Directed Energy For Relativistic Propulsion and Interstellar Communications

An orbital planetary defense system that is also capable of beamed power propulsion allows mildly relativistic spacecraft speeds using existing technologies. While designed to heat the surface of potentially hazardous objects to the evaporation point to mitigate asteroid threats the system is inherently multi-functional with one mode being relativistic beamed spacecraft propulsion. The system is called DE-STAR for Directed Energy Solar Targeting of Asteroids and exploRation. DE-STAR is a proposed orbital platform that is a modular phased array of lasers, powered by the sun. Modular design allows for incremental development, test and initial deployment, lowering cost, minimizing risk and allowing for technological co-development, leading eventually to an orbiting structure that could be erected in stages. The main objective of DE-STAR would be to use the focused directed energy to raise the surface spot temperature of an asteroid to ~3,000 K, allowing direct evaporation of all known substances. The same system is also capable of propelling spacecraft to relativistic speeds, allowing rapid interplanetary travel and relativistic interstellar probes. Our baseline system is a DE-STAR 4, which is a 10 km square array that is capable of producing a 30 m diameter spot at a distance of 1 AU from the array. Such a system allows for engaging an asteroid that is beyond 1 AU from the DE-STAR 4. When used in its “photon rail gun mode”, a DE-STAR 4 would be capable of propelling a 1, 10, 102, 103, 104 kg spacecraft that is equipped with a 30 m diameter reflector to 1 AU in approximately 0.3, 1, 3, 10, 30 days, respectively, with speeds of about 4%, 1.2%, 0.4%, 0.15%, 0.05% the speed of light at 1 AU. With continued illumination to 3 AU the spacecraft, with a 30 m diameter reflector, would reach speeds √2 faster. A DE-STAR 4 could propel a 102 kg probe with 900 m diameter reflector to 2% the speed of light with continued illumination out to 30 AU, and ultimately to 3% the speed of light after which the spacecraft will coast. Such speeds far exceed the galactic escape velocity. Smaller systems are also extremely useful and can be built now. For example, a DE-STAR 1 (10 m size array) would be capable of evaporating space debris at 104 km (~diam. of Earth) while a DE-STAR 2 could divert volatile-laden asteroids 100 m in diameter by initiating engagement at ~0.01-0.5 AU. All sized systems can be used to propel varying sized systems for both testing and for interplanetary use. An extreme case is a wafe scale spacecraft (WaferSat) with a 1 m reflector that can achieve \u3e25%c in about 15 minutes. The phased array configuration is capable of creating multiple beams, so a single DE-STAR of sufficient size could engage several threats simultaneously or propelling several spacecraft. 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 “ping-ponging” between two systems in either a photon rail gun mode or power ion engines. There are a number of other applications as well including SPS for down linking power to the Earth via millimeter or microwave. A larger system such as a DE-STAR 6 system could propel a 104 kg spacecraft to near the speed of light allowing for true interstellar travel. The same technology can also be used for extremely long range communications with continuous communication between Earth and the interstellar spacecraft. This technology also has direct implications for interstellar and intergalactic beaming allowing for SETI across the universe for civilizations that have mastered this technology. There are a number of other applications for the system. While decidedly futuristic in its outlook many of the core technologies now exist and small systems can be built to test the basic concepts as the technology improves. While there are enormous challenges to fully implementing this technology the opportunities enabled are truly revolutionary

Directed Energy Active Illumination for Near-Earth Object Detection

On 15 February 2013, a previously unknown ~20 m asteroid struck Earth near Chelyabinsk, Russia, releasing kinetic energy equivalent to ~570 kt TNT. Detecting objects like the Chelyabinsk impactor that are orbiting near Earth is a difficult task, in part because such objects spend much of their own orbits in the direction of the Sun when viewed from Earth. Efforts aimed at protecting Earth from future impacts will rely heavily on continued discovery. Ground-based optical observatory networks and Earth-orbiting spacecraft with infrared sensors have dramatically increased the pace of discovery. Still, less than 5% of near-Earth objects (NEOs) 100 m/~100 Mt TNT have been identified, and the proportion of known objects decreases rapidly for smaller sizes. Low emissivity of some objects also makes detection by passive sensors difficult. A proposed orbiting laser phased array directed energy system could be used for active illumination of NEOs, enhancing discovery particularly for smaller and lower emissivity objects. Laser fiber amplifiers emit very narrow-band energy, simplifying detection. Results of simulated illumination scenarios are presented based on an orbiting emitter array with specified characteristics. Simulations indicate that return signals from small and low emissivity objects is strong enough to detect. The possibility for both directed and full sky blind surveys is discussed, and the resulting diameter and mass limits for objects in different observational scenarios. The ability to determine both position and speed of detected objects is also discussed

