telescope (Li et al., 2006) and ground-based observations (Reddy et al. 2015). Dawn data led to the identification of five major colour units. The youngest units identified by crater counting, termed bright and bluish units, are exclusively found at equatorial and intermediate latitudes. We identified correlations between the distribution of the colour units, crater size, and formation age, inferring a crustal stratigraphy. Surface brightness and spectral properties are not correlated. The youngest surface features are the bright spots at crater Occator (~Ø 92km). Their colour spectra are highly consistent with the presence of carbonates while most of the remaining surface resembles modifications of various types of ordinary carbonaceous chondrites.
INTRODUCTION
Observations of Ceres, the largest object in the asteroid belt, have suggested that the dwarf planet is a geologically differentiated body with a silicate core and an ice-rich mantle. Data acquired by the Dawn spacecraft were used to perform a three-dimensional characterization of the surface to determine if the geomorphology of Ceres is consistent with the models of an icy interior.
RATIONALE
Instruments on Dawn have collected data at a variety of resolutions, including both clear-filter and color images. Digital terrain models have been derived from stereo images. A preliminary 1:10 M scale geologic map of Ceres was constructed using images obtained during the Approach and Survey orbital phases of the mission. We used the map, along with higher-resolution imagery, to assess the geology of Ceres at the global scale, to identify geomorphic and structural features, and to determine the geologic processes that have affected Ceres globally.
RESULTS
Impact craters are the most prevalent geomorphic feature on Ceres, and several of the craters have fractured floors. Geomorphic analysis of the fracture patterns shows that they are similar to lunar Floor-Fractured Craters (FFCs), and an analysis of the depth-to-diameter ratios shows that they are anomalously shallow compared with average Ceres craters. Both of these factors are consistent with FFC floors being uplifted due to an intrusion of cryomagma.
Kilometer-scale linear structures cross much of Ceres. Some of these structures are oriented radially to large craters and most likely formed due to impact processes. However, a set of linear structures present only on a topographically high region do not have any obvious relationship to impact craters. Geomorphic analysis suggests that they represent subsurface faults and might have formed due to crustal uplift by cryomagmatic intrusion.
Domes identified across the Ceres surface present a wide range of sizes (<10 km to >100 km), basal shapes, and profiles. Whether a single formation mechanism is responsible for their formation is still an open question. Cryovolcanic extrusion is one plausible process for the larger domes, although most small mounds (<10-km diameter) are more likely to be impact debris.
Differences in lobate flow morphology suggest that multiple emplacement processes have operated on Ceres, where three types of flows have been identified. Type 1 flows are morphologically similar to ice-cored flows on Earth and Mars. Type 2 flows are comparable to long-runout landslides. Type 3 flows morphologically resemble the fluidized ejecta blankets of rampart craters, which are hypothesized to form by impact into ice-rich ground.
CONCLUSION
The global trend of lobate flows suggests that differences in their geomorphology could be explained by variations in ice content and temperature at the near surface. Geomorphic and topographic analyses of the FFCs suggest that cryomagmatism is active on Ceres, whereas the large domes are possibly formed by extrusions of cryolava. Although spectroscopic analysis to date has identified water ice in only one location on Ceres, the identification of these potentially ice-related features suggests that there may be more ice within localized regions of Ceres’ crust.
Dawn high-altitude mapping orbit imagery (140 meters per pixel) of example morphologic features
( A ) Occator crater; arrows point to floor fractures. ( B ) Linear structures, denoted by arrows. ( C ) A large dome at 42° N, 10° E, visible in the elevation map. ( D ) A small mound at 45.5° S, 295.7° E. ( E ) Type 1 lobate flow; arrows point to the flow front.
INTRODUCTION
Classic volcanism prevalent on terrestrial planets and volatile-poor protoplanets, such as asteroid Vesta, is based on silicate chemistry and is often expressed by volcanic edifices (unless erased by impact bombardment). In ice-rich bodies with sufficiently warm interiors, cryovolcanism involving liquid brines can occur. Smooth plains on some icy satellites of the outer solar system have been suggested as possibly cryovolcanic in origin. However, evidence for cryovolcanic edifices has proven elusive. Ceres is a volatile-rich dwarf planet with an average equatorial surface temperature of ~160 K. Whether this small (~940 km diameter) body without tidal dissipation could sustain cryovolcanism has been an open question because the surface landforms and relation to internal activity were unknown.
RATIONALE
The Framing Camera onboard the Dawn spacecraft has observed >99% of Ceres’ surface at a resolution of 35 m/pixel at visible wavelengths. This wide coverage and resolution were exploited for geologic mapping and age determination. Observations with a resolution of 135 m/pixel were obtained under several different viewing geometries. The stereo-photogrammetric method applied to this data set allowed the calculation of a digital terrain model, from which morphometry was investigated. The observations revealed a 4-km-high topographic relief, named Ahuna Mons, that is consistent with a cryovolcanic dome emplacement.
