Titan and exobiological aspects of the Cassini-Huygens mission

Titan, the largest satellite of Saturn, has a dense N2-CH4 atmosphere rich in organic compounds, both in gas and in aerosol phases. Its surface is probably covered by oceans of liquid methane-ethane mixtures, with many dissolved organics. This quasi planet appears as a natural laboratory to study chemical evolution toward complex organic systems in a planetary environment over a long time scale. With the Cassini-Huygens mission NASA and ESA will jointly send an orbiter (Cassini) around Saturn and a probe (Huygens) in the atmosphere of Titan. This mission, currently planned to be launched in 1996-1997 for a Saturn - Titan arrival in 2004, offers a unique opportunity to study in detail extra-terrestrial organic processes. Consequently, it has important implications in the field of exobiology and the origins of life.     

The Mars Sample Return Project.

The Mars Sample Return (MSR) Project is underway. A 2003 mission to be launched on a Delta III Class vehicle and a 2005 mission launched on an Ariane 5 will culminate in carefully selected Mars samples arriving on Earth in 2008. NASA is the lead agency and will provide the Mars landed elements, namely, landers, rovers, and Mars ascent vehicles (MAVs). The French Space Agency CNES is the largest international partner and will provide for the joint NASA/CNES 2005 Mission the Ariane 5 launch and the Earth Return Mars Orbiter that will capture the sample canisters from the Mars parking orbits the MAVs place them in. The sample canisters will be returned to Earth aboard the CNES Orbiter in the Earth Entry Vehicles provided by NASA. Other national space agencies are also expected to participate in substantial roles. Italy is planning to provide a drill that will operate from the Landers to provide subsurface samples. Other experiments in addition to the MSR payload will also be carried on the Landers. This paper will present the current status of the design of the MSR missions and flight articles.     

Cassini Saturn-escape trajectories to Jupiter,Uranus, and Neptune

Potential encore-mission scenarios have been considered for the Cassini mission. In this paper we discuss one of the end-of-life scenarios in which the Cassini spacecraft could perform a Saturn escape via gravity assists from Titan. It is shown that such satellite-aided escape requires a small deterministic maneuver (e.g., Δv<50 m/s), but provides enough energy for the Cassini spacecraft to reach a range of targets in our Solar System, as close to the Sun as the asteroid belt or as far as the Kuiper belt. The escape sequence could be initiated from an arbitrary point during the on-going Cassini mission. Example tours are presented in which the final Titan flyby places the spacecraft into ballistic trajectories that reach Jupiter, Uranus, and Neptune. After years of heliocentric flight, the spacecraft could impact on the target gas giant or perform a flyby to escape from the Solar System (if not to another destination). The concept can be generalized to a new kind of missions, including nested-grand tours, which may involve satellite-aided captures and escapes at more than one planet.     

A concept for NASA's Mars 2016 astrobiology field laboratory

The Mars Program Plan includes an integrated and coordinated set of future candidate missions and investigations that meet fundamental science objectives of NASA and the Mars Exploration Program (MEP). At the time this paper was written, these possible future missions are planned in a manner consistent with a projected budget profile for the Mars Program in the next decade (2007-2016). As with all future missions, the funding profile depends on a number of factors that include the exact cost of each mission as well as potential changes to the overall NASA budget. In the current version of the Mars Program Plan, the Astrobiology Field Laboratory (AFL) exists as a candidate project to determine whether there were (or are) habitable zones and life, and how the development of these zones may be related to the overall evolution of the planet. The AFL concept is a surface exploration mission equipped with a major in situ laboratory capable of making significant advancements toward the Mars Program's life-related scientific goals and the overarching Vision for Space Exploration. We have developed several concepts for the AFL that fit within known budget and engineering constraints projected for the 2016 and 2018 Mars mission launch opportunities. The AFL mission architecture proposed here assumes maximum heritage from the 2009 Mars Science Laboratory (MSL). Candidate payload elements for this concept were identified from a set of recommendations put forth by the Astrobiology Field Laboratory Science Steering Group (AFL SSG) in 2004, for the express purpose of identifying overall rover mass and power requirements for such a mission. The conceptual payload includes a Precision Sample Handling and Processing System that would replace and augment the functionality and capabilities provided by the Sample Acquisition Sample Processing and Handling system that is currently part of the 2009 MSL platform.     