Simulations of Directed Energy Thrust on Rotating Asteroids

Asteroids that threaten Earth could be deflected from their orbits using directed energy to vaporize the surface, as the ejected plume creates a reaction thrust that alters the asteroid’s trajectory. In this situation, a critical issue is the rotation of the asteroid relative to the directed energy beam, as this will reduce the average thrust magnitude and modify the thrust direction. Flux levels required to evaporate surface material depend on the surface material composition, rotation rate, albedo, and thermal and bulk mechanical properties of the asteroid. The observed distribution of asteroid rotation rates is used, along with an estimated range of material and mechanical properties, as input to a 4D thermalphysical model to calculate the resultant thrust vector. The model uses a directed energy beam, striking the surface of a rotating sphere with specified material properties, beam profile, and rotation rate. The model calculates thermal changes in the sphere, including vaporization and mass ejection of the target material. The amount of vaporization integrated over the target is used to determine the thrust magnitude and the phase shift relative to the non-rotating case. As the object rotates beneath the beam, the energy spreads out, decreasing temperature and vaporization causing both a phase shift and magnitude decrease in the average thrust vector. This produces a 4D analytical model of the expected thrust profile for rotating objects

Directed Energy Deflection Laboratory Measurements

We report on laboratory studies of the effectiveness of directed energy planetary defense as a part of the DE-STAR (Directed Energy System for Targeting of Asteroids and exploRation) program. DE-STAR and DE-STARLITE are directed energy stand-off and stand-on programs, respectively. These systems consist of a modular array of kilowatt-class lasers powered by photovoltaics, and are capable of heating a spot on the surface of an asteroid to the point of vaporization. Mass ejection, as a plume of evaporated material, creates a reactionary thrust capable of diverting the asteroid’s orbit. In a series of papers, we have developed a theoretical basis and described numerical simulations for determining the thrust produced by material evaporating from the surface of an asteroid. In the DE-STAR concept, the asteroid itself is used as the deflection propellant . This study presents results of experiments designed to measure the thrust created by evaporation from a laser directed energy spot. We constructed a vacuum chamber to simulate space conditions, and installed a torsion balance that holds an asteroid sample. The sample is illuminated with a fiber array laser with flux levels up to 60 MW/m2 which allows us to simulate a mission level flux but on a small scale. We use a separate laser as well as a position sensitive centroid detector to readout the angular motion of the torsion balance and can thus determine the thrust. We compare the measured thrust to the models. Our theoretical models indicate a coupling coefficient well in excess of 100 μN/W optical, though we assume a more conservative value of 80 μN/W optical and then degrade this with an optical encircled energy efficiency of 0.75 to 60 μN/W optical in our deflection modeling. Our measurements discussed here yield about 45 μN/W absorbed as a reasonable lower limit to the thrust per optical watt absorbed

Optical Modeling for a Laser Phased-Array Directed Energy System

We present results of optical simulations for a laser phased array directed energy system. The laser array consists of individual optical elements in a square or hexagonal array. In a multi-element array, the far-field beam pattern depends on both mechanical pointing stability and on phase relationships between individual elements. The simulation incorporates realistic pointing and phase errors. Pointing error components include systematic offsets to simulate manufacturing and assembly variations. Pointing also includes time-varying errors that simulate structural vibrations, informed from random vibration analysis of the mechanical design. Phase errors include systematic offsets, and time-varying errors due to both mechanical vibration and temperature variation in the fibers. The optical simulation is used to determine beam pattern and pointing jitter over a range of composite error inputs. Results are also presented for a 1 m aperture array with 10 kW total power, designed as a stand-off system on a dedicated asteroid diversion/capture mission that seeks to evaporate the surface of the target at a distance of beyond 10 km. Phase stability across the array of λ/10 is shown to provide beam control that is sufficient to vaporize the surface of a target at 10 km. The model is also a useful tool for characterizing performance for phase controller design in relation to beam formation and pointing

A Complex Regulatory Network Coordinating Cell Cycles During C. elegans Development Is Revealed by a Genome-Wide RNAi Screen

