Directed Energy laser pushed sail study

Philip Lubin, University of California, Santa Barbara, proposes to expand their investigations started in their NIAC Phase I of using directed energy to allow the achievement of relativistic flight to pave the way to the first interstellar missions. All of the current conventional propulsion systems are incapable of reaching the high speeds necessary to enable interstellar flight. Directed energy offers a path forward that, while difficult, is feasible. It is not an easy path and it does have many milestones to cross in order to get to the point of achieving the speeds needed. Along the roadmap we propose are important and useful “waypoints” that both allow testing and feed back to the larger design but are also useful for many applications. The consequences of this program are truly transformative not only for achieving relativistic flight for small probes but also for larger spacecraft at lower speeds suitable for rapid interplanetary travel. The Phase II work will consist of refining our roadmap and building and testing a small phased array prototype to test many of the concepts developed in the Phase I. They will also further our work on the wafer scale spacecraft design including work on the critical integrated laser communications system. We will also explore and test the inverse mode of using the array for reception which is critical to receiving the laser communications from the spacecraft.

Detailed directed energy progress and the asteroid defense work that can be adapted for interstellar exploration

Toward directed energy planetary defense (Optical Engineering 53(2), 025103 (February 2014))

Asteroids and comets that cross Earth’s orbit pose a credible risk of impact, with potentially severe
disturbances to Earth and society. We propose an orbital planetary defense system capable of heating the surface of potentially hazardous objects to the vaporization point as a feasible approach to impact risk mitigation. We call the system DE-STAR, for Directed Energy System for Targeting of Asteroids and exploRation. The DESTAR is a modular-phased array of kilowatt class lasers powered by photovoltaic’s. Modular design allows for incremental development, minimizing risk, and allowing for technological codevelopment. An orbiting structure would be developed in stages. The main objective of the DE-STAR is to use focused directed energy to raise the surface spot temperature to ∼3000 K, sufficient to vaporize all known substances. Ejection of evaporated material creates a large reaction force that would alter an asteroid’s orbit. The baseline system is a DESTAR 3 or 4 (1- to 10-km array) depending on the degree of protection desired. A DE-STAR 4 allows initial engagement beyond 1 AU with a spot temperature sufficient to completely evaporate up to 500-m diameter asteroids in 1 year. Small objects can be diverted with a DE-STAR 2 (100 m) while space debris is vaporized with a DE-STAR 1 (10 m)

Beam power to distant probes—the system can be used to beam power to very distant spacecraft. At 1 AU the flux is 70 MW∕m2 or about 50,000 times the flux of the sun. At the edge of the solar system (30 AU) it is about 80 kW∕m2. At 225 AU the beam is about as bright as the sun is above Earth’s atmosphere. Similarly, it could be used to provide power to distant outposts on Mars or the Moon or literally to machine on the lunar surface (or possibly Mars). The latter would be a complex sociological and geopolitical discussion no doubt.

Spacecraft rail gun mode—while photon pressure is modest, it is constant until the beam diverges to be larger than the reflector. In a companion paper, Bible et al.2 discuss using this mode to propel spacecraft at mildly relativistic speeds. For example, a 100-, 1000-, 10,000-kg spacecraft with a 30-m diameter (9 kg, 10-μm-thick multilayer dielectric) reflector will reach 1 AU (∼Mars) in 3, 10, 30 days. Stopping is an issue! The 100-kg craft will be going at 0.4%c at a 1 AU and 0.6%c at the edge of the solar system. This is 1800 km∕s at the edge of the solar system with just a 30-m reflector. This speed is far greater than the galactic escape speed and nearly 100 times faster than the Voyager spacecraft. If a reflector could be built to intercept the beam out to the edge of the solar system (900-m diameter) the same craft would be going 2% at the edge of the solar system and 3% if illumination stayed on for about 2 months. We do not currently know how to build kilometer-class reflectors that are low enough mass, though we do know how to build 30-m reflectors and 100 m appears feasible. There is work on graphene sheets that may allow for future extremely large, extremely low mass reflectors that may allow for fully relativistic speeds. Future generation may build even larger DE-STAR 5 and 6 units to allow highly relativistic probes.

Relativistic Propulsion Using Directed Energy by Johanna Bible, Isabella Johansson , Gary B. Hughes, Philip M. Lubin

We propose a directed energy orbital planetary defense system capable of heating the surface of potentially hazardous objects to the evaporation point as a futuristic but feasible approach to impact risk mitigation. The system is based on recent advances in high efficiency photonic systems. The system could also be used for propulsion of kinetic or nuclear tipped asteroid interceptors or other interplanetary spacecraft. A photon drive is possible using direct photon pressure on a spacecraft similar to a solar sail. Given a laser power of 70GW, a 100 kg craft can be propelled to 1AU in approximately 3 days achieving a speed of 0.4% the speed of light, and a 10,000 kg craft in approximately 30 days. We call the system DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation. DE-STAR is a modular phased array of solid-state lasers, powered by photovoltaic conversion of sunlight. The system is scalable and completely modular so that sub elements can be built and tested as the technology matures. The sub elements can be immediately utilized for testing as well as other applications including space debris mitigation. The ultimate objective of DE-STAR would be to begin direct asteroid vaporization and orbital modification starting at distances beyond 1 AU. Using phased array technology to focus the beam, the surface spot temperature on the asteroid can be raised to more than 3000K, allowing evaporation of all known substances. Additional scientific uses of DE-STAR are also possible.

Planetary Defense using directed energy systems

2015 Planetary Defense Conference in Frascaty, Italy. Philip Lubin discusses Directed Energy Planetart Defense. Travis Brashears discusses the laboratory measurements of directed energy while simulating space conditions.

More background material at the Deepspace UC Santa Barbara site

SOURCES – Deepspace UCSB, Philip Lubin, NASA NIAC