Mars Express spacecraft: design and development solutions for affordable planetary missions

The spacecraft designed to support the ESA Mars Express mission and its science payloads is customized around an existing avionics well suited to environmental and operational constraints of deep-space interplanetary missions. The reuse of the avionics initially developed for the Rosetta cometary program thanks to an adequate ESA cornerstone program budget paves the way for affordable planetary missions.The costs and schedule benefits inherited from reuse of up-to-date avionics solutions validated in the frame of other programs allows to focus design and development efforts of a new mission over the specific areas which requires customization, such as spacecraft configuration and payload resources. This design approach, combined with the implementation of innovative development and management solutions have enabled to provide the Mars Express mission with an highly capable spacecraft for a remarkably low cost. The different spacecraft subsystems are all based on adequate design solutions. The development plan ensures an exhaustive spacecraft verification in order to perform the mission at minimum risk. New management schemes contribute to maintain the mission within its limited funding.Experience and heritage gained on this program will allow industry to propose to Scientists and Agencies high performance, low-cost solutions for the ambitious Mars Exploration Program of the forthcoming decade.     

Preliminary assessment of a small robotic rover for Titan exploration

Titan is a very interesting target in deep space exploration. With its solid surface on which a rover can easily travel and its methane lakes which can be sailed it is the ideal target for a deep space mission which includes a mobile platform. In the present paper the general layout of a rover for a mission to Titan is studied, dealing with the mobility, power generation and trajectory control issues. A four-wheels configuration with slip steering was chosen; to compare this solution with the more conventional strategy based on steering wheels, simulations were performed on some trajectories computed through the well known ‘potential’ method, using both slip steering and conventional steering control, for different vehicle speeds. The comparison between the simulated trajectories allows to state the adequateness of the proposed approach.The results here obtained apply not only to a future mission to Titan, but also to other missions designed for the exploration of the satellites of the outer planets having a size comparable with that of Titan and the largest Kuiper belt objects like Pluto and 136472 Makemake.     

LIFE: Life Investigation For Enceladus A Sample Return Mission Concept in Search for Evidence of Life

Abstract Life Investigation For Enceladus (LIFE) presents a low-cost sample return mission to Enceladus, a body with high astrobiological potential. There is ample evidence that liquid water exists under ice coverage in the form of active geysers in the "tiger stripes" area of the southern Enceladus hemisphere. This active plume consists of gas and ice particles and enables the sampling of fresh materials from the interior that may originate from a liquid water source. The particles consist mostly of water ice and are 1-10?μ in diameter. The plume composition shows H(2)O, CO(2), CH(4), NH(3), Ar, and evidence that more complex organic species might be present. Since life on Earth exists whenever liquid water, organics, and energy coexist, understanding the chemical components of the emanating ice particles could indicate whether life is potentially present on Enceladus. The icy worlds of the outer planets are testing grounds for some of the theories for the origin of life on Earth. The LIFE mission concept is envisioned in two parts: first, to orbit Saturn (in order to achieve lower sampling speeds, approaching 2 km/s, and thus enable a softer sample collection impact than Stardust, and to make possible multiple flybys of Enceladus); second, to sample Enceladus' plume, the E ring of Saturn, and the Titan upper atmosphere. With new findings from these samples, NASA could provide detailed chemical and isotopic and, potentially, biological compositional context of the plume. Since the duration of the Enceladus plume is unpredictable, it is imperative that these samples are captured at the earliest flight opportunity. If LIFE is launched before 2019, it could take advantage of a Jupiter gravity assist, which would thus reduce mission lifetimes and launch vehicle costs. The LIFE concept offers science returns comparable to those of a Flagship mission but at the measurably lower sample return costs of a Discovery-class mission. Key Words: Astrobiology-Habitability-Enceladus-Biosignatures. Astrobiology 12, 730-742.     

