PRINCIPIUM The Newsletter of the Initiative for Interstellar Studies Issue 21 | May 2018 ISSN 2397-9127 ■ “Slow down!”: How to park an interstellar rocket ■ The Orbits of Seveneves (2) - the orbits explained ■ Imagining Interstellar - Art by Efflam Mercier ■ 69th International Astronautical Congress 2018 - Papers by the i4is Team ■ BOOK REVIEWS: ■ Going Interstellar - Build Starships Now! ■ Rendezvous with Rama, a retrospective ■ NEWS FEATURES - ■ Breakthrough Discuss 2018: i4is debate novel R O propulsion technologies F E V ■ I PROCSIMA - Diffractionless Beamed Propulsion for T A I Breakthrough Interstellar Missions T I N ■ BIS report on nanosats from the UK I ■ Interstellar News & Project Lyra Update S T U D I E S www.i4is.org Scientia ad sidera Knowledge to the stars Principium | Issue 21 | May 2018 1 Microcomputer Workshop, Catching A Little Bit of Heaven. News also of the BBC Sky at Night Editorial programme on 'Oumuamua and the NASA online Welcome to Principium, the quarterly newsletter learning resource -Asteroid Ace for Schools. We from i4is, the Initiative for Interstellar Studies - and also report on Darryl Seligman's published work our US-based Institute for Interstellar Studies. We In Situ Exploration of `Oumuamua-like objects. aim to report on and support all things interstellar. Future events include the 16th Reinventing Space And a special welcome if you are a new reader . conference in London in November and the 69th IAC in Bremen, Germany, in October - with several Please tell us if we have your details incorrect (info@ of our team presenting. And our own upcoming i4is.org). events including Our Introduction feature for Principium 21 is “Slow down!”: How to park an interstellar rocket by • the second Interstellar Challenge for Schools at the regular contributor Tishtrya Mehta. It's based on University of Warwick, in September work by a good friend of i4is, Prof Dr Claudius • an i4is summer school at the Royal Institution, Gros. London, Skateboards to Starships, in August Our front cover this time is an image created by the • an imminent presentation, The Stellar Challenger- TU Delft, Evolving Asteroid Starships project. More A Concept Study by Mark Hempsell, President of about it in the Interstellar News. the BIS at our HQ, the Mill, Friday 1 June. Our rear cover is an impression of the Gaia And we announce our first Starship Engineer astrometry observatory currently bringing us Summer School, also at the Mill, in August. unprecedented detail on thousands of our nearest And we have three News Features - a report of the stellar neighbours from its orbit around Lagrange i4is contribution on novel propulsion technologies point 2. to the 2018 Breakthrough Discuss conference, The astronautical world gets together each year in news of a NASA-funded project PROCSIMA - the International Astronautical Congress (IAC). Diffractionless Beamed Propulsion for Breakthrough We present abstracts of nine papers by i4is team Interstellar Missions and of a BIS study group report members accepted for the 69th IAC in Bremen, on options for launching nanosats from the UK. Germany, in October 2018. Our major feature introducing Z-pinch fusion We have the second and concluding part of Sander propulsion based on the Project Icarus Firefly Elvik's analysis in The Orbits of Seveneves - Part concept is postponed to our August issue, P22. 2 - the orbits explained. Here he gives some simple We will also have a piece, Nomadic Planets and orbital dynamics from the novel, Seveneves. Neal Interstellar Exploration by Marshall Eubanks of Stephenson writes both outer space and 'inner space' Asteroid Initiatives and other contributions to the but for this one his time at Blue Origin may have interstellar endeavour plus news of all the upcoming helped. events mentioned in our News this time and more Two book reviews this time - Going Interstellar about the October IAC conference, especially the - Build Starships Now! an anthology of fiction i4is presence at this biggest astronautical event of and non-fiction edited by Les Johnson and Jack the year. McDevitt, and Rendezvous with Rama, by Arthur Comments on i4is and all matters interstellar are C Clarke, a retrospective review in the light of that always welcome, rather Rama-shaped interstellar asteroid the i4is Lyra John I Davies, Editor, [email protected] team have been studying. One of our newer visual art contributors, Efflam Join in the conversation by following the i4is on our Mercier, has a picture feature Imagining Interstellar Facebook page www.facebook.com/InterstellarInstitute and in our professional network on LinkedIn www. showing more of Andreas Hein's AI starship and a linkedin.com/groups/4640147 - and check the i4is blog, wider work from Efflam's brilliant imagination. The Starship Log www.i4is.org/the-starship-log. Follow us on Twitter at @I4Interstellar and seek out our • Our