The development and homeostasis of multicellular animals requires precise coordination of cell division and differentiation. We performed a genome-wide RNA interference screen in Caenorhabditis elegans to reveal the components of a regulatory network that promotes developmentally programmed cell-cycle quiescence. The 107 identified genes are predicted to constitute regulatory networks that are conserved among higher animals because almost half of the genes are represented by clear human orthologs. Using a series of mutant backgrounds to assess their genetic activities, the RNA interference clones displaying similar properties were clustered to establish potential regulatory relationships within the network. This approach uncovered four distinct genetic pathways controlling cell-cycle entry during intestinal organogenesis. The enhanced phenotypes observed for animals carrying compound mutations attest to the collaboration between distinct mechanisms to ensure strict developmental regulation of cell cycles. Moreover, we characterized ubc-25, a gene encoding an E2 ubiquitin-conjugating enzyme whose human ortholog, UBE2Q2, is deregulated in several cancers. Our genetic analyses suggested that ubc-25 acts in a linear pathway with cul-1/Cul1, in parallel to pathways employing cki-1/p27 and lin-35/pRb to promote cell-cycle quiescence. Further investigation of the potential regulatory mechanism demonstrated that ubc-25 activity negatively regulates CYE-1/cyclin E protein abundance in vivo. Together, our results show that the ubc-25-mediated pathway acts within a complex network that integrates the actions of multiple molecular mechanisms to control cell cycles during development

Directed energy missions for planetary defense

Directed energy for planetary defense is now a viable option and is superior in many ways to other proposed technologies, being able to defend the Earth against all known threats. This paper presents basic ideas behind a directed energy planetary defense system that utilizes laser ablation of an asteroid to impart a deflecting force on the target. A conceptual philosophy called DE-STAR, which stands for Directed Energy System for Targeting of Asteroids and exploration, is an orbiting stand-off system, which has been described in other papers. This paper describes a smaller, stand-on system known as DE-STARLITE as a reduced-scale version of DE-STAR. Both share the same basic heritage of a directed energy array that heats the surface of the target to the point of high surface vapor pressure that causes significant mass ejection thus forming an ejection plume of material from the target that acts as a rocket to deflect the object. This is generally classified as laser ablation. DE-STARLITE uses conventional propellant for launch to LEO and then ion engines to propel the spacecraft from LEO to the near-Earth asteroid (NEA). During laser ablation, the asteroid itself provides the propellant source material; 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 1- to 15-year targeting time (laser on time) depending on the system design. The mission fits within the rough mission parameters of the Asteroid Redirect Mission (ARM) program in terms of mass and size. DE-STARLITE also has much greater capability for planetary defense than current proposals and is readily scalable to match the threat. It can deflect all known threats with sufficient warning

DE-STARLITE: A Directed Energy Planetary Defense Mission

This paper presents the motivation behind and design of a directed energy planetary defense system that utilizes laser ablation of an asteroid to impart a deflecting force on the target. 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

Investigating the Effect of Galaxy Interactions on Star Formation at 0.5<z<3.0

Observations and simulations of interacting galaxies and mergers in the local universe have shown that interactions can significantly enhance the star formation rates (SFR) and fueling of Active Galactic Nuclei (AGN). However, at higher redshift, some simulations suggest that the level of star formation enhancement induced by interactions is lower due to the higher gas fractions and already increased SFRs in these galaxies. To test this, we measure the SFR enhancement in a total of 2351 (1327) massive ($M_*>10^{10}M_\odot$) major ($1<M_1/M_2<4$) spectroscopic galaxy pairs at 0.5<z<3.0 with $\Delta V <5000$ km s$^{-1}$ (1000 km s$^{-1}$) and projected separation <150 kpc selected from the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find that the highest level of SFR enhancement is a factor of 1.23$^{+0.08}_{-0.09}$ in the closest projected separation bin (<25 kpc) relative to a stellar mass-, redshift-, and environment-matched control sample of isolated galaxies. We find that the level of SFR enhancement is a factor of $\sim1.5$ higher at 0.5<z<1 than at 1<z<3 in the closest projected separation bin. Among a sample of visually identified mergers, we find an enhancement of a factor of 1.86$^{+0.29}_{-0.18}$ for coalesced systems. For this visually identified sample, we see a clear trend of increased SFR enhancement with decreasing projected separation (2.40$^{+0.62}_{-0.37}$ vs.\ 1.58$^{+0.29}_{-0.20}$ for 0.5<z<1.6 and 1.6<z<3.0, respectively). The SFR enhancement seen in our interactions and mergers are all lower than the level seen in local samples at the same separation, suggesting that the level of interaction-induced star formation evolves significantly over this time period.Comment: 23 pages, 13 figures, Accepted for publication in Ap

Relativistic Propulsion Using Directed Energy

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