Limits on interstellar messages

Despite the fact that major efforts have been expended on passive searches for extraterrestrial signals, few deliberate “transmissions” to potential alien recipients have occurred. These have generally taken the form of simple graphics depicting such things as our appearance, location, and biological construction. In this paper, we consider (a) the fundamental technical and astronomical limitations to interstellar messaging—in other words, how many “bits” could any society reasonably send, and (b) what might be a likely transmission strategy. These considerations suggest approaches for SETI programs, as well as giving insight into the types of messages we might construct for eventual replies to received signals.     

The conventionality of pictorial representation in interstellar messages

Pictorial messages have previously been advocated for interstellar communication because such messages are presumed to be capable of presenting information in a non-arbitrary and easily intelligible manner. In contrast to this view, pictorial messages actually represent information in a partially conventional way. This point is demonstrated by examining pictorial representations of human beings from a range of cultures. While such representations may be understood quite readily by individuals familiar with the conventions of a particular culture, to the uninitiated outsider, such representations can be unintelligible. In spite of the partially arbitrary nature of pictorial representation, we may be able to construct messages that would teach extraterrestrial intelligence (ETI) some of the conventions by which we view pictures. One such approach is to pair numerical information about geometrical objects with pictorial representations of the same objects. Problems of conventionality can also be addressed in part through use of (1) multiple representations of the same object, (2) contextual cues, (3) three- and four-dimensional representations and (4) non-visual representations.     

A human language corpus for interstellar message construction

The aim of HuLCC (the human language chorus corpus), is to provide a resource of sufficient size to facilitate inter-language analysis by incorporating languages from all the major language families: for the first time all aspects of typology will be incorporated within a single corpus, adhering to a consistent grammatical classification and granularity, which historically adopt a plethora of disparate schemes. An added feature will be the inclusion of a common text element, which will be translated across all languages, to provide a precise comparable thread for detailed linguistic analysis for translation strategies and a mechanism by which these mappings can be explicitly achieved. Methods developed to solve unambiguous mappings across these languages can then be adopted for any subsequent message authored by the SETI community. Initially, it is planned to provide at least 20,000 words for each chosen language, as this amount of text exceeds the point where randomly generated text can be disambiguated from natural language and is of sufficient size useful for message transmission [1] (Elliot, 2002). This paper details the design of this resource, which ultimately will be made available to SETI upon its completion, and discusses issues ‘core’ to any message construction.     

A non-earthcentric approach to life detection

The ultimate goal of a comprehensive life detection strategy is never to miss life when we encounter it. To accomplish this goal, we must define life in universal, that is, non-Earthcentric, measurable terms. Next, we must understand the nature of biosignatures observed from the measured parameters of life. And finally, we must have a clear idea of the end-member states for the search--what does life, past life, or no life look like (in terms of the measured parameters) at multiple spatial and temporal scales? If we can approach these problems both in the laboratory and in the field on Earth, then we have a chance of being able to detect life elsewhere in our solar system. What are the required limits of detection at each of those scales? What spatial, spectral, and temporal resolutions are necessary to detect life? These questions are actively being investigated in our group, and in this report, we present our strategy and approach to non-Earthcentric life detection.     

一种正向乘波前体设计方法初步研究

以定楔角乘波体设计方法为基础,研究了影响高超/超声速乘波体"乘波"的主要因素,给出了前体前缘实际气流压缩角的确定方法及影响因素,可知在相同的来流马赫数和压缩角δ下,随着前缘角θ和气流与前缘夹角α的增加,实际气流偏转角γ减小。据此,基于幂函数进气道前体构形,给出了前缘激波不脱体的限制条件及具体的判定方法,分析了乘波体典型几何特征参数对前缘激波不脱体的影响规律,结果显示在相同的来流马赫数和压缩角度下,增大前缘形状因子n,减小前体的长宽比L/W及增大前缘角均有利于激波不脱体。根据给出的前体几何参数对前缘激波脱体的影响规律曲线,对一种"前体几何外形构造+前缘激波附体条件限制"的正向前体乘波器工程设计方法进行了研究,给出了具体设计流程,并进行了初步的数值仿真验证,表明通过该方法设计的乘波前体流动特征与预期的结果吻合,说明文中所给出的激波附体条件及影响规律是可信的,乘波前体设计方法是可行的。     

The dialogic model: representing human diversity in messages to extraterrestrials