Principal Investigators and mission leadership

Principal Investigators of small and medium sized space and earth science missions face many challenges during formulation, design, development, integration and test, launch, and operations; these challenges may be more easily met by team leaders with prior mission experience. This paper reports the results of the first known demographic study of NASA's Principal-Investigator-led missions and makes recommendations for preparing additional space scientists to lead. The addition of a Deputy Principal Investigator to proposal teams could reduce the burden on the Principal Investigator and provide an opportunity for additional scientists to gain mission leadership experience useful on future missions. The pool of mission-knowledgeable scientists could further be expanded to include scientists earlier in their careers via carefully managed Participating Scientist Programs. Adding Deputy Principal Investigators and Participating Scientist Programs to missions as a matter of course would reinforce effective management practices, open the field of proposers, and provide concrete ways to mentor the next generation of Principal Investigators.     

利用气动减速的国外深空探测器热控设计特点分析

气动减速技术能在耗费较少燃料的情况下,使探测器顺利进入预定环绕轨道.面向气动减速技术的深空探测器迎风面需要承受较高的气动热负荷与气动力,使得迎风面热控材料的耐热与耐冲击能力成为探测器设计的关键.文章对国外相关应用实例进行了调研和综述,并在此基础上总结了此类深空探测器热控系统的设计特点,可为气动减速技术在我国深空探测任务...     

RADAR “SAIL” satellite concept

The Radar SAIL concept is based on the use of a rectangular antenna lying in the dawn-dusk orbital plane with the length (along speed vector) smaller than the height. Such geometry makes it possible to place the solar cells on the back of the antenna, to use gravity gradient stabilisation, and to implement multipath-free GPS interferometric measurement of the antenna deformation thus allowing structural relaxation. Less obviously, the geometry favours the RADAR design too, by allowing grating lobes and therefore a lower density of built-in electronic in the active antenna. The antenna can be thin and packed for launch inside a cylinder-shaped bus having pyrotechnic doors for the antenna deployement and bearing the rest of the payload and the service equipment. With respect to a standard design of performant missions, cost savings come from the bus, whose functions (AOCS, power supply) are simplified, from the launch since the mass budget and the stowing configuration become compatible with medium size rockets (LLV2/3, DELTA-LITE, LM-4.), and from the active antenna built-in electronics.

The RADAR SAIL concept is all the more cost effective when the mission requires a large, high and short antenna, i.e. high resolution (<5m), low frequency band (L or S or even P), high revisiting, multiple frequencies. Mission implementation and funding can be favored by the new capability to share the satellite between autonomous regional operators. Combined with ground DBF (digital beam forming) technique, the concept allows extremely simple and low cost missions providing a fixed wide swath (10 to 15 m resolution within 500km to 1000 km swath) for systematic surveillance or monitoring.     

A complexity-based risk assessment of low-cost planetary missions: when is a mission too fast and too cheap?

Under constrained budgets and rigid schedules, NASA and industry have greatly increased their utilization of small satellites to conduct low-cost planetary investigations. Recent failed small planetary science spacecraft such as Mars Polar Lander (MPL) and Mars Climate Orbiter (MCO), and impaired missions such as Mars Global Surveyor (MGS) have fueled the ongoing debate on whether NASA's “Faster, Better, Cheaper” (FBC) approach is working. Several noteworthy failures of earth-orbiting missions have occurred as well including Lewis and the Wide-field Infrared Experiment (WIRE). While recent studies have observed that FBC has resulted in lower costs and shorter development times, these benefits may have been achieved at the expense of lowering probability of success. One question remaining to be answered is when is a mission “too fast and too cheap” that it is prone to failure? This paper assesses NASA FBC missions in terms of a complexity index measured against development time and spacecraft cost. A comparison of relative failure rates of recent planetary and earth-orbiting missions are presented, and conclusions regarding dependence on system complexity are drawn.     

