Icarus Interstellar: Visions of Our Starship Future
At a recent interstellar conference, some of the biggest names in starship design came together to formulate how we might reach out to another star.
Guest article by Michel Lamontagne, Robert Swinney and Robert Freeland of Icarus Interstellar.
Last November at the Tennessee Valley Interstellar Workshop (TVIW), Rob Swinney -- a former Royal Air Force squadron leader, engineer, and MSc who's now in charge of Project Icarus -- presented a progress report on the work being done under the project. With a classical baritone British accent lending weight to his words, Swinney reviewed the history of the project, from the inspiration of the original Project Daedalus report by the British Interplanetary Society (BIS) in 1978, to the decision in 2009 by a group of BIS and Tau Zero enthusiasts to update the study, to the latest work being done in 2014.
The original Daedalus study was conceived to address a key aspect of the Fermi paradox: "If intelligent extra-terrestrials exist and interstellar travel is possible, then where are they?" The Daedalus study was intended to determine if it was indeed possible to engineer a realistic starship, using only reasonable extrapolations of existing technologies. The conclusion was a resounding yes, supported by a detailed and remarkably thorough design for an unmanned interstellar flyby probe using inertial confinement fusion (ICF) of pre-manufactured Deuterium-Helium3 (DHe3) pellets. The Daedalus design served as a benchmark for interstellar vessels for the next 30 years.
However, in 2009, over thirty years after the initial report, many felt it was time to revisit the technologies and ideas behind Daedalus to see how they had survived the test of time. There was also a desire to incorporate new findings into the design, and to interest a new generation in the field of starship design while the originators of the work were still around to lend a hand. The new project was named after Icarus, the son of Daedalus, despite it's connotations of failure, in homage to a line in the original Daedalus report:
"It is hoped that these 'cunningly wrought' designs of Daedalus will be tested by modern-day equivalents of Icarus, who will hopefully survive to suggest better methods and techniques which will work where those of Daedalus may fail, and that the results of this study will bring the day when mankind will reach out to the stars."
Project Icarus is indeed furthering this goal. In retrospect, certain portions of the Daedalus report seem optimistic and should be updated:
Daedalus proposed the use of relativistic electron beams to compress the fuel pellets, but subsequent research has shown that electron beams could never provide the necessary punch. More recent research into inertial confinement fusion (ICF) has used lasers or ion beams instead. Nevertheless, the recent failure of the 20-year, $4 billion National Ignition Facility (NIF) to achieve break-even fusion has highlighted the difficulty of mastering ICF, even under ideal conditions.
The use of He3 to fuel Daedalus is a major hurdle, because He3 is unavailable on Earth, and so must be mined from the gas giants. Such mining operations would be prohibitively complex and expensive at present, and will likely remain so for (many) decades to come.
The limited availability of declassified information on nuclear technology at the time led the Daedalus team to make some unrealistically optimistic assumptions about the ability of the engine core to prevent damaging neutron and x-ray radiation from impacting the vessel.
Tritium cores were used in the fuel pellets to help spark ignition, but the heat generated in the fuel tanks by tritium decay (half-life 12 years) would have ruptured the pellets without a significantly beefier cryogenic system.
Pellet rupture would also have occurred as the tanks emptied, unless a substantial additional mass of tank pressurant were provided to maintain tank pressurization.
Finally, Daedalus imagined two R2D2-like droids -- with diagnostic capabilities advanced by even today's standards -- to identify and repair all failures aboard the vessel while it was en-route.
So what are the new parameters for a fusion starship? First and foremost, the present generation of designers is no longer content to send a flyby probe, opting instead for a fully-decelerated vessel that can release a swarm of durable sub-probes into the target system to explore it fully. Full deceleration mandates longer trip times, but the explosion of exoplanet discoveries has lent new urgency to launch. The use of deuterium-He3 (DHe3) fusion has therefore been abandoned in favor of pure deuterium-deuterium (DD) fusion, despite its much greater neutron output.
Deuterium is already routinely extracted from the Earth's oceans for use in heavy-water fission reactors, so fuel acquisition is no longer a hurdle.
