The guinness world record for the fastest spacecraft was achieved when NASA’s Juno probe was pulled into Jupiter’s massive gravity well, accelerating the probe to a maximum velocity of 165,000 MPH (nearly 17 times the speed of sound from a physics standpoint). While, in essence, this may seem nearly unfathomable to earthly measures, to those seeking to accomplish interstellar travel perceive this achieved speed to be a grain of sand on a beach compared to the preconditioned speed to manifest this reality. Beside the fact that the speeds required for interstellar travel (necessitating a high percentage of the speed of light) in a human lifetime far exceed what current methods of spacecraft propulsion can provide, the distance required to travel between stars (typically hundreds of thousands of AU) would entail travel times lasting decades to millennia, or even longer.Despite these challenges, with the use of speculative physics, a few projects (the Breakthrough Starshot, Project Icarus, and Lightsail, to name a few) have been proposed, ranging from giant arks that would carry entire societies and ecosystems to microscopic space probes. There are many different spacecraft propulsion systems tenable to meeting this demanded velocity, including those utilizing nuclear fusion-based propulsion, solar -powered sail, and interstellar ramjets, among other considerations. Yet, more importantly, why does any of this matter? With the current risks posed by global warming, there is overwhelming evidence that over half of the species on Earth will be extinct before the turn of the century. Indications sourcing from natural disasters and drastic obscurities in weather behavior signal the ramifications that are due to impact the social and economic fabric of the world in a few decades. While the motives for pursuing interstellar travel are generally for explorative purposes, in some respects, it has also become a search for a new planet to call home. Of course, before contemplating a spacecraft design that is plausible for such a journey, the potential complications that lie in the way of this actuality must be resolved before materializing prototypes for this mission. The closest known star, Proxima Centauri, is some 268,332 AU away, which is relative to 4.243 light-years away. The fastest spacecraft launched-to-date,  the Voyager 1, has covered 1/600 of a light-year in 30 years and is currently approaching 1/18,000 the speed of light. Given this rate, a journey to Proxima Centauri would take roughly 80,000 years to complete. Without factoring in issues relating to required kinetic energy, interstellar dust and gas obstructions (and other space debris) in the interstellar medium, and the psychological effects of long-term isolation for proposed manned missions, an interstellar journey that cannot be completed within 50 years should not be started at all. The ‘wait calculation’ premise plays off of the assumption that a civilization that is still on a progressing curve of propulsion system velocity and not yet having reached the limit should alternatively invest its resources into designing a better propulsion system. This hypothesis leads to the deliberation of the various projects—both past and present—undertaken to attempt to suffice the requirements necessary for carrying out the mission successfully. In 1973, the British Interplanetary Society (now, the oldest space advocacy organisation in the world) initiated a five year program to design an unmanned spacecraft that was capable of interstellar flight. Project Daedalus was the first to tackle the question of the possibility of interstellar travel, while the goal of the project was to discover the feasibility of getting a person to travel to a variety of different target stars, using near-future technology, within their lifespan. The barriers of reaching speeds fast enough and with enough generating power while not burning the spacecraft to a crisp were not easily overcome. The Project Daedalus team decidedly ended up with a nuclear pulse rocket that could transgress these limitations: small thermonuclear bombs would detonate inside cusp-shaped magnetic fields behind the spacecraft, thrusting it forward at the highest potential efficiency.A velocity of more than 10,000 kilometers per second would have to be achieved to complete the mission requirements, yet, that was only a small part of the challenge. In fact, a more ambiguous question would be to ask: who would steer it? A sophisticated, autonomously operating system would have to take the reigns, freighting passengers across the galaxies. The fuel to power the reactors would have to come from a helium-3 isotope, which would derive from mining the atmosphere of Jupiter or the Moon by a large hot air balloon, leading to yet another obstacle to