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The technology for even the most advanced missions in the solar system doesn't need advances in basic science. Traveling through the solar system can be described through what is called ‵hard science fiction', i.e. science fiction strictly based on scientific knowledge. Interstellar exploration is a completely different matter. Robotic flyby missions to the nearest stars using nanoprobes can be performed using technologies based on known science, while anything beyond this requires advances which we don't know how to implement, or even we are not sure whether they are possible at all. The point applies not only to the technological aspects but even the scientific bases on which the relevant technologies may rest. The missions requiring less scientific-technological advances, are slow missions, like space arks (generation ships) or missions based on hibernation with travel times up to hundred years. To implement both, the uncertainties are more related to the advances in space medicine and biology than in propulsion and physics. The fastest travels allowed by the current interpretations of the relativity theory are relativistic missions in which the time contraction at speeds closing the speed of light is exploited to decrease the travel time for the astronauts, although the travel time seen by those who remain on Earth is close, in years, to the distance traveled expressed in light years. However, the energy required for this type of missions is large and grows drastically with the increase of time contraction. Faster than light travel, which seems to be possible following some interpretations of relativity involving either wormholes or some sort of warp drive, requires substantial advances in fundamental physics. A symptom of this is that the novels dealing with interstellar travels belong more to the space opera – which doesn't follow strict scientific credibility – than to the hard science fiction subgenre. No novel of this kind explains details about how the relevant machinery works, and even less scientifically realistic are the movies, TV series, and videogames of this kind. Moreover, to achieve a travel time allowing to reach distant star systems in reasonable times using warp drives, the authors of Star Trek had to resort to the Warp Factor which is essentially a nonlinear scale. This makes the requirements for FTL travel even more difficult to achieve. • Interstellar travel requires advances in technology and, in some cases, in science. • Generation ships, which travel for centuries, require only technological advances. • Slow travel with hibernated crew is simpler but requires to develop long term hibernation. • Faster than light (FTL) travel might be not incompatible with present day science. • Interstellar travel as fast as in science fiction, requires speeds hundreds times FTL. [ABSTRACT FROM AUTHOR]

This paper analyzes the design of an alpha-decay sail. While previous studies have been conducted on the feasibility of alpha-decay sails, none have investigated the effects of different backing materials and backing material thicknesses on propulsion. This paper conducts simulations using the particle simulation toolkit Geant4 to determine the thrust produced from alpha-decay sails constructed of 238Pu and a backing layer made of aluminum, beryllium, lithium, or polyethylene. The results demonstrate that alpha-decay sails can be a very useful form of in-space propulsion, having the potential to dramatically decrease travel time beyond distances of 100 AU. [ABSTRACT FROM AUTHOR]

This article explores how Simon Jimenez's The Vanished Birds participates in but also moves beyond the discourse of techno-Orientalism through its depiction of characters, companies, and interstellar travel. Readers encounter a seemingly quintessential techno-Orientalist construct when they meet the book's protagonist, Fumiko. But their attention is soon redirected to a corporate entity whose predatory capitalist practices make it the new, menacing techno-Orientalist figure in the plot. The novel intervenes in discourses of techno-Orientalism by emphasizing how exploitative economic power dynamics are not limited to actors such as individuals or nation-states, as they are typically understood, but include corporate entities. This article thus contends that more precision is necessary when defining techno-Orientalist constructs and encourages readers to expand their perspectives as they immerse themselves in the Asian American science fictional world. [ABSTRACT FROM AUTHOR]

