Going Interstellar (collection)

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.