Disposal Orbit Research Articles

Disposal orbits for GEO spacecraft: A method for evaluating the orbit height distributions resulting from implementing IADC guidelines

Abstract Geostationary orbit (GEO) is the most commercially valuable Earth orbit. The Inter-Agency Space Debris Coordination Committee (IADC) has produced guidelines to help protect this region from space debris. The guidelines propose moving a satellite at the end of its operational life to a disposal orbit, which is designed so that satellites left there will not infringe the operational GEO region within a period of at least 100 yr. Standards are being developed through the International Organisation for Standardization to translate the IADC guidelines into engineering practice. This article presents an analytical method for calculating the distribution of final orbits assuming the IADC guidelines in GEO are implemented, as a function of distributions of satellite parameters (mass per unit area, solar radiation pressure reaction coefficient), the fuel measurement uncertainty, and the desired reliability of the disposal manoeuvre. Results show that typically the fuel measurement uncertainty dominates the distribution of perigee heights rather than the scatter in satellite properties or desired manoeuvre reliability. The method is simple to implement and allows the effects of changes in system parameters to be evaluated quickly.

The new NASA orbital debris mitigation procedural requirements and standards

NASA has issued major updates to its principal orbital debris mitigation policy directive and standards. The new NASA procedural requirements for limiting orbital debris (NPR 8715.6A), with its supporting NASA Standard 8719.14, both refine earlier orbital debris mitigation documents and in some areas expand their applicability. Organizational and individual responsibilities along with general directives are set forth in NPR 8715.6A. New requirements include routine conjunction assessments for all maneuverable NASA spacecraft in LEO and GEO, prompt notifications of intended or unintended debris generation, preparation and maintenance of formal end-of-mission plans, and disposal of vehicles in operation around the Moon and Mars and at the Earth–Sun Lagrangian points. NASA Standard 8719.14 replaces the 1995 NASA Safety Standard 1740.14 with no major new requirements but with several refinements and additions, some of which had already been adopted informally. Compliance with human casualty risk limitations from reentering debris will be calculated explicitly and not be expressed in terms of average debris casualty area. Moreover, the minimum kinetic energy threshold for potentially injurious reentering debris is set at 15 J. The overarching requirement for the disposal of GEO spacecraft and launch vehicle orbital stages is to ensure that the vehicles do not come within GEO+200 km for at least 100 years after end of mission, rather than setting specific requirements for the disposal orbit. Spacecraft operating in or routinely transiting LEO must remain in the region for no more than 25 years after end of mission or 30 years after launch, whichever occurs sooner. A comprehensive new NASA handbook on orbital debris has also been prepared to provide background on the orbital debris environment and the related NASA mitigation requirements and standards.

Ground assisted rendezvous with geosynchronous satellites for the disposal of space debris by means of Earth-oriented tethers

Previous studies have shown that extended length Earth-oriented tethers in the geosynchronous (GEO) region can be used to re-orbit satellites to disposal orbits. One such approach involves the extension of a GEO based tether, collection of a debris object, and retraction of the tether, which transfers the retracted configuration to a higher energy orbit for debris disposal. The re-extension of the tether after debris disposal returns the configuration to the near-GEO altitude. The practical feasibility of such a system depends on the ability to collect GEO debris objects, attach them to a deployed tether system, and retract the tethers for transfer to the disposal orbits. This study addresses the collection and delivery of debris objects to the deployed tether system in GEO. The investigation considers the number, type and the characteristics of the debris objects as well as the collection tug that can be ground controlled to detect, rendezvous and dock with the debris objects for their delivery to the tethers system. A total of more than 400 objects are in drift orbits crossing all longitudes either below or above the geostationary radius. More than 130 objects are also known to librate around the stable points in GEO with periods of libration up to five or more years. A characterization of the position and velocity of the debris objects relative to the collection tug is investigated. Typical rendezvous performance requirements for uncooperative GEO satellites are examined, and the similarities with other approaches such as the ESA's CX-OLEV commercial mission proposal to extend the life of geostationary telecommunication satellites are noted.

Resonant dynamics of Medium Earth Orbits: space debris issues

The Medium Earth Orbit region is the home of the navigation constellations. It is shown how the orbits of these constellations of satellites are strongly affected by the so-called inclination dependent luni-solar resonances. The analytical theory of these resonances is recalled and a large set of numerical integrations is used to investigate the stability of the orbits of the constellations over very long time spans. The stability issue is important in the definition of possible disposal strategies for the constellation spacecraft, after their end-of-life. Two possible disposal strategies are envisaged involving either stable or unstable orbits (from the eccentricity growth point of view). In particular it is shown how, to have disposal orbits with moderately short lifetime (of the orders of 40–50 years), a very large disposal maneuver would be required to rise the inital eccentricity to values above ~ 0.3.

