Between the exponential growth of the commercial space industry (aka. NewSpace) and missions planned for the Moon in this decade, it’s generally agreed that we are living in the “Space Age 2.0.” Even more ambitious are the proposals to send crewed missions to Mars in the next decade, which would see astronauts traveling beyond the Earth-Moon system for the first time. The challenge this represents has inspired many innovative new ideas for spacecraft, life-support systems, and propulsion.
In particular, missions planners and engineers are investigating Directed Energy (DE) propulsion, where laser arrays are used to accelerate light sails to relativistic speeds (a fraction of the speed of light). In a recent study, a team from UCLA explained how a fleet of tiny probes with light sails could be used to explore the Solar System. These probes would rely on a low-power laser array, thereby being more cost-effective than similar concepts but would be much faster than conventional rockets.
The study was conducted by Ho-Ting Tung, an aerospace engineering grad student from UCLA, and assistant professor Artur R. Davoyan, both of whom are members of the Davoyan Research Group (DRG), of which Prof. Davoyan is the founder. This group is dedicated to the study of directed energy and light-material interactions for the purpose of developing “space photonics.” The paper that describes their findings recently appeared in the journal Nano Letters, an publication overseen by the American Chemistry Society (ACS).
For decades, scientists have investigated light sails as a possible means of space exploration. These spacecraft offer many advantages over conventional concepts, foremost of which is how they forego the need for propellant. For most designs, propellant constitutes a big chunk of a spacecraft’s mass, which necessitates large storage tanks, resulting in additional mass, and so on. Where interstellar space travel is concerned, it becomes a terrible burden.
Using conventional propulsion, getting to even the nearest star system – Proxima Centauri, located about 4.25 light-years away – could take several thousand years. For this reason, multiple organizations are exploring light sail mission concepts as a means of interstellar travel. This includes Breakthrough StarshotProject Dragonfly, and Project Lyra, which involve using large arrays up to 100 GigaWatts (GW) in power to propel spacecraft to relativistic speeds and achieve interstellar travel.
But as Prof. Davoyan told Universe Today via email, these approaches have applications for exploring the Solar System as well:
“Getting to other star systems is very hard due to astronomical distances. For example, the closest system is about 4 light years away from us. Reaching it with any conventional way of propulsion would require thousands of years.There are several different approaches that are considered to accelerate spaceflight: mainly fusion propulsion and directed energy, such as with the use of lasers.
“At the same time, even getting to the outer reaches of our solar system, such as to outer planets, the Kuiper belt, and entering the interstellar medium is very very challenging. It takes years of flight time and mission development. We discuss a new way of using beamed laser propulsion to send probes to outer planets.”
Artist’s impression of the Dragonfly spacecraft concept. Credit and Copyright: David A Hardy (2015)
For the sake of their study, Ho-Ting and Davoyan considered various spacecraft profiles with varying degrees of size and laser wattage. These included an array ranging from 100 kiloWatts (kW) to 1 megaWatt (MW), which is low-power compared to interstellar concepts. Like Starshot and Dragonfly, they calculated for gram-scale probes ranging from 10 to 100 grams in mass. From this, they envisioned a wafer probe about 45 cm (18 inches) in diameter with integrated electronics on one side and a nanoscale structure on the other.
Beyond directed energy, this concept incorporates another of the Davoyan Research Group’s areas of expertise. This is the field known as nanophotonics, the science of how materials that are a few nanometers