Examples of observation selection corresponding to time ct. The value Ot indicates an observation of target t. For simplicity, the slew time between observations is not considered. Section a represents the visibility (i.e., fulfillment of the hard constraints) and integration time of each target in minutes. The line indicates the time window where the target is visible, and the integration time of the observations in minutes is indicated in parentheses. Portions b–f present the objects planned in the mid-term plan that are available at ct. Portion b shows how the short-term scheduler discards O5 because it is not active in the mid-term plan at ct. Thereafter, O3 is shifted and starts at 17:35 because the observation ends inside its visibility period as it is visible until 18:30. Next, in c, O4 is not visible after 18:09 and it cannot be completed if it is delayed until 17:53. Thus, O4 is removed from mid-term plan. Consequently, there is a gap between 17:53 and 18:08 that is filled with one or several new observations. In this case, we assume that two new observations are executed (O6, O7). Portion d depicts how the gap is only filled until 18:04 because no visible target that is not already in the mid-term plan fits in the remaining window. O1 is advanced and it will start at 18:04 because it is visible at this time. In e, O2 is not visible until 18:22, so it cannot be advanced. The gap between 18:19 and 18:23 is filled with one or several new observations. In this case, we assume that one new observation is executed (O8). Finally, in f, O2 can start at the time scheduled by the mid-term plan. Portion g shows the observations executed by the short-term scheduler according to the process described.