Interstellar News this time includes a followers too! Project Lyra Update and includes news of ESA Contact us on email via [email protected]. All issues of Principium are at www.i4is.org/Principium. interest in DSTART - TU Delft Starship Team and their Evolving Asteroid Starships and of i4is The views of our writers are their own. We aim team presentations at the 44th annual Asilomar for sound science but not editorial orthodoxy. Principium | Issue 21 | May 2018 2 “Slow down!”: How to INTRODUCTION park an interstellar rocket Tishtrya Mehta Solar physicist Tishtrya Mehta is a regular Principium contributor. Here she brings us an introduction to momentum braking, based on work by Professor Dr Claudius Gros, Johann Wolfgang Goethe-Universität, Institut für Theoretische Physik, Frankfurt/Main Germany. So goes the old saying 'What goes up, must come upon contact with the Earth. In space there down'. Since the dawn of human flight we've is no 'road' as such, just a sparsely populated come to learn that this phrase no longer rings true 'interstellar medium' (ISM) which is of a very and we have since launched probes, rockets and low density and so offers little friction in platforms deep into space without the intention ordinary circumstances. This is why we can of them ever returning to Earth. One of the most accelerate probes to such high speeds in space celebrated is the New Horizons probe which and expect little resistance and allow the probe recently enjoyed a flyby of everyone's favourite to continue at a largely unchanged velocity dwarf planet Pluto, sending back breath-taking many years after the initial acceleration. images of the small rock in incredible detail, Critically, the ISM is not a complete vacuum FEATURE and has continued to hurtle through space with and the material within it, even if low density, no intention of slowing down. This is a problem contains a significant amount of ionised facing aerospace engineers as so far we have molecules which can be harnessed to serve developed successful technologies capable of as means to slow down a probe, which is the accelerating fast enough to reach interstellar key mechanism behind the idea of momentum distances, but now we must face the challenge of braking. slowing the craft down sufficiently so it may fall So how does it work? Momentum braking into orbit around its target or at least attempt a relies on transferring the kinetic energy of flyby with a significant enough duration to collect the probe to its surroundings, in this case the and transmit valuable data. ISM, which can be effectively carried out Currently the most appealing and realistic target via the use of a magnetic sail. Prof Gros puts for interstellar travel is the Proxima Centauri forward a candidate of a Biot-Savart magnetic system, headed by a low-mass red dwarf star, sail in his 2017 paper [1] which consists of a a mere 4.25 light-years from us. Thus, using a superconducting loop tethered to a payload, probe that can accelerate to around a tenth of the the mass of which doesn't exceed 1.5 tonnes. speed of light, a journey seems feasible within A Biot-Savart loop carries a current in a closed the duration of a human lifetime. A difficulty lies circle, which in turn creates a magnetic field. in decelerating a probe travelling at 3 x 104 km/s This magnetic field changes the trajectory of to a near stationary state, as our usual methods nearby ionized particles, (usually H+, ionised of braking involve copious friction between the hydrogen; the simplest and most abundant moving object and a stationary medium; think of element found in the universe) and causes them the wheels of a slowing car against the surface to be reflected, which slows the craft using of a road, or an Apollo capsule crashing to a halt conservation of momentum. [1] C Gros, Universal scaling relation for magnetic sails: momentum braking in the limit of dilute interstellar media, 2017, J.Phys. Commun, I, 045007, arxiv.org/abs/1707.02801 Principium | Issue 21 | May 2018 3 The laws of Physics dictate that in any closed system (where nothing enters or leaves the 'frame' during the interaction) momentum cannot be lost, only transferred between different bodies. So the momentum lost by the craft must be equal to the momentum gained by the particle. We can look at this further by considering the equation where p is momentum, m is mass and v is velocity. So The mass of the particles encountered by the craft in a given unit of time, say Tunit, can be + given by the density of H ions per m3 (np) swept out by the area of the sail multiplied by the velocity of the craft and the mass per proton (mp) ie Figure 1: Tracks from particles in a cloud chamber. Source: CERN 2 The particles are assumed to perfectly reflect (which cerncourier.com/cws/article/cern/28742 gives the greatest change in momentum, and so "A classic bubble chamber photograph.