Space debris mitigation in geosynchronous orbit

In order to preserve the geosynchronous region, the Inter-Agency Space Debris Coordination Committee (IADC) proposed and endorsed a re-orbiting strategy for spacecraft at the end-of-life: they should be disposed above the synchronous altitude and passivated, to reduce the risk of inadvertent explosions. The recommended perigee altitude of the disposal orbit took into account all relevant perturbations and was a function of the expected perturbing acceleration induced by solar radiation pressure. It was intended to prevent any further interference with a properly defined geostationary protected region. This paper addresses four main aspects related to space debris mitigation in geosynchronous orbit, by reviewing the rationale and expected effectiveness of spacecraft end-of-life disposal. First, the role played by the initial eccentricity vector on the trajectory evolution of disposed satellites. Second, the collision risk posed by debris clouds and the importance of passivation to prevent energetic breakups. Third, the impact of the operational limitations characteristic of aging spacecraft (e.g. reliability of residual propellant estimates, maneuver constraints and subsystems performance) on the definition of practicable disposal strategies. Last, the potential problem represented by low energy, non-explosive, fragmentations leading to the release of debris with high area-to-mass ratio. Based on the modeling results obtained, some possible mitigation solutions are discussed, including possible enhancements or revisions of the IADC recommendation.

Collision Risk Posed to the Global Positioning Systemby Disposed Upper Stages

Block IIF satellites in the Global Positioning System will be directly inserted into the constellation by the Evolved Expendable Launch Vehicle. However, the upper stages will not be able to relocate to recommended disposal orbits above the constellation and will remain at least partially in the constellation. The purpose of this study is to determine the collision risk posed to the operational constellation by the disposed upper stages. The analysis includes the effect of the long-term eccentricity growth of the upper-stage disposal orbits. Because eccentricity growth is very sensitive to the initial conditions of the disposal orbit, it is necessary to account for the statistical spread in the initial conditions. This spread is caused by dispersions in launch vehicle and upper-stage maneuvers and by inability to predict the sequence of orbit planes in which disposal will occur. A Monte Carlo procedure was used to quantify this statistical variation. Only one version of the launch vehicle was considered here. Study results include 5-, 50-, and 95-percentile profiles over 200 years of cumulative collision probability and cumulative number of collision avoidance maneuvers that may have to be performed by operational constellation satellites.

Economic case for the retirement of geosynchronous communication satellites via space tugs

Both the United Nations (UN) and the US Federal Communications Commission (FCC) have published a ruling that calls for geostationary earth orbit (GEO) satellites to be placed in a disposal orbit at the end of their operational lives. Current procedures utilize spacecraft residual propellant and represent a major life-limiting factor for GEO satellites. An alternative approach would be to allow a space tug to capture and move the satellites after all of their fuel has been exhausted. This extended lifetime can provide significant additional revenue to some satellite operators. Before committing to such a capability, however, the lifecycle costs of a space tug infrastructure must be carefully weighed against the opportunity costs of the current retirement practice. This paper investigates the questions of tug costs, perceived benefits, and service fee. It builds a framework that can be used in evaluating various on-orbit servicing opportunities and proposes that the service fee should be charged as a percentage of the additional revenue received by the satellite operators and analyzes how cost estimation uncertainties affect the value of on-orbit tugging. The presented analysis concludes that until advanced propulsion systems gain greater use, retirement via a space tug will be of value for the 10–20 most expensive GEO assets.

Case Study of Upper-Stage Disposal for Geosynchronous Debris Mitigation

Debris mitigation guidelines and directives specify that geosynchronous satellites and their corresponding upper stages be disposed at end of life in a graveyard zone above the densely populated geosynchronous ring. Although modern satellites often can comply without significant mission degradation, upper stages generally are not designed in a manner that permits easy compliance. This case study analyzed the options available to a typical modern upper stage for either complying with disposal guidelines or for reducing debris risk when compliance cannot be achieved. Results of the study showed that even upper stages incapable of moving to the recommended disposal orbit 300 km above synchronous altitude can still perform significant geosynchronous debris mitigation via proper selection of their blowdown/depletion procedure.