RESULTS
The ~17-km-wide and 4-km-high Ahuna Mons has a distinct size, shape, and morphology. Its summit topography is concave downward, and its flanks are at the angle of repose. The morphology is characterized by (i) troughs, ridges, and hummocky areas at the summit, indicating multiple phases of activity, such as extensional fracturing, and (ii) downslope lineations on the flanks, indicating rockfalls and accumulation of slope debris. These morphometric and morphologic observations are explained by the formation of a cryovolcanic dome, which is analogous to a high-viscosity silicic dome on terrestrial planets. Models indicate that extrusions of a highly viscous melt-bearing material can lead to the buildup of a brittle carapace at the summit, enclosing a ductile core. Partial fracturing and disintegration of the carapace generates slope debris, and relaxation of the dome’s ductile core due to gravity shapes the topographic profile of the summit. Modeling of this final phase of dome relaxation and reproduction of the topographic profile requires an extruded material of high viscosity, which is consistent with the mountain’s morphology. We constrained the age of the most recent activity on Ahuna Mons to be within the past 210 ± 30 million years.
CONCLUSION
Cryovolcanic activity during the geologically recent past of Ceres constrains its thermal and chemical history. We propose that hydrated salts with low eutectic temperatures and low thermal conductivities enabled the presence of cryomagmatic liquids within Ceres. These salts are the product of global aqueous alteration, a key process for Ceres’ evolution as recorded by the aqueously altered, secondary minerals observed on the surface.
Perspective view of Ahuna Mons on Ceres from Dawn Framing Camera data (no vertical exaggeration)
The mountain is 4 km high and 17 km wide in this south-looking view. Fracturing is observed on the mountain’s top, whereas streaks from rockfalls dominate the flanks.
Before NASA's Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres's formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres's largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres's shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content.
A 3-dimensional advanced guidance scheme is necessary to perform a successful precise lunar landing mission. This paper outlines a 3-dimensional comparison of different methods of solution of motion control equations for guidance scheme of lunar descent. It also proposes a 3-dimensional advanced solution that allows a full depiction for a descent vehicle motion from orbital states down to the final landing event. In the conventional 2-dimensional methods of solution, some inadequate assumptions exist that limit the validity of the solutions. The proposed research solves those problems and eventually allows a complete representation of the descent module motion for successful pinpoint lunar landing.
The new HIMA Quad (QMR) Architecture now available for Safety and Critical Control Applications is a major breakthrough in safety performance. The architecture provides four (4) processors, and remedies problems associated with dual processor architecture, as regards the dangerous undetected failure of one of the two (dual) processors. This major technological enhancement allows the safety system to operate at the SIL 3 level (RC6) on either one or both channels for an unrestricted period of time, without the need for external devices of any kind. As such, it achieves a significant increase in both safety and availability which exceeds that provided by TMR architectures by a factor of three. In addition, it has significantly less susceptibility to common cause failure because of the absolute separation, isolation and operation of the redundant channels. Given the safety performance and availability improvements, the most attractive advantage of this new architecture is a lower overall life cycle cost, which will enable it to be used effectively on both small and large safety projects.
DNA methylation was the first epigenetic mark to be discovered, involving the addition of a methyl group to the 5′ position of cytosine by DNA methyltransferases, and can be inherited through cell division. DNA methylation plays an important role in normal human development and is associated with the regulation of gene expression, tumorigenesis, and other genetic and epigenetic diseases. Differential methylation is now known to play a central role in the development and outcome of most if not all human malignancies.
Bisulfite conversion is a commonly used approach for gene-specific DNA methylation analysis. Treatment of DNA with bisulfite converts cytosine to uracil while leaving 5-methylcytosine intact, allowing for single-nucleotide resolution information about the methylated areas of DNA. PCR-based methods are routinely used to study DNA methylation on a gene-specific basis, after bisulfite treatment. Variations of this method include bisulfite sequencing, methylation-specific PCR, real-time PCR-based MethyLight, and methylation-sensitive high-resolution melting PCR. Several whole-epigenome profiling technologies such as MethylC-seq reduced representation bisulfite sequencing (RRBS) and the Infinium Human methylation 450 K bead chip are now available allowing for the identification of epigenetic drivers of disease processes as well as biomarkers that could potentially be integrated into clinical practice.
A panel of experts invited by Aerospace America share its views on issues involved in space nuclear power and propulsion. The budget issue related to the development and operation of space nuclear systems is also addressed. The role of Los Alamos in developing the nuclear elements of these systems is also discussed. The advantages of testing nuclear thermal rockets (NTR) over testing nuclear electric power (NEP) systems is also elaborated.
