Knowing of Grover Swartzlander’s pioneering work on diffractive solar sails, I was not surprised to learn that Amber Dubill, who now takes the idea into a Phase III study for NIAC, worked under Swartzlander at the Rochester Institute of Technology. The Diffractive Solar Sailing project involves an infusion of $2 million over the next two years, with Dubill (JHU/APL) heading up a team that includes experts in traditional solar sailing as well as optics and metamaterials. A potential mission to place sails into a polar orbit around the Sun is one possible outcome. [Addendum: The original article stated that the Phase III award was for $3 million. The correct amount is $2 million, as changed above]. But let’s fall back to that phrase ‘traditional solar sailing,’ which made me wince even as I wrote it. Solar sailing relies on the fact that while solar photons have no mass, they do impart momentum, enough to nudge a sail with a force that over time results in useful acceleration. Among...

Not long ago we looked at Greg Matloff’s paper on von Neumann probes, which made the case that even if self-reproducing probes were sent out only once every half million years (when a close stellar encounter occurs), there would be close to 70 billion systems occupied by such probes within a scant 18 million years. Matloff now considers interstellar migration in a different direction in a new paper addressing how M-dwarf civilizations might expand, and why electric sails could be their method. It’s an intriguing notion because M-dwarfs are by far the most numerous stars in the galaxy, and if we learn that they can support life, they might house vast numbers of civilizations with the capability of sending out interstellar craft. They’re also crippled in terms of electromagnetic flux when it comes to conventional solar sails, which is why the electric sail comes into play as a possible alternative, here analyzed in terms of feasibility and performance and its prospects for enabling...

Centauri Dreams tracks ongoing work on beamed sails out of the conviction that sail designs offer us the best hope of reaching another star system within this century, or at least, the next. No one knows how this will play out, of course, and a fusion breakthrough of spectacular nature could shift our thinking entirely – so, too, could advances in antimatter production, as Gerald Jackson’s work reminds us. But while we continue the effort on all alternative fronts, beamed sails currently have the edge. On that score, take note of a soon to be available two-volume set from Philip Lubin (UC-Santa Barbara), which covers the work he and his team have been doing under the name Project Starlight and DEEP-IN for some years now. This is laser-beamed propulsion to a lightsail, an idea picked up by Breakthrough Starshot and central to its planning. The Path to Transformational Space Exploration pulls together Lubin and team’s work for NASA’s Innovative Advanced Concepts office, as well as work...

The continuing release of papers related to or referring to the Breakthrough Starshot sail concept is good news for the entire field. Interstellar studies as an academic discipline has never had this long or sustained a period of activity, and the growing number of speakers at space-related conferences attests to the current vitality of starflight among professionals and the general public alike. Not all interstellar propulsion concepts involve laser-beaming, of course, and we’ll soon look at what some would consider an ever more exotic concept. But today I’m focusing on a paper from Ho-Ting Tung and Artur Davoyan, both in the Mechanical and Aerospace Engineering Department at UCLA. You could say that these two researchers are filling in some much needed space between the full-bore interstellar effort of Breakthrough Starshot, the Solar System-oriented laser work of Andrew Higgins’ team at McGill, and much smaller, near-term experiments we could run not so far from now. Of the many...

One of the benefits of a project like Breakthrough Starshot is that it moves the ball forward in terms of the academic research that underpins advances in technologies. I seriously doubt that Starshot will result in an Alpha Centauri probe reaching these stars within the next 50 years, given among other things the conundrum of data retrieval from a fleet of chip-sized micro-craft. But we all gain from the fact that scientists are tackling these issues in a well-funded and coordinated way. The research library grows. As a field, interstellar studies has always been resource-starved, not to mention winning scant attention among the larger community of scientists and engineers at conferences and in publications. But it has drawn on a consistent thread of interest that now gains new energies. That benefits the entire effort. And let's not forget the power of looking far into the future to get a conception of what we can do with scaled-down projects in the near term, as for example Andrew...

