Jonathan W. Campbell

Optimum parameters for laser launching objects into low Earth orbit

We derive optimum values of parameters for laser-driven flights into low Earth orbit (LEO) using an Earth-based laser, as well as sensitivity to variations from the optima. These parameters are the ablation plasma exhaust velocity v E and specific ablation energy Q * , plus related quantities such as momentum coupling coefficient C m and the pulsed or continuous laser intensity that must be delivered to the ablator to produce these values. Different optima are found depending upon whether it is desired to maximize mass m delivered to LEO, maximize the ratio m / M of orbit to ground mass, or minimize cost in energy per gram delivered. Although it is not within the scope of this report to provide an engineered flyer design, a notional, cone-shaped flyer is described to provide a substrate for the discussion and flight simulations. The flyer design emphasizes conceptually and physically separate functions of light collection at a distance from the laser source, light concentration on the ablator, and autonomous steering. Approximately ideal flight paths to LEO are illustrated beginning from an elevated platform. We believe LEO launch costs can be reduced 100-fold in this way. Sounding rocket cases, where the only goal is to momentarily reach a certain altitude starting from near sea level, are also discussed. Nonlinear optical constraints on laser propagation through the atmosphere to the flyer are briefly considered.

The Impact Imperative: Laser Ablation for Deflecting Asteroids, Meteoroids, and Comets from Impacting the Earth

Impacting at hypervelocity, an asteroid struck the Earth approximately 65 million years ago in the Yucatan Peninsula area. This triggered the extinction of almost 70% of the species of life on Earth including the dinosaurs. Other impacts prior to this one have caused even greater extinctions. Preventing collisions with the Earth by hypervelocity asteroids, meteoroids, and comets is the most important immediate space challenge facing human civilization. This is the Impact Imperative. We now believe that while there are about 2000 earth orbit crossing rocks greater than 1 kilometer in diameter, there may be as many as 200,000 or more objects in the 100 m size range. Can anything be done about this fundamental existence question facing our civilization? The answer is a resounding yes! By using an intelligent combination of Earth and space based sensors coupled with an infra‐structure of high‐energy laser stations and other secondary mitigation options, we can deflect inbound asteroids, meteoroids, and comets...

Laser launching a 5-kg object into low Earth orbit

Approximately ideal flight paths to low-Earth orbit (LEO) are illustrated for laser-driven flights using a 1-MW Earth-based laser, as well as sensitivity to variations from the optima. Different optima for ablation plasma exhaust velocity VE, specific ablation energy Q*, and related quantities such as momentum coupling coefficient Cm and the pulsed or CW laser intensity are found depending upon whether it is desired to maximize mass m delivered to LEO, maximize the ratio m/M of orbit to ground mass, or minimize cost in energy per gram delivered. A notional, cone-shaped flyer is illustrated to provide a substrate for the discussion and flight simulations. Our flyer design conceptually and physically separates functions of light collection, light concentration on the ablator, and steering. All flights begin from an elevated platform. Flight simulations use a detailed model of the atmosphere and appropriate drag coefficients for sub- and supersonic flight in the continuum and molecular flow regimes. A 6.2-kg payload is delivered to LEO from an initial altitude of 35 km with launch efficiencies approaching vacuum values of about 100 kJ/g.

Power beaming for orbital debris removal

Orbital debris in low-Earth orbit ranging in size from 1 to 10 cm in diameter can be detected but not tracked reliably enough to be easily avoided by spacecraft. In addition, shielding protection is extremely difficult and costly to accomplish for sizes above 1 - 2 cm. Debris in this size regime traveling at mean velocities on the order of 20000 miles per hour may cause catastrophic damage. Using adaptive optics technologies, a ground-based pulsed laser of sufficient power ablating the debris particles surface to produce small momentum changes may, in several hundred pulses, lower a target debris particles perigee sufficiently for atmospheric capture. A single laser facility could remove all of the 1 - 10 cm debris below 1500 km in altitude in approximately three years. A technology demonstration of ground based laser removal is proposed which would pave the way for the implementation of such a debris removal system. The cost of the proposed demonstration is comparable with the estimated annual cost of spacecraft operations in the present orbital debris environment.

Ground-based laser propulsion for orbital debris removal

Orbital debris in low-Earth orbit in the size range from 1 to 10 cm in diameter can be detected but not tracked reliably enough to be avoided by spacecraft. It can cause catastrophic damage even to a shielded spacecraft. With adaptive optics, a ground-based pulsed laser ablating the debris surface can produce enough propulsion in several hundred pulses to cause such debris to reenter the atmosphere. A single laser station could remove all of the 1–10 cm debris in three years or less. A technology demonstration of laser space propulsion is proposed which would pave the way for the implementation of such a debris removal system. The cost of the proposed demonstration is comparable with the estimated annual cost of spacecraft operations in the present orbital debris environment.