A Dialogic Model of constructing a unified reply message is suggested in which differences between perspectives are valued, rather than minimized. In this model, a diversity of views is seen as a virtue. Consensus in the broad sense of agreeing to include multiple perspectives is encouraged, while consensus in the narrow sense of everyone agreeing about all parts of the message is seen as overly restrictive, if not impossible. In the Dialogic Model, even perspectives that are irreconcilable with one another might be included in a single reply. Drawing upon multiple perspectives allows us to expand beyond our own preconceptions, gives extraterrestrials several ways to understand our views of the world, and portrays the breadth of human concerns.Seven benefits of beginning work on a reply message immediately are identified: (1) concretely understanding the challenge of creating an adequate reply; (2) helping decode messages from extraterrestrials; (3) creating interstellar compositions as a new form of art; (4) having a reply ready in case we receive a message; (5) providing a sense of concrete accomplishment; (6) preparing for an active search strategy; and (7) gaining public support for SETI.     

Project Icarus: A review of local interstellar medium properties of relevance for space missions to the nearest stars

I review those properties of the interstellar medium within 15 light-years of the Sun, which will be relevant for the planning of future rapid (v≥0.1c) interstellar space missions to the nearest stars. As the detailed properties of the local interstellar medium (LISM) may only become apparent after interstellar probes have been able to make in situ measurements, the first such probes will have to be designed conservatively with respect to what can be learned about the LISM from the immediate environment of the Solar System. It follows that studies of interstellar vehicles should assume the lowest plausible density when considering braking devices, which rely on transferring momentum from the vehicle to the surrounding medium, but the highest plausible densities when considering possible damage caused by the impact of the vehicle with interstellar material. Some suggestions for working values of these parameters are provided. This paper is a submission of the Project Icarus Study Group.     

A nonvariational approach to multiple finite-burn propellant optimization

In this paper a nonvariational approach to the finite-burn minimum fuel problem is presented. In particular, attention is focused on one of the computer codes of a sophisticated software package at Telespazio for dealing with a fuel minimization under nonlinear equality and inequality constraints. In this program thrust in an inverse-square gravitational field is considered. A short thrusting arc is dealt with by a transition matrix. A long burning arc is segmented in a suitable number of subarcs where the transition matrix formulation holds. Use of appropriate penalty functions allows the mission analyst to consider several equality and inequality constraints. The minimum search algorithm consists of a modified version of the Levenberg-Marquardt method. The overall computer code is able to accept even some rough estimate of the optimal profile. A wide spectrum of transfer flights is presented.     

The art and science of interstellar message composition: a report on international workshops to encourage multidisciplinary discussion

Throughout the history of the Search for Extraterrestrial Intelligence (SETI), there has been widespread recognition of the profound societal implications of detecting intelligence beyond Earth. At the SETI Institute, interstellar message construction serves as the focus of a multidisciplinary attempt to prepare for the cultural impact of signal detection and the critical events that would follow. Interstellar message construction at the SETI Institute builds upon the recommendations of the 1991–1992 Workshops on the Cultural Aspects of SETI, while also exploring opportunities for multidisciplinary contributions on new topics. Through a series of international workshops in Toulouse, Paris, Zagreb, Washington, and Bremen, the SETI Institute and partner organizations have fostered broad-based discussion about some of the most important decisions that would follow detection of extraterrestrial intelligence, including “should we reply?” and if so, “what should we say, and how might we say it?”. Several of the themes addressed at these workshops will be highlighted, including the relationship between art and science in designing messages, the value of interactive messages, and the importance of better understanding the nature of language.     

Cooperation and dialogical modeling for designing a safe Human space exploration mission to Mars

This paper proposes an approach for a complex and innovative project requiring international contributions from different communities of knowledge and expertise. Designing a safe and reliable architecture for a manned mission to Mars or the Asteroids necessitates strong cooperation during the early stages of design to prevent and reduce risks for the astronauts at each step of the mission. The stake during design is to deal with the contradictions, antagonisms and paradoxes of the involved partners for the definition and modeling of a shared project of reference. As we see in our research which analyses the cognitive and social aspects of technological risks in major accidents, in such a project, the complexity of the global organization (during design and use) and the integration of a wide and varie d range of sciences and innovative technologies is likely to increase systemic risks as follows: human and cultural mistakes, potential defaults, failures and accidents. We identify as the main danger antiquated centralized models of organization and the operational limits of interdisciplinarity in the sciences. Beyond this, we can see that we need to take carefully into account human cooperation and the quality of relations between heterogeneous partners. Designing an open, self-learning and reliable exploration system able to self-adapt in dangerous and unforeseen situations implies a collective networked intelligence led by a safe process that organizes interaction between the actors and the aims of the project. Our work, supported by the CNES (French Space Agency), proposes an innovative approach to the coordination of a complex project.     

