While the pre-launch AO was dedicated to Key Programmes (KPs) only, the in-flight AOs will not be restricted to a particular kind of proposal. The concept of KPs is no longer applicable to this call, however, the concepts of 'Large' and 'Normal' Programmes are introduced, LPs and NPs. An LP is an observing programme requiring in excess of 100 hours of observing time, all other observing programmes are NPs.

It is clear that the scientific motivation for an observing programme needing a especially large amount of observing time has to be particularly high and well justified. Since more than half of the total nominally available observing time for Herschel has already been allocated to LPs in the form of KPs this requirement is strongly emphasized in the current AO.

The above requirement is reflected in different page limits and additional demands on justifications for LPs as described in the Herschel PDFLaTeX form applicable to LPs.