The stability of disposal orbits at super-synchronous altitudes

An investigation of the stability of super-synchronous disposal orbits using University of Southampton's debris analysis and monitoring architecture for the geosynchronous environment (DAMAGE) is presented. The DAMAGE orbital propagator was used to analyse the influence of the initial perigee, eccentricity, right ascension of ascending node (RAAN) and argument of perigee, and the initial lunar RAAN, on the evolution of disposal orbit perigee over a 200-year period. This propagator includes perturbations arising from low-order gravitational harmonics, third-body influences and solar radiation pressure (SRP). The results of two sensitivity studies are presented. The first evolved 14,112 disposal orbits with initial perigees at the minimum altitude suggested by the IADC guideline, whilst the second study evolved 17,920 disposal orbits with initial perigees from 42,374 to 42,464 km . The studies show that the initial perigee and eccentricity of the disposal orbit are the most important factors for maintaining the orbit above the protected region. Some sensitivity to the initial lunar RAAN, disposal orbit RAAN and argument of perigee was also found. These findings suggest that the IADC guideline specifying a preferred initial perigee is appropriate if it accompanies a guideline for the initial eccentricity of the disposal orbit.

Long-term evolution of navigation satellite orbits: GPS/GLONASS/GALILEO

A recent study was performed to examine whether long-term growth in the eccentricity evolution exists for the disposal orbits of navigation satellite systems such as GPS, GLONASS, and GALILEO. Previous studies examined the orbit stability for GPS Block II satellites. The orbits of the non-operational GPS Block I satellites are included in this study because they are at 63.4° inclination, which is different from GPS Block II. Similar to earlier studies, long-term perturbations and stability of these orbits are understood through analytical and numerical investigations. Initially near circular, these types of orbits may evolve into orbits with large eccentricity (as much as 0.7 over 150 years). Analytical approximations through doubly-averaged equations reveal that the cause is due to the resonance induced by Sun/Moon and J 2 secular perturbations. A total of 105 non-operational GLONASS satellites and upper stages and 10 GPS/Block I satellites were propagated for 200 years. Results show that the GLONASS satellites will start to enter the operating GPS constellation after 40 years. The uncovered resonance effect is strongly dependent on orbit inclination and altitude. The effect becomes more pronounced for GALILEO orbits due to their higher altitude, 3000 km above GPS. Strategies to minimize the significant eccentricity growth are identified in this study. These results directly impact the safety of future navigation satellites in the altitude region from 19,000 to 24,000 km. The dependence on initial inclination may help the designers of GPS III and GALILEO systems select the proper inclination for minimizing the large eccentricity growth. The maximum eccentricity growth for GPS and GALILEO can be significantly reduced by selecting operational inclinations a few degrees from the current nominal values for both programs.

Collision Risk Posed to the Global Positioning System by Disposal Orbit Instability

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Orbital Debris Environment Model in the Geosynchronous Region

The Kyushu University orbital debris environment model in the geosynchronous region has been updated to provide a better and more accurate description and understanding of orbital debris environment than the previous model. The main advantage of the present model over the previous model is to introduce more realistic breakup dispersion to estimate collision hazards to other spacecraft caused by breakup fragments. The results from the new model indicate that all aged satellites should move into a disposal orbit at the end of mission to reduce potential hazards to operational satellites. However, boosting up all aged satellites cannot preserve the current orbital environment sufficiently because debris fragments from explosions are still hazardous to operational satellites. The results also indicate that safekeeping procedures for all rocket bodies and spacecraft that remain in the geosynchronous region after completion of their mission are required as well as in low Earth orbit.

静止および静止投棄軌道上物体の単調増加の結果

To date more than 800 spacecraft, upper stages, and apogee kick motors are known to reside in geosynchronous and nearby orbits, including geosynchronous disposal (i.e., collection) orbits. U.S. and European ground-based sensors have detected an even larger number of debris greater than 10cm in diameter. Using projections of geosynchronous deployment characteristics and disposal rates, NASA and Kyushu University models of the geosynchronous and super-geosynchronous orbital regimes have examined the sensitivity of the long-term satellite population to various scenarios. Emphasis has been placed on the rate of collisions in the geosynchronous orbit and in the higher collection orbits and on the significance of cross-regime contamination. The sensitivity of the long-term environment to low velocity (0–1km/s) collision breakup model parameters and on the minimum height of collection orbits has also been explored. Results are presented in terms of both satellite population and spatial density.

