Les Johnson - Going Interstellar

One of the main differences between Daedalus and Icarus is the requirement that there be some deceleration at the target system. Daedalus had a cruise velocity 12% of light speed, and would have raced through the target system within days. It would have been in close proximity to any planet for only a matter of seconds. This short encounter time would severely restrict the scientific return from the mission, and so Icarus is committed to address the issue of deceleration.

Project Icarus is clearly a highly scientific endeavor whose success will be measured by the credibility and quality of the work that is created. Despite these academic ambitions, there are additional motives behind the project that are worthy of further examination.

One such motive is to use Icarus as a vehicle for training a new generation of interstellar engineers. The field of interstellar propulsion is sprinkled with luminaries whose names have become synonymous with the field of interstellar propulsion. These visionaries include VIPs such as Robert Bussard, Bob Forward, Greg Matloff, Robert Frisbee and Alan Bond, whose names will be immediately recognizable to interstellar aficionados. To maintain the healthy vision of a future where interstellar travel is possible, a new generation of capable enthusiasts is required. Project Icarus was designed with this specific motive in mind, and a quick glance at the Icarus designers reveals an average age close to thirty. Thus, one hope is that, upon completion of the project, an adept team of competent interstellar engineers will have been created, and that this team will continue to kindle the dream of interstellar flight for a few more decades until, presumably, they too become grey and find their own enthusiastic replacements.

Another parallel objective of Project Icarus is to evolve the possibility of interstellar flight from being merely feasible to actually being practical. The Daedalus design demonstrated that, with sufficient determination, a craft could be built using known principles of physics that could reach another star system in approximately fifty years. However, some critical components to Daedalus may lead a conservative spectator to believe that Daedalus was too ambitious.

Two impractical aspects of the original Daedalus spring to mind. The first is a feature of the propulsion system which necessitates the firing of marble-sized pellets, consisting of mainly deuterium and Helium-3, into a reaction chamber at a rate of 250 pellets per second. These pellets would then be ignited by high powered relativistic electron beams in a process known as inertial confinement fusion (ICF). Though considered a credible way to liberate energy from the fusion fuel, the fusion ignition rate of 250 hertz is difficult to be taken seriously given that the National Ignition Facility (NIF), a large U.S. fusion ignition project located at the Lawrence Livermore Laboratory, will likely accomplish only one such event per day under ideal conditions! Thus, an improvement on this rate by a factor of approximately twenty-one million would be required to achieve Daedalus fusion pellet ignition rates. While certainly not impossible, this pellet frequency requires a rather vast improvement on current technology. However, it’s important to recognize that the NIF is a physics demonstrator, and that it is not designed to be optimized for rapid ignition rates.

The second feature of Daedalus that appears improbable is the choice of fuel. As mentioned earlier, Helium-3 is a critical component and incredibly rare on Earth. Jupiter would have to be mined by sophisticated orbiting balloons and its Helium-3 ultimately transported to the Daedalus . Again, while certainly not impossible, such planetary mining operations would very likely imply that a massive space-based infrastructure should already be in place. The original Daedalus team acknowledged that a culture with this capability would likely be centuries ahead of our own. Estimates for the total costs of building a Daedalus class spacecraft lie in the ten to one hundred trillion dollar range. With the current NASA budget for 2011 lying close to eighteen billion dollars, increasing it a thousand times is not impossible, given sufficient ambition, but viewed from today’s geopolitical landscape, it is highly unlikely.

A full and systematic treatise regarding the additional and subtle impracticalities of the Daedalus design are beyond the scope of this essay. Suffice to say that most scientists of today would consider the design to be overly ambitious; rather than marvel at its audacity, those same scientists would likely dismiss Daedalus as unrealistic. For this reason, one parallel objective of Project Icarus is to create a credible engineering design that is feasible with minimal extrapolations of current technology. One way of accomplishing this is through incremental improvements of the relevant Technology Readiness Levels (TRL).

The TRL scale is used to gauge the relative maturity of a concept. The scale has nine levels, with TRL 1 being the lowest level of technological maturity, and TRL 9 the highest. For example, the definition of TRL 1 is: “Basic principles observed and reported: Transition from scientific research to applied research. Essential characteristics and behaviors of systems and architectures. Descriptive tools are mathematical formulations or algorithms.”

Contrast this with the other end of the scale, TRL 9, which is defined as: “Actual system ’mission proven’ through successful mission operations (ground or space): Fully integrated with operational hardware/software systems. Actual system has been thoroughly demonstrated and tested in its operational environment. All documentation completed. Successful operational experience. Sustaining engineering support in place.”

The nine levels are a convenient way to assess the maturity of a technology.

Many features of the Daedalus design lie in the TRL 1 to TRL 3 range, indicating a low level of maturity. One measure of success for Project Icarus will be the evolution of critical interstellar technologies to a higher TRL level, since this assists in the promotion of the design credibility. For this reason, TRL evolution and comparison to Daedalus for key research areas is a valuable objective for Project Icarus .

One final, and particularly interesting, parallel motive is to use the project as an experiment in the efficacy of volunteer researchers collaborating in a purely virtual capacity. In many ways, Project Icarus may represent a new way for scientific research to be conducted. The Icarus team currently consists of twenty-nine team members, located across six different countries. The researchers are not paid for their efforts and are primarily motivated by a passion for the field. Interaction between team members is mostly conducted by email. However, a private internet forum also exists where the team can engage in extended discussions on a variety of topics. Internet telephony is also utilized, on occasion, as the need for (virtual) face-to-face communication arises. This mainly electronic team is, in itself, an interesting experiment in the virtualization of scientific collaboration and, should the outcome be successful, Project Icarus could serve as a prototype for future scientific and engineering endeavors.

One of the Terms of Reference of Project Icarus is that the propulsion system must be ‘mainly fusion-based,’ which is currently considered TRL 2. This mandate to use fusion was based on the fact that Daedalus was itself fusion-powered. As the successor to Daedalus it seemed appropriate for Icarus to utilize this same energy source so as to maintain continuity with the original project. Alternatives to this form of propulsion do exist, and popular non-fusion options include solar sailing and even antimatter. The fusion decision was made early on and met with no objections from any team members.