• Interstellar exploration is defined as bi-objective multi-vehicle problem with profits. • Mission return increases approximately linearly with mission duration. • Lower probe numbers enable more efficient routing through shorter transfers. In the past decade, the discovery of exoplanets has sparked new interests in the idea of interstellar travel and exploration. Despite various proposals for probe concepts and relevant technologies, there is a lack of extensive literature on viable exploration strategies for journeys beyond a single star system. Such exploration strategies might not only have implications on technology development strategies for achieving interstellar exploration but could also enrich existing models for galactic exploration feeding into solutions of the Fermi Paradox. This article presents optimal strategies for the exploration of a large number of near-by stars, using a dedicated, novel methodology, which sets it apart from existing literature: For the first time, the mission design problem of interstellar exploration is redefined as a bi-objective multi-vehicle open routing problem with profits. It is tackled by an adapted hybrid multi-objective genetic algorithm, which is further improved and modified according to the problem characteristics (e. g. large search space). The overall mission model assumes probes traveling on straight trajectories, utilizing flybys, and maintaining an average velocity of 10% of the speed of light. Surpassing prior research that typically relies on statistical models or restricted star data, the star models are founded on the second Gaia data release (Gaia DR2), which represents the most extensive star catalogue to the date of this study and is employed for the first time in the context of interstellar exploration. The resulting star model contains a maximum of 10,000 stars within a spherical region around Sol, covering a distance of 110 light years. It is found, that the number of explored stars J 1 scales with mission duration J 2 and probe number m according to J 1 ∼ J 2 m 0.66 , which provides an initial guidance for future interstellar mission design. Furthermore, the routes and selection of stars vary depending on the number of probes used: When conducting missions with a large number of probes, stars in close proximity to the Solar System are given more focus. On the other hand, missions with a small number of probes include more distant stars to facilitate shorter transfers along the route. Based on these findings, the following recommendations for interstellar exploration strategies can be drawn: When energy resources such as fuel reserves are scarce and the exploration mission is not limited to nearby stars, low probe numbers are more efficient. In contrast, high probe numbers enable faster exploration of nearby stars but involve less resource-efficient transfers, making them a suitable option for small, remotely propelled probe concepts. To address crowding effects in high probe number missions, swarm-based probe concepts are recommended based on the scaling law characteristics derived. [ABSTRACT FROM AUTHOR]

A propulsion concept in which a spacecraft interacts with both a stream of high-velocity macroscopic pellets and the mass of the interplanetary or interstellar medium is proposed. Unlike previous pellet-stream propulsion concepts, the pellets are slower than the spacecraft and are accelerated backwards as they are overtaken by it, imparting a forward acceleration on the spacecraft. This maneuver is possible due to the interaction with a fixed medium (e.g., interstellar medium); as the spacecraft travels through the medium, it is able to extract power from the relative wind blowing over the spacecraft. As viewed from the rest frame, the kinetic energy of the pellets is transferred to the spacecraft; the source of energy for the propulsive maneuver (i.e., whether the source is the pellets or the wind) is thus reference-frame dependent. This concept relies upon the relative velocities (or shear) between the pellet stream and the fixed medium in order to concentrate the energy of the pellets into the spacecraft and is therefore termed wind–pellet shear sailing. The equations governing the mass ratio of pellets to the spacecraft and its dependence on the final spacecraft velocity are derived, analogous to the classical rocket equation; the critical role of the efficiency of the power extraction and transfer process is identified. Natural sources of energy (photon and particle fluxes from the sun) are considered as a means to accelerate the pellets, produced from in-situ sources of material in the solar system, to velocities of 1000 to 6000 km/s. Techniques for onboard generation of power via electromagnetic interaction with the interstellar medium (ISM) are reviewed, with a repetitively stroked plasma magnet being identified as a promising approach. The necessity of the spacecraft to detect and track the pellets as they are overtaken dictates the desired properties of the pellets. Pellet pushers (i.e., accelerators) on board the spacecraft are also preliminarily explored in their engineering considerations, with electric field accelerators of charged nanometric particles, Lorentz-force accelerated ionized pellets, or expansion of vaporized pellets via a nozzle being highlighted as potential approaches. A preliminary mission profile is defined in which a 500-kg scientific payload is delivered to orbit about α -Centauri, using wind–pellet shear sailing as the intermediate stage to bring the spacecraft from 2% to 5.5% of c , with a total mission duration (launch to arrival) of 27 years. The concept design illustrates the potential for synergy at the low-velocity end with advanced solar photon or solar-wind sailing and at the high-velocity end with the q -drive concept. • A new concept is proposed: a spacecraft overtakes pellets, transferring their energy to the spacecraft. • The concept exploits the use of free energy sources available in space. • Analysis suggests spacecraft may be accelerated from 2% to 5% of the speed of light. • The technique may be combined with other propulsion devices to achieve greater speeds. • A mission to return data from nearby stars within 30 years of launch may be possible. [ABSTRACT FROM AUTHOR]

