Alberto Agueda, GMV; Marc Belmonte, GMV; Diego Escobar, GMV; Adrián Hernández, GMV; David López, CDTI, Igone Urdampilleta, CDTI
Keywords: Passive Ranging, PR, Time Difference of Arrival, TDoA, Collision Avoidance, Operations Center CA, S3TOC,
Abstract:
The number of man-made objects sent to space has risen in the last decades, leading to an overcrowded environment of resident space objects and orbital debris. Consequently, the space cataloging activities are becoming increasingly challenging year after year.
Currently, there are over 500 operational satellites only in Geostationary Earth Orbit (GEO), with a typical maneuver frequency of a couple of weeks for chemical and hours for electrical satellites. Space Surveillance and Tracking (SST) systems predominantly observe them using optical or radar sensors. The cost of these sensors, as they continue to depend on active and complex systems, is quite notorious in terms of development, operation and maintenance.
Passive ranging is proposed as a lower-cost alternative to the existing techniques, capable of providing the same or improved latency, timeliness (24/7 access to data without climate conditions or sunlight dependency) and accuracy.
The concept of passive ranging is rather straightforward. It is based on the acquisition of the relative Time Difference of Arrival (TDoA) of the payload carrier signal, emitted by active satellites and received by several distant stations on the ground. The use of these systems is usually limited to satellites in geostationary orbit since their emission patterns in Ku-band are extensive as opposed to the narrow Ka-band satellites. Pointing to GEO satellites is manageable from the ground (being satellites virtually fixed in space) and their visibility (if available) is constant over time. Nonetheless, this technique can also be applied to other orbital regimes (LEO, MEO and HEO) even though the visibility is not continuous, passes are short and pointing is more complex.
The main reasons for proposing the concept of passive ranging to support the Collision Avoidance (CA) service via an improvement of orbit determination (OD) are, among others, the fact that it constitutes an independent and accurate source of low latency and high frequency data, while being completely autonomous and automated, and keeping a significantly lower cost for deployment, operations and maintenance than the other typical SST systems. It allows for a rapid detection and estimation of maneuvers in the order of few hours and it can be integrated to SST dedicated operation centers.
This paper is divided into three main sections. First, an overview of the development of a passive ranging system is provided along with a feasibility and performance study (in terms of orbit determination) including a budget error. It has been estimated that the orbital precision performance obtained for a hypothetical 4-station network in Spain is such that the 1-sigma position errors after 10 days of propagation are in the order of 150m along-track and 75m in radial (with a linear secular growth with time), and 50m cross-track (constant over time). In comparison, it is noted that the typical accuracies achievable in GEO with the use of telescopes are at least an order of magnitude worse, considering an observation accuracy of 0.5-1 arcsecs for telescope measurements.
Then, an end-to-end software prototype for a passive ranging system is presented. It allows to entirely simulate a passive ranging network for a set of user-defined GEO active satellites and to process real TDoA data as well. In both cases, the orbital information for the tracked satellites is maintained based on the processing of the TDoA data, including the detection and estimation of maneuvers. When simulating the full network, the observation strategy is user-defined and the TDoA data is obtained through the correlation of signal samples of a synthetic DVB-S2 compliant signal.
Since the addition of a passive ranging solution would make the tracking of active satellites using optical sensors redundant, the divergences from the current activities of these sensors are also assessed. This enables a more regular optical tracking of space objects such as space debris or other active satellites that emit a signal not observable to the passive ranging system.
Regarding this last activity, the improvement of the CA service of the S3TOC is also estimated for different scenarios. For each scenario (using different types of objects, at different time horizons from the OD) the quality of the obtained orbits will be assessed as well as the number of objects with orbital accuracy below the thresholds used in the EU-SST architecture studies. Lastly, a latency performance analysis of the orbital solutions obtained after the execution and detection of a maneuver will be carried out to evaluate the impact on the cataloging and provisioning of CA services in the S3TOC.
Date of Conference: September 27-20, 2022
Track: Optical Systems & Instrumentation