A fast high-precision six-degree-of-freedom relative position sensor

Lasers are commonly used in high-precision measurement and profiling systems. Some laser measurement systems are based on interferometry principles, and others are based on active triangulation, depending on requirements of the application. This paper describes an active triangulation laser measurement system for a specific application wherein the relative position of two fixed, rigid mechanical components is to be measured dynamically with high precision in six degrees of freedom (DOF). Potential applications include optical systems with feedback to control for mechanical vibration, such as target acquisition devices with multiple focal planes. The method uses an array of several laser emitters mounted on one component. The lasers are directed at a reflective surface on the second component. The reflective surface consists of a piecewise-planar pattern such as a pyramid, or more generally a curved reflective surface such as a hyperbolic paraboloid. The reflected spots are sensed at 2-dimensional photodiode arrays on the emitter component. Changes in the relative position of the emitter component and reflective surface will shift the location of the reflected spots within photodiode arrays. Relative motion in any degree of freedom produces independent shifts in the reflected spot locations, allowing full six-DOF relative position determination between the two component positions. Response time of the sensor is limited by the read-out rate of the photodiode arrays. Algorithms are given for position determination with limits on uncertainty and sensitivity, based on laser and spot-sensor characteristics, and assuming regular surfaces. Additional uncertainty analysis is achievable for surface irregularities based on calibration data

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

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 Interstellar Propulsion of WaferSats

In the nearly 60 years of spaceflight we have accomplished wonderful feats of exploration and shown the incredible spirit of the human drive to explore and understand our universe. Yet in those 60 years we have barely left our solar system with the Voyager 1 spacecraft launched in 1977 finally leaving the solar system after 37 years of flight at a speed of 17 km/s or less than 0.006% the speed of light. As remarkable as this is, we will never reach even the nearest stars with our current propulsion technology in even 10 millennium. We have to radically rethink our strategy or give up our dreams of reaching the stars, or wait for technology that does not exist. While we all dream of human spaceflight to the stars in a way romanticized in books and movies, it is not within our power to do so, nor it is clear that this is the path we should choose. We posit a technological path forward, that while not simple; it is within our technological reach. We propose a roadmap to a program that will lead to sending relativistic probes to the nearest stars and will open up a vast array of possibilities of flight both within our solar system and far beyond. Spacecraft from gram level complete spacecraft on a wafer (“wafer sats”) that reach more than ¼ c and reach the nearest star in 15 years to spacecraft with masses more than 105 kg (100 tons) that can reach speeds of near 1000 km/s such systems can be propelled to speeds currently unimaginable with our existing propulsion technologies. To do so requires a fundamental change in our thinking of both propulsion and in many cases what a spacecraft is. In addition to larger spacecraft, some capable of transporting humans, we consider functional spacecraft on a wafer, including integrated optical communications, optical systems and sensors combined with directed energy propulsion. Since “at home” the costs can be amortized over a very large number of missions. The human factor of exploring the nearest stars and exo-planets would be a profound voyage for humanity, one whose non-scientific implications would be enormous. It is time to begin this inevitable journey beyond our home

Interrogating the molecular composition of asteroids from a remote vantage: Progress in the laboratory

With the goal of landing crewed missions on the Moon and Mars in the next decade, mineral deposits on asteroids represent a potentially important resource for emerging space colonies. Deep-space missions can contemplate in-situ resource utilization, should suitable compounds be present. A necessary step for eventual resource exploitation is characterization of material abundances within candidate asteroids. Mineral maps could be generated by deploying CubeSat spacecraft to targeted asteroids, using Remote Laser Evaporative Molecular Absorption (R-LEMA) spectroscopy. In the R-LEMA scheme, a directed energy beam is used to probe molecular composition of a remote target. The laser-heated spot serves as a high-temperature blackbody source and ejected molecules create a plume of surface materials in front of the spot. Molecular composition is investigated by using a spectrometer to view the heated spot through the plume. Laboratory experiments allow comparison between predicted and measured profiles. Preliminary experiments described in this paper make use of solid-state samples so as to develop a library of spectra for comparison to future spectra obtained from samples in the gas phase