Demonstrations of photonically-propelled materials for solar and laser sailing have relied on indirect techniques for determining the propulsion efficiency. These methods, utilizing drop towers or cameras to determine differential displacement, are necessarily low-throughput and cannot be easily compared directly. Furthermore, the methods require sample sizes that are prohibitive to the fabrication of low TRL photonic materials (e.g. thin-film metasurfaces) that discourages rapid iterative testing. Herein, a nanocantilever-based test bed is proposed to simplify and standardize the determination of the characteristic acceleration for a given sail swatch. The proposed system is designed to allow for flexible, automated spectral analysis, requiring sample sizes ∼10 μm2. This system is scalable to the micro- and macroscale as material technologies mature and advance toward deployment scale. • Laser sources irradiating cantilever systems lead to measurable force deflection. • Quantify spectral characteristics of light sails for mission qualification. • Sail candidate materials may be directly tested for failure. • Requires swatches on the order of μm2. • Allows for high-throughput iteration. [ABSTRACT FROM AUTHOR]

Civilizations ahead of our own may wish to control their star system's motion for a variety of reasons, ranging from the avoidance of cataclysmic cosmic events to the facilitation of interstellar, and perhaps intergalactic, colonization. Such an endeavor can be achieved via the construction of megastructures known as stellar engines, which utilize a star's own resources to gradually accelerate the star system in the desired direction over extended periods of time. Here, we conceptualize the 'Star Tug', a stellar engine capable of producing significantly higher accelerations than previous stellar engine concepts. The Star Tug consists of an engine positioned ahead of the star along the desired direction of acceleration. The engine is gravitationally bound to the star and utilizes mass acquired from the star as propellant to generate thrust which counterbalances the force of gravity between it and the star. As long as the propellant exhaust velocity exceeds the escape velocity of the star system, the star system should accelerate. Depending on efficiency and engineering constraints, the Star Tug may be capable of accelerating a sun-like star to relativistic velocities within megayear time scales. • Stellar engines are structures that manipulate the motion of entire star systems. • The 'Star Tug' can produce higher accelerations than prior stellar engine concepts. • The Star Tug may be able to accelerate a sun-like star to relativistic velocities. [ABSTRACT FROM AUTHOR]

Stellar engines, megastructures used to control the motion of a star system, may be constructible by technologically advanced civilizations and used to avoid dangerous astrophysical events or transport a star system into proximity with another for colonization. This work considers two designs for stellar engines, for both human applications in the solar system and for advanced civilizations around arbitrary stars more generally, and presents analytic calculations of the maximum acceleration and deflection of a star in its galactic orbit. The first is a large 'passive' solar sail, similar to that proposed by Shkadov, which we find produces accelerations of order 10 − 12 m / s 2 for sun-like stars. The second 'active' engine uses a thermonuclear driven jet, as in a Bussard ramjet, which collects matter from the solar wind to drive He fusion. This engine requires additional mass to be lifted from the sun, beyond what is provided by the nascent solar wind, but may achieve accelerations up to 10 − 9 m / s 2 producing deflections of 10 pc in as little as 1 Myr for a sun-like star. While passive engines may be insufficient for catastrophe avoidance on short timescales, they can produce arbitrary deflections of a star in its galactic orbit over a stellar lifetime. Active engines are sufficient for retrograde galactic orbits or galactic escape trajectories, which we argue are useful to expansionist civilizations. These populations of stars may be candidates for observationally detecting megastructures. • Stellar engines may be used to arbitrarily manipulate a star's galactic orbit. • Solar sails, as in Shkadov, produce large orbital deflections on gigayear timescales. • Thermonuclear ramjets produce large orbital deflections on megayear timescales. • Hypervelocity or retrograde stars may be candidates for observing megastructures. [ABSTRACT FROM AUTHOR]

The author discusses the theme of interstellar travel in science fiction. Focusing mainly on science fiction films and television programs, she mentions early depictions of space travel, mentions the use of generation ships and hyperspace travel as forms of interstellar travel, and presents examples from various films and programs.