add to an ever-growing list. In all, a final report published in 1978 declared that interstellar flight was indeed feasible, but a working prototype has yet to be designed. But to call Project Daedalus a pipe dream would be doing it a disservice. There are numerous indications that space agencies and universities of today have been considering the Project Daedalus ideas, such as using nuclear power as propulsion. The now over thirty-year-old project has laid much of the groundwork of interstellar travel and was the first of its kind.Project IcarusMembers of the British Interplanetary Society teamed up with the Tau Zero Foundation in 2009 to design a credible interstellar space probe, using the same nuclear fusion-based propulsion system as the one designed for the Daedalus Project. The project’s goals are to complete a set of technical reports that lay out all the details of an interstellar probe, while motivating the next generation of scientists, who will be completing the designs of this spacecraft. The engineering project is currently looking for volunteers to bring it to completion.LIGHTSAILThe Planetary Society launched a project called LightSail to examine the possibility of a spacecraft that was purely solar-powered and propelled by sunlight alone. A first iteration (LightSail 1) completed a “shakedown cruise” in orbit and transmitted its first signals back to Earth. Its successor, LightSail 2, is set to launch aboard a SpaceX Heavy Falcon rocket in 2018. The concept of a solar sail used for propulsion in space is not a new one. Alongside the discovery of the photon, astronomers such as Johannes Kepler in the 1600s were already hypothesizing about the possibility of harvesting the energy of the sun and transferring that momentum to another object as the source of propulsion. Stephen Hawking has voiced his own desire to launch a light sail called Breakthrough Starshot. At a recent event in Norway, Hawking described the small space probe that could travel “on a beam of light,” reaching roughly 160 million k/h (100 million mph). The project has yet to overcome significant hurdles and many rounds of funding.BUSSARD RAMJETIn 1960, an American physicist conceptualized an interstellar spacecraft that was able to travel at a significant fraction of the speed of light. Rather than being “weighed down” by the mass of the payload, Bussard’s ramjet relied on harvesting hydrogen and using it as a propellant. Like the original Daedalus Project, the ramjet would use hydrogen in a nuclear fusion reactor to supply the energy needed to carry it to distant stars. According to his calculations, the ramjet would need a collection area of nearly 10,000 square kilometers. The resulting mass would be astronomical, making it more or less infeasible.ANTIMATTER ROCKETSLong gone are the dreams of fueling an interstellar probe with hydrogen isotopes in a nuclear reaction. The new frontiers of interstellar travel have moved their focus to antimatter thrusters, but reactions between antimatter and matter have very violent consequences. Assuming the possibility of directing the huge amounts of energy created in a single direction, the energy outburst caused by the atoms’ mutual annihilation could be collected and used as a rocket propellant — but we are far from being able to test this in reality. An antimatter rocket has inherent limitations: (1) an immense load of dangerous gamma radiation that results from an antimatter reaction; (2) creating enough antimatter for fuel; and (3) limiting the size of the payload. NASA’s Institute for Advanced Concepts has been funding research into a new design for an antimatter-powered spaceship that overcomes the first challenge. By relying on newly discovered positrons (rather than antiprotons), the resulting gamma rays would be far lower in energy. More recent designs have overcome the second challenge by designing a kind of antimatter sail. Gerald Jackson, former Fermilab physicist, created a Kickstarter to test an antimatter thruster and make antimatter-based propulsion a reality. Another estimated $100 million will have to be raised to develop an Earth-based test.THE IXS ENTERPRISE NASA designed its own Star Trek-like space warping ship in 2016 that shares a lot of similarities with the USS Enterprise. Ship designer Mark Rademaker’s goal was to “motivate young people to pursue a STEM career,” he told The Washington Post. Rather than relying on nuclear fusion or antimatter reactions, the IXS Enterprise takes advantage of a warp drive that, according to io9, would expand “empty space behind a starship…pushing the craft in a forward direction.” The large rings around the spacecraft serve to form a “warp bubble” to reduce the energy requirements for the warp drive.


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