Heiner Klinkrad

Analysis of the effectiveness of space debris mitigation measures using the delta model

Abstract Firstly, the paper outlines the different space debris mitigation measures proposed or in use by the national space agencies in order to reduce and stabilise the predicted long-term growth of the space object population. The rationale for analysing the effectiveness of these different mitigation techniques with space debris models is introduced. Then, the features of Debris Environment Long Term Analysis (DELTA) model are described. Special attention is given to the DELTA model approach for the detailed simulation of realistic mitigation measure scenarios. The model predictions of long-term debris environment evolution for these scenarios are then analysed and discussed in terms of their relative efficiency in reducing the debris population and the consequences for the collision risks in key operational orbits.

Sensitivity of long-term orbital debris environment evolution to the deployment of nano-satellite swarms

Abstract Nano-satellites, classified as having a mass in the kilogram range, appear to be emerging as a growing industry in recent years. They offer affordable access to space on only a modest budget, or, due to their small size, they can be easily deployed in large numbers or ‘swarms’ in a distributed network for many different civil and military applications. However, if their popularity grows significantly, then the sheer number of nano-satellites added to the most populated regions of low Earth orbit would increase the collision risk and add to the space debris problem in the long-term. The current proposals for nano-satellite missions are reviewed in this paper. An overall outlook for the nano-satellite industry and for a nano-satellite launch traffic model is given. Then, a sensitivity study is conducted to analyse the long-term impact of nano-satellite swarms on the orbital debris environment for different generic mission designs. These designs vary in terms of the number of satellites and the satellite mass. It has been found that the deployment of a single nano-satellite swarm consisting of a thousand or more members into the most crowded region of low Earth orbit would have a modest, but observable impact on the future collision rate and debris population growth.

Debris model validation and interpretation of debris measurements using ESA's proof tool

Abstract During the last years a number of observation campaigns to monitor the Earths space debris environment using radar and optical sensors have been performed. In addition, space debris models like the ESA MASTER Model have been developed based on the simulation of debris generating events. To validate the models using the results of a measurement campaign, a filter has to be applied to transform the object data into detection rates considering the observation scenario and the instrument parameters. PROOF (Program for Radar and Optical Observation Forecasting, developed under ESA-ESOC contract) is such a filter and thus a link between models and measurements. This paper addresses validation aspects of the MASTER-99 debris population using the PROOF tool. Besides, emphasis is given to the method of PROOF and on the demonstration of the consistency of its results. It is shown in this context that the sensitivity of the modelled instruments matches measured thresholds for both instrument types (telescope and radar). For the validation of the MASTER-99 model, PROOF has been applied for the simulation of the latest TIRA and Haystack beam-park experiments. The comparison shows that the modelling of the space debris environment shows some deficiencies in the 80° inclination band and at altitudes of 900–1000km. For the GEO region, data from the ESA Space Debris Telescope have been used. The PROOF results reveal a lack of decimetre sized GEO objects in the MASTER model.

Observing the Geostationary Ring

Based on orbital data contained in the DISCOS database, the situation in the geostationary ring is analysed. In January 2007, from 1121 known objects populating the geostationary region, 354 are controlled within their allocated longitude slots, 448 are drifting above, below or through GEO, and 147 are in a libration orbit. For 165 objects there is no orbital information available. In the last ten years from 1997 to 2006,152 spacecraft reached their end of life; 56 were reorbited in compliance with the Inter-Agency Space Debris Coordination Committee (IADC) recommendation, 54 were reorbited below the minimum recommended altitude, and 42 were abandoned or lost without any end-of-life disposal manoeuvre. Apart from these catalogued objects, the ESA 1-m telescope has observed many smaller debris (down to about 15 cm) in this orbital region representing a non-negligable collision risk for geostationary spacecraft.

The consideration of non fragmentation debris in the master model

Abstract The 1997 MASTER model (ESAs meteoroid and space debris terrestrial reference) considers man made objects due to historical launches and fragmentation debris larger than 100 μm . This paper addresses the improvements of the MASTER model by consideration of also non-fragmentation debris down to 1 μm in diameter. For this purpose, debris generated by solid rocket motor firings, surface degradation particles, impact ejecta, and NaK droplets released by nuclear reactors in space are currently being implemented in the model. All debris sources are considered from LEO up to the geosynchronous region. The new MASTER debris population is analysed in terms of the spatial distribution and resulting object flux, and it is compared with measurement data. Although the number of man-made objects represented in the model has been increased significantly, it is shown that the required resources to run the model are acceptable in terms of computer time and storage. The new model architecture, especially the parametric source term description, enables effective maintenance and model upgrade in response to ongoing debris measurements and source model improvements. The user branch of the MASTER model now provides a graphical interface for all platforms supported.

