ISO TR 16158:2021 pdf download – Space systems — Avoiding collisions among orbiting objects.
They are derived from past observations of satellites. Ephemerides are time-ordered sets of position and velocity within which one interpolates to estimate the position and velocity at intermediate times. Ephemerides need to span the future time interval of interest, where the equations of motion having been propagated by the provider. Observations are measurements of satellite position and velocity from one or more well-characterized and registered instruments. The recipient can use those observations to estimate the evolution of the trajectory either through direct numerical integration of governing equations or by developing orbital elements for subsequent propagation. ISO/TR 11233 describes the way a provider’s orbit determination scheme is codified. There are normative formats for orbital elements and ephemerides (see ISO 26900). See CCSDS 503.0-B-2 for normative formats for transmitting observations. It is extremely important to realize that trajectory estimates are derived from measurements that cannot be precise such as spheres. Therefore, they are called “estimates. ” The input information can include characterized uncertainties. Uncertainty in any of the independent variables or parameters introduces imprecision in all the dependent variables that describe the evolution. The appropriate expression of uncertainty is, therefore, a square matrix whose dimension is the number of elements of the state, called a state vector. If uncertainties are not provided or are wrong, one cannot determine properly the probability that two objects can collide. 5.1.2 Propagating all orbits over the interval of interest All orbits being under consideration are best forecasted by the model in which they were created. Since orbit determination and propagation are uncertain, the propagation scheme can be well suited for this interval. ANSI/AIAA S-131-2010 is a normative reference for orbit propagation. Osculating orbit estimates grow imprecise over time intervals long compared to the time span of underlying observations. This imprecision is sufficient to make collision probabilities misleading. Therefore, conjunction assessment in low Earth orbit is unreliable at the present state of the art for periods longer than approximately one week beyond the latest orbit determination, depending on the orbit of interest. Some particularly stable orbits can be estimated reliably for longer periods. Probability of collision can be estimated over long periods using consistent statistical descriptions of satellite orbits and the evolution of the debris environment. These techniques estimate whether a conjunction will occur or not but cannot expose which specific objects can be involved. 5.2 Initial filtering 5.2.1 All against all The most complete process would examine each object in orbit against all others over the designated time span. Most techniques eliminate A-B duplication, defined as screening B against A in addition to A against B. Therefore, the number of screenings necessary is not the factorial of the number of satellites. It is impossible to know how many objects orbit the Earth. Many escape perception. The best a satellite operator can do is to consider those that have been detected. One cannot screen against unknown objects that one estimates can be present. 5.3 Eliminating infeasible conjunctions 5.3.1 General Much of the population in orbit physically cannot encounter many other satellites during the period of interest. For example, even if uncontrolled, geostationary satellites 180 degrees apart in longitude are not threats to each other. 5.3.2 Sieve Sieve techniques employ straightforward geometric and kinematic processes to narrow the spectrum of feasible conjunctions based on the minimum separation between orbits.

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