Disposal of spacecraft at end of life in geosynchronous orbit

A number of national and international organizations have adopted a policy of removing spacecraft at the end of life from the geosynchronous ring. However, a resolution of several technical issues still remains before an international policy can be developed and implemented by all users of geosynchronous orbits. The present study reviews the cataloged population of objects in the geosynchronous ring. The probability of collision is computed as a function of range and orbital inclination of an object. Long-term stability of supersynchron ous disposal orbits and of the geopotential stable points is examined. Several disposal options are considered. The results of the study show that the use of the supersynchronous orbits for disposal purposes is economical and effective in significantly reducing the collision hazard. The use of the geopotential stable points for disposal of spacecraft at the end of life, on the other hand, was found to be impractical. I. Introduction B ECAUSE of the uniqueness and usefulness of the geosynchronous equatorial orbit (GEO), the population of objects in this orbit has increased continuously. Reference 1 shows, for example, that at the beginning of 1988, there were 286 cataloged satellites residing in this orbit, not including spent upper stages. Of these, 110 to 130 operating satellites were on station along with 150 that are nonfunctional or abandoned. ,. Reference 2, on the other hand, shows that of the approximately 453 cataloged objects traversing GEO altitudes, only about 150 are geostationary. The others are either geosynchronous or in highly elliptical (Molniya) semisynchronous orbits. There are also a number of military spacecraft, the orbjts of which are not generally availably in published form. To reduce the collision hazard within GEO, approximately 30 to 35 satellites have been removed from GEO at the end of life. Several strategies are available for disposing of GEO satellites, suqh as moving them to stable longitudes or raising them to orbits above geostationary altitude. The benefits of removing old spacecraft from GEO are a) the freeing of desirable longitudinal positions for repl^cement spacecraft and b) the reduction of collision damage potential, which can become high for collocated satellites.3 The primary issues involved are a) the protection of GEO as a unique natural resource and b) operational considerations such as cost effectiveness of the maneuver, risks of explosion, structural breakup, or other malfurigtions in carrying out the maneuver and national and international policy considerations. Other issues include the potential impact on future traffic to GEO and the perturbative effects on disppsal orbits (e.g., solar radiation and the sun/moon gravitational perturbations). In other words, abandoned rocket stages or satellites should not be a hazard to future missions, and their orbits should not intersect GEO over long periods of time.

The scientific and technical aspects of the geostationary orbit

The GSO is populated at present by less than 170 active satellites, by more than 110 non-functional objects and by an unknown number of debris. The number of radiocommunication Space Stations notified to the IFRB, in the co-ordinating process and with advance publication is 457. The simplified description of the GSO with a spherical Earth as the only attracting body is insufficient and misleading. Perturbations by the attraction of the Moon and the Sun and by other minor natural forces have to be taken into account in order to arrive at a realistic description of the orbit. Since natural forces do not admit of a geostationary satellite, man-made station-keeping is necessary to maintain the satellite at or near its nominal orbital position. The presence of non-functional objects and debris in the GSO is a source of possible danger to active satellites. The probability of a collision is small on the average but may be considerably higher at overcrowded longitudes. The probability of collision will increase in the future and will be very important for large space structures. Scientific grounds underlying sovereignty claims over segments of the GSO are discussed. International agreements on restricting the amount of non-functional objects and debris and on a systematical removal of inactive satellites into disposal orbits are indispensable for a continued use of the benefits of the GSO.

A practical approach to the disposal of highly toxic and long-lived spent nuclear fuel waste between Venus and Earth

Extraterrestrial disposal, while not the only alternative (there is at least one very safe terrestrial method), nevertheless assures definite and irreversible removal of the most toxic and long-lived waste from the biosphere. In the foreseeable future, there is far less need to retrieve nuclear waste for later use then to dispose of it in a publicly acceptable manner, beginning in the near future (middle 1980s). It is, therefore, more important to assure safety in the weakest link of this disposal process—transportation into near-Earth orbit—than to engage in a retrievable disposal beyond Earth. The disposal “site” should lie at minimum safe transfer energy level. Primary candidate is the space between Venus and Earth. The number of propulsion phases should be a minimum, preferably only one (out of near-Earth orbit). Lunar gravity assist can be helpful to achieve higher inclination of the heliocentric orbit relative to the ecliptic. Solidified spent fuel isotopes and actinides, sufficient to reduce the residual terrestrial waste to the radiation level of natural uranium deposits after 30–40 yr instead of 1000–1500 yr, is deposited into heliocentric orbits. Transportation systems, requirements, costs and the associated socio-economic benefit potentials of an environmentally more benign and a more vigorous nuclear power generation program are presented. Prior to solidification, an interim storage of 10 yr, following removal from the reactor, may be required. The Shuttle, with one Orbiter modified as Nuclear Waste Carrying Orbiter (NWCO) and an out of near-Earth orbit booster, provides a safe and economic transportation system at (1979$) disposal mission costs from surface to disposal orbit of less than 0.5¢/ kWhe or ⩽ 0.1¢/ kWhe (some 70% of overall exo-disposal cost), depending on level of orbital operations (this at basic Shuttle flight cost of $30M). The orbital operations mode can be selected according to lead time and costs, and can be advanced sequentially, lowering disposal costs while at the same time financing the development of orbital operations techniques needed also for other and larger-scale exo-industrial activities. An average of 10–15 disposal missions of the NWCO is required annually, at the given conditions, to service the spent fuel of 173 reactors 1978 in operation in W. Europe, Japan and North America.