Abstract Propellantless propulsion is believed to be the best option for interstellar travel. However, photon rockets or solar sails have thrusts so low that maybe only nano-scaled spacecraft may reach the next star within our lifetime using very high-power laser beams. Since 2012, a dedicated breakthrough propulsion physics group was founded at the Institute of Aerospace Engineering at TU Dresden to investigate different concepts based on non-classical/revolutionary propulsion ideas that claim to be at least an order of magnitude more efficient in producing thrust compared to photon rockets. Most of these schemes rely on modifying the inertial mass, which in turn could lead to a new propellantless propulsion method. Our intention is to develop an excellent research infrastructure to test new ideas and measure thrusts and/or artefacts with high confidence to determine if a concept works and if it does how to scale it up. At present, we are focusing on two possible revolutionary concepts: The EMDrive and the Mach-Effect Thruster. The first concept uses microwaves in a truncated cone-shaped cavity that is claimed to produce thrust. Although it is not clear on which theoretical basis this can work, several experimental tests have been reported in the literature, which warrants a closer examination. We are building several models of different sizes to understand scaling laws and the interaction with the test environment. The second concept is theoretically much better understood and is believed to generate mass fluctuations in a piezo-crystal stack that creates non-zero time-averaged thrusts. Apart from theoretical models, we are testing and building several such thrusters in novel setups to further investigate their thrust capability. In addition, we are performing side-experiments to investigate other experimental areas that may be promising for revolutionary propulsion. To improve our testing capabilities, several cutting-edge thrust balances are under development to compare thrust measurements in different measurement setups to gain confidence and to identify experimental artefacts. Highlights • Thorough investigation of breakthrough propulsion concepts. • Thrust balance development to test EMDrive and Mach-Effect thrusters. • Complementary experiments to test physics behind claims. • Education project towards interstellar spaceflight. [ABSTRACT FROM AUTHOR]

Abstract In traditional form-finding of a deployable mesh reflector (DMR), the nodes of the DMR mesh are placed on the desired working surface and the surface accuracy of the DMR is measured either by the deviation of the nodes from the desired working surface or by the deviation of the mesh from its best-fit surface. Placement of nodes on working surface and inaccurate measures of surface accuracy cause non-negligible surface errors that cannot be further reduced. To deal with these issues and to further improve surface accuracy of DMRs, a new mesh geometry design method, called the Projecting Surface Method (PSM), is presented in this paper. The highlight of the PSM is that it purposely places the nodes of a DMR off its working surface, to achieve higher surface accuracy. To this end, a direct RMS error measuring the deviation of a DMR mesh from its desired working surface is introduced and a projecting surface for hosting the nodes of the DMR mesh is defined. By the direct RMS error and projecting surface, an optimization process produces a mesh geometry with its best-fit surface closest to the desired working surface, leading to significant surface error reduction. As shown in numerical examples of DMRs with 37, 271 and 817 nodes, the PSM can reduce surface errors by 50% or more. The proposed method is usable with existing form-finding methods for further improvement of surface accuracy of DMRs. Highlights • A newly defined RMS error for precise measurement of surface accuracy. • Establishment of a projecting surface for form-finding of mesh reflectors. • Purposely placing mesh nodes off the working surface of a reflector in design. • Significant reduction of surface errors (by 50–97%). • Usable with any existing form-finding method for further surface error reduction. [ABSTRACT FROM AUTHOR]