Nevertheless, mankind has still not achieved controlled exo-energetic fusion, so there remains an open question as to the technique most suitable for a fusion starship. The lack of a clear winner in the slow race for fusion in the world's laboratories has left the designers with a quandary: What type of fusion should Icarus to use for the main drive? To try to resolve the issue, Project Icarus held an internal Design Competition at the BIS headquarters in London in 2013. Four teams presented designs, and a winner was selected: the Munich University based WARR Ghost team, which produced a design using laser driven fast ignition Inertial Confinement Fusion.
However, despite being unanimously considered the best overall design for its attention to ship system details and quality, the competition failed to settle the question of the best option for fusion propulsion. The Ghost team ship was huge, dwarfing the original Daedalus by a factor of five or more, and other fusion processes offered smaller ships with better performance.
Consequently, the decision was made to push forward on at least two engine types, ICF and Z-pinch. Moreover, although the lead fuel is the D/D reaction, a stand-alone study will continue to explore the use of He3, both as an update to the original Daedalus paper, and because all of the fusion designs could benefit from He3 if it were, in fact, obtainable.
One interesting outcome of the competition was the commonality of certain elements in the various designs. Payloads, communications, exploration methods, secondary power systems, some elements of fuel handling, will be common to all designs. The following features of the ship became clear:
It's going to be It's going to be a It's going to be a
Swinney also announced that Project Icarus had added another team to the group in 2014: the Drexel university Icarus Interstellar chapter. Furthermore, the Drexel team has progressed rapidly on a vessel design using Plasma Jet Magneto Inertial Fusion (PJIMF), that may deliver the most efficient drive yet. PJMIF involves a salvo of converging plasma jets that form a uniform liner, which compresses a magnetized target to fusion conditions. It is an Inertial Confinement Fusion (ICF) / Magnetic Confinement Fusion (MCF) hybrid approach that has the potential for a multitude of benefits over both ICF and MCF, such as lower system mass and significantly lower cost. The Drexel team named their design "Zeus".
The Project Icarus team held a Design Workshop in Atlanta just prior to the TVIW, and it was attended by representatives for all of the teams discussed above. Designer Lukas Schrenk flew in from Munich to represent the Ghost team; Designers Robert Freeland and Michel Lamontagne flew in from Florida and Canada, respectively, to represent Firefly, and the Drexel team drove down from Philadelphia to present Zeus. Rob Swinney flew in from London to coordinate the meeting. This provided a rare opportunity for the international team to engage in face-to-face design meetings, and rapid refinements were made to all three designs.
Following this meeting, four members of the team drove up to Oak Ridge for the TVIW, where Swinney gave his talk. In his conclusion, Swinney set a tentative date for completion of the final Project Icarus Report for 2015, likely in conjunction with the next Icarus Interstellar Starship Congress to be held in August. The final report will include sections that parallel those in the original Daedalus report, plus an important section on precursor missions. A visit to the 550 AU gravitational lens is in the plans, as well as Oort cloud explorations and options for quick trips to the outer planets. Rob Swinney finished his talk with the ultimate open ended statement: "The universe is for exploring, it's time to get out there!"
As an interesting aside, Swinney noted that there's a link between the past and future of Project Icarus. The vehicle that may be selected to ferry equipment and fuel to the construction site in low-Earth orbit is Skylon, which is being developed by Reaction Engines Limited. The driving force behind Skylon is none other than Alan Bond, the innovative and tenacious aerospace designer who was also one of the principal writers of the Daedalus report, back in 1978.
Project Icarus is a theoretical study to design a fusion-powered interstellar spacecraft using current or near-future technology. Icarus Interstellar is a 501(c)(3) charity that serves as an umbrella for several projects, including Project Icarus, Project Forward for beamed propulsion, Project Hyperion for manned interstellar flight, and Project XP4 for exotic propulsion technologies. The British Interplanetary Society (BIS), the Tau Zero Foundation (TZF), the Tennessee Valley Interstellar Workshop (TVIW), and the Initiative for Interstellar Studies (I4IS) are all active in interstellar research as well.