Hans-Peter Röser

Oxygen plasma flow properties deduced from laser-induced fluorescence and probe measurements

Estimation of the local dissociation degree and the local mass-specific enthalpy of a pure oxygen plasma flow determined mainly from laser-induced fluorescence measurements are reported. Measurements have been conducted for several generator parameters in an inductively heated plasma wind tunnel. Additional probe measurements of total pressure together with the deduced translational temperature are used to estimate the local mass-specific enthalpy. For a reference condition, full dissociation has been measured. The measured translational temperature of atomic oxygen for this condition is T = 3500 K. Subsequently, the local mass-specific enthalpy has been derived using these local density and temperature measurements. For the reference condition the estimated value of h = 27 MJ/kg is in good agreement with the probe measurements and results from diode laser absorption spectroscopy.

Influence of Electrode Shape on Performance of Pulsed Magnetoplasmadynamic Thruster SIMP-LEX

The pulsed magnetoplasmadynamic thruster SIMP-LEX (Stuttgart impulsing magnetoplasmadynamic thruster for lunar exploration) is developed to serve as a main propulsion system for the lunar mission BW1. Optimizing the thrusters performance is necessary to increase the efficiency and the mean exhaust velocity without increasing the systems mass and energy requirements. Results of experiments varying the flare angle and the gap between the electrodes, the applied voltage, as well as using tongue-shaped or rectangular electrodes are shown and evaluated by means of a statistical approach using Taguchi matrices. Furthermore, an analytical approach toward the influence on the change in inductance along the x axis for these parameters was taken and the resulting performance characteristics are presented. Both tongue shape and flare angle, show a positive effect on the performance, that is, impulse bit, mean exhaust velocity, and thrust efficiency. A maximal I bit is given for a flare angle of ≈20 deg.

Measurement Issues In Pulsed Laser Propulsion

Various measurement techniques have been used throughout the over 40‐year history of laser propulsion. Often, these approaches suffered from inconsistencies in definitions of the key parameters that define the physics of laser ablation impulse generation. Such parameters include, but are not limited to the pulse energy, spot area, imparted impulse, and ablated mass. The limits and characteristics of common measurement techniques in each of these areas will be explored as they relate to laser propulsion. The idea of establishing some standardization system for laser propulsion data is introduced in this paper, so that reported results may be considered and studied by the general community with more certain understanding of particular merits and limitations. In particular, it is the intention to propose a minimum set of requirements a literature study should meet. Some international standards for measurements are already published, but modifications or revisions of such standards may be necessary for applic...

TECHNOLOGY DEMONSTRATION WITH THE MICRO-SATELLITE FLYING LAPTOP

The Flying Laptop is a micro-satellite currently under development by the Institute of Space Systems. Several promising technologies will be implemented. A high performance attitude control system with a pointing accuracy of 11 arcseconds, operating in a target pointing mode for image acquisition is necessary to achieve the planned scientific measurements. For communication a high speed Ka-band link using a traveling wave tube will be utilized. The on-board computer consists of a reconfigurable, redundant and self-controlling field programmable gate array with high computational power. In addition to the new technologies for the satellite bus a capable functional verification environment is under development applicable to the Flying Laptop.

High speed analysis of free flights with a parabolic thruster

A laser‐based rangefinder with high temporal resolution, synchronized with a laser burst, is employed for fast on‐site analysis of pulsed free flights. Additional high speed recordings from two different angles of view allow for full 3D‐reconstruction of the trajectory and calibration of the rangefinder data. This reveals the whole dynamics of the flyer including the lateral and angular impulse coupling components as well as information on the detonation process. The employment of an ignition pin enhances the reproducibility of the momentum coupling due to a more reliable plasma ignition during the flight. The impact of initial lateral offset is studied and shows beam‐riding properties of the parabolic craft within a small range. Back‐driving forces are derived and compared with the theoretical model. The flight stability is evaluated with respect to the minimization and compensation of the lateral and angular momentum in a hovering experiment. Stable laser acceleration ranges up to 3 m altitude. Ballisti...