Abstract Two technological problems must be solved before daring to interstellar flight: fuel and propulsion. The highest energy-density 'fuel' is antimatter in its solid or liquid state and this fuel is likely to be our primary choice for multi-ton relativistic rockets. High-energy ion thrusters powered by annihilation reactors promise superior performance in comparison with direct propulsion by annihilation products. However the power generator onboard can significantly enlarge the rocket dry mass thus limiting the achievable speed. Two physical factors that stand against our dream of the stars are thermodynamics and radiation hazard. Heat-disposing radiator also increases the rocket dry mass. Interstellar gas turns into oncoming flux of hard ionizing radiation at a relativistic speed of the rocket while the oncoming relativistic interstellar dust grains cause mechanical damage. Economy and psychology will play a decisive role in voting for or against the manned interstellar flights. Highlights • Technical challenges are discussed. • High-energy ion thruster is our only option. • Achievable rocket speed as a function of exhaust mass is estimated. • Limiting physical and social factors are indicated. • Robotic rocket is argued to be preferred. [ABSTRACT FROM AUTHOR]

As the major part of space life supporting systems, artificial gravity requires further study before it becomes mature. Spinning tether system is a good alternative solution to provide artificial gravity for the whole spacecraft other than additional devices, and its longer tether length could significantly reduce spinning velocity and thus enhance comfortability. An approximated overload-based feedback method is proposed to provide estimated spinning velocity signals for controller, so that gravity level could be accurately controlled without complicated GPS modules. System behavior in high eccentricity transfer orbits is also studied to give a complete knowledge of the spinning stabilities. The application range of the proposed method is studied in various orbit cases and spinning velocities, indicating that it is accurate and reliable for most of the mission phases especially for the final constant gravity level phase. In order to provide stable gravity level for transfer orbit missions, a sliding mode controller based on estimated angular signals is designed for closed-loop control. Numerical results indicate that the combination of overload-based feedback and sliding mode controller could satisfy most of the long-term artificial gravity missions. It is capable of forming flexible gravity environment in relatively good accuracy even in the lowest possible orbital radiuses and high eccentricity orbits of crewed space missions. The proposed scheme provides an effective tether solution for the artificial gravity construction in interstellar travel. [ABSTRACT FROM AUTHOR]

While special relativity imposes an absolute speed limit at the speed of light, our Universe is not empty Minkowski spacetime. The constituents that fill the interstellar/intergalactic vacuum, including the cosmic microwave background photons, impose a lower speed limit on any object travelling at relativistic velocities. Scattering of cosmic microwave photons from an ultra-relativistic object may create radiation with a characteristic signature allowing the detection of such objects at large distances. [ABSTRACT FROM AUTHOR]

Nanoscale spacecrafts have shed light on an audacious but promising vision for interstellar travel to neighboring planets beyond the solar system. The nanocrafts can be accelerated to a significant fraction of light speed, which leads to the possibility of completing the otherwise millennia space missions using the current rocket propulsion technology in several decades. However, electrical energy is a severe challenge for long-term interstellar travel. Mechanical energy metamaterials have been proposed as a promising technology integrated multiscale architected structures with energy materials, which have opened an exciting venue for energy harvesting under extreme conditions such as the cosmic environment. Mechanical energy metamaterials are envisioned as an alternative energy solution to address the power issue of nanocrafts in interstellar travel. Here, this article comprehensively overviews the debut and development of mechanical energy metamaterials and discusses the potential and application paradigm for energy harvesting in the cosmic environment. We first clarify the main feature and functionality of mechanical metamaterials and summarize the recent findings on typical mechanical energy metamaterials. Next, we identify the characteristics and challenges of the cosmic environment, deliberate the fundamental energy issue of interstellar travel, and examine the stringent criteria to design mechanical energy metamaterial nanosails for electrical power. Discussion indicates that kinetic energy resulted in cosmic dust grains collision and photovoltaic energy from starlight can be the main energy sources for mechanical energy metamaterials. In the end, we propose the applications of mechanical energy metamaterial nanosails in the nano space energy systems (nano-SES) to address the energy challenges in interstellar travel by generating electrical power from the kinetic and photovoltaic energies. [ABSTRACT FROM AUTHOR]