Landsat continuity timeline. The original slide’s graphic was lost in PDF conversion.
In short: the Landsat program has provided continuous Earth imagery since 1972, with
at least one operational satellite at almost every moment.
Current operational pair: Landsat 8 (2013) + Landsat 9 (2021).
Landsat Next is planned for launch ~2030 with 26 bands at higher temporal cadence.