A two-dimensional approach to multibody free dynamics in space environment

The equation of motion of a multibody system, described here as a chain of rigid bars and revolute joints orbiting around the Earth, is derived.

For each bar two translational and one rotational equilibrium equations are written. The forces acting on each body are the gravitational forces and the reaction forces (unknown) acting on it's end joints. The complete set of equilibrium equations consists of N_X differential equations, where N_X is the order of the state vector. The total number of unknowns is N_X+N_R where N_R=2N_J and N_J is the number of joints. The N_R additional equations, to make the system determinate, are provided by the nondifferential compatibility equations.

The resulting system is a set of differential algebraic equations (DAE) for which the well-known method of reducing the system to ordinary differential equations (ODE) is applied.

Since the internal forces are associated with the relative displacements between the bodies, which are small fractions of the distance of the multibody spacecraft from the center of the Earth, the task of obtaining these forces from inertial coordinates, from a numerical viewpoint, could be impossible. So the problem is reformulated in such a way that the equation of motion of the system, contains global quantities where no internal forces appear, and local equations where internal forces do appear. In the latter one, only quantities of the same order of the spacecraft dimensions are present. Numerical results complete the work.     

A wavelet and Zernike-polynomial-based shearing interferometry approach to analyse hydrodynamic instabilities at interfaces

We present a hybrid algorithm to analyse complex interferograms with significant fringe deformations without an a-priori given zero-phase image containing the optical aberration of the instrument. Situations of this type frequently appear in fluid physics experiments using lateral shearing interferometers. The algorithm proposed employs a wavelet transformation in parallel with an approximation of the phase field directly after the experimental container is filled applying Zernike polynomials. As a result the aberrations of the interferometer can be described by a few coefficients. The subtraction of these phase aberrations can be traced back to a complex multiplication in the wavelet space which strongly reduces the effort of the phase unwrapping using the Goldstein algorithm. We explain the performance of the algorithm, which is not restricted to a particular interferometer type, by applying it to interferograms captured during a recent microgravity experiment.     

A combinatorial approach to biochemical space: description and application to the redox distribution of metabolism

Redox chemistry is central to life on Earth. It is well known that life uses redox chemistry to capture energy from environmental chemical energy gradients. Here, we propose that a second use of redox chemistry, related to building biomass from environmental carbon, is equally important to life. We apply a method based on chemical structure to evaluate the redox range of different groups of terrestrial biochemicals, and find that they are consistently of intermediate redox range. We hypothesize the common intermediate range is related to the chemical space required for the selection of a consistent set of metabolites. We apply a computational method to show that the redox range of the chemical space shows the same restricted redox range as the biochemicals that are selected from that space. By contrast, the carbon from which life is composed is available in the environment only as fully oxidized or reduced species. We therefore argue that redox chemistry is essential to life for assembling biochemicals for biomass building. This biomass-building reason for life to require redox chemistry is in addition (and in contrast) to life's use of redox chemistry to capture energy. Life's use of redox chemistry for biomass capture will generate chemical by-products-that is, biosignature gases-that are not in redox equilibrium with life's environment. These potential biosignature gases may differ from energy-capture redox biosignatures.     

Taking a common-pool resources approach to space sustainability: A framework and potential policies

This paper examines Nobel Prize Winner Elinor Ostrom's principles for sustainable governance of common-pool resources (CPR), capturing the best practices of CPRs over the years, which avoid the “Tragedy of the Commons” without being either completely privatized or controlled by a Leviathan entity. Ostrom's principles highlight, inter alia, the need for clear boundary definitions, rules tailored to fit the domain, who has a say in formulation of collective-choice agreements and operational rules, monitoring of behavior, graduated penalties, and conflict resolution mechanisms. In the context of the space domain they highlight issues such as the definition of where space begins, gaps in the existing liability regime, the concept of collaborative space situational awareness, and how best to include emerging and developing space actors in negotiations and decision making. The paper concludes that Ostrom's principles highlight specific areas on which to focus initial space sustainability efforts and national and international policy. It also recommends further analysis into how best to translate her principles to the space domain, where they may not be wholly applicable because of the unique nature of space, and how to evolve space governance institutions and mechanisms to best suit the unique environment of outer space.     