2020 GE is an interesting, and soon to be useful, near-Earth asteroid. Discovered in March of 2020 through the University of Arizona's Catalina Sky Survey, 2020 GE is small, no more than 18 meters or so across, placing it in that class of asteroids below 100 meters in size that have not yet been examined up close by our spacecraft. Moreover, this NEA will, in September of 2023, obligingly make a close approach to the Earth, allowing scientists to get that detailed look through a mission called NEA Scout. This is a mission we've looked at before, and I want to stay with it because of its use of a solar sail. Scheduled to be launched with the Artemis 1 test flight using the Space Launch System (SLS) rocket no earlier than March of this year, NEA Scout is constructed as a six-unit CubeSat, one that will be deployed by a dispenser attached to an adapter ring connecting the rocket with the Orion spacecraft. After separation, the craft will unfurl a sail of 86 square meters, deployed via...

I’ve learned that you can’t assume anything when giving a public talk about the challenge of interstellar flight. For a lot of people, the kind of distances we’re talking about are unknown. I always start with the kind of distances we’ve reached with spacecraft thus far, which is measured in the hundreds of AUs. With Voyager 1 now almost 156 AU out, I can get a rise out of the audience by showing a slide of the Earth at 1 AU, and I can mention a speed: 17.1 kilometers per second. We can then come around to Proxima Centauri at 260,000 AU. A sense of scale begins to emerge. But what about propulsion? I’ve been thinking about this in relation to a fundamental gap in our aspirations, moving from today’s rocketry to what may become tomorrow’s relativistic technologies. One thing to get across to an audience is just how little certain things have changed. It was exhilarating, for example, to watch the Arianne booster carry the James Webb Space Telescope aloft, but we’re still using...

Can you imagine the science we could do if we had the capability of sending a probe to Jupiter with travel time of less than a month? How about Neptune in 18 weeks? Alex Tolley has been running the numbers on a concept called Wind Rider, which derives from the plasma magnet sail he has analyzed in these pages before (see, for example, The Plasma Magnet Drive: A Simple, Cheap Drive for the Solar System and Beyond). The numbers are dramatic, but only testing in space will tell us whether they are achievable, and whether the highly variable solar wind can be stably harnessed to drive the craft. A long-time contributor to Centauri Dreams, Alex is co-author (with Brian McConnell) of A Design for a Reusable Water-Based Spacecraft Known as the Spacecoach (Springer, 2016), focusing on a new technology for Solar System expansion. by Alex Tolley In 2017 I outlined a proposed magnetic sail propulsion system called the Plasma Magnet that was presented by Jeff Greason at an interstellar...

The first laboratory work on pushing a space sail with microwaves was performed by Jim and Greg Benford at the Jet Propulsion Laboratory back in 1999, with the results presented the following year at a European conference. Leik Myrabo (then at Rensselaer Polytechnic Institute) was, at about the same time, performing experiments with lasers at Wright-Patterson Air Force Base in Ohio. When you think about the problems of laboratory work on these matters, consider the fact of gravity, meaning that you are working in a 1 g gravity well with diaphanous materials whose acceleration depends on how hot you can allow them to become. Advances in materials and in particular in lightweight carbon structures allowed the Benfords' experiments to succeed, with the help of a 10-kilowatt microwave beam that produced significant acceleration on the test object. But I'm reminded by looking at a new paper on sail technologies using no beam at all that the Benfords also demonstrated something else....

I’ve focused on aerographite these past several days because sail materials are a significant determinant of the kind of missions we can fly both in the near-term and beyond. The emergence of a new ‘contender’ to join graphene as a leading candidate for deep space missions is worthy of note. Whether or not this ultra lightweight material produced by teams at the Technical University of Hamburg and the University of Kiel lives up to its promise will depend upon a thorough investigation of its properties as adapted for sails, one which has already begun. Sail materials matter because we have already begun flying spacecraft with these technologies, so that as we climb the learning curve in terms of design and engineering, we need to be thinking about how to increase performance to allow ambitious missions, and perhaps even audacious ones like Breakthrough Starshot, though the authors of the first paper on aerographite for sails are skeptical about whether the material could withstand...