Key features of a satellite skin force modelling technique by means of Monte-Carlo ray tracing

Abstract With the increasing accuracy requirements on precise orbit prediction (e.g. for geodetic satellites like ERS-1), the accurate modelling of non-gravitational forces has become an important factor. The key features of a skin force modelling software shall be described which has been implemented by MATRA under ESA contract. The software covers free-molecular aerodynamics, direct and indirect solar radiation pressure effects (diffuse and specular earth albedo, and earth IR), and is supported by state-of-the-art environmental models, and spacecraft geometry and thermo-optical surface models.

Identification of Solid Rocket Motor Retro-Burns in the LDEF IDE Impact Data

The Interplanetary Dust Experiment (IDE) carried by the Long Duration Exposure Facility (LDEF) satellite detected a large amount of impact events recurring for a number of LDEF orbits. Such events show signatures of particle clouds that intersect the orbit of LDEF. In an effort to identify the impact of particles released during specific solid rocket motor burns, a new look at the IDE impact records was taken. The generation of dust particles due to solid rocket burns and the orbit conjunction of the released objects with LDEF was simulated. For the first time, an agreement of specific IDE impact features with the re-entry firings of Russian photo-reconnaissance satellites could be derived.

A Model for the High Area-to-Mass Ratio Debris in GEO

Recent observations performed using the ESA Space Debris Telescope (ESA-SDT) in Tenerife, Spain have revealed a new type of orbital debris. These objects with an area-tomass ratio of up to 30 m 2 /kg are currently not included in debris models like MASTER-2005. Their diameters are in the order of tens of centimeters. In this paper, a first approach to a new debris source model for the type of debris discovered during the ESA-SDT observations will be presented. The model will describe the parameters of the observable high area-tomass ratio objects that can be generated by two types of events. The first is a delamination of thermal insulation material from a spacecraft. The second type of event is a spacecraft fragmentation. The investigation of the design of candidate spacecraft can provide the first parameters of a model. These can be used to determine the overall size distribution of the released insulation material for both types of events. After an implementation of the model and a simulation that takes into account the orbit distribution and evolution of candidate spacecraft, a new debris population can be simulated.

Modelling the Meteoroid Stream Flux onto Targets in Earth Orbits

In contrast to the highly dynamic space debris environment, the annual mean meteoroid environment can be assumed to be static. However, the activity during the year consists of a superposition of a sporadic background flux with a number of seasonally recurring meteoroid streams. The damage potential of these mainly very small particles results from their high relative velocities (more than 70 km/s) and the resulting kinetic energy. Thus, it is important to analyse the effects of the meteoroid streams on targets in Earth-bound orbits. This paper describes the model approach that is used in ESA-MASTER-2005 (Meteoroid and Space Debris Terrestrial Environment Reference) to account for the meteoroid stream flux. It gives flux predictions for a set of targets in different Earth orbits and compares the stream flux against the meteoroid background and debris flux.

Improvements in Modelling of Solid Rocket Motor Particle Release Events

The ESA space debris population model MASTER-2001 (Meteoroid and Space Debris Terrestrial Environment Reference) considers 1,032 firings of solid rocket motors (SRM) with the associated generation of SRM slag and dust particles in its current version. The resulting particle population is a major contribution to the space debris environment in Earth orbit. For the modelling of each particle release event a detailed knowledge of the size distribution is essential. However, the knowledge of the particle sizes after passing the motor nozzle throat is poor. The current SRM dust implementation in the MASTER model assumes a fixed size distribution which is identically used for both large upper stages and small apogee motors. This assumption can lead to an over-representation of large dust particles in regions where mainly apogee motors are used (i.e. GEO), and an under-representation in lower altitudes where large stages predominate. In this paper, a concept for the improvement of SRM particle size modelling is discussed based on validation results with impact measurements obtained from space returned hardware. It will be shown that an introduction of a nozzle throat diameter dependency into the size distributions for both dust and slag enables a more precise modelling of SRM particle release events. The improved size distributions are going to be used by the MASTER-2005 space debris model which is currently under development by the Institute of Aerospace Systems and QinetiQ (UK) under ESA contract.