The need for accessing historical Earth Observation (EO) data series strongly increased in the last ten years, particularly for long-term science and environmental monitoring applications. This trend is likely to increase even more in the future, in particular regarding the growing interest in global change monitoring which is driving users to request time-series of data spanning 20 years and more. The need to support the United Nations Framework Convention on Climate Change (UNFCCC) is also further driving demand for historical data series. The contents of EO data archives are continuously growing from a few years to decades and therefore, their value as a scientific time-series is ever-increasing. Hence, there is a strong need to preserve the EO space data without time constraints and to ensure that they are accessible and exploitable by the community. The preservation of EO space data can also be considered as a responsibility of the Space Agencies or data owners as they constitute a humankind asset. The Heritage Space Programme responds to the mandate of preserving, making accessible, and valorising ESA heritage space data and associated information holdings generated by payloads and instruments on-board space platforms from ESA and ESA-managed Third Party Missions with a strong focus on their accessibility and exploitability. Over 40 Earth Observation missions and 80 EO campaigns are initially included in the Heritage Space programme starting from 2023. As part of the programme activities, a particular focus is put on the generation of long time series of coherent data in support of climate change monitoring activities, needs and related applications. This paper describes the activities implemented at ESA for the generation of a long time series of data starting from the ESA Heritage Third Party Missions (TPM) L-band SAR instruments data holdings. These activities consisted of the recovery of data from old media, their consolidation, archiving, reprocessing and dissemination to end users.