Use of laser radar for small space object experiments

This report briefly reviews the development, capabilities, and current status of pulsed high-power coherent CO2 laser radar systems at the Maui Space Surveillance System (MSSS), HI, for acquisition, tracking, and sizing of orbiting objects. There are two HICLASS systems, one integrated to the 0.6 m Laser Beam Director and one just integrated Summer 2000 to the 3.7 m Advanced E-O System (AEOS). This new system takes full advantage of the large AEOS aperture to substantially improve the ladar range and sensitivity. These improvements make the AEOS HICLASS system potentially suitable for tracking and characterization experiments of small < 30 cm objects in low-earth-orbits.

The Impact Imperative: A Space Infrastructure Enabling a Multi-Tiered Earth Defense

Impacting at hypervelocity, an asteroid struck the Earth approximately 65 million years ago in the Yucatan Peninsula a m . This triggered the extinction of almost 70% of the species of life on Earth including the dinosaurs. Other impacts prior to this one have caused even greater extinctions. Preventing collisions with the Earth by hypervelocity asteroids, meteoroids, and comets is the most important immediate space challenge facing human civilization. This is the Impact Imperative. We now believe that while there are about 2000 earth orbit crossing rocks greater than 1 kilometer in diameter, there may be as many as 200,000 or more objects in the 100 m size range. Can anything be done about this fundamental existence question facing our civilization? The answer is a resounding yes! By using an intelligent combination of Earth and space based sensors coupled with an infrastructure of high-energy laser stations and other secondary mitigation options, we can deflect inbound asteroids, meteoroids, and comets and prevent them &om striking the Earth. This can be accomplished by irradiating the surface of an inbound rock with sufficiently intense pulses so that ablation occurs. This ablation acts as a small rocket incrementally changing the shape of the rocks orbit around the Sun. One-kilometer size rocks can be moved sufficiently in about a month while smaller rocks may be moved in a shorter time span. We recommend that space objectives be immediately reprioritized to start us moving quickly towards an infrastructure that will support a multiple option defense capability. Planning and development for a lunar laser facility should be initiated immediately in parallel with other options. All mitigation options are greatly enhanced by robust early warning, detection, and tracking resources to find objects sufficiently prior to Earth orbit passage in time to allow significant intervention. Infrastructure options should include ground, LEO, GEO, Lunar, and libration point laser and sensor stations for providing early warning, tracking, and deflection. Other options should include space interceptors that will carry both laser and nuclear ablators for close range work. Response options must be developed to deal with the consequences of an impact should we move too slowly.

Acquisition, tracking, and sizing of small space objects

High-powered, pulsed CO2 coherent ladar systems and their potential application to space debris tracking and characterization.

Thermal metrology for a space-based gravity experiment

A proposed space-based test of gravitational theory requires unique performance for thermometry and ranging instrumentation. The experiment involves a cylindrical test chamber in which two free-floating spherical test bodies are located. The test bodies are spheres which move relative to each other. The direction and rate of motion depend on the relative masses and orbit parameters mediated by the force of gravity. The experiment will determine Newtons gravitational constant, G; its time dependence, as well as investigate the equivalence principle, the inverse square law, and post- Einsteinian effects. The absolute value of the temperature at which the experiment is performed is not critical and may range anywhere from approximately 70 to 100 K. However, the experimental design calls for a temperature uniformity of approximately 0.001 K throughout the test volume. This is necessary in order to prevent radiation pressure gradients from perturbing the test masses. Consequently, a method is needed for verifying and establishing this test condition. The presentation is an assessment of the utility of phosphor-based thermometry for this application and a description of feasibility experiments. Phosphor thermometry is well suited for resolving minute temperature differences. The first tests in our lab have indicated the feasibility of achieving this desired temperature resolution.

Impulse coupling measurements for an ORION demonstration

We discuss results of recent measurements of laser impulse coupling coefficients completed at the LHMEL Nd:glass laser facility at Wright-Patterson AFB. Impulse coupling was measured at 125 ns pulse duration and 1.06 μm wavelength on specially designed heterogeneous targets in vacuum. With these targets, we obtained substantially enhanced impulse at modest laser fluence. One application of this work is to provide a means to execute a demonstration of the ORION concept using repetitively-pulsed, kW-class, diffraction-limited lasers with pulse energy on the order of 100 J.