Beam-Riding of a Parabolic Laser Lightcraft

The impulse coupling characteristics of a parabolic laser-driven thruster (‘lightcraft’) are investigated in free flight experiments using a pulsed CO2 high energy laser. The analysis of 3D high speed recordings reveals lateral force components as well as angular momentum re-orientating the lightcraft towards the laser beam in the case of slight misalignment. Beam-riding properties are examined with respect to the initial lateral offset at the launch position. The results are compared with model data derived from raytracing analysis of the intensity distribution on the surface of an ignition pin which is located on the lightcraft’s symmetry axis. Based on model data, beam-riding abilities are characterized with respect to initial offset and inclination by means of Julia sets. The parameter space of tolerable misalignment is explored with respect to laser burst parameters and compared with experimental data.

Experimental Determination of the Impulse Coupling Coefficient - Standardization Issues

In research on beamed energy propulsion, the momentum coupling coefficient cm is a central figure of merit to characterize a propulsion system. The determination of cm is based on the measurement of imparted impulse and laser pulse energy. Nevertheless, the knowledge of laser pulse length, laser spot area and ablated mass is of great importance for the comparability of experimental results in laser ablative propulsion. The use of a great variety of measurement techniques for these parameters throughout the scientific community implies the risk of misunderstandings and might impede the comparability of results. In this paper, we present critical issues concerning the measurement of the aforementioned key parameters with respect to possible standardization issues. As an example, a simple laser propulsion experiment will be presented and compared with an experimental model from a different research group.

SOFIA, an airborne observatory for infrared astronomy

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint US/German project operating a 2.7 m infrared airborne telescope onboard a modified Boeing 747-SP in the stratosphere at altitudes up to 13.7 km. SOFIA covers a spectral range from 0.3 µm to 1.6 mm, with an average atmospheric transmission greater than 80%. After successfully completing its commissioning, SOFIA commenced regular astronomical observation in spring 2013, and will ramp up to more than one hundred 8 to 10 h flights per year by 2015. The observatory is expected to operate until the mid 2030s. SOFIAs initial complement of seven focal plane instruments includes broadband imagers, moderate-resolution spectrographs and high-resolution spectrometers. SOFIA also includes an elaborate program for Education and Public Outreach. We describe the SOFIA facility together with its first light instrumentation and include some of its first scientific results. In addition, the education and public outreach program is presented.

Flight experiments on energy scaling for in-space laser propulsion

As a preparatory study on space‐borne laser propulsion, flight experiments with a parabolic thruster were carried out on an air cushion table. The thruster was mounted like a sail on a puck, allowing for laser‐driven motion in three degrees of freedom (3 DOF) in artificial weightlessness. Momentum coupling is derived from point explosion theory for various parabolic thruster geometries with respect to energy scaling issues. The experimental data are compared with theoretical predictions and with results from vertical free flights. Experimental results for the air‐breakdown threshold and POM ablation inside the thruster are compared with fluence data from beam propagation modeling.

Remotely Controlled Steering Gear For A Laser‐Driven Rocket With A Parabolic Thruster

A new steering concept for laser‐driven parabolic thrusters is presented. As an alternative to the well‐tried spin‐stabilization, our concept provides rocket stabilization and trajectory control and is suitable for the injection of a laser‐driven launcher into a planetary orbit: Angular and lateral momentum components are systematically applied to the rocket by specific variation of the ignition configuration inside the parabolic thruster. The effect of the tilting angle of the steering gear from the axis of symmetry on momentum coupling is examined, as well as the influences of pulse energy and ignition geometry. Based on the experimental results, an off‐axis detonation is modeled with respect to the fluence distribution at the ignition area and the resulting force components. A demonstrator model of a laser‐driven rocket with a parabolic thruster has been constructed, including a remotely controlled steering gear and a separate payload fraction. Test flights employing a high energy CO2 laser have been p...