Aerographite is an ultra lightweight material made of carbon microtubes, just the sort of thing that seizes the imagination in terms of material for space sails powered by solar photons or laser beam. Such materials are much in my thinking these days and have been for some time, ever since I first read some of Robert Forward’s papers on using laser beaming to boost enormous sails to a substantial fraction of lightspeed. What kind of materials would be used, and how could the mass be kept low enough to allow significant payloads to be deployed? These days, we think in terms of much smaller sails with miniaturized payloads of the sort advocated by Breakthrough Starshot. But of course advances in sail technology enable a wide range of concepts, and the place to start is with laboratory experiment -- this is where we are with aerographite right now -- moving into space demonstrators that can be low-cost and near-term. The kinds of missions conceivable with aerographite include fast...

Invented at the Technical University of Hamburg and developed with the aid of researchers at the University of Kiel, a new material called aerographite offers striking prospects for solar sail missions within the Solar System as well as interstellar precursor implications. Judging from the calculations in a just published paper in Astronomy & Astrophysics, aerographite conceivably enables a mission to Proxima Centauri with a flight time of less than two centuries. We are not talking about laser-driven missions here, but rather meter-scale craft that would be pushed to interstellar velocities by solar radiation; i.e., true solar sails. But let’s focus near-term before going interstellar. I’ve been talking to René Heller (Max Planck Institute for Solar System Research, Göttingen) about the paper, along with co-authors Guillem Anglada-Escudé (Institut de Ciencies Espacials, Barcelona), Michael Hippke (Sonneberg Observatory, Germany) and Pierre Kervella (Observatoire de Paris). Just what...

When we consider pushing a sail to 20 percent of lightspeed, which is the target velocity for Breakthrough Starshot, it's interesting to think about how laser propulsion differs from sunlight. After all, while constructing a huge laser array presents numerous challenges on Earth, we already have a star to work with, and sail technology that is beginning to be tested in space. Consider, too, that we have operational spacecraft like the Parker Solar Probe that are exploring regions close to the Sun, helping us learn more about heat shields, even as we plan missions like Solar Cruiser, whose sail would enable interesting non-Keplerian orbits near the Sun. Wouldn't it be easier to find ways to use our Sun's own energies to drive our starship by getting a boost from gravitational effects? A closer look reveals the power of solar sails in nearby space (i.e., within the system), while illuminating the problems at interstellar distances. For getting a solar sail up to the highest possible...

The electric sail is an intriguing propulsion concept that Pekka Janhunen at the Finnish Meteorological Institute has been championing for some years. It’s currently the subject of a NASA Phase II study and continues to draw attention despite the fact that we’re in the early stages of turning what looks like sound physical theory into engineering. What captures the imagination here is the same thing that is so attractive about solar sails -- in both cases, we are talking about carrying no propellant, but instead relying on natural sources to do the work. Here we have to be careful about terminology, because it’s all too easy to refer to solar photons as a kind of ‘wind,’ especially since the predominant metaphor is sailing. So let’s draw the lines sharply. There is indeed a ‘solar wind’ in today’s parlance, but it refers not to light but to the stream of particles, plasma and magnetic fields flowing out from the Sun into the heliosphere. An electric sail will ride this solar wind to...

One thing that James E. Webb insisted on during his tenure as NASA administrator was that the space program was larger than an attempt to get humans to the Moon. The man who did so much to ensure that Apollo would succeed, and who will be rightfully honored in the form of the James Webb Space Telescope, was a proponent of exploration throughout the Solar System through robotic craft, and weather and communications satellites that would become part of a permanent reliance on a growing space infrastructure. Marc Millis noted some of the results in his recent essay. For while the frustration of abandoning the Moon in the 1970s lingers, we do have over 4600 spacecraft in Earth orbit, many of them doing the kind of work Webb envisioned. We've completed the initial reconnaissance of the Solar System and made our first tentative ventures into the Kuiper Belt and out past the heliopause. We're charting exoplanets and looking to explore Saturn's largest moon. So these are things to keep in...