A comment on "the far future of exoplanet direct characterization"--the case for interstellar space probes

Following on from ideas presented in a recent paper by Schneider et al. on "The Far Future of Exoplanet Direct Characterization," I argue that they have exaggerated the technical obstacles to performing such "direct characterization" by means of fast (order 0.1c) interstellar space probes. A brief summary of rapid interstellar spaceflight concepts that may be found in the literature is presented. I argue that the presence of interstellar dust grains, while certainly something that will need to be allowed for in interstellar vehicle design, is unlikely to be the kind of showstopper suggested by Schneider et al. Astrobiology as a discipline would be a major beneficiary of developing an interstellar spaceflight capability, albeit in the longer term, and I argue that astrobiologists should keep an open mind to the possibilities.     

The overredundant spacecraft—A competitive approach to future telecommunication satellites

Present operational space telecommunication systems are based on simultaneous availability of more than one satellite on orbit, mainly a spare satellite in addition to the operational one.Considering the costs associated to the delivery of extra flight models and to extra launchers, the question is asked whether it would not be advantageous to launch a very limited number of “overredundant” spacecraft instead of several standard satellites.The paper gives main conditions of reliability, size and redundancy concept under which an “overredundant” spacecraft could be a competitive approach to future operational systems.     

Italian industry's approach to space

European space activities began in the 1960's. The development of what was initially scientific research and which later spread to the enthusiastic involvement of Europe's most advanced industry is by now familiar history. The organization of ELDO and ESRO, which eventually gave way to today's ESA, occured in a span of less than a decade. Many major European countries also commenced their national space programmes during this period. This report examines the space initiatives taken by Italian industry.     

Formation routes of interstellar glycine involving carboxylic acids: possible favoritism between gas and solid phase

Despite the extensive search for glycine (NH?CH?COOH) and other amino acids in molecular clouds associated with star-forming regions, only upper limits have been derived from radio observations. Nevertheless, two of glycine's precursors, formic acid and acetic acid, have been abundantly detected. Although both precursors may lead to glycine formation, the efficiency of reaction depends on their abundance and survival in the presence of a radiation field. These facts could promote some favoritism in the reaction pathways in the gas phase and solid phase (ice). Glycine and these two simplest carboxylic acids are found in many meteorites. Recently, glycine was also observed in cometary samples returned by the Stardust space probe. The goal of this work was to perform theoretical calculations for several interstellar reactions involving the simplest carboxylic acids as well as the carboxyl radical (COOH) in both gas and solid (ice) phase to understand which reactions could be the most favorable to produce glycine in interstellar regions fully illuminated by soft X-rays and UV, such as star-forming regions. The calculations were performed at four different levels for the gas phase (B3LYP/6-31G*, B3LYP/6-31++G**, MP2/6-31G*, and MP2/6-31++G**) and at MP2/6-31++G** level for the solid phase (ice). The current two-body reactions (thermochemical calculation) were combined with previous experimental data on the photodissociation of carboxylic acids to promote possible favoritism for glycine formation in the scenario involving formic and acetic acid in both gas and solid phase. Given that formic acid is destroyed more in the gas phase by soft X-rays than acetic acid is, we suggest that in the gas phase the most favorable reactions are acetic acid with NH or NH?OH. Another possible reaction involves NH?CH? and COOH, one of the most-produced radicals from the photodissociation of acetic acid. In the solid phase, we suggest that the reactions of formic acid with NH?CH or NH?CH?OH are the most favorable from the thermochemical point of view.     

Mass-, time-, and energy-characteristics of the interstellar flights during the long proper time of astronauts

The existence of extraterrestrial intelligence (ETI) and extraterrestrial scientific-technical civilization (STC) is of principal importance for CETI (communication with extraterrestrial intelligence) and SETI (search for extraterrestrial intelligence). According to Kardashev and Bracewell, the Earth-like STC in their farther development can expand to the nearby planetary systems of the Galaxy, creating galactic community (Bracewell's galactic club).In a previous paper the possibilities of the one-step relativistic rocket interstellar flight during the proper time of life of one-two generations of astronauts were analysed. The realization of such interstellar flights is very improbable, even to the nearest stars. These results could be true for the case of the comparatively short proper time of astronauts, i.e. large acceleration. But flights to the nearest stars could be realized with small and very small accelerations. In the present paper are calculated the proper times t in the reference systems connected with the astronauts (S₂), as well as the times T in the reference systems (S₁)-inertial, velocities v in S₁, mass ratios, powers and energies for various flights, exhaust velocities u and accelerations a. Results are critically discussed.