A paper submitted to the Journal of the British Interplanetary Society by Philip Lubin of the UC Santa Barbara Physics Department last April, is suddenly drawing a great deal of attention, in part because it resulted in a NASA Innovative Advanced Concept (NIAC) award. The title of the paper, A Roadmap to Interstellar Flight, and of the award, DEEP IN Directed Energy for Interstellar Propulsion, probably didn’t hurt either.
The proposal is an update of the long standing idea of using directed energy in the form of lasers to accelerate a mass to extremely high velocities, including in some circumstances to a substantial fraction of the speed of light.
It all depends on the power of the laser array and the size of the mass, but the point of the proposal is that the needed technologies have sufficiently advanced in recent years so as to bring the concept from purely notional to one that could be deployed on a small scale without requiring any significant technological breakthroughs. Most importantly, it is supremely scalable, allowing for a modest beginning to eventually lead to truly mind-boggling results, such as a 100 kg spacecraft on a three day journey to Mars, or a “wafer-sized” spacecraft accelerated to 30 percent of the speed of light in approximately 10 minutes.
In the case of the payloads sent to Mars or elsewhere in the solar system for that matter, it is just as important to have a means of slowing down, a requirement which likely demands a similar apparatus on the receiving end. For the first steps of automated interstellar exploration however, flyby missions are contemplated in which the same laser/reflector combination is used to transmit and receive data being sent back at the speed of light, albeit at very low transmission rates. Scale the system however, and with an increase in the size of the payload to 100kg and look what you get:
“At the nearest star (Proxima Centauri) at a distance of about 4 ly the data rate at Earth from the spacecraft is about 70 Mbps. Live streaming HD video looks feasible all the way to our nearby interstellar neighbors.”
From the paper:
There has been a game change in directed energy technology whose consequences are profound for many applications including photon driven propulsion.
This allows for a completely modular and scalable technology without “dead ends”. We propose a system that will allow us to take the step to interstellar exploration using directed energy propulsion combined with miniature probes including some where we would put an entire spacecraft on a wafer to achieve relativistic flight and allow us to reach nearby stars in a human lifetime. Combined with recent work on wafer scale photonics, we can now envision combining these technologies to allow for a realistic approach of sending probes far outside our solar system and to nearby stars. As a part of our effort we propose a roadmap to allow for staged development that will allow us not only to dream but to do.”
Finally, there are the “other benefits”:
“As we outline in our papers the same basic system can be used for many purposes including both stand-on and stand-off planetary defense from virtually all threats with rapid response (emphasis added), orbital debris mitigation, orbital boosting from LEO to GEO for example, future ground to LEO laser assisted launchers, standoff composition analysis of distant object through molecular line absorption, active illumination of asteroids and other solar system bodies, beamed power to distant spacecraft among others.”
The roadmap envisions five stages of ground testing before demonstrating the concept in space for the first time. And guess which object currently in orbit boasts a solar array (100 kw) sufficiently sized to support such a test?
The International Space Station.