October 13, 2014

DESTAR phased array laser systems for defending against asteroids and for space exploration

A laser phased array directed energy system has been designed and simulated. Lubin and Hughes calculated the requirements and possibilities for DE-STAR systems of several sizes, ranging from a desktop device to one measuring 10 kilometers, or six miles, in diameter. Larger systems were also considered. The larger the system, the greater its capabilities.

For instance, DE-STAR 2 –– at 100 meters in diameter, about the size of the International Space Station –– "could start nudging comets or asteroids out of their orbits," Hughes said. But DE-STAR 4 –– at 10 kilometers in diameter, about 100 times the size of the ISS –– could deliver 1.4 megatons of energy per day to its target, said Lubin, obliterating an asteroid 500 meters across in one year.

The speed of interplanetary travel –– far beyond what is possible with chemical propellant rockets used today –– could be increased with this sized system, according to Lubin. It could also power advanced ion drive systems for deep space travel, he said. Able to engage multiple targets and missions at once, DE-STAR 4 "could simultaneously evaporate an asteroid, determine the composition of another, and propel a spacecraft."

Larger still, DE-STAR 6 could enable interstellar travel by functioning as a massive, orbiting power source and propulsion system for spacecraft. It could propel a 10-ton spacecraft at near the speed of light, allowing interstellar exploration to become a reality without waiting for science fiction technology such as "warp drive" to come along, Lubin said.

Recent and rapid developments in highly efficient conversion of electrical power to light allow such a scenario now, Lubin said, when just 20 years ago it would not have been realistic to consider.

Additional mission tasks include powering or recharging of very distant probes, standoff power to remote facilities, standoff photon drive propulsion of small spacecraft that can achieve mildly relativistic speeds, laser powered conventional (thermal) propulsion (no oxidizer needed), laser powered ion dive, standoff composition analysis of remote objects including asteroids, active illumination detection of asteroids (LIDAR), space debris removal, SPS mode for sending excess powered to the ground or airborne systems via micro or millimeter waves as well as laser, satellite orbital boosting (LEO to GEO for example), extremely long range high speed IR communications to spacecraft and exoplanets and standoff terraforming possibilities among many others. Smaller versions of the same system design can be used for “stand-on” applications for orbital diversion by taking the laser system to the target asteroid in a dedicated mission as well as for close in composition analysis.

Toward directed energy planetary defense. 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). © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.OE.53.2.025103]

The system consists of an array of phase-locked modest power laser amplifiers.

Baseline calculations are developed using a 1.06-μm wavelength to produce sufficient flux at 1 AU that will sustain evaporation which requires greater than ∼5-MW∕m2 flux at target. Existing Yb laser fiber amplifiers at 1.06-μm wavelength have efficiencies near 40%. Space solar PV has efficiency of about 35% in one sun (not concentrated) with near 50% when concentrated. They assume modest improvements of both laser and PV to 70%, which is not unreasonable in the timeframe.

They assume sunlight to laser power of about 50%, resulting in 0.7 Gigawatts per square kilometer.

A 10 kilometer system would have 70 Gigawatts.

Propulsion of kinetic or nuclear tipped asteroid interceptors or other interplanetary spacecraft is possible using a "photon rail gun" mode from direct photon pressure on a spacecraft propelling a 100-kg craft to 1 AU in 3 days and a 10,000-kg craft to 1 AU in 30 days. A DE-STAR could also provide power to ion propulsion systems, providing both a means of acceleration on the outbound leg, and deceleration for orbit insertion by rotating the spacecraft and using mirrors to divert the DE-STAR beam into the ion generation cavity. Vaporization and de-orbiting of debris in Earth orbit could be accomplished with a DE-STAR 1 or 2 system. DE-STAR 3 and 4 arrays may allow standoff interrogation of asteroid composition by observing absorption lines in the blackbody spectrum of a vaporizing surface spot. There are a number of other applications as well, including SPS. Multi-function capability aids in justifying such a system.

A simluation paper on the DESTAR system

DE-STARLITE - A Directed Energy Planetary Defense Mission

The proposed system is called DE-STARLITE for Directed Energy System for Targeting of Asteroids and ExploRation – LITE as it is a small, stand-on unit of a larger standoff DE-STAR system. Pursuant to the stand-on design, ion engines will propel the spacecraft from low-Earth orbit (LEO) to the near-Earth asteroid (NEA). During laser ablation, the asteroid itself becomes the "propellant"; thus a very modest spacecraft can deflect an asteroid much larger than would be possible with a system of similar mission mass using ion beam deflection (IBD) or a gravity tractor. DE-STARLITE is capable of deflecting an Apophis-class (325 m diameter) asteroid with a 15-year targeting time. The mission fits within the rough mission parameters of the Asteroid Redirect Mission (ARM) program in terms of mass and size and has much greater capability for planetary defense than current proposals and is readily scalable to the threat. It can deflect all known threats with sufficient warning.

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