Solar sails are a case of science fiction anticipating the scientific journals, though in an odd way. Engineer Carl Wiley (writing as Russell Saunders) described the physics of solar sailing and some early engineering concepts in the pages of John Campbell's Astounding back in 1951, but he did it in a nonfiction article of the kind the magazine routinely ran. Richard Garwin would discuss sails in the scientific literature in "Solar Sailing: A Practical Method of Propulsion within the Solar System," which ran in 1958 in the journal Jet Propulsion. Then we waited for fictional treatments, which began with Cordwainer Smith's wonderful "The Lady Who Sailed the Soul" (Galaxy, April 1960) and a string of stories from top authors of the time in just a few quick years -- Jack Vance's "Gateway to Strangeness" (Amazing Stories, 1962), Poul Anderson's "Sunjammer" (Analog 1964), Arthur C. Clarke's story of the same name, later renamed "The Wind from the Sun" (Boy's Life, 1964). Sails of the...

Beamed propulsion has clear advantages when it comes to pushing a payload up to interstellar flight speeds, which is why Breakthrough Starshot is looking at laser strategies. But what about a neutral particle beam in conjunction with a magnetic sail? We've discussed the possibilities before (see Interstellar Probe: The 1 KG Mission), where I wrote about Alan Mole's paper in JBIS, followed by a critique from Jim Benford. Mole, a retired aerospace engineer, is now collaborating with plasma physicist Benford (CEO of Microwave Sciences) to examine a solution to the seemingly intractable problem of beam divergence. Getting around that issue could be a game-changer. Read on for the duo's thoughts on sending a 1 kg probe to a nearby star system with a flight time in the range of 70 years. Part 2 of this study, outlining engineering issues and the practical realities of cost, will follow. by James Benford and Alan Mole We advance the concept for a 1 kg probe that can be sent to a nearby star...

One reason we look so often at sail technologies in these pages is that they offer us ways of leaving the propellant behind. But even as we enter the early days of solar sail experimentation in space, we look toward ways of improving them by somehow getting around their need for solar photons. Robert Zubrin's work with Dana Andrews has helped us see how so-called magnetic sails (magsails) could be used to decelerate a craft as it moved into a destination system. Now Zubrin looks at moving beyond both this and solar wind-deflecting electric sails toward an ingenious propellantless solution. Zubrin presented the work at last April's Breakthrough Discuss meeting, and today he fills us in on its principles and advantages. Read on for a look at a form of enhanced electric sail the author has christened the Dipole Drive. by Robert Zubrin Abstract The dipole drive is a new propulsion system which uses ambient space plasma as propellant, thereby avoiding the need to carry any of its own. The...

One of the reasons I described Greg Matloff as the 'renaissance man of interstellar studies' in my Centauri Dreams book is the continuing stream of ingenious ideas that he develops and delivers through papers and conference presentations. I found the holographic sail concept below fascinating, and would have referenced Bob Forward myself if Greg hadn't already done it in the text. These two must have been great to hear in conversation! Read on to learn how Greg, a physicist at New York City College of Technology (CUNY) came up with the idea, a process that deftly blended science and art and may provide solutions to some of the more intractable problems posed by Breakthrough Starshot. The author of The Starflight Handbook among many other books (volumes whose pages have often been graced by the artwork of the gifted C Bangs), Greg has been inspiring this writer since 1989. By Greg Matloff It was perhaps inevitable that I would be asked to serve on the Advisor's Board of Yuri Milner's...

Yesterday's post on PROCSIMA (Photon-paRticle Optically Coupled Soliton Interstellar Mission Accelerator) has been drawing a good deal of comment, and I wanted to dig deeper into the concept this morning by presenting some correspondence between plasma physicist Jim Benford, a familiar face on Centauri Dreams, and PROCSIMA's creator, Chris Limbach (Texas A&M Engineering Experiment Station). As we saw yesterday, PROCSIMA goes to work on the problem of beam spread in both laser and particle beam propulsion concepts. In my own email exchange with Dr. Limbach, he took note of the comments to yesterday's Centauri Dreams article, with a useful nod to a concept called 'optical tweezers' that may be helpful. So let me start with his message of April 4, excerpting directly from the text: I took a quick glance at the comments, and I see that the laser guiding (i.e. waveguide) effect is fairly well understood, but the guiding of the particles is less clear. I admit this is the less intuitive...