Recent space missions rely more and more on the cooperation between different spacecraft in order to achieve a desired objective. Among the spacecraft proximity operations, the orbital rendezvous is a classical example that has generated a large amount of studies since the beginning of the space exploration. However, the motivations and objectives for the proximity operations have considerably changed. The need for higher autonomy, better security and lower costs prompts for the development of new guidance and control algorithms. The presence of different types of constraints and physical limitations also contributes to the increased complexity of the problem. In this challenging context, this dissertation represents a contribution to the development of new spacecraft guidance and control algorithms. The works presented in this dissertation are based on a structural analysis of the spacecraft relative dynamics. Using a simp! lified model, a new set of parametric expressions is developed for the relative motion. This parametrization is very well suited for the analysis of the geometric properties of periodic relative trajectories and for handling different types of state constraints. A formal connection is evidenced between the set of parameters that define constrained trajectories and the cone of positive semi-definite matrices. This result is exploited in the design of spacecraft relative trajectories for proximity operations, in the impulsive control framework. The resulting guidance algorithms enable the guaranteed continuous constraints satisfaction, while still relying on semi-definite programming tools. The problem of the robustness of the computed maneuvers with respect to navigation uncertainties is also addressed.
The Space Launch System (SLS) is envisioned as a heavy-lift vehicle that will provide the foundation for future beyond-low-Earth orbit (LEO) exploration missions. Previous studies have been performed to determine the optimal configuration for the SLS and the applicability of commercial off-the-shelf in-space stages for Earth departure. Currently, NASA is analyzing the concept of an Exploration Upper Stage (EUS) that will provide LEO insertion and Earth departure burns. This paper will explore candidate in-space stages based on the EUS design for a wide range of beyond LEO missions. Mission payloads will range from small robotic systems up to human systems with deep space habitats and landers. Mission destinations will include cislunar space, Mars, Jupiter, and Saturn. Given these wide-ranging mission objectives, a vehicle-sizing tool has been developed to determine the size of an Earth departure stage based on the mission objectives. The tool calculates masses for all the major subsystems of the vehicle including propellant loads, avionics, power, engines, main propulsion system components, tanks, pressurization system and gases, primary structural elements, and secondary structural elements. The tool uses an iterative sizing algorithm to determine the resulting mass of the stage. Any input into one of the subsystem sizing routines or the mission parameters can be treated as a parametric sweep or as a distribution for use in Monte Carlo analysis. Taking these factors together allows for multi-variable, coupled analysis runs. To increase confidence in the tool, the results have been verified against two point-of-departure designs of the EUS. The tool has also been verified against Apollo Moon mission elements and other human-rated space systems. This paper will focus on trading key propulsion technologies including chemical, Nuclear Thermal Propulsion (NTP), and Solar Electric Propulsion (SEP). All of the key performance inputs and relationships will be presented an- discussed in light of the various missions. For each mission there are several trajectory options and each will be discussed in terms of delta-velocity (DV) required and transit duration. Each propulsion system will be modeled, sized, and judged based on its applicability to the whole range of beyond-LEO missions. Criteria for scoring will include the resulting dry mass of the stage, resulting propellant required, time to destination, and an assessment of key enabling technologies. In addition to the larger metrics, this paper will present the results of several coupled sensitivity studies. The ultimate goals of these tools and studies are to provide NASA with the most mass-, technology-, and cost-effective in-space stage for its future exploration missions.
Strata is a low-mass, low-power, and low-volume impulse ground penetrating radar operating at 400 MHz and capable of defining subsurface stratigraphy and structure at the spatial resolution of tens of centimeters to 10-15 m depth. Strata would be used along transects suitable for to characterizing regolith properties on the Moon or distinguishing habitable environments on Mars.
A low-thrust trajectory design study is performed for a mission to send humans to Ceres and back. The flight times are constrained to 270 days for each leg, and a grid search is performed over propulsion system power, ranging from 6 to 14 MW, and departure V∞V∞, ranging from 0 to 3 km/s. A propulsion system specific mass of 5 kg/kW is assumed. Each mission delivers a 75 Mg payload to Ceres, not including propulsion system mass. An elliptical spiral method for transferring from low Earth orbit to an interplanetary trajectory is described and used for the mission design. A mission with a power of 11.7 MW and departure V∞V∞ of 3 km/s is found to offer a minimum initial mass in low Earth orbit of 289 Mg. A preliminary supply mission delivering 80 Mg of supplies to Ceres is also designed with an initial mass in low Earth orbit of 127 Mg. Based on these results, it appears that a human mission to Ceres is not significantly more difficult than current plans to send humans to Mars.
Results from this study provide a basis for the selection of an aperture size appropriate for a research and development ground-based receiver for deep space optical communications. Currently achievable or near-term realizable hardware performance capabilities for both a spacecraft optical terminal and a ground terminal were used as input parameters to the analysis. Links were analyzed using OPTI, our optical link analysis program. Near-term planned and current missions were surveyed and categorized by data rate and telecommunications-subsystems prime power consumption. The spacecraft optical-terminal transmitter power was selected by matching these (RF) data rates and prime power requirements and by applying power efficiencies suitable to an optical communications subsystem. The study was baselined on a Mars mission. Results are displayed as required ground aperture size for given spacecraft transmitter aperture size, parametrized by data rate, transmit optical power, and wavelength.