The methodology for providing the space station controlled deorbit in the conditions of an emergency situation.

For modern space stations operating in near-Earth orbit for a long time (decades) it is characterized by a significant increase in weight and complexity of the design. This circumstance significantly complicates the planning and implementation of the process of bringing space stations from orbit. As an example, the mass of the ISS in 2022 exceeded 440 tons, which, even in the prospect of having three Progress spacecraft docked to the station, means a low thrust-to-weight ratio of the station as a spacecraft and complicates the implementation of its controlled data from orbit within the accepted requirements and restrictions on the planning of the chain of flight operations, time for the implementation of the data from orbit scenario, and the size of the area of debris scattering in an uninhabited area of the Pacific Ocean.

It should also be noted that at the final stage of the operation of space stations, the reliability of structural elements and indicators of the resource and operating time of on-board systems are significantly reduced, which in turn increases the likelihood of NSHS when performing complex dynamic operations associated with the reduction of the space station as a large object from orbit.

A characteristic feature of the implementation of the process of reducing the CS from orbit is its irreversibility when descending to an altitude of 279 km.

All the factors and limitations outlined above, as well as the risks associated with the aggressive effects of the atmosphere and the external space environment, necessitate careful operational control of the parameters of the space station movement and the state of the onboard systems (OS) for timely detection and parrying of possible emergency that can lead to a violation of the implementation of the nominal plan for the station from orbit, a significant exit of the area the scattering of debris beyond the designated limits or even to the uncontrolled deorbit of the space station.

In this paper, we consider those emergencies that may arise directly in the process of starting the implementation of the plan for de-orbiting at the final stage of operation of the space complex, without affecting possible emergency situations at previous stages.

First of all, monitoring and analysis of the state of the space station must be carried out in relation to those BS, the NS in whose work can significantly affect the implementation of controlled deorbit lead to a critical emergency situation. So, for example, it is necessary to pay special attention to the operation of the combined propulsion system (CPS), the state of functional cargo units (FCU or «FGB») with fuel and the operation of the motion control and navigation system (MCNS) as a control and maintenance of the station orientation, as well as other service OS related to their work.

Identification of the emergencies at an early stage will reduce the determination of the moment of time for the implementation of a backup scenario or taking measures to fend off the anomaly that has arisen and its development into the NHS, which can lead to unacceptable consequences. To this end, a methodology has been developed for analyzing the telemetry data of the space station for detecting anomalies in the operation of the OS and predicting the occurrence of emergencies, followed by the formation and issuance of recommendations for controlling the movement of the station in the process of its data from orbit. Also, in order to perform an operational assessment of the influence of the moment of time of emergencies detection on the trajectory of deorbit, a method for modeling the ballistic scheme of deorbiting from orbit is proposed using the example of the ISS. The paper describes a cyclogram for issuing recommendations for controlling the movement of the orbital station in the conditions of emergency situations for various station configuration options and emergency scenarios. It is also necessary to take into account the impact of errors in the forecast of station resource expenditures (for example, fuel costs for maintaining the orientation of the space station during the execution of control pulses for deorbit).

As a conclusion, it should be noted:

1. After the start of the implementation of the planned scenario for the deoribt of the space station from orbit, the most significant emergency that can have a significant negative impact on the resulting trajectory of deorbit are problems in the operation of the propulsion and fuel systems of Progress and FGB, as well as problems of stability and stabilization of the station.
2. The developed anomaly detection algorithm and the method of modeling the ballistic deorbit scheme are capable of performing an operational assessment of the impact of emergency on the flight path of the OS and contribute to maintaining controlled deorbit.
3. Early detection of problems in the operation of the vessel system will save and prevent unforeseen fuel costs for maintaining orientation.