嫦娥五号平动点拓展任务轨道方案研究

中国嫦娥五号探测器成功实现月球采样返回任务,为最大限度利用任务资源,研究了利用嫦娥五号轨道器的平动点拓展任务轨道方案,设计了平动点轨道及其转移轨道.首先,给出了任务轨道设计的轨道动力学模型,包括圆型限制性三体问题模型和精确力模型.其次,基于嫦娥二号和嫦娥5T1平动点拓展任务设计经验,介绍了平动点轨道直接转移与入轨等轨道...     

Principal investigators and project managers: Insights from Discovery

NASA’s Discovery, Explorer, and Mars Scout mission lines have demonstrated over the past 15 years that, with careful planning, flexible management techniques, and a commitment to cost control, small space science missions can be built and launched at a fraction of the price of strategic missions. Many credit management techniques such as co-location, early contracting for long-lead items, and a resistance to scope creep for this, but it is also important to examine what may be the most significant variable in small mission implementation: the roles and the relationship of the principal investigator, responsible to NASA for the success of the mission, and the project manager, responsible for delivering the mission to NASA. This paper reports on a series of 55 oral histories with principal investigators, project managers, co-investigators, system engineers, and senior management from nearly every competitively selected Discovery mission launched to date that discuss the definition and evolution of these roles and share revealing insights from the key players themselves. The paper will show that there are as many ways to define the principal investigator/project manager relationship as there are missions, and that the subtleties in the relationship often provide new management tools not practical in larger missions.     

探月飞行的调相轨道

早期的探月飞行都采用直接由地球飞到月球的地月转移方式,探测器由运载火箭直接发送到地月转移轨道,这样做的好处是飞行时间比较短,只需3至5天的时间。20世纪90年代开始的新一轮探月活动中采用了一种新的飞行方式,探测器飞离地球前,先在绕地球飞行的调相轨道上运行若干圈,这样做的好处有三：一是可以在运载火箭能力不够的情况下,由探测器来补充;二是可以减小转移轨道中途修正的负担;三是可以扩大发射机会窗口。文章以嫦娥一号探测器及美、日的两个月球探测器为例,详细讨论了这种新的飞行方式,同时还对我国后续探月计划的飞行轨道提出了初步建议。     

Short profile for the human spacecraft Soyuz-TMA rendezvous mission to the ISS

Reduction of flight duration after insertion till docking to the ISS is considered. In the beginning of the human flight era both the USSR and the USA used short mission profiles due to limited life support resources. A rendezvous during these missions was usually achieved in 1–5 revolutions. The short-term rendezvous were made possible by the coordinated launch profiles of both rendezvousing spacecraft, which provided specific relative position of the spacecraft or phase angle conditions. After the beginning of regular flights to the orbital stations these requirements became difficult to fulfill. That is why it was decided to transfer to 1- or 2-day rendezvous profile. The long stay of a crew in a limited habitation volume of the Soyuz-TMA spacecraft before docking to the ISS is one of the most strained parts of the flight and naturally cosmonauts wish to dock to the ISS as soon as possible. As a result of previous studies the short four-burn rendezvous mission profile with docking in a few orbits was developed. It is shown that the current capabilities of the Soyuz-FG launch vehicle and the Soyuz-TMA spacecraft are sufficient to provide for that. The first test of the short rendezvous mission during Progress cargo vehicle flight to the ISS is planned for 2012. Possible contingencies pertinent to this profile are described. In particular, in the majority of the emergency cases there is a possibility of an urgent transfer to the present 2-day rendezvous profile. Thus, the short mission will be very flexible and will not influence the ISS mission plan. Fuel consumption for the nominal and emergency cases is defined by statistical simulation of the rendezvous mission. The qualitative analysis of the short-term and current 2-day rendezvous missions is performed.     

Priorities in space for the USA

This article follows the story of Shuttle development, in the context of the history of the US space programme from Apollo to the Space Station. The Shuttle was chosen as one of a series of ‘space spectaculars’ and has proven to be prohibitively expensive and unreliable, practical only for a very limited number of specialized missions. The Space Station, too, cannot be economically supplied, even if the USA could afford to build it. The author concludes that NASA should cancel the Space Station and the replacement orbiter for Challenger, and engage on a major programme of launch vehicle development, independent of the US military. The aim should be a dramatic reduction of launch vehicle costs, making spaceflight practical, and a truly independent NASA which could restore the USA to space preeminence.     

Market-based approaches for controlling space mission costs: the Cassini Resource Exchange

Using economic incentives to control costs is a new concept for space missions. The basic tenets of market-based approaches run counter to typical centralized management techniques often utilized for complex space missions. NASA's Cassini mission to Saturn used a market trading system to assist the Science Instrument Manager in guiding the development of the spacecraft's science payload. This system allowed science instrument teams to trade resources among themselves to best manage their resources (mass, power, data rate, and budget). Thus, Cassini Project management was no longer responsible for adjudicating and reallocating resources that result from instrument development problems. Instrument teams were responsible for directly managing their resources and if they ran into a development problem it was their responsibility to resolve their problem by descoping or through the use of a 'resource exchange.' Under the trading system, instrument cost growth was less than 1% and the total payload mass was under its allocation by 7%. This result is in stark contrast to the 50%–100% increases in these resources on past missions.     

Phoenix--the first Mars Scout mission

NASA has initiated the first of a new series of missions to augment the current Mars Program. In addition to the systematic series of planned, directed missions currently comprising the Mars Program plan, NASA has started a series of Mars Scout missions that are low cost, price fixed, Principal [correction of Principle] Investigator-led projects. These missions are intended to provide an avenue for rapid response to discoveries made as a result of the primary Mars missions, as well as allow more risky technologies and approaches to be applied in the investigation of Mars. The first in this new series is the Phoenix mission which was selected as part of a highly competitive process. Phoenix will use the Mars 2001 Lander that was discontinued in 2000 and apply a new set of science objectives and mission objectives and will validate this soft lander architecture for future applications. This paper will provide an overview of both the Program and the Project.     

The evolution of a serviceable EURECA

Within the European space platform program the EURECA is being established as a ground-based platform for short microgravity missions. The development towards a serviceable platform for longer, scientific missions is described. The plan of an advanced space-based platform for increasing payload demands is outlined. The platform design and the adaptation to scientific missions and servicing operations are investigated. The cost-effective utilization of the different platform types using new operational concepts is analyzed in parametric life cycle cost calculations for different payloads and mission scenarios.     

Aeroshell design techniques for aerocapture entry vehicles

A major goal of NASA's In-Space Propulsion Program is to shorten trip times for scientific planetary missions. To meet this challenge arrival speeds will increase, requiring significant braking for orbit insertion, and thus increased deceleration propellant mass that may exceed launch lift capabilities. A technology called aerocapture has been developed to expand the mission potential of exploratory probes destined for planets with suitable atmospheres. Aerocapture inserts a probe into planetary orbit via a single pass through the atmosphere using the probe's aeroshell drag to reduce velocity. The benefit of an aerocapture maneuver is a large reduction in propellant mass that may result in smaller, less costly missions and reduced mission cruise times. The methodology used to design rigid aerocapture aeroshells will be presented with an emphasis on a new systems tool under development. Current methods for fast, efficient evaluations of structural systems for exploratory vehicles to planets and moons within our solar system have been under development within NASA having limited success. Many systems tools that have been attempted applied structural mass estimation techniques based on historical data and curve fitting techniques that are difficult and cumbersome to apply to new vehicle concepts and missions. The resulting vehicle aeroshell mass may be incorrectly estimated or have high margins included to account for uncertainty. This new tool will reduce the guesswork previously found